# NITRATE LEACHING UNDER WINTER OILSEED RAPE AS AFFECTED BY SOWING DATE AND EARLY INCORPORATION OF SLURRY

Lena Engström, Sofia Delin

Soil and Environment, Skara, Sweden

## Objectives

In previous studies, nitrate leaching has not increased when winter oilseed rape, sown at normal to late sowing dates (18-25 August) directly after ploughing, is fertilised with 30-60 kg nitrogen per hectare at sowing. The nitrogen uptake in late autumn was obviously enough so that fertiliser or soil mineral nitrogen would not cause increased leaching. However, there is an increased risk for higher leaching after early cultivation and fertilisation followed by late sowing, since the nitrogen uptake may be too late and too small. In order to investigate how nitrate leaching is affected by early and late sowing after 1) early ploughing and slurry application and 2) early ploughing and mineral nitrogen fertiliser applied at sowing, two field experiments were performed 2012/2013 and 2013/2014 on a sandy soil at Götala farm, near Skara in Västergötland, Sweden.

## Method

The experiments were of randomized block design, with four blocks and five treatments. The previous crop was a two year old grass-clover ley in the first experiment and a barley crop following a grass-clover ley in the second experiment. The soil was ploughed 30 July, after dairy slurry application. Dairy slurry (60 and 100 kg total nitrogen per hectare, in the first and second experiment respectively) was applied on 30 July in both the treatment with early sowing (1 August) and the treatment with later sowing (20 August). Treatments with mineral nitrogen fertilisers were also ploughed on 30 July and 60 kg nitrogen (50 % nitrate, 50 % ammonium) per hectare was applied at each sowing date. In spring, 100 kg nitrogen per hectare (mineral fertiliser) was applied to the winter oilseed rape. Soil water samples were taken regularly from suction cups at 80 cm soil depth for nitrate analysis. For calculation of nitrate leaching the measured drainage runoff was used from a nearby leaching experiment with a tile draining system on a similar soil. The yearly drainage, 1 July-30 June 2012/2013, was 190 mm (normal) and mainly in the period September-January. The total drainage runoff 2013/2014 was low, 120 mm and occurred mainly in the period December-February.

## Results

In both experimental years the nitrogen uptake in late autumn was similar regardless of sowing date and if slurry or mineral nitrogen fertiliser had been applied. The reason was a long and warm autumn in 2012 that enabled the later sown crop to catch up with the early sown. Similarly, a dry period between the early and late sowing date in 2013 enabled the later sown crop to catch up with the early sown in that year. There were no differences in yield between early and late sowing. Due to dry periods in June 2013 and July 2014, water was limiting yield and may have contributed to reduce differences in yield potential between sowing dates. In early sown oilseed rape other factors such as plant death due to frost in the first experiment and a lot of weed in the second experiment, may have limited the yield levels. The effect on yield from slurry or mineral nitrogen fertiliser at sowing of oilseed rape was similar, 360-740 kg/ha in yield increase.

The yearly nitrate leaching under early sown and fertilised oilseed rape was just as small as for unfertilised both years, regardless if slurry (60 or 100 kg total nitrogen per hectare) was ploughed in just before sowing or mineral fertiliser (60 kg nitrogen per hectare) was applied at sowing after ploughing. Nitrate concentration in soil was generally higher after the late sowing date than the early. This caused the yearly nitrate leaching to be 52 % higher after late sowing than early both years (significant higher in one year), regardless if slurry (30 July) or mineral fertiliser (at sowing) was applied. The reason was most likely that ploughing date was the same for both sowing dates (30 July) and that soil nitrogen, mineralised in soil after ploughing, moved down the soil profile and was out of reach for the crop sown 20 August and therefore caused higher leaching than the earlier sowing.
## Conclusions

An equal effect on nitrogen uptake in late autumn and yield can be obtained for application of mineral nitrogen fertiliser (60 kg total-N/ha) or slurry (60 or 100 kg total-N/ha) at early sowing after ploughing.

Nitrate leaching can be expected to increase when sowing of oilseed rape is delayed after ploughing, regardless if fertilised with mineral nitrogen fertiliser at sowing or slurry three weeks earlier.

Sowing of oilseed rape directly after ploughing and fertilisation (slurry or mineral fertiliser), instead of three weeks later, can be an efficient way of reducing the risk for nitrate leaching during autumn and winter, especially at sites where leaching can be high e.g. on light textured soils and soils with high nitrogen mineralisation.
# DEVELOPING ‘N-CIRCLE’: A PRIORITISED AGENDA TOWARDS ‘CLOSED-LOOP’ AGRICULTURAL NITROGEN CYCLING FOR CHINA AND EUROPE

Roger Sylvester-Bradley², Xiaotang Ju⁴, Hongbin Liu³, Pete Smith¹, 14 others⁵, 17 others⁶

¹University of Aberdeen, Scotland, UK, ²ADAS UK Ltd., Cambridge, UK, ³Chinese Academy of Agricultural Sciences, Beijing, China, ⁴China Agricultural University, Beijing, China, ⁵⁹ institutions, Various, China, ⁶⁵ other institutions, Various, UK

## Objectives

China's agriculture is increasing its productivity rapidly, but low efficiency of nitrogen (N) use through over-fertilization increasingly threatens its sustainability [3]. Agriculture in Europe, by contrast, has had static production for twenty years but has a strong knowledge-base and infrastructure for pollution control. A new Virtual Joint Centre (VJC) between the UK and China, ‘N-Circle’, has been established to enhance the sustainability of N use in China, whilst also testing how agricultural productivity might be released from N use constraints in Europe. This paper describes the VJC’s ‘N-Circle’ philosophy and approach (Materials & Methods), its component aims and activities (Results) and its feasible outcomes (Conclusions).

## Method

The N-Circle VJC is led by the University of Aberdeen with four research partners from the UK and nine from China; over the three years from 2016 it is funded by almost €4 million from the BBSRC and Newton Fund, and over €5 million from sources in China. Whilst easy changes may be possible initially, systematic changes will take more time and require broader engagement. Thus the VJC is set up to become stakeholder-driven, branded and self-perpetuating beyond the life of the project.

The vision is of closed-loop N cycling, achieved not only by individual innovations, but by promoting high-level appreciation of N cycling such that macro-synergies are exploited. Examples are co-designing (i) application methods for fertilisers (and manures) with their chemical formulation, (ii) fertiliser management with crop breeding, (iii) crop breeding with food processing and feed formulation, and (iv) livestock feeding with manure composition and management [7].

Thus the VJC comprises bilateral multidisciplinary teams (described below) with expertise along an innovation pipeline feeding into a multi-organisation change agenda, identified by an ‘N Circle’ quality mark. The research teams are undertaking an integrated programme of laboratory analyses, field experiments, modelling and outreach. Target agro-ecosystems include the highly populated crop production region of the North China Plain experiencing critical water and air pollution due to overuse of N (>400 kg ha¹ yr¹) [5], as well as the North Eastern, North Western and South Western regions where N overuse can also be serious (100-250 kg N ha¹ yr¹).

As the VJC’s programme gains momentum, new N cycling strategies, incorporating the new innovative approaches, will be compared with ‘Business as Usual’ strategies using the VJC’s modelling framework, and optimal strategies will be resolved and promulgated with local policy-makers and other stakeholders to achieve the most effective attainable impacts within each region. New strategies can draw upon features of local agricultural knowledge, beliefs and practices and will build-in new systematic information to attain sustainability.

## Results

N-Circle’s (NC) bilateral teams are working at strategic scales on virtual system integration (NC1), system impacts (NC7), and implementation (NC8), and also at finer scale on innovations within each system-sector (NC2-6). Team activities are:

- NC1: Developing options for near-closed-loop N cycling.
The process-model ECOSSE [1] will integrate sector-specific outcomes (NC2-6), analyse whole-system sensitivities and uncertainties, and summarise relationships for incorporation in decision tools based on the Cool Farm Tool [4].

NC7: Demonstrating feasible impacts through up-scaled studies.

Findings from plot, field and farm scale (NC2-6) will be expanded to catchment scale using spatially distributed data, so that policy options can be explored and optimised.

NC8: Providing out-reach and dissemination to farmers, extension services, and policy-makers.

Relationships, organisations, networks and branding will be established, with governance that ensures the VJC will persist beyond the project, becoming stakeholder-driven, principled, branded and permanent.

Concurrently, sector-level innovation teams will explore technical targets expected to provide largest or most synergistic impacts on N inputs and N emissions, described here in order of dependence (NC6 to NC2):

NC6: Reducing end-user N demand and N excretion

A socioeconomic analysis and animal experiments will explore how the content and types of N in foods and livestock feeds might be optimised, to maximise N-retention and minimise N-excretion, and how successful approaches (such as feeding high-energy, low-protein grains) might be implemented in China.

NC5: Defining mechanisms to reduce crop N demand, and crop-stock transfers, by

(c) Using artificial microRNA transgenes to genetically tailor seed proteins more closely to requirements in foods and feeds, hence minimising N export in grain and crop demand for N.

(b) Testing whether N-efficient canopy phenotypes excel in Carbon (C) uptake, assimilation or partitioning, using C¹³ and N¹⁵ isotopes, and an endophytic diazotroph inoculant [2].

(a) Developing a canopy N model that enables real time, weather-related optimisation of crop N supply for C assimilation, and supports extant canopy sensing technologies.

NC4: Devising rotations and agronomic practices that maximise leguminous N capture

Exploring how amounts of N fixed (and transferred to adjacent non-legumes) relate to photosynthate availability (affected by light capture and competing sinks), and defining optimal legume-based rotations accordingly.

NC3: Providing options to reduce reenhouse gas (GHG) emissions arising from N applications

Testing how nitrite relates to other soil mineral N species. Then modelling mineral N dynamics, nitrous oxide (N₂O) emissions and crop uptake so to identify practical strategies that minimise N₂O without diminishing economic crop responses to added N.

NC2: Defining practices to enhance recovery of applied N

Testing short-term soil mineral N responses to C & N applications as fertiliser or manure so to devise techniques that temporarily perturb N immobilisation, hence enhance crop N recovery.

## Conclusions

The ultimate outcomes of the ‘N-Circle’ VJC will be (i) greater understanding of the mechanisms underpin-
ning agricultural management for sustainable N cycling, (ii) a rigorous evaluation of the potential for sus-
tainable N cycling to deliver future sustainable intensification of Chinese and European agriculture and (iii)
an agenda to achieve this. Exciting technological synergies are feasible if the power of multiple innovations
in molecular, chemical, micro-biological, agronomic and engineering technologies can be integrated and up-
scaled into economically viable systems at field, farm and regional scales.

Acknowledgement

The JVC's authors in the UK are P_Smith, E_Baggs, N_Morley, J_Hillier (University of Aberdeen), R_Rees, I_Bingham, K_Topp, J_Houdijk, R_Roehe (SRUC), D_Baulcombe, C_Gilligan, H_Griffiths (Cambridge University), Y_Lu (University of East Anglia), R_Sylvester-Bradley, R-Thorman, D_Kindred, L_Sagoo, R_Gooday, S_Wynn (ADAS), and in China are H_Liu, K_Yi, W_Cao, S_Wu, H_Wang, T_Ren, L_Wang (Chinese Academy of Agricultural Sciences), X_Ju, X-Q_Wang (China Agricultural University, Beijing), Z_Cai (Nanjing Normal University), W-Shi, X_Yan (Chinese Academy of Sciences, Nanjing), G_Pan (Nanjing Agricultural University), Z_Shen (Beijing Normal University), X_Wang (Capital Normal University), and B_Gu (Zhejiang University).

References

[1] Bell, MJ., etal. 2012. Nutr. Cycl. AgroEcosys. 92, 161

[2] Cocking, E.C. et al. 2006. *In Vitro Cell. Dev. Biol. Plant* **42**, 74-82.

[3] Duan, Y., etal. 2014. *Field Crops Res.* 157, 47-56.

[4] Hillier J et al. 2011. Environ. Model Software 26, 1070-1078

[5] Norse, D. & Ju, X. 2015. *Agric. Ecosys. Env.* 209, 5-14

[6] Smith, P. 2013. *Global Food Sec.* **2**, 18-23

[7] Sylvester-Bradley, R., & Withers, P. 2012. Proc. Fert. Soc. 700.
# CHARACTERISTICS OF NITROGEN BALANCE IN OPEN-AIR AND GREENHOUSE VEGETABLE CROPPING SYSTEMS OF CHINA

Chaopu Ti, Xiaoyuan Yan

*Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China*

## Objectives

Vegetable production in China has increased significantly over the past three decades. In general, vegetable fields are often characterized by intensive cropping rotations (multiple harvests within a year) and high nitrogen (N) application rates. Hence, given the increased cultivation of vegetables and its environmental impacts, the objectives of the present study were to (i) identify and assess the N balances in the vegetable cropping systems of China, (ii) determine the primary N loss pathways as affected by N fertilizer rates and NUE, and (iii) discuss the potential pollutants in open-air and greenhouse vegetable cropping systems.

## Method

According to the Organisation for Economic Cooperation and Development (OECD) methodology [1], inorganic fertilizers, livestock manure, biological N fixation, and atmospheric deposition are considered as inputs. Outputs included crop harvest, NH3 volatilization, N leaching and runoff, soil accumulation, and gaseous loss from nitrification and denitrification. The N use efficiency was calculated as total N (N in inorganic fertilizer plus N in manure) uptake by vegetables from treatments with applied N fertilizer.

Data on the total area of vegetable cultivation in China in 2010 was obtained from the National Bureau of Statistic of China [2]. We collected N flux data (for example, application rates of chemical fertilizer, crop production, and NH3 volatilization) of open-air and greenhouse vegetable cropping systems from field measurements taken during the vegetable growing season that are published in peer-reviewed Chinese and English journals. For example, a total of 42 and 65 experimental datasets for chemical N fertilizer input in greenhouse and open-air cropping systems, respectively, from 17 publications, were considered in this study.

## Results

Evaluation results showed that N balances in the vegetable cropping systems of China were characterized by high fertilizer N input, large N losses, and N storage in the soil. Total N input in open-air and greenhouse vegetable cropping systems was 5.44 and 2.60 Tg, respectively, in 2010, with chemical N fertilizer dominating this total input. More than 60 % of total N input was lost into the environment through gaseous loss from nitrification and denitrification, leaching, runoff, and NH3 volatilization. Greenhouse vegetable cropping systems can produce more fresh vegetables than open-air systems but require higher N inputs, accumulate more N in the soil, and pose a greater impact on the environment. The NUE of greenhouse vegetable cropping systems was less than 20 %, much lower than that of open-air systems. The latter was similar to the NUEs of the main cereal crops in China but was still substantially lower than the world average NUE. Large inputs of N to vegetable cropping systems with lower crop N uptake will lead to environmental problems such as groundwater pollution and soil acidification.

## Conclusions

In our study, estimation of N balances in both open-air and greenhouse vegetable cropping systems in China was established. Results showed that the total N input in open-air and greenhouse vegetable cropping systems in 2010 was 5.44 and 2.60 Tg, respectively. Chemical fertilizer N input in the two cropping systems was 201 kgN ha⁻¹ per season (open-air) and 478 kg N ha⁻¹ per season (greenhouse). The N use efficiency (NUE) was 25.9±13.3 and 19.7±9.4 % for open-air and greenhouse vegetable cropping systems, respectively, significantly lower than that of maize, wheat, and rice. Approximately 30.6 % of total N input was accumulated in soils and 0.8 % was lost by ammonia volatilization in greenhouse vegetable system, while N accumulation and ammonia volatilization accounted for 19.1 and 11.1 %, respectively, of total N input in open-air vegetable systems.
Acknowledgments

This study was supported by the Key Research Program of the Chinese Academy of Sciences (No. KZZD-EW-10-04-2).

References

[1] Organisation for Economic Co-operation and Development, 2008. Environmental performance of agriculture in OECD countries since 1990. Organisation for Economic Cooperation and Development, Paris

[2] National Bureau of Statistic of China. 2011. China statistical yearbook 2011, China Statistic Press, Beijing
# DISSIMILATORY NITRATE REDUCTION PROCESSES AND THEIR CONTRIBUTION TO NITROGEN LOSS IN CHINESE PADDY SOILS

Jun Shan, Xiaoyuan Yan

Institute of Soil Science, Nanjing, China

## Objectives

In paddy fields, nitrogen (N) is generally the central element limiting rice production and the waterlogged conditions during the main stage of rice growth provides unique environment for dissimilatory nitrate reduction processes including denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA). In this study, soil core incubations and slurry experiments with ¹⁵N tracer technique were performed to quantify the rates of denitrification, anammox, and DNRA processes in 11 typical Chinese paddy soils aiming at: 1) evaluating the relative contribution of denitrification, anammox, and DNRA to total nitrate removal and 2) elucidating the key influencing factors regulating the dissimilatory nitrate reduction processes in the paddy soils.

## Method

In the present study, 11 representative soil samples were collected across China covering 11 parent materials. The physico-chemical and biological properties including pH, total C and total N, soil organic carbon (SOC), soil nitrate and ammonium, soil sulfate, particle distributions, abundances of denitrification functional genes (*narG*, *nirS*, *nosZ*), and abundances of anammox functional genes (*hzsB*) were sequentially analyzed. Net N2 fluxes in these soils were determined by soil-core incubation combined with N2/Ar technique as described by Li et al. [1]. Potential rates of denitrification and anammox in the soils were measured via slurry experiments in combination with ¹⁵N tracer technique [2]. Potential DNRA rates were determined by the combination of the ammonium oxidation technique and membrane inlet mass spectrometry (MIMS) analysis [3]. All the experiments were performed in triplicates.

## Results

The net N₂ fluxes measured by soil-core incubation in combination with N₂/Ar technique ranged from 9.07 to 29.86 nmol N g⁻¹ h⁻¹, while the rates of denitrification measured by ¹⁵N tracing technique ranged from 2.37 to 8.31 nmol N g⁻¹ h⁻¹, implying denitrification rates based on ¹⁵N tracer significantly underestimated the nitrogen removal rates compared with soil-core incubation. The potential rates of anammox and DNRA measured by ¹⁵N tracing technique ranged from 0.15 to 0.77 nmol N g⁻¹ h⁻¹ and 0.03 to 0.54 nmol N g⁻¹ h⁻¹, respectively. Denitrification, anammox and DNRA play different role in controlling the fate of nitrate in the paddy soils, both denitrification and anammox results in permanently nitrate removal from paddy soils, whereas DNRA converts nitrate into ammonium, which is biologically available and less mobile than nitrate and thus contributing to N conservation in paddy soils. Among the nitrate reduction processes in the paddy soils, denitrification is predominant contributing 76.8-92.1% to total nitrate reduction, as compared to 1.4-9.2% for Anammox and 0.5-17.6% for DNRA. Net N₂ fluxes, denitrification and anammox rates were significantly correlated with soil organic carbon (SOC) content, soil nitrate concentration, and the abundance of *nosZ* genes, whereas DNRA rates showed significantly correlation with C/N ratios, DOC/NO₃⁻- and sulfate concentration. The positive correlations between net N₂ fluxes and denitrification rates with the contents of SOC and nitrate were in good agreement with previous studies [4], which were probably related to the supply of C sources and substrates for denitrifying bacteria. The closely relationship between DNRA and DOC/NO₃⁻- indicating that DNRA is prone to occur in environment with higher labile C sources to nitrate, in consistent with previous studies [5, 6].

## Conclusions

Denitrification was shown to be the predominant pathway for nitrate removal in the paddy soils, averagely contributing 85% of the total nitrate reduction. In contrast, anammox and DNRA played minor roles in the nitrate removal, on average accounting for 5.3% and 9.1% of the total nitrate reduction. The net N₂ fluxes,
denitrification and anammox rates in the tested soils were significantly correlated with SOC, nitrate and
nosZ abundances. DNRA was closely related to C/N ratios, DOC/NO₃⁻ and sulfate concentration. This study
provides the first results of the dissimilatory nitrate reduction processes and the associated contribution to
nitrate removal in the paddy soils strengthening the understanding of nitrate dynamics in paddy field.

References

[1] Li et al., 2013. J. Soils Sediments 13, 783-792.

[2] Risgaard-Petersen et al. (2003). Limnol. Oceanogr-Meth. 1, 63-73.

[3] Yin et al. (2014) Environ. Sci. Technol. 48, 9555-9562.

[4] Yang et al. (2015) Appl. Environ. Microbiol. 81, 938-947.

[5] Lu et al. (2015) J. Soils Sediments 15, 1169-1177.

[6] Rutting et al. (2011) Biogeosciences 8, 1779-1791.
# MORE BENEFIT FROM COVER CROPS BY HARVESTING

Hannu Känkänen¹, Oiva Niemeläinen¹, Erika Winquist¹, Kaisa Kuoppala¹, Maritta Kymäläinen², Katariina Manni²

¹Natural Resources Institute Finland (Luke), Jokioinen, Finland, ²Häme University of Applied Sciences (HAMK), Tammela, Finland

## Objectives

The area of cover crops (CCs) increased greatly in Finland in 2015. Last growing season CCs were grown on about 250 000 ha, mainly because of subsidies in agri-environmental program had been raised, currently 100 € ha⁻¹. However, growing CCs could be intensified on most of the fields and thus to reach better effect in reducing nitrogen (N) leaching or fixing N from atmosphere. This would diminish eutrophication in waters and, in case of legume CCs, need for N fertilizers. Further, good growth of CCs is also related to positive effect on soil fertility. A field study was started in 2015, aiming at intensified use of CCs, by means of harvesting the crop in autumn. Feasibility of the biomass for forage or biofuel production will be examined.

## Method

Keeping the nutrients in the fields, instead of waters -project ('Nutrient resource') aims at intensifying nutrient recycling in agriculture and decreasing nutrient load to waters. The study introduced here strives for the goal by intensifying cropping systems with help of harvesting CCs in autumn.

Two separate fertilization systems were included in the trial: 'an arable farm' was fertilized solely with synthetically produced fertilizer, and 'a livestock farm' was fertilized with the manure and synthetic fertilizer. The amount of N given in mineral fertilizer was 70 kg ha⁻¹ for the 'arable farm' and 45 kg ha⁻¹ for the 'livestock farm'. The latter got additionally 40 kg ha⁻¹ soluble N in manure.

In both systems Italian ryegrass (*Lolium multiflorum* Lam.) with two seeding rates (7 and 20 kg ha⁻¹), a mixture of perennial grasses {English ryegrass (*Lolium perenne* L., 6 kg ha⁻¹), timothy (*Phleum pratense* L., 2 kg ha⁻¹), meadow fescue (*Festuca pratensis* Huds., 4 kg ha⁻¹) and tall fescue (*Festuca arundinacea* Schreb., 4 kg ha⁻¹)}, red clover (*Trifolium pratense* L., 6 kg ha⁻¹) and a mixture of red clover (6 kg ha⁻¹) and Italian ryegrass (7 kg ha⁻¹) were undersown in spring barley (*Hordeum vulgare* L.). In addition, oilseed radish (*Raphanus sativus* L., 20 kg ha⁻¹) was sown after barley harvest in two treatments, either after barley with red clover or without undersowing. Moreover, white clover (*Trifolium repens* L.) was undersown into the 'arable farm'. Barley was harvested for grain, but in one treatment at the 'livestock farm' it was harvested earlier as whole crop silage. The undersown crop was red clover and Italian ryegrass mixture.

Grain yield of barley and harvested biomass of CCs were measured. In addition, CC yields were analysed for feeding values. Plant samples were taken in order to study competition between main crop and undersown crop. Small silage samples for biofuel studies in laboratory were taken, too. Total N was examined both in barley grains and CC biomass.

## Results

Rainy spring delayed sowing of the trial until late May. Barley was harvested one month later than usual because of slow accumulation of temperature sum until warm period in August. This caused rather short time for CCs to grow after the barley was harvested on 27th August. Oilseed radish was sown too late, in early September, to grow enough. Both barley and CCs grew well through the season. However, clovers obviously suffered somewhat of herbicide treatment.

The yields of CCs consisting of grasses were higher in the 'livestock farm', obviously because of higher soluble N and possibly because of N release from manure in late summer. Also barley benefited of higher N application.
Grain yield of pure barley was 5400 kg ha⁻¹ in the ‘arable farm’ and 5750 kg ha⁻¹ in the ‘livestock farm’. Grain yield was affected by competition of the undersown CC, and mostly adhered to opposite order with CC yield. Italian ryegrass decreased the grain yield by 800 – 900 kg ha⁻¹ at seeding rate 20 kg ha⁻¹, and by 350 – 550 kg ha⁻¹ at seeding rate 7 kg ha⁻¹. In the ‘livestock farm’ grain yield was 270 kg ha⁻¹ lower when red clover was undersown compared to no undersowing, but in the ‘arable farm’ it was 100 kg ha⁻¹ higher with red clover. White clover did not show any effect on barley grain yield.

Highest CC dry matter yield in the ‘livestock farm’, about 2000 kg ha⁻¹, was reached when seeding rate of 20 kg ha⁻¹ for Italian ryegrass was used. The yield was 300 kg ha⁻¹ lower with lower seeding rate. Perennial grasses yielded about 1250 kg ha⁻¹. Yields for all grass species were 400 – 600 kg ha⁻¹ lower in ‘arable farm’ compared to ‘livestock farm’. Clover yields were low, 500 – 700 kg ha⁻¹, despite of farming system. CC yields included straw from barley stubble, the share of which was the higher the lower was the total yield. Barley was cut three weeks earlier in the whole crop silage treatment. However, the biomass of CC remained low. Distinctly the CC did not compensate lost biomass in earlier cut with extra growth after it. The season was dry right after the whole crop silage harvest which might have resulted to the performance of the CC in that treatment.

The N content of the harvested CC biomass was greatly affected by the straw from barley stubble. When barley was harvested for whole crop silage, the N content of CC was nearly 3%, otherwise 1.5% or less. Obviously straw material in otherwise green CC biomass decreases usability for forage. The highest biomethane potential (400 dm³ kg⁻¹ DM) was obtained with a mixture of perennial grasses.

## Conclusions

New means to use CCs are desired, when improving their positive effects on N management and soil fertility. According to first results of Nutrient resource -project, biomass production of undersown CCs could be adequate for profitable harvest in late autumn. However, when the target is high biomass yield in autumn by high yielding undersown CC species, grain yield of the main crop inevitably decreases. Therefore after main crop harvest established cruciferous CC is a feasible method but only when the main crop is harvested not later than in early August. Results from quality analysis of the CC biomass have to be studied carefully before conclusions of the usability for feeding and biofuel use. However, according to first results, CCs seem to have a high biomethane potential and provide an excellent raw material for biogas production. When having data from the projects second year (2016), a holistic analysis is carried out to evaluate the value of the system for the Finnish agriculture.
ORGANIC VERSUS CONVENTIONAL- CAN δ¹⁵N BE USED AS AN INDICATING PARAMETER
IN GARLIC, SWEET PEPPER AND CARROT?

Anja Mahne Opatić¹,⁵, Marijan Nečemer², Nina Kacjan Maršić³, Nataša Šink⁴, Tina Perko³, Sonja Lojen¹,⁵

¹Department of Environmental Sciences O-2, Institute "Jožef Stefan", Jamova cesta 39, Ljubljana, Slovenia,
²Department of Low and Medium Energy Physics F-2, Institute "Jožef Stefan", Jamova cesta 39, Ljubljana,
Slovenia, ³Department of Agronomy, University of Ljubljana, Biotechnical Faculty, Jamnikarjeva cesta 101
11, Ljubljana, Slovenia, ⁴Biotechnical center Naklo, Strahinj 99, Ljubljana, Slovenia, ⁵Interational Postgrad-
uate School Jožef Stefan, Jamova cesta 39, Ljubljana, Slovenia

**Objectives**

Since organic farming has expanded and organic products attain higher prices, mislabelling and adulteration have become the most serious problems in many areas of food industry. The application of synthetic nitrogen fertilizers with δ¹⁵N values close to 0‰ shall result in the δ¹⁵N of plants grown under conventional production systems being lower than of those grown under organic conditions. The aim of our work was to investigate whether the N isotopic composition (δ¹⁵N) of produce can reveal the use of synthetic nitrogen fertilizer in organic production using different N fertilizer types and combinations of them in order to leave a specific δ¹⁵N fingerprint in garlic (Allium sativum L.), sweet pepper (Capsicum annuum L.) and carrot (Daucus carota subsp. Sativus L.). The influence of different fertilizing regimes (using synthetic and organic fertilizers with different δ¹⁵N) on the N isotopic composition of vegetables was evaluated in two pot and one field experiment.

**Method**

*Experimental design*

A pot experiment with garlic and sweet pepper was performed in a greenhouse, while carrot was grown in the field. Six treatments were applied in a completely randomised design with four replications for garlic, three replications for sweet pepper and five replications for carrot, as follows: an unfertilised control (C), two single organic fertilizations with different organic fertilizers (Org 1, Org 2), a single synthetic fertilization (S) and combinations of organic and synthetic fertilizations (Org 1 + S, Org 2 + S). Within every treatment there were three biological replications for garlic, two for sweet pepper and three for carrot. The same organic fertilizers with different δ¹⁵N (Org 1 with δ¹⁵N = 9.85‰ and Org 2 with δ¹⁵N = 3.9‰, respectively) were applied in all three experiments. As single synthetic fertilizer (S) synthetic fertilizer with δ¹⁵N = 0.4‰ was used.

Analysis

At each sampling event, three plants were destructively sampled for each treatment. Samples were dried in an oven at 60°C until constant weight. The analysis was carried out using a Europa Scientific (U.K.) Europa 20-20 continuous flow isotope ratio mass spectrometer with ANCA S-L unit in order to determine nitrogen isotope ratio and N content. About 5 mg of homogenised samples for δ¹⁵N and N content analysis were weighed, compressed in a tin capsule and introduced into autosampler. Samples were analysed in duplicates and the average was adopted. If the difference between two values for δ¹⁵N exceeded 0.2‰, the analysis was repeated. The accuracy of the δ¹⁵N isotopic analysis was checked with the certified reference materials and in-house standards. Additionally, δ¹⁵N and N content of soil used in pot experiments were tested. Basic statistics included analysis of variance by ANOVA with Duncan's test for comparisons of means.

**Results**

No statistically significant difference was found between δ¹⁵N values and N content of soil, fertilized with organic or synthetic fertilizers or combination of them in pot experiments with garlic and sweet pepper.

In garlic, statistically significant differences were found in mean δ¹⁵N values between Org 1 (with mean δ¹⁵N
= 6.15 ± 0.4) and all the other treatments (C with δ¹⁵N = 3.3 ± 0.3; Org 2 with δ¹⁵N = 4.4 ± 0.3; S with δ¹⁵N = 3.0 ± 0.3; Org 1 + S with δ¹⁵N = 4.7 ± 0.5; Org 2 + S with δ¹⁵N = 3.4 ± 0.6), reflecting the higher δ¹⁵N value of organic fertiliser Org 1. Statistically significant difference in mean δ¹⁵N values between garlic fertilized with synthetic fertilizer and both organic fertilizers was observed. Combined treatment Org 1 + S was resulted in significantly different δ¹⁵N value than conventional treatment (S), in contrast to Org 2 + S, where the difference was not significant. In comparison with control, significant differences were observed in Org 1, Org 2 and Org 1 + S regimes, meanwhile no apparent differences were determined in S and Org 2 + S regimes. Similar to δ¹⁵N values, the highest N content was determined in garlic treated with Org 1 (2.4 ± 0.2 g/ 100 g) and Org 1 + S (2.3 ± 0.0 g/ 100 g), showing statistically significant difference in comparison with other treatments, including treatment with synthetic fertilizer and control.

In sweet pepper and carrots, no statistically significant differences were found nor in δ¹⁵N values, neither in N content irrespective of the fertilization regime.

## Conclusions

Considering the obtained results, δ¹⁵N of sweet pepper and carrot alone could not be used even as a rough marker to discriminate between organic and conventional production, while δ¹⁵N in garlic showed a statistically significant difference, reflecting the higher δ¹⁵N values of organic production compared to that of conventional production. However, the addition of synthetic fertilizer to basal organic fertilization could not be detected by this method. Results obtained suggest that the method was found insufficiently sensitive to detect low or moderate rates of synthetic N fertiliser which could be illegally applied to organically grown garlic, sweet pepper and carrot and it seems not possible to detect and identify the combined use of organic and synthetic fertilisers. Consequently, δ¹⁵N could not be used as indicator of organic way of production by itself, but only as a supporting, additional indicator in combination with other parameters.

## Acknowledgements

This study was financially supported by European Commission- Community Research and Development Information Service in the scope of project 621329 ISO-FOOD ERA Chair for isotope techniques in food quality, safety and traceability, and research programme P1-0143 financed by the Slovenian Research Agency.
# PLANT AND MICROBIAL BIOMASS, NITROUS OXIDE AND CARBON DIOXIDE EMISSIONS IN INTENSIVELY MANAGED PERMANENT GRASSLAND UNDER CONTROLLED CONDITIONS AS AFFECTED BY NITROGEN LEVEL

Christoph Knoblauch¹, Conor Watson¹, Rolf Becker², Nicole Wrage-Mönnig³, Clara Berendonk⁴, Florian Wichern¹

¹Faculty of Life Sciences, Rhine-Waal University of Applied Sciences, Kleve, Germany, ²Faculty of Communication and Environment, Rhine-Waal University of Applied Sciences, Kamp-Lintfort, Germany, ³Faculty of Agricultural and Environmental Sciences, University of Rostock, Rostock, Germany, ⁴Chamber of Agriculture North Rhine-Westphalia, Kleve, Germany

## Objectives

Nitrogen fertilization of grassland aims at maximizing yield and feed quality. However, fertilization also has to reduce negative side effects, such as gaseous and liquid N losses. It is therefore necessary to predict the biomass, its N uptake and the N mineralization. Consequently, a plant growth model for grassland needs to be combined with an N mineralization model. Our study contributes to a project developing an integrated model for N uptake prediction in grassland. Therefore, the N status of different soil and plant pools and N losses have to be assessed in relation to cuts at different times. The objectives were to (1) establish the N response curve of permanent grassland under controlled growth conditions, (2) evaluate the relationship between biomass and vegetation indices as measured with optical sensors, (3) estimate the fertilization-associated N₂O losses and (4) effects on the soil microbial biomass as the driver of mineralization in soils.

## Method

The effects of inorganic N fertilization on plant growth and on C and N mineralization, microbial biomass and soil respiration in grassland soils was investigated in a 100-day pot experiment. Soil samples and plant sods were taken from an unfertilized control plot of a field trial on permanent grassland dominated by *Loli-um perenne* L. in Kleve, Germany (51°46′54″ N, 06°09′47″ E, 13 m a.s.l.). The soil of the field trial is classified as gleyic Cambisol and silty clay. In the greenhouse, the fresh soil samples and sods were allocated to pots, each with a volume of 0.01 m³ and adjusted to a water holding capacity of 50%. Reflecting the field trial design, samples were divided into three nitrogen fertilization levels and an unfertilized control with 7 replicates for each treatment. To this end, calcium ammonium nitrate was applied at 85, 170 and 340 kg N ha⁻¹. To mimic field conditions, fertilizer was applied in four portions at the beginning of the experiment and after each cut. During the greenhouse experiment, all pots were equipped with sensors monitoring soil temperature and gravimetric water content. Gas fluxes of CO₂ and N₂O were measured two to three times a week according to a closed dynamic chamber principle using a photo-acoustic gas analyser (Innova 1412i). Before each cut, the normalized differenced vegetation indices were determined using commercial hand-held optical sensors as means of indirect detection of plant biomass and N status. After cutting, the aboveground plant biomass was weighed. At the end of the experiment, soil samples were taken to analyse the extractable organic C and inorganic N fractions and the microbial biomass N (MBN) and C (MBC). Microbial biomass was estimated by chloroform-fumigation extraction including a pre-extraction step.

## Results

Soil respiration rates were constant over time for all four fertilizer levels and cuts indicating no influence of inorganic fertilizer application on mineralization processes. However, N₂O fluxes showed significant differences between fertilizer treatments as expected. Thus, the cumulative N₂O flux of the treatment with 340 kg N ha⁻¹ had increased 2.5-fold over the control plot on average; the application of 170 kg N ha⁻¹ still showed 1.5-fold higher values in comparison to the control. Next to differences in total fluxes, an abrupt rise of the flux rate directly after fertilization was determined. Over time, emission rates decreased continuously until the next cut. Thus, our results confirmed former observations, that N₂O emissions in intensively managed grassland are less influenced by mowing, but rather by the N level. The N input therefore will be an important model parameter helping in predicting N losses.
On the other hand, MBC and MBN slightly decreased with increasing fertilization. Yet, contents of MBC ranged from 429 µg C (g soil)-¹ to 743 µg C (g soil)-¹, reflecting the resilience of the high microbial biomass in this intensively managed permanent grassland. In contrast to the microbial biomass, a clear increase of the inorganic N content with elevated fertilizer input was detected as expected. Contents of inorganic N at the largest fertilizer level were on average 43% higher than the control and 30% higher than the application with 85 and 170 kg N ha-¹, which has to be considered for future model development. Similarly, aboveground biomass increased with increasing fertilizer level. This difference was detectable using optical sensors and the normalized differenced vegetation index.

## Conclusions

We were not able to detect any significant effect of inorganic N fertilization on the soil microbial biomass, probably due to its high level and the high soil organic C content of the grassland soil, which might buffer any possible effects. However, the amount of applied N influenced the activity of the microorganisms responsible for N₂O production. The expected clear relationship between N input and N₂O emissions on the one hand and plant biomass on the other hand under optimal moisture conditions in the presented experiment, will be used for future models aiming at N uptake prediction in permanent grassland. Future studies will further elaborate on the relationship between optical sensor data, N input, biomass development and N₂O emissions to provide a reliable data basis for the models.
# GLOBAL ANALYSIS OF LIVESTOCK PRODUCTION AND NUTRIENT BALANCES

Qian Liu, Jingmeng Wang, Yong Hou, Wei Qin, Oene Oenema

Wageningen University, Wageningen, The Netherlands

## Objectives

Livestock production is rapidly responding to changing markets and technological developments in many countries in the world. These responses have large influences on nitrogen (N) and phosphorus (P) balances, depending in part on the level of integration between crop and livestock production at regional and national levels. Integration of crop and livestock production is commonly defined by (i) the fraction of animal feed consumed that is produced on the farm or domestically, and (ii) by the reliance on external nutrient inputs. Our main hypothesis is that countries with rapidly increasing livestock numbers in specialized systems have rapidly increasing N and P surpluses, and that countries with low and stable livestock numbers have low N and P surpluses.

## Method

Here we report on a global analysis of changes in livestock production, N and P surplus at country level between 1961 and 2010, using data from FAOSTAT and World Bank, and additional model calculations.

## Results

We found that livestock density (LSU) and human population density increased roughly at the same rate globally, but with huge differences between countries. Countries with high export orientation ratio (EOR) of livestock products increased livestock numbers more strongly than countries without export. Extremely rapid increases in livestock number and extremely high LSU occurred in some Arab countries. Countries with a high livestock/crop product ratio and a high import orientation ratio (IOR) are characterized by limited agricultural land, high GDP and high population density per unit agricultural land, as in some Arab countries. We found positive relationships between LSU and N and P surpluses, suggesting indeed that livestock production has a greater influence on N and P surpluses than crop production within countries. There is however a large variation, which is in part related to differences between countries in the level of integration between crop and livestock production. As the information about the level of integration is scarce, we derived a number of proxies at national level, and related these proxies to the level of integration and N and P balances. We propose a two-dimensional, graphical approach, plotting the total ‘new’ N and P inputs on the X-axis and the total harvested crop and total animal production (in terms of N and P) on the Y-axis. We show that these relationships greatly differ between countries and relate to the levels of integration of crop and animal production, and animal protein intake per capita.

## Conclusions

In conclusion, N and P surpluses at national level are related to the level of integration between crop and animal production systems. Most ruminants by nature live in integrated systems, while pig and poultry systems increasingly become specialized, especially in rapidly developing countries.
# SOIL MINERAL NITROGEN CONTENT AND NITROGEN UPTAKE BY CROPS AFTER THE USE OF DIFFERENT ORGANIC FERTILIZERS

Miroslav Florian, Michaela Smatanova, Sarka Buranova

Central Institute for Supervising and Testing in Agriculture, Brno, Czech Republic

## Objectives

Nitrates are one of the most critical contaminants of waters. In order to protect water sources from nitrates of agricultural origin a set of rules has been implemented on European level (Nitrate directive). In the Czech Republic so called nitrates vulnerable areas account for more than 40 % of total agricultural land. The Action plan, valid in these areas, asks for proper management concerning nitrogen fertilization. The Central Institute for Supervising and Testing in Agriculture (ÚKZÚZ) is a control authority for the issues of Nitrate directive. With substantial growth in numbers of biogas plants in the Czech Republic has an urgent need of proper digestion residues management emerged.

The aim of this paper was to evaluate the impact of digestate, slurry and compost on mineral nitrogen content in topsoil, yield and nitrogen uptake by silage maize, spring barley and winter oilseed rape in vulnerable areas management.

## Method

Field experiments were established in the Czech Republic (Central Europe) at three testing stations of ÚKZÚZ in S1 (49°33′45.700″N, 15°32′20.613″E), S2 (49°5′55.717″N, 15°52′29.782″E) and S3 (49°43′51.489″N, 16°30′11.644″E) which are situated in vulnerable areas. S1 is located on sandy loam soil in 505 m a.s.l, average annual temperature is 7.7 °C with 632 mm precipitation, S2 is on loamy soil in 425 m a.s.l, average annual temperature is 8.0 °C with 481 mm precipitation and S3 on sandy loam soil in 460 m a.s.l, average annual temperature is 6.5 °C with 624 mm precipitation.

For the purpose of this paper three experimental years (2013 - 2015) were evaluated. Crops were grown in the order: silage maize, spring barley and winter oilseed rape. Five treatments with different types of fertilizers were used: 1. control (unfertilized); 2. mineral N (Calcium ammonium nitrate); 3. slurry; 4. digestate (anaerobic, from agricultural biogas plant) and 5. compost. Fertilizers were directly applied to the silage maize and to the winter oilseed rape. Determining of the fertilizers doses was based on the presumed total nitrogen consumption in harvest: 150 kg N ha⁻¹ to the maize and 80 kg N ha⁻¹ to the rape. Digestate and slurry are in the category of quick-release nitrogen fertilizers, while the compost is classified as a slow-release nitrogen fertilizer. For this reason its application dose was doubled.

Following characteristic features were obtained: Dry matter yield (DMY, t ha⁻¹): fresh matter yield was converted into dry matter content, samples for dry matter determination were dried at 105 °C; Soil mineral nitrogen content (Nmin, mg N kg⁻¹) in topsoil after harvest and Nitrogen uptake (NU, kg N ha⁻¹) as the sum of the main and by-product. Determination of nitrate content in soil was performed by ion selective electrode, while ammonium nitrogen content was carried out spectrophotometrically following the indophenol method.

Statistical assessment of the results was performed between treatments in the STATISTICA 12.0 program (StatSoft, Tulsa, USA) with the Main effects ANOVA followed by the Tukey's test at the level of significance P<0.05.

## Results

The highest content of Nmin in the topsoil was observed after the use of mineral fertilizers, particularly after the harvest of silage maize (5.5 mg N kg⁻¹ which means 45 % increase than control treatment). The lowest recorded values from all fertilized treatments were for the digestate treatment, where average values of Nmin after harvested maize and barley were about 48 % lower (3.8 mg N kg⁻¹) than for mineral N. Overall, the lowest values of Nmin in the topsoil were found after growing of maize and the highest after barley,
although the crop was not directly fertilized. The content of the mobile fraction of nitrogen (N-NO₃⁻) in the soil, which threatens surface and ground water, after application of digestate and compost was according to national standards on safe content.

The highest effect on average DMY of all experimental crops was observed for mineral N treatment: 15.0 t ha⁻¹ of maize, 4.7 t ha⁻¹ barley grain and 1.8 t ha⁻¹ rape seeds. From the experimental crops winter oilseed rape had the highest response to mineral nitrogen fertilization (about 62 % higher than control and about 33 % higher than slurry). The highest values of DMY in comparison with other organic fertilizers were obtained after fertilization with slurry. Digestate decreased the DMY in average only from 5 % (14.2 t ha⁻¹ maize) to 39 % (1.3 t ha⁻¹ rape) compared to mineral fertilizers. Fertilizing with compost as a fertilizer with slow-releasable nitrogen was less effective than digestate with quick-release nitrogen.

The results of DMY of individual treatments correspond to NU by crops. The highest values of NU occurred after the application of nitrogen in mineral form: 170.4 kg ha⁻¹ maize, 81.4 kg ha⁻¹ barley and 74.5 kg ha⁻¹ rape. The highest NU after organic fertilizing was reached on the slurry treatment: 159.6 kg ha⁻¹ maize, 67.6 kg ha⁻¹ barley and 55.4 kg ha⁻¹ rape, which means 12 %, 20 % and 29 % increase compare to the control treatment. In comparison with the other treatments were lower values of NU found for digestate and compost treatments (147.1 and 150.2 kg ha⁻¹ for maize, 58.3 and 66.6 kg ha⁻¹ for barley and 50.4 and 46.4 kg ha⁻¹ for rape).

## Conclusions

It is evident from our results that the highest response to nitrogen fertilization was observed after the use of mineral fertilizers, which led to the highest yields of all crops and also to the highest nitrogen uptakes. However, the highest contents of mineral nitrogen in the soil were found after the harvest, which may pose a risk for ground water resources. From organic fertilized treatments the highest yields and nitrogen uptakes were proved for slurry. The use of this fertilizer resulted to the lowest mineral nitrogen content in soil after harvest of rape and it was a very suitable organic fertilizer in terms of maize yield. Digestate and compost treatments were slightly below the yields of slurry treatment. With lower influence on barley yield the digestate treatment showed its limited long term fertilizing effect. On the other hand the use of compost increased yields due to a slow release nitrogen effect in the second year after the application. The lowest content of mineral nitrogen in soil for digestate treatment was determined after the harvest of maize and barley, but there was also detected the lowest nitrogen uptake from all treatments, which suggests the loss of nitrogen into the environment. Digestates are organic fertilizers which due to the high proportion of available ammonia nitrogen are a relevant alternative to save mineral fertilizers. However, mainly in vulnerable areas it is necessary to properly manage their use with respect to different site conditions and cultivated crops.
# USE OF SOIL ECa MEASUREMENT FOR EVALUATING SOIL SPATIAL VARIABILITY FOR NITROGEN MANAGEMENT IN SUPER-INTENSIVE OLIVE OIL TREE ORCHARDS

Miquel Pascual¹, Josep Rufat², Amadeu Arbonés², Alex Escolà¹, Josep R. Rosell¹, José A. Martinez-Casasno-vas¹, Josep M. Villar¹, Marta Vilarrasa¹

¹University of Lleida, Lleida, Spain, ²IRTA, Lleida, Spain

## Objectives

High-density olive crop systems require intensive irrigation and nutrition to improve yield and to sustain subsequent oil quality [1]. The enhancement of the water and nutritional status of olive trees benefits yield and oil quality [2]. However, intensive cropping practice is not without risks, for example, an excess of N negatively affects oil quality [3] [4]. Tree response to N application is closely linked to management practices and soil characteristics. In semi-arid conditions, soils exhibit great spatial heterogeneity, which is related mainly to soil depth, texture, and salt content, which together hinder the achievement of satisfactory N efficiency.

This study addresses the effect of soil variability on N management in the context of the optimization of oil tree production.

## Method

The trial was conducted on a commercial adult olive plot (cv.Arbequina) in Torres de Segre (Lleida) over four years (2010-2013). The climate is continental Mediterranean-type. The area receives a mean annual rainfall of 324 mm, which is irregularly distributed, and annual ETo (Penman-Monteith) is 1101 mm. The trees were planted in 2002 at 4.5 m × 2.2 m growing in a soil of variable depth. The soil is silty-loam textured and calcareous (pH = 8) with an organic matter content of 1.5%.

The trees were irrigated by means of autocompensated drip emitters (2.3 Lh-1) spaced 0.6 m along a dripline. Irrigation water came from the Segre river, which is of good quality. Soil moisture was monitored continuously with ECH2O-10 capacitance probes (Decagon Devices Inc., Pullman, Washington, USA). Two irrigation treatments were crossed with four fertilization treatments, with four replicates randomly distributed in blocks. The following irrigation treatments were applied: FI, or irrigation applied as 100% of the water requirements throughout the year, according to the FAO methodology [5]; RDI (deficit irrigation), or restricted irrigation in summer scheduled as follows: March to June, 100% of the requirements; July to September 10th, 25% of the requirements, and September and October, 100% of the requirements.

Fertilization treatments resulted in the combination of two rates of N (0 and 50 kg N ha⁻¹; N0 and N50 respectively) and two rates of K (0 and 100 kg of K2O ha⁻¹; K0 and K100 respectively). Plant growth was assessed by means of pruning weight. Meanwhile, fruit yield, oil yield, and oil content on a fresh matter basis were used as productive indicators. Leaf and fruit nutrients were analyzed in July and at harvest time, respectively. Fruit oil content was determined by nuclear magnetic resonance (NMR). The variability of soil properties was determined measuring apparent electrical conductivity of soil (ECa) continuously and geo-referenced with a VERIS 3200 equipment (Veris Technologies, Inc., Salina, KS). Statistical analysis of the results was performed using the JMP-SAS software (JMP, Version 12 Pro. SAS Institute Inc., Cary, NC, 1989-2014).

## Results

N treatments significantly increased the nitrogen leaf content. The non-fertilized treatment (N0) resulted in a decline in leaf N content over the years. In contrast, the N treatment (N50) resulted in an increase in nutrient over the four years in all the treatments. Leaf N content was high in all cases, according to the standards for leaf N interpretation. Also, the main trend of the effect of year x N interaction indicated that N concentration in leaves declined and varied between years in plots that did not receive N and K were not applied.

Oil yield was not affected by irrigation, but N application enhanced production and was also positively affected by K application, thereby evidencing an additive effect of N-K on oil yield. Taken together, the results suggest that N derived from the mineralization of soil organic matter was insufficient to achieve high yields
on non N-fertilized plots. Annual tree growth, estimated as pruning weight, was affected by deficit irrigation and significantly declined over the years on non-fertilized N plots, thereby also indicating a differential response of plant growth on unfertilized plots with respect to fertilized ones. A spatial statistic model including geoferenced results were analyzed by introducing a correction of model residuals calculus provided by initial soil ECa. The results show a strong influence of soil depth and salt content on the effects of N and K on yield and plant growth. Simultaneously, in all cases, trees in deep soil exhibited a lower yield and harvest index (as yield/vegetative biomass) than those on shallow soils. This experiment demonstrates that introduction of ECa measure in geo-analysis models constitutes a useful method for evaluation of N effects and to improve fertilization management.

## Conclusions

By integrating limiting factors, the ECa soil measurement has the capacity to identify soil heterogeneity. Commercial equipment for soil ECa measurements currently provides a useful tool for proximal field mapping and for precise N management. This technique can be used at the field level at reasonable cost and con- fers a significant potential economic and environmental benefit.

## References

[1] Naor, A. et al., 2013. Irrig. Sci. 31, 781-791.

[2] Erel, R. et al., 2008. J. Am. Soc. Hortic. Sci. 133, 639-647.

[3] Fernández-Escobar, R. et al., 2009. Eur. J. Agron. 31, 223-232.

[4] Erel, R. et al., 2013. J. Agric. Food Chem. 61, 11261-72.

[5] Allen, R.G. et al., 1998. FAO Irrigation and drainage paper 56. Irrig. Drain. 1-15.
# MODELLING THE EFFECT OF POST-HARVEST MANAGEMENT MEASURES ON NITRATE LEACHING DURING AUTUMN AND WINTER

Jeroen De Waele¹, Karoline D'Haene², Joost Salomez³, Georges Hofman¹, Stefaan De Neve¹

¹Department of Soil Management, Ghent University, Ghent, Belgium, ²Plant Sciences Unit, Institute for Agricultural and Fisheries Research (ILVO), Merelbeke, Belgium, ³Flemish Government, Department of Environment, Nature and Energy, Brussels, Belgium

## Objectives

In Europe, nitrate (NO₃⁻) leaching from farmland remains the predominant source of nitrogen (N) loads to ground- and surface waters. There is a serious risk of NO₃⁻ leaching during winter as residual soil mineral N content at harvest (RSMN) is often high. In this study, we evaluated NO₃⁻ leaching for different scenarios after cut grassland, silage maize, potatoes, sugar beets and winter wheat on a silt loam and a sandy soil in Flanders. Our research questions were: i) Can it be guaranteed that the threshold values of the Nitrates Directive (50 mg NO₃⁻ l⁻¹ in ground- and surface water) will not be exceeded when applying maximum allowed fertilisation rates for these five crops; ii) What kind of post-harvest management measures are effective to reduce the NO₃⁻ concentration; iii) What is the effect of the variability of RSMN and weather conditions on NO₃⁻ losses during the winter period?

## Method

Nitrate leaching and other soil N processes were simulated with the EU-rotate_N model using meteorological data of 23 autumn-winter seasons (1992-2015). First, we simulated a “worst-case” scenario with incorporation of crop residues five days after harvest of the main crop. We also simulated following alternative post-harvest management scenarios: i) sowing of winter crops (either catch or cash crops), ii) the removal of sugar beet leaves at harvest, and iii) the incorporation of straw after winter wheat. After winter wheat we also simulated a pig slurry application (60 kg total N ha⁻¹) before sowing mustard. All scenarios were simulated using real data of a selected representative silt loam soil and sandy soil in Flanders, using calibrated N mineralisation parameters and calibrated growth parameters for the catch crops. For cut grassland, the simulation started from the sowing of the grass in spring and ran until the 31st of March of the following year, but we assigned a RSMN content to the soil at the last mowing early November. All other simulations started at a given RSMN value at the harvest of the main crop and ran until the 31st of March of the following year. The assigned RSMN values were calculated from a large data set in previous studies and corresponded roughly to the RSMN found after applying the maximum allowed N fertilisation rates on the studied crops in Flanders [1]. We evaluated the different scenarios by comparing the mean NO₃⁻ concentration in ground- and surface water after dividing the simulated NO₃⁻ concentration at a depth of 90 cm by a factor of 2.1 to include natural attenuation processes occurring during transport towards ground- and surface water. As RSMN values also show variation due to differences in soil organic matter content and weather conditions during the growth of the main crop, we performed a Monte Carlo simulation to assess the combined effect of variability in RSMN and weather conditions on the variability in NO₃⁻ concentrations in the leaching water.

## Results

In the worst-case scenarios, the simulated attenuated mean NO₃⁻ concentration (NCₐt), expressed in mg NO₃⁻ l⁻¹ for the silt loam and sandy soil, respectively, was lowest for cut grassland (18±4 and 27±6), intermediate for winter wheat (38±6 and 49±13), sugar beet (38±6 and 61±15) and silage maize (49±6 and 58±15) and highest for potatoes (76±10 and 86±20). Sowing winter crops resulted on average in a 6 to 83% reduction in NCₐt in the silt loam soil and in a 5 to 59% reduction in the sandy soil. The reduction in NCₐt strongly depended on the mean simulated N uptake of the winter crops, which varied between 18 and 92 kg N ha⁻¹ and between 9 and 76 kg N ha⁻¹ on the silt loam and sandy soil, respectively. Nitrogen uptake was lowest for grass and winter rye sown after the harvest of maize and for winter wheat after sugar beets due to the late sowing time. For undersown grass in maize, N uptake was 2 to 3 times higher than for grass, resulting in a NCₐt below 50 mg NO₃⁻ l⁻¹. However, our simulations did assume the ideal development of the undersown grass during the maize growth, while it is known that the moment of undersowing a catch crop is very
critical: sowing early induces a risk of competition with the main crop, while sowing late might result in a poor development of the catch crop. After potatoes, N uptake of winter crops was higher than after maize and sugar beets, but insufficient to result in a NC<sub>att</sub> below the norm, and measures will be needed to reduce RSMN in order to comply with the requirements of the Nitrates Directive. After winter wheat, N uptake of catch crops was high and NC<sub>att</sub> was strongly reduced, even with a pig slurry application at the time of sowing the catch crop, as this pig slurry application increased N uptake by about 40 kg N ha<sup>-1</sup> on both soils. Crop residue removal after sugar beets and incorporation of winter wheat residues resulted on average in a 16 to 37% reduction in NC<sub>att</sub> and in a 21 to 40% reduction on the silt loam and the sandy soil, respectively. Removal of sugar beet leaves strongly resulted in a larger decrease of NC<sub>att</sub> than the incorporation of wheat straw.

Monte Carlo simulations showed that RSMN and NC<sub>att</sub> were positively correlated for most scenarios and that the variability in NCatt due to different weather conditions increased with higher RSMN. Only for 8 out of 17 scenarios on the silt loam and for 4 scenarios on the sandy soil, more than 90% of the simulated NCatt values remained below the threshold value of 50 mg NO<sub>3</sub><sup>-</sup> l<sup>-1</sup>.

## Conclusions

For cut grassland the simulated average NC<sub>att</sub> did not exceed the threshold value of 50 mg NO<sub>3</sub><sup>-</sup> l<sup>-1</sup> on both soil types. In order to comply with the Nitrates Directive (under currently maximum allowed fertilisation rates), post-harvest management measures seem to be necessary on sandy soils for the 4 other crops, and on silt loam soils for silage maize and potatoes. Sowing catch crops in August, even after application of 60 kg N ha<sup>-1</sup> as pig slurry, seems to be very effective. For crops which are harvested late in the season, the potential management options are limited. Potatoes are a problem crop because of the high RSMN values: as post-harvest measures did not reduce NC<sub>att</sub> below the norm, it will be necessary to harvest potatoes earlier to allow a better development of catch crops or to reduce RSMN e.g. by fractionation of N fertilization or by growing more N efficient potato varieties. Undersowing grass in silage maize and removing N rich crop residues like sugar beet leaves are promising options to reduce NO<sub>3</sub><sup>-</sup> leaching losses. However, to ensure that both practices will be implemented by farmers, it will be crucial to guarantee that the maize yield is minimally affected and that alternative uses for the harvested sugar beet leaves are lucrative.

## References

[1] D'Haene, K. et al., 2014. Agriculture, Ecosystems and Environment 192, 67-79.
# NITROGEN APPLICATION OF ORGANIC FERTILIZER IN TIMOTHY (PHLEUM PRATENSE L.) SEED PRODUCTION

Eva Stoltz, Ann-Charlotte Wallenhammar

Rural Economy and Agricultural Society/HS Konsult AB, Örebro, Sweden

## Objectives

Timothy seed is an important crop in Central Sweden. Prevailing N recommendation in conventional timothy seed production is application of 35-40 kg N ha⁻¹ in autumn and 80-120 kg ha⁻¹ the following spring the seeding year. In older stands i.e. first and second seed year, autumn N application is not recommended. The availability of N in organic fertilizers is often lower than in conventional fertilizer, therefore autumn application may be of greater relevance in the first and second seed year of organic seed stands.

The objective was to develop N fertilization recommendations in organic Timothy seed production by investigating the effect of different distribution regimes of N during autumn and spring on seed yield and N leakage in fields of various stand ages. The granulated organic fertilizer Biofer was used.

## Method

The investigations were carried out in six field experiments located at different sites in Central Sweden; Örebro County and Östergötland, established in Timothy seed fields 2012 and 2013. There were three experiments each year, in the cultivar SW Switch, in stands of various age; seeding year, first seed year and second seed year. A total rate of 120 kg N ha⁻¹ applied as Biofer (10-3-1) was distributed in five different doses in autumn (9-29 September); 0, 30, 60, 90 and 120 kg⁻¹, and the rest the following spring (11 Mars-10 May), i.e. 120, 90, 60, 30 and 0 kg ha⁻¹, respectively. The five treatments had four replications and a randomized block design was used. An experimental seeder was used to broadcast Biofer at the soil surface. Biofer is a bone meal product commonly used in organic crop production in Sweden. The major part of N in Biofer is organically bound to proteins and about one tenth is ammonium nitrogen [1].

The trials were harvested and seed yield measured. Soil samples were collected at 0-30 cm and 30-60 cm from the surface on three occasions; late autumn (end of October or beginning of November), spring (before spring application of Biofer) and after harvest, for analyses of mineral N (NH₄-N and NO₃-N).

The software JMP 9.0 was used for statistical analyses. An ANOVA followed by Tukey's HSD test (*p*<0,05) was used to identify significant differences between treatments.

## Results

Splitting the total rate of N as Biofer (10-3-1) between autumn and spring is beneficial for all ages of Timothy stands. Earlier findings in conventional trials demonstrated that splitting the N-application between autumn and spring was favorable in stands of the first seed year, but did not improve yield in older stands [2].

The results of two trials harvested the first seed year showed a small difference between the four treatments with doses 0, 30, 60 and 90 kg N ha⁻¹ applied in autumn and 120, 90, 60 and 30 kg N ha⁻¹ in spring. The seed yield ranged from 752 to 808 kg ha⁻¹ in the trial 2012 and from 415 to 438 kg ha⁻¹ in the trial 2013. All N applied in autumn showed the significantly lowest seed yield (736 kg ha⁻¹ and 374 kg ha⁻¹, 2012 and 2013 respectively), but was not always significantly lower than all other treatments.

The results of two trials harvested the second seed year showed that seed yield tended to be highest when doses 30, 60 and 90 kg N ha⁻¹ were applied in autumn and 90, 60 and 30 kg N ha⁻¹ in spring, however, there were no significant differences between any of the treatments. The treatments with best performance in yield ranged from 554 to 564 kg ha⁻¹ in the trial 2012 and from 711 to 728 kg ha⁻¹ in the trial 2013, as compared to yields in treatments where all N was applied in autumn or spring ranging from 497 to 535 kg ha⁻¹ and 675 to 688 kg ha⁻¹, in 2012 and 2013 respectively.
The results of the two trials the third seed year showed significantly higher yield in treatments with doses 0, 30 and 60 kg N ha⁻¹ applied in autumn and 120, 90 and 60 kg N ha⁻¹ respectively, applied in spring, than the treatment where all N was applied in autumn, in the trial 2012. Treatments with doses 30, 60, 90 and 120 kg N ha⁻¹ applied in autumn and 90, 60, 30 and 0 kg N ha⁻¹ in spring, tended to have higher seed yield ranging from 462 to 475 kg ha⁻¹ compared with 437 kg ha⁻¹ in the treatment with full N-dose applied in spring in the trial 2013.

Measurements of soil mineral N concentrations showed small differences between treatments. Only one of the six trials i.e. the seeding year trial harvested 2013, showed a significant increase in soil mineral N in late autumn. The increase was found in the treatments with autumn application of 90 and 120 kg N ha⁻¹ with 15.7 and 19.6 kg N ha⁻¹ compared with 8.6-11.6 kg N ha⁻¹ in the other treatments.

## Conclusions

Our recommendation is splitting the N dose between autumn (30-90 kg ha⁻¹) and spring when a total rate of 120 kg ha⁻¹ as Biofer (10-3-1) is applied to Timothy seed stands of all ages. The results demonstrate that the risk of N leakage is insignificant when Biofer is applied according to our recommendations to Timothy stands.

## Acknowledgements

The investigation was financed by the Swedish Board of Agriculture.

## References

[1] Lundström, C., Lindén, W. 2001. Series B crops and soils Report 8, Department of Agricultural Research, SLU, Skara, Sweden.

[2] Wallenhammar, A-C, Anderson, L.E. 2002. NJF report 341. Grass and clover seed production, Ystad, Sweden 24-26, June 2002, p 129-136.
ASSESSING MICROBIAL ACTIVITY IN DIGESTATE-FERTILIZED CROPS WITH
FERTIMETRO: A PATENTED DEVICE EXPLOITING BURIED COTTON THREAD BAITS TO
OPTIMIZE N AND P FERTILIZATION

Carmelo Maucieri, Giuseppe Concheri, Andrea Squartini, Maurizio Borin

Department of Agronomy, Food, Natural Resources, Animals and Environment (DAFNAE) - University of Padua, Legnaro (PD), Italy

Objectives

This study is part of a wider program aiming at the definition of ideal cropping strategies to limit CO2 emis-
sions while preserving soil fertility. These involve the application of anaerobic digestion effluent (digestate)
as organic fertilizers. In our approach we applied digestate to plots where different crops were grown with
or without arbuscular mycorrhizal fungi (AMF) inoculation. The analyzed responses, in addition to soil CO2
emission and biomass production, were focused on soil microbial activity and its response to local supple-
mentation of N or phosphorus (P). This was achieved by burying ‘bait’ threads of cotton in the first 15 cm
soil layer, recovering the fibers after a week and measuring the occurred degradation by pulling them until
breakage in a dynamometer. Plain threads were compared with some previously soaked in N or P solutions.
Such approach in terms of method and device constitutes a patent from the University of Padova.

Method

The trial, began in 2014, included 48 growth boxes elevated 1.3 m above ground level [1] vegetated with: gi-
ant reed (Arundo donax) miscanthus (Miscanthus x giganteus), sunchoke (Helianthus tuberosus), corn (Zea
mays), sorghum (Sorghum bicolor) and perennial ryegrass (Lolium perenne). On 1st April 2014, the digestate
liquid fraction was spread for an amount corresponding to 250 kg N ha⁻¹ and 27.4 kg P ha⁻¹. Half of the plots,
during sowing or transplanting were inoculated with AMF (Glomus intraradices, G. mosseae, G. etunicatum
and G. clarum) at 500 propagules/m². Four replicates were carried out. Soil CO₂ emission was evaluated
adopting the static non-stationary chamber technique.

The biodegradation level of organic matter by soil microorganisms was assessed following a novel method and using a purposely defined patented device (University of Padova, Italy, PCT/IB2012/001157, June 13, 2012, Squartini, Concheri, Tiozzo) measuring the degradation of cotton and silk threads that are placed in the soil for a week (October 2014). A small vertical hole was made in the soil with a spade, then threads (15 cm long) were carefully placed vertically and the hole was filled with soil. The extent of degradation of these threads, compared to that of unburied controls, is taken as an index of the cellulosolytic (cotton) or proteolytic (silk) attitudes of the soil microbial populations. In each plot, three sets of threads (untreated, pre-treated with nitrogen, pre-treated with phosphorus) per fiber (cotton and silk) were buried. The nitrogen- or phosphorus- pre-treated versions of the threads, as defined by the above quoted patent, are used to assess to what extent such additions can further stimulate microbial activity in comparison to the plain untreated threads. Their residual resistance to breakage was determined using a digital dynamometer to measure the peak force required to rupture them by applying progressive tractional force. The thread resistance was calculated as: R = (Ri / Rni) x 100 (where: R= resistance percentage; Ri = rupture value of the thread buried in the soil; Rni = rupture value of a control filament when new). Resistance was converted into the degradation percentage (D) by subtracting resistance percentage values from 100.

Results

At the end of the first growing season giant reed showed a significantly higher dry biomass production in the mycorrhized plots (22.8±1.5 Mg ha⁻¹) in comparison with the non-mycorrhized (18.4±2.8 Mg ha⁻¹) ones. On the opposite, sorghum showed a significantly higher dry biomass production in the non-mycorrhized treatment (36.6±4.3 Mg ha⁻¹) than in the mycorrhized one (30.5±2.1 Mg ha⁻¹). No significantly different production was found between mycorrhized and non-mycorrhized plots for sunchoke (28.9±5.9 Mg ha⁻¹), miscanthus (19.0±2.0 Mg ha⁻¹), corn (32.0±1.7 Mg ha⁻¹) and lolium (7.9±0.9 Mg ha⁻¹).
Fertimetro data consisted in measurements of the extent of degradation (increased fragility of the buried threads) in the different plots with or without mycorrhization. For the plain control thread, microbial cellulolytic activity (cotton fiber weakening) was affected by crop species. Presumably, besides chemical allelopathy effects, this can in part reflect the evapotranspiration intensity linked to the amount of foliar biomass, which in turn can deplete soil water availability for microbial activity. Low levels of cotton thread degradation were observed for arundo and sunchoke in comparison to the high levels shown by miscanthus, corn, sorghum and ryegrass. Fertimetro results confirm the trend of soil CO₂ emissions measured during plants growing season (May-September) with the lowest CO₂ fluxes monitored for giant reed and sunchoke (median value 291.3 mg m⁻² h⁻¹) whereas the highest ones were monitored for miscanthus, corn, sorghum and lo lium with a median value of 460.5 mg m⁻² h⁻¹. Furthermore, during growing season giant reed and sunchoke determined lower soil temperature (-6.5%) and moisture (-13.0%) than other ones, which showed an average value of 22.3°C and 28.2% respectively.

In the absence of mycorrhizal inoculation, N-treated and P-treated threads generally displayed higher degradation in comparison to the control, indicating nutrient limitation under those conditions. Considering all plant species, mycorrhizal inoculation determined significantly higher soil CO₂ emissions (median value 460.3 mg m⁻² h⁻¹) than boxes without inoculation (median value 374.5 mg m⁻² h⁻¹). In given crops (corn with threads +N) or miscanthus and sunchoke in threads +P), inoculating soil with mycorrhizae depressed microbial cellulolytic activity on the nutrient-supplemented cotton baits, which can be interpreted with competition phenomena or with excess nutrient availability in relation to its mobilization from bulk soil brought by the extending mycelium. Despite species-specific responses under mycorrhizal inoculation in terms of N and P availability, no specular trend was observed for biomass production. This result suggests that crop production also depends on the species-specific nutrients use efficiency and the mycorrhizal inoculation effect on it.

## Conclusions

AMF inoculation increases giant reed and decreases sorghum dry biomass production whereas no effect seems to be exerted on the others species.

Fertimetro data indicate the usefulness of the thread baits system in assessing soil fertility and unraveling ongoing dynamics in the plant-soil-microbiome complex interplay.

It should be considered that results have been obtained in only one growing season (the first growing season for perennial species and in only one growing season for annual ones) in an organic agro-ecosystem. Further investigation are needed in the following years to confirm our findings when more stable conditions between plants and their cropped environment will be reached.

## Acknowledgment

Research was supported by ValDige project "Valorizzazione del digestato per la riduzione delle perdite di CO₂" DGR n°1604 del 31/07/2012 financed by PSR Regione Veneto (2007-2014) misura 124, Domanda n. 2307827.

## References

[1] Morari, F. 2006. Soil Science Society of America Journal, 70(6), 1860-1871.
# ASSESSMENT OF ECOSYSTEM SERVICES RENDERED BY AGROMINING OF NICKELIFEROUS SOILS: ASSOCIATION OF LEGUMINOUS AND HYPERACCUMULATOR?

Ramez SAAD¹,², Ahmad KOBAISSI³, Christophe ROBIN⁴,⁵, Guillaume ECHEVARRIA¹,², Emile BENIZ-RI¹,²

¹Université de Lorraine, Laboratoire Sols et Environnement, Vandœuvre-lès-Nancy, France, ²INRA, Laboratoire Sols et Environnement, Vandœuvre-lès-Nancy, France, ³Université Libanaise, Laboratoire Biologie Végétale et Environnement, Beirut, Lebanon, ⁴Université de Lorraine, Laboratoire Agronomie et Environnement Nancy-Colmar, Vandœuvre-lès-Nancy, France, ⁵INRA, Laboratoire Agronomie et Environnement Nancy-Colmar, Vandœuvre-lès-Nancy, France

## Objectives

Ultramafic soils, known for their physical and chemical anomalies, contain significant amounts of trace elements such as nickel (Ni) and present a hostile environment for plant growth and profitable agricultural production. Ultramafic flora includes the particular hyperaccumulators plants, able to accumulate high Ni-concentration in their shoots. Objectives of agromining are extracting strategic metals, with high economic values, from degraded soils and then improving their agronomic properties. Based on providing ecosystem services to society from these degraded soils, developing more efficient cropping systems for agromining can be achieved by association of hyperaccumulators and legumes through enhancing soil fertility. Our objective was to investigate whether *Lens culinaris*, can grow and form functional nodules (fix N₂) on a Ni-contaminated soil. Our main goal is to use *Lens culinaris* in rotation or co-cropping with a hyperaccumulator, on a natural ultramafic Ni-rich soil, in order to enhance the growth of hyperaccumulator plants and Ni phytoextraction.

## Method

We performed a two months mesocosm study in controlled conditions based on three treatments: lentil and ryegrass separately sown in soils with increasing Ni concentrations and lentil sown in sand also with increasing Ni concentrations. The soil was previously cultivated with nodulated pea, thus naturally containing *Rhizobium leguminosarum* and was artificially contaminated with different concentrations of nickel sulfate (0-90 mg Ni kg⁻¹). We used the ¹⁵N natural abundance (δ¹⁵N) technique to estimate the proportion of N in lentils that could be ascribed to biological nitrogen fixation (BNF), i.e. fixed from the air (%Ndfa). We used ryegrass (*Lolium perenne* L.) grown in additional contaminated pots as non-fixing control plants to estimate δ¹⁵N of the N uptake from soil. We used lentils grown on sandy substrate and inoculated with a *Rhizobium* strain to estimate the δ¹⁵N of the legume when completely dependent on N₂. Biotic parameters investigated were: nodule numbers, Ni, carbon (C) and nitrogen (N) in plant organs, plant biomass, nitrate reductase activity (NRA), chlorophyll and carotenoids in shoots. Different abiotic parameters were also investigated on soil: pH, cation exchange capacity (CEC), total Ni concentration, Ni-DTPA, exchangeable Ni²⁺, ammonium and nitrates, C and N concentrations. The experiment had a completely randomized block design with three replicates. Variance analysis was carried out on all data using one-way ANOVA (Tukey test with a confidence interval of 95%). Also, normality tests and k-sample comparison of variances were analyzed. Furthermore, all the parameters studied were submitted to PCA. These statistical analyses were done on XLSTAT software.

## Results

Most of the physicochemical and biological parameters were significantly affected by the Ni concentrations. Nodule number per plant was lower under high soil-Ni than control (0 mg Ni kg⁻¹). Nodules lost their capacities to fix N₂ at highest Ni concentration (90 mg Ni kg⁻¹). For many parameters, there were no significant differences between control and treatments up to 60 mg Ni kg⁻¹. Decreased atmospheric N₂ fixation should be related to decreased symbiotic activity of microbes at highest Ni soil concentration. These outcomes affected Ndfa and shoot biomass which were negatively correlated to Ni additions to the soil. Shoots and roots of contaminated treatments showed greater Ni concentrations. Ni-accumulation in plants reduced plant biomass and roots stored higher Ni-amount than shoots as reported by previous studies. Physiologically, stress
caused by Ni-phytotoxicity had a contradictory effect on chlorophyll content in leaves. It is known that trace
metals have a negative effect on the chlorophyll content reducing photosynthesis. Our hypothesis regarding
the increase of chlorophyll in fresh leaves at highest Ni concentration was associated to the reduction of
plant biomass: pigments were concentrated in smaller leaves. Thus, the ratio of total chlorophyll content to
leaf area is higher. Added soil-Ni deleteriously affected NRA. Ni inhibited nitrate translocation from roots to
shoots and then reduced the amount of leaf nitrate. This fact implied a lower NRA. In addition, the metabo-
lites issued from the photosyntetic metabolism are essential in the process of the nitrate reduction. Therefore,
the reduced photosynthesis affected the nitrates absorbtion and reduction. Shoots N and C contents were also
significantly decreased by soil-Ni concentrations which limit nutrient and water uptake from the soil and
thus reducing the biomass production and dry matter accumulation. Also, the nitrogen fixed from the air and
nitrates assimilation from the soil was reported to be reduced by the heavy metal toxicity and consequently
reducing plant N content. No amounts of ammonium were detected in our soil. This was due to the main
destiny of ammonia in the soil to nitrate by the process of nitrification. In general, ammonia was found to be
present in low amounts in comparison to nitrates. Soil pH and CEC decreased with increasing soil-Ni con-
centrations and this was due to the complexation of Ni²⁺ to soil surface sites and to the Ni²⁺ exchange with
other cations from CEC, in both cases there is release of surface H⁺ ions. Furthermore, the stability of the Ni
onto the organic particles and the polymerization of cation-bound organic matter diminished the CEC in the
soil at high Ni concentrations. Soluble N pool in the soil and nitrate ions were reversely affected by soil-Ni
concentrations due to reduced ability of lentils to absorb nutrients at higher Ni concentrations.

Conclusions

Our results confirmed that the lentil is able to grow on a soil containing elevated amounts of Ni-DTPA sim-
ilar to those generally found in serpentine soils. This legume could be used in association with a hyperaccu-
mulator plant (co-cropping or rotation) with the aim of optimizing the Ni agromining by the hyperaccumula-
tor. Our study established that lentils can tolerate high concentrations of available nickel in the soil, although
physiological stress is induced in the presence of significant concentrations of this trace metal. Lentils can
still produce nodules that fix nitrogen from the air for most of the range of Ni additions tested here that are
at least one order of magnitude above acceptable levels for most crops and typical from serpentine soils. The
quantity of available Ni found in the serpentine soil, which will be used in the future work, is in the range
of the concentrations investigated in this experiment. Our upcoming work will be to test *Lens culinaris* in
inter- or co-cropping with a hyperaccumulator plant, *Alyssum murale*, to enhance its biomass production by
providing nitrogen and permit this hyperaccumulator to extract more valuable Ni.
# DOES BIOCHAR REDUCE AMMONIA EMMISIONS FROM DIFFERENT AMENDMENTS TO AGRICULTURAL SOILS?

Renata MS Pinto¹, Ana-Rita Fonseca¹, Lidia Sas-Paszt², *Claudia M d S Cordovil¹*

¹Universidade de Lisboa, Instituto Superior de Agronomia, LEAF, Lisbon, Portugal, ²Research Institute of Horticulture, Pomologiczna 18, 96-100 Skierniewice, Poland

## Objectives

Atmospheric ammonia (NH3) is a key air pollutant effecting eutrophication and acidification of ecosystems (1), and agricultural systems are pointed out as the main anthropogenic source of atmospheric NH3, either from N fertilizer use or animal production and manure spreading (2). Biochar affects N cycling in soils and offers potentially tightens the N cycle in agricultural ecosystems. Biochar can take up N via ion exchange, remove NH3 via adsorption, and stimulate immobilisation reducing NO3 leaching.

Biochar can efficiently adsorb NH3 (3)], potentially reducing NH3 losses by volatilization, and can be applied to soil to improve soil fertility and mitigate climate change(4).

The objective was to evaluate the effect of biochar application to soils, with different background uses (mixed and organic farming), on the sequestration of N. Biochar was applied at different rates, amended with urea and compost, as N sources, and NH3 emissions were measured from soil - amendment mixtures.

## Method

Two different soils were collected from agricultural fields with different farming practices backgrounds (mixed and organic farming). In the mixed farming system, fresh poultry manure and mineral fertilizers are usually applied to soil, while in the organic farming system soil is regularly amended with compost produced with a mixture of poultry manure and vegetable crop residues collected from a greenhouse. Soil was collected from the 0-20 cm layer from both fields, air dried and sieved (< 2.0 mm).

Six different treatments were performed on each soil type: control unamended soils (CM, CO); application of biochar at 5% and 10% rates (MB5, MB10); application of urea (U) or of compost (O) in amounts equivalent to 170 kg N ha⁻¹; application of urea + biochar at 5% and 10% rates (UB5, UB10); application of compost + biochar at 5% and 10% rates (OB5, OB10). Urea was added to the soil from mixed farming system and the compost was applied to the organic farming soil. All amendments were performed at the beginning of the experiment in sufficient number to allow destructive triplicate sampling at each sampling time. When applicable, biochar and compost were mixed to the soils and urea was diluted in water and applied to the soil surface. Soil + amendments mixtures, watered with distilled water at 60% water holding capacity previously determined, were placed in plastic containers linked to polyurethane foam ammonia collectors placed 1cm above the soil + mixture surface (5). For each sampling date, 36 foam absorbers were collected (3 replicates per 6 treatments per 2 soil types), in a total of 5 sampling dates (T1 = 2 days, T2 = 4 days, T3 = 7 days, T4 = 9 days, T5 = 11 days). Temperature and relative humidity were monitored during this period (6 hour intervals).

For N-NH4 analysis, foam absorbers were washed with 200 mL of distilled water and vacuum filtered. Ammonium nitrogen was determined with a segmented flow autoanaliser.

Data was interpreted using analysis of variance (ANOVA) using Statistica ®. Fishers LSD tests were used to show the significant differences at 95% confidence.

## Results

Biochar application at both rates to the mixed farming soil significantly decrease ammonia volatilization, compared to control. Ammonia volatilisation decreased between CM and MB5 (for T1 and T2), and MB10 (for T1, T2 and T3); between U and UB5 (for T1 and T2), and UB10 (for T1, T2, T3 and T4). Comparing CM to MB5 the decreased was 38% at T1 and 61% at T2. MB10 treated samples showed 64% reduced losses at T1, 54% at T2 and 46% at T3.

When urea was applied to the soil and also amended with biochar, there was also a decrease effect on ammonia volatilization in many cases. Comparing between U and UB5 ammonia losses decreased 25% at T1 and
47% at T2. UB10 reduced losses by 76% for T1, 43% for T2, 37% for T3 and by 46% for T4. Biochar can thus reduce N losses by volatilisation from the agricultural soil system. Other authors (6) have also found that NH3 volatilisation from 15N-labelled ruminant urine declined by 45% after incorporating either 15 or 30 t ha⁻¹ of biochar to soil. Mandal et al. (2016) obtained NH3 volatilization decreases as high as 71% from a urea treated soil, after biochar application. Furthermore, the captured NH3 has the potential to be used later by the plants since it is bioavailable in soils (3).

No significant effect of biochar application was observed in treatments where organic farming soil was used, as biochar did not seem to impact on ammonia volatilization from this soil type. This was probably a consequence of the cumulative use of compost as an alternative to the application of fresh organic residues (fresh poultry manure) or mineral fertilizers (urea), which may have increased soil organic matter content in this soil. However, in this case most NH3 emissions may have occurred during poultry manure composting (7) were significant NH3 losses can take place. However not addressed in the present work, biochar can also be applied during composting to reduce NH3 losses by volatilization (8). The effect of biochar as a tool for nitrogen sequestration from soils, seems to be more efficient in soils with less organic matter content which is consistent with previous findings that state that biochar has a nutrient adsorption effect (3). Reductions in NH3 loss vary with N source and biochar characteristics. Manure derived biochars may act as N fertilizers. Short- and long-term implications on N immobilisation and mineralization are specific to soil-biochar combinations and further studies are required to predict N cycling responses. As an environmentally beneficial agricultural management tool, the most promising aspects are: the reduction of NH3 volatilisation, the development of slow release N fertilisers and the reduction of N₂O emissions using fresh biochar additions to soils

## Conclusions

Agricultural systems should ensure food production with minimal negative impacts on the environment. Agricultural soils are a major source of NH3, which can be lost by volatilisation following the application of organic and chemical fertilizers. Losses must be prevented to mitigate climate change and reduce economic losses for farmers. Biochar has potential to be an N input and a mitigation agent for environmentally detrimental N losses. When urea was added to the soil from the mixed farming system, greater NH3 emissions were observed, and reduction in those emissions due to biochar application ranged from 25% to 76%, thus promoting the mitigation of nitrogen losses into the environment and promoting a more efficient use of N. NH3 volatilisation was lower from the soil having an organic management history, and biochar amendment to soil had no effect on NH3 emissions in this case. However in this case, the main NH3 emissions could have occurred during composting and biochar could also be placed at this time to uptake NH3.

Further studies need to be done to quantify to what extent the biochar application may contribute to nitrogen sequestration in soil.

## References

[1] Sutton et al. 2009. Springer ISBN978-1-4020-9120-9

[2] Beusen et al. 2008. Atmos.Environ. 42:6067-6077.

[3] Taghizadeh-Toosi et al. 2012a. Plant Soil 350:57-69.

[4] Lehmann et al. 2011. Soil.Biol.Biochem. 43:1812-1836.

[5] Alves et al. 2011. R.Bras.Ci.Solo 35:133-140.

[6] Taghizadeh-Toosi et al. 2012b. Plant Soil 353:73-84.

[7] Peigné and Girardin 2004. Water Air Soil Pollut. 153:45-68.

[8] Steiner et al. 2010. J.Environ.Qual. 39(4):1236-1242.
# N₂O FLUXES FROM AN AGRICULTURAL SOIL IN GERMANY DURING A COMPLETE CROP ROTATION: UNCERTAINTIES, ENVIRONMENTAL INSIGHTS AND MODEL PERFORMANCE

Carlo Lammirato, Ulrike Lebender, Jens Tierling, Joachim Lammel

Yara International, Research Centre Hanninghof, Duelmen, Germany

## Objectives

The objective of this presentation is to report on the outcomes of a 3 years (2013, 2014, 2015) N₂O emissions monitoring campaign on an agricultural soil in North-Western Germany. The field experiment aimed at identifying differences in N₂O emissions for fertilization with two N forms: calcium ammonium nitrate (CAN) and urea. This talk will focus mainly on the following aspects of the information generated by the campaign:

* Analysis of uncertainty for individual flux determination (i.e. measuring method induced uncertainty)

* Analysis of uncertainty for averaged fluxes (i.e. measuring method induced uncertainty + spatial variability induced uncertainty)

* Analysis of daily and cumulative N₂O fluxes for 2013, 2014 and 2015: flux dynamics for each year, effect of fertilizer forms on yearly cumulative emissions, differences among years

* Comparison between measured and modelled (LandscapeDNDC) N₂O fluxes

## Method

The experimental field (51°57′51.3″N 7°18′39.2″E) is located close to the city of Münster. It consists of an agricultural soil (sandy loam, 16.8 % clay, pH = 5.7, soil organic C = 1.0 %) cultivated with a rotation of winter barley (2013), oilseed rape (2014) and winter wheat (2015). The average yearly total precipitation is 759 mm.

The treatments consisted of control (no nitrogen fertilization), N fertilization with CAN and N fertilization with urea. Nitrogen amounts and splitting were different in each of the three years, and followed the local common management practice for each of the crops. All treatments started in 2003 and were replicated 4 times.

N₂O (and CO₂) fluxes were determined with the manual chamber + gas chromatography method. From 2013-03-07 to 2015-12-31 fluxes were determined on 259 days between approximately 9:00 am and 11:00 am. During the first 26 sampling dates gas samples were taken 0, 20 and 40 minutes after chamber closure. For all following sampling dates, samples were taken 0, 15, 30, 45 and 60 minutes after chamber closure.

If less than three concentrations were available for one chamber closure, the flux was considered not available. Fluxes were calculated with linear regressions through all remaining data points.

The coefficient of determination (R²) and the normalized root mean squared error (NRMSE) of the linear regressions were used as metrics for the uncertainty in each daily flux determination. The coefficient of variation (CV) was taken as metric for the uncertainty in the averaged daily fluxes (4 replicates). All calculations were done in R.

The ancillary data collected during the monitoring campaign will be used to simulate N₂O fluxes with the LandscapeDNDC model.

## Results

Analysis of uncertainty for the individual fluxes shows, in the vast majority of the cases, a R² above 0.8 and a NRMSE below 0.15 for fluxes above 5 g N₂O · N ha⁻¹ day⁻¹. Below this value the uncertainty in the mag-
nitude of the fluxes tends to increase very quickly. Fluxes below this magnitude are frequent and they contribute in a non-negligible way to the yearly cumulative fluxes. The uncertainty in the determination of the CO₂ fluxes was vastly smaller, and this indicates that the measuring protocol was applied according to best practice. A small number of the measured negative N₂O fluxes are characterized by a relatively high R² and low NRMSE: it is a strong indication that the soil acted as a N₂O sink under some circumstances. However, negative fluxes were infrequent and of relatively small magnitude.

The uncertainty of the averaged daily N₂O fluxes was quantified by means of the CV. The uncertainty in the averaged daily fluxes has two sources: i) uncertainty in the quantification of the individual flux and ii) difference in fluxes among replicate plots for the same treatment (i.e. spatial variability). The coefficients of variation for the averaged daily fluxes are relevant: for averaged fluxes above 5 gN₂O-N ha⁻¹ day⁻¹ the average coefficient of variation equals 55.9 %. Below this value the CVs increase quickly.

The daily N₂O fluxes during the three years show strong temporal variability, but the pattern for the two fertilized treatments is very similar during the whole measuring period.

Total cumulative emissions (g N₂O-N ha⁻¹) were:

1. 2013: Control = 854 ± 156; CAN = 1899 ± 296; urea = 1726 ± 211

2. 2014: Control = 1438 ± 1231; CAN = 6031 ± 1215; urea = 4566 ± 1608

3. 2015: Control = 810 ± 412; CAN = 1966 ± 400; urea = 2716 ± 560

The fertilized treatments clearly show higher pre-harvest emissions relative to the controls, while cumulative post-harvest emissions are much less affected by direct N inputs. For the control, post-harvest emissions amounted to 89, 95 and 57 % of the total in 2013, 2014 and 2015 respectively. For the two fertilized treatments they were approximately 55, 46 and 31 % in each of the three years.

The comparison between measured N₂O fluxes and N₂O fluxes simulated by LandscapeDNDC will allow better data interpretation.

## Conclusions

Data on N₂O emissions from long term field experiments provide the benchmark for the validation of simulation models like LandscapeDNDC. It is thus important to carefully evaluate the “uncertainty level” of measured emissions. The measuring protocol used in this study generally provides “reliable” individual flux estimates if the magnitude of the flux is above 5 gN₂O-N ha⁻¹ day⁻¹. However, the CVs of the averaged daily fluxes show that the spatial flux variability is a major source of uncertainty. If cumulative fluxes are evaluated, the temporal variability has to be considered as third source of uncertainty: this aspect is not discussed here but high frequency measuring campaigns show that N₂O fluxes can vary considerably even within 24 hours.

We observed a consistent seasonal pattern in the daily fluxes over three years: pre-harvest emissions are clearly enhanced by N fertilization while the difference in post-harvest emissions between the control and the fertilized treatments is much smaller.

In none of the three years was a significant difference detected between CAN and urea. The most significant difference which was observed is that among years: emissions in 2014 where significantly higher relative to 2013 and 2015 for both fertilized treatments (but not for the controls). The crops were cultivated in different years and a rigorous comparison is thus not possible; nevertheless, the data indicate that oilseed rape induced higher emissions relative to the cereals.
INTERNATIONAL TRADE OF ANIMAL FEED AND DECOUPLING OF NITROGEN AND
PHOSPHORUS CYCLING IN CROP AND ANIMAL PRODUCTION; CASE-STUDIES OF
ELEVEN COUNTRIES

jingmeng wang, qian liu, yong hou, wei qin, oene oenema

Wageningen University, Wageningen, The Netherlands

Objectives

International trade of crop and animal products has contributed to the specialization and agglomeration of
crop and animal production systems, which altered nutrient cycling. Animals in specialized farming sys-
tems are fed increasingly with maize and soybeans. This has increased animal productivity, and resulted in
uncoupling of crop and animal production, but with large differences between countries. To explore "why
are countries so different in the trade of maize and soybeans, and what are the impacts on nitrogen (N) and
phosphorus (P) cycling?", three hypotheses were examined: (i) trade of maize and soybeans, is related to the
specialization of animal farming in net importing countries, and to the specialization of crop systems in net
exporting countries, (ii) changes in the import of maize and soybeans are reflected by changes in nutrient
surpluses at country levels, and (iii) policy measures may reduce the impacts of the specialization of crop
and livestock production.

Method

A country-specific analysis was carried out of changes in the trade of maize and soybeans and changes in
livestock production (pigs, poultry, dairy cattle and beef cattle) characteristics between 1961 and 2011, using
data derived from national statistics (e.g. FAOSTAT). The impacts of these changes on N and P cycling were
based on additional model calculations. We selected seven major importing countries[1], which together ac-
counted for 30-60% of the total global trade of maize and soybeans, depending on year. Similarly, we select-
ed four main exporting countries[2], which accounted for 65-85% of the total trade of maize and soybeans.

Results

We observed that changes in the import of maize and soybeans are related to changes in livestock density (LSU) for importing countries, however with large variations between countries. For example in China, increases in pig number were significantly related to increases in the import of maize and soybeans (p<0.05), and increases in poultry number to that of soybeans. For exporting countries, the growth rate of maize and soybeans was larger than the rate of increase of the livestock production.

Embedded N and P in imported maize and soybeans used for feed was about 27% and 19% of the total amounts of N and P in traded crops, respectively. Main importing countries have specialized livestock production systems, based on import of maize and soybeans. Increases in imports over time were clearly related to increases of N and P surpluses in for example China, The Netherlands and Germany. Nutrient management policies have greatly reduced the N and P surpluses in the Netherlands and Germany, and possibly will do so in China in the near future.

Main exporting countries (USA, Brazil, Argentina) of maize and soybeans have large areas of agricultural
land per capita, but also have specialized and economically highly competitive livestock production systems,
which are spatially disconnected from the farms specialized in maize and soybeans production. India is a
special case; it has little agricultural land per capita but recently became an exporter of maize and soybeans
and at the same time greatly increased its poultry production.

Conclusions

In summary, changes in the international trade of maize and soybeans reflect in part specialization of crop
production and animal production in exporting countries and specialization of livestock production in importing countries. These contrasting patterns affect the nutrient cycling within and between countries, and affect also the N and P surpluses in those countries. The results of our study provide new insights into relationship between international trade of feed and the specialization of crop and livestock production system as well as their impacts on N and P balances.

## References

[1] Importing countries (China, Japan, Indonesia, Germany, Netherland, Spain, France)

[2] Exporting countries (USA, Brazil, Argentina, India).
# ARABLE MAIZE FOLLOWING PERMANENT GRASSLAND - IMPACT OF TILLAGE ON GREENHOUSEGAS-EMISSIONS, CARBON-BALANCE AND NITRATE-LEACHING

Inger Struck, Christof Kluß, Thorsten Reinsch, Antje Hermann, Ralf Loges, Friedhelm Taube

Christian-Albrechts University, Kiel, Germany

## Objectives

Silage maize is the primary energy source for intensive dairy and biogas production in Germany. Consequently, to comply with an increasing demand, the maize acreage has expanded steadily. This was accompanied by land use changes, i.e. the conversion of permanent grasslands, which generally implies a depletion of soil carbon and nitrogen stocks, favouring greenhouse gas (GHG) emissions such as N2O, CO2, CH4 and nitrate leaching depending on sward age in short-term. With respect to an increasing demand of biomass as well as climate protection and sustainable intensification there is an increased need for beneficial production systems (e.g. ley systems) while keeping environmental burdens as low as possible. Consequently the aim of the current field experiment is to identify mitigation potentials of direct seeding in comparison to conventional soil cultivation practice for silage maize following grassland in northern Germany.

## Method

Measurements of this study were conducted at the experimental station 'Hohenschulen' situated in the Eastern Upland of Schleswig-Holstein, northern Germany. The dominating climate is temperate-humid with a mean annual temperature and precipitation of 9.7 °C and 1007 mm in 2015, respectively. Typical soil types are Luvisols and Pseudogley-Luvisols with mostly a sandy-loam texture. The experiment is designed as a randomized split plot layout with three replicates. Prior maize seeding the 10 year old grassland sward was herbicide killed (glyphosate) in March 2015. Seeding was conducted in two treatments: Conventional tillage (CT) and no-till practice (NT). For CT the old grassland sward was first rotovated (-10 cm) and then ploughed (25 cm) followed by a rotary harrow for seedbed preparation. In NT treatments seeding was conducted using a direct seed drilling machine which slits open the soil for grain deposition and reseals it afterwards. In addition to different tillage treatments N-fertilization varied in two levels (0 and 180 kg N ha⁻¹ a⁻¹).

GHG emissions, nitrate leaching, yield and soil parameters gathered from CT and NT were compared with a 4 cut clover-grass sward composed of original grassland (CO). CO2, N2O and CH4 gas flux measurements started in March 2015 with the use of the closed static chamber method [1]; [2]. N2O and CH4 samples were generated weekly and subsequent to management practices such as tilling, ploughing, seeding and fertilization. Soil respiration and the net ecosystem exchange (NEE) of CO2 was determined every 2-4 weeks during growing season. In the present study round opaque chambers were used to gain ecosystem respiration data, whereas transparent chambers came into use for NEE. Nutrient losses through leaching processes were measured using ceramic suction cups installed within the field plots. Furthermore continuous growth sampling for both above- and below-ground biomass production was realized throughout the whole year.

## Results

First results show a slight advantage of NT compared to CT for N2O losses. Overall N2O emissions from maize were three- or twofold higher than from CO for the fertilized and unfertilized treatment, respectively. Highest emission peaks were measured just after grassland conversion in CT as well as for fertilizer application in NT. For CT maximum N2O fluxes were slightly lower than for NT maize and shifted in time by about one week, probably due to more unfavourable soil conditions for denitrification, such as low soil water contents and higher O2 concentration [3]. Further evaluation of soil water contents and soil mineral nitrogen data might reveal potential dependencies of N2O emission peaks on these abiotic factors.

Short term CO2 emissions immediately after grassland conversion, first by rotary cultivator loosening the old sward followed by mouldboard plough, showed a distinct increase in carbon emissions during the first six hours, probably because of released CO2 from soil pores. Mid-term CO2 emissions are currently being
evaluated.

## Conclusions

First results indicate that different soil properties after CT and NT have a strong influence on GHG emissions. For a comprehensive evaluation of both maize sowing systems in terms of global warming potential a detailed consideration of the two major greenhouse gases is necessary, as well as indirect emissions (e.g. nitrogen leaching) have to be taken into account. To assess the over-all environmental impact the total carbon budget (carbon export from harvested products and carbon inputs through above- and belowground biomass production) also needs to be considered.

## References

[1] Mosier, A. R. & Hutchinson, G. L. 1981. Nitrous oxide emissions from cropped fields. Journal of Environmental Quality. Vol 10, no 2.

[2] Drösler, M. 2005. Trace gas exchange and climatic relevance of bog ecosystems, Southern Germany. Dissertation, Technische Universität München.

[3] Baggs, E.M., Stevenson, M., Pihlatie, M., Regar, A., Cook, H. & Cadisch, G. 2003. Nitrous oxide emissions following application of residues and fertilizer under zero and conventional tillage. Plant and Soil, 254: 361-370.
# EVALUATION OF THE SUB-GRID VARIABILITY OF MODELS SIMULATING ATMOSPHERIC NITROGEN FLUXES AT THE REGIONAL SCALE FROM MODELS INTEGRATING PROCESSES AT THE LANDSCAPE SCALE

Niramson Azouz¹, Jean Louis Drouet¹, Matthias Beekmann², Pierre Cellier¹

¹INRA, Thiverval-Grignon, France, ²LISA, Créteil, France

## Objectives

Atmospheric concentrations and dry deposition rates of ammonia (NH3) may be high near the nitrogen sources and strongly decrease a few hundred meters away. The high spatial variability of NH3 concentrations and deposition rates makes it difficult to simulate accurate regional maps. To quantify the impact of deposition on nearby ecosystems, local models with high resolution are usually use, but they cannot be applied at large scales. Averaging NH3 fluxes in grids of models operating at the regional scale may lead to under- or over-estimation of the NH3 fluxes. They cannot highlight hotspots of NH3 deposition and their impacts on ecosystems. The study aims at quantifying NH3 deposition from two models, one operating at the local scale and the other at the regional scale. Results will provide insights for using the knowledge on sub-grid variability in local models to improve the nitrogen fluxes simulated in grids of regional models.

## Method

Several models of local and regional deposition of NH3 were developed either based on Gaussian or Eulerian dispersion schemes. The NH3 deposition schemes range from deposition velocities to multi-layer approaches being the most common scheme. Their spatial scales range from a few meters to several kilometers, with models being more adapted to very short range and others to regional NH3 deposition. A few models take into account wet and aerosol deposition, as well as chemical reactions in the gas phase. OPS-st is the short term version of the Operational Priority Substances (OPS) model, which is a regulatory model used to calculate the concentrations and deposition rates of air pollutants at local and national scales in the Netherlands [1]. OPS-st includes a module to calculate the contribution of local sources to receptors by using the Gaussian plume theory.

CHIMERE is an Eulerian off-line chemistry-transport model [2]. External forcing are required to run simulations: meteorological fields, primary pollutant emissions, chemical boundary conditions. Using these input data, CHIMERE calculates and provides the atmospheric concentrations of tens of gas-phase and aerosol species over local to continental domains.

Hereafter, NH3 sources were assumed to be at the ground level. OPS-st and CHIMERE were used to simulate the daily average deposition of NH3 for different grid sizes from data of the WRF meteorological database. This dataset was chosen since it was already used in the CHIMERE model, it was simple to modify for different scenarios and it covered all Europe. To compare the predictions from both models, several hypothetical scenarios were designed to reproduce the heterogeneity of NH3 fluxes and concentrations within domains of a few hundred square meters. Few parameters were modified in both models to have the same initial conditions and settings for the different scenarios. Changing parameters and input variables gave the possibility to simulate contrasted studied cases and compare the results simulated by both models.

## Results

Patterns of NH3 dry deposition were spatially heterogeneous, depending on the model, the distance of the receptors from the source and the grid size. NH3 dry deposition in OPS-st was very local (i.e., a few meters from the source) and the total amount decreased very rapidly as a function of the distance. This highly localized deposition was also accompanied by a heterogeneous distribution over the domain area: dry deposition next to the source was higher when the grid size was smaller.

Results showed that NH3 deposition at 2 km downwind might represent up to 60 % of the total dry deposition. This distance might increase with increasing source height, increasing atmospheric stability, increasing wind speed and decreasing roughness at the surface. The predominant factors controlling short range depo-
sition were turbulent mixing at the source height which was influenced by wind speed, atmospheric stability and surface roughness. Increasing wind speed led to decreased local deposition of NH3 that was due to more dilution of the NH3 emitted by the source and deposited downwind. The change of the deposition distance with the different resolutions was accompanied by a change of the deposition peak next to the source. However, this difference disappeared after about 2 km from the source, even when deposition was higher far from the source at coarse resolution. All model inputs were identical, but a few variables contributed to an additional bias between models (e.g., source height, wind speed, wind direction) although simulated outputs (e.g., emission rate, exit velocity, boundary layer height) might produce higher bias between both models.

On the one hand, the Eulerian model represents the turbulence through the vertical diffusion coefficient which depends on the meteorological conditions. On the other hand, the Gaussian equation derives from the same dispersion equation as in the Eulerian model, but it assumes a constant and homogeneous wind. Thus, the plume evolution simulated with the Eulerian model represented well the plume dispersion at long range, but underestimated the dispersion at short range. Gaussian models, used on short-range experiments, better represent this behaviour by adapting the dispersion to the distance from the source.
A strong positive correlation was shown between dry deposition velocity and wind speed. Dry deposition decreased with increasing wind speed in all meteorological conditions. This result was consistent with previous studies that showed that the magnitude of dry deposition strongly depends on wind speed. NH3 transport was highly affected by the aerodynamic driving force of the wind speed. High wind speed tended to increase friction velocity that accelerates NH3 transport.

## Conclusions

A theoretical and statistical comparison of an Eulerian model (CHIMERE) with a Gaussian plume model (OPS-st) was performed on simplified hypothetical scenarios. We showed that it is not possible, on theoretical cases, to have the same dispersion pattern near the source with the Eulerian model and with the Gaussian model. The Gaussian model was equivalent to the Eulerian model in which the diffusivity depends on the distance from the source. With this theoretical underestimation of dispersion and dry deposition for CHIMERE model near the source, we performed a statistical comparison between the dry deposition outputs of both models.

Although CHIMERE could not accurately reproduce the dispersion and deposition near the source in a theoretical case, it produced acceptable averaged results for the whole simulation domain. One advantage of CHIMERE is that it may be used in much more complex cases of inhomogeneous turbulence than the cases for which it was conceived. However, NH3 deposition near the source could be improved by using spatial statistical relationships given by the OPS-st model to redistribute NH3 dry deposition near the source without modifying the code of the Eulerian model.

## References

[1] Van Jaarsveld, J.A. 2004. The Operational Priority Substances model. Description and validation of OPS-Pro 4.1. RIVM-report 500045001. RIVM, Bilthoven, The Netherlands.

[2] Menut, L., Bessagnet, B., Khvorostyanov, D., Beekmann, M., et al. 2014. CHIMERE 2013: a model for regional atmospheric composition modelling. Geoscientific Model Development, 6(4), 981-1028.
# ANAEROBIC DIGESTION OF ORGANIC MANURES AND EFFECTS ON NITRATE LEACHING ESTIMATED UNDER DANISH CONDITIONS

Peter Sørensen, Christen D. Børgesen

Aarhus University, Department of Agroecology, Tjele, Denmark

## Objectives

Part of the organically bound nitrogen (N) in manure and organic waste is converted to inorganic N by anaerobic digestion (AD) in biogas plants, and it influences both the fertilizer value of the manure and N leaching. The objective of this work was to estimate long-term effects of AD of organic manures on N leaching under Danish conditions using a novel model. This also included effects of contrasting soil and climatic conditions and estimation of the temporal effect of AD when using different types of feedstock inputs in the biogas plant.

## Method

Calculations of long-term N leaching were compared after application of untreated or digested manures using a new model described in detail by [1]. The change in the relationship between inorganic N and organic N by digestion is particularly important for the long-term leaching of N, and the model was used to calculate the long-term impact of digestion on N leaching. The proportion between organic N and inorganic N was assessed for different manure types. Based on a review of a number of old experiments in which N leaching was compared after application of mineral fertiliser and manure, we found that leaching from applied organic N and inorganic N is approximately similar in the first year after application. We used the empirical N-LES4 model [2] to estimate the first-year leaching from application of inorganic N and organic N in fertilisers in typical crop rotations on both dairy and plant production farms. Leaching estimates in the N-LES4 model is influenced by crop type, soil clay content and water drainage, and leaching estimates have been made for two contrasting conditions in Denmark: on sandy soil with a high precipitation and on loamy soil combined with low precipitation. The long term leaching of mineralized organic N is higher than for spring-applied inorganic N as N mineralization also takes place during autumn/winter when there is little or no crop N uptake [3, 4]. Based on calculations with the FASSET model mineralized N was assumed to be leached with a leaching factor that is twice as high as that for spring-applied inorganic N. The long-term time course of leaching was calculated using a model for the temporal mineralization of manure N. A similar average mineralization course was used for organic N in all manure types.

## Results

With the current Danish fertiliser legislation total N inputs to land are unchanged after AD and an expected higher fertiliser value of the digestate is not accounted for in fertiliser planning. Under such conditions unchanged N leaching is estimated after the 1st year relative to the supply of untreated biomass/manure, while over a 10 year horizon a reduction in N leaching of 1.0 to 1.4 % of the manure total N input is estimated on loamy soils and a reduction of 1.9 to 2.7 % of the manure N input on sandy soils with high precipitation. Over a 50-year horizon, the corresponding reduction in N leaching after digestion is estimated to 1.5-2.2 % of the manure N input on loamy soils and 2.8-4.2 % on sandy soils. For example this means a long-term (50 yrs) reduction in N leaching of 2.5-7 kg N/ha by application of 170 kg total N/ha in manure. After AD of manures the fertiliser value is expected to increase by about 8 % points [1]. If mineral fertiliser N application is reduced correspondingly this results in a further reduction of N leaching equivalent to 1.0-1.8 % of total manure N application.

Scenarios with different combinations of manure and biomass were compared. Utilization of bioenergy crops like maize-silage for co-digestion in biogas production was estimated to increase N leaching depending on the proportion of N supplied with the energy crop. By use of high proportions of maize silage N leaching will exceed that from untreated manure with the present regulation due to a higher organic N input to land. For example it is estimated that application of 12 % maize-silage (by fresh weight) results in a slight increase of N leaching in the first year equivalent to 1-2 % of the manure N input while after 50 years there
is no significant change in leaching compared to using undigested manure. Similarly, slightly increased long-
term N leaching can be expected if new wastes, like household wastes, are introduced for land application
using anaerobic digestion. This occurs because the input of total N per hectare will increase by such practice,
as the extra organic manure input with a low N utilisation rate replaces inorganic N with a higher utilization
rate.

Conclusions

A new simple model was developed and used for estimating the temporal effect of anaerobic digestion of organic manures on N leaching under Danish climatic conditions. The calculations indicate no effect of AD on N leaching in the first year, but with time an increasing reduction is estimated and after 50 years a leaching reduction equivalent to 1.5-4 % of the yearly manure total N input is estimated. This applies when total N application is unchanged with and without AD. A further reduction in N leaching can be achieved if the higher expected fertiliser value after AD is accounted for and mineral fertiliser N application is reduced. By addition of new organic inputs to biogas plants, e.g. in the form of a maize silage energy crop, the reduction in N leaching decreases and may even cause higher N leaching than by use of the untreated manure.

References

[1] Sørensen P., Børgesen C.D. 2015. DCA report no 65, Aarhus University.

[2] Kristensen K., Waagepetersen J., Børgesen C.D., Vinther F.P., Grant R., Blicher-Mathiesen G. 2008. DJF Plant Science no 139. 1-25.

[3] Thomsen I.K., Kjellerup V., Jensen B. 1997. Plant and Soil 197, 233-239.

[4] Sebilo M., Mayer B., Nicolardot B., Pinay G., Mariotti A. 2013. PNAS 110, 18185-18189.
# THE EFFECTS OF SOIL TYPE AND CAULIFLOWER CROP RESIDUE PLACEMENT ON NITROUS OXIDE AND AMMONIA EMISSIONS

Leif Nett¹, André Sradnick¹, Roland Fuß², Heinz Flessa², Matthias Fink¹

¹Leibniz-Institute of Vegetable and Ornamental Crops Großbeeren and Erfurt, Großbeeren, Brandenburg, Germany, ²Von Thünen Institute, Institute of Agricultural Climate Research, Braunschweig, Lower Saxony, Germany

## Objectives

The decomposition of vegetable crop residues, e.g. from Brassica species, can cause substantial nitrous oxide (N₂O) and ammonia (NH₃) emissions due to their high nutrient and water contents. One promising approach to reduce these harmful emissions is the right choice of post-harvest tillage technique. The published results on the effects of different crop residue placement techniques on N₂O and NH₃ emissions so far do not give a consistent picture. One of the key issues is the diverse experimental conditions, in particular with respect to soil characteristics. To shed light on the soil-specific effects of residue placement technique on N₂O and NH₃ emissions, we studied the effects of cauliflower crop residue placement and soil type in a full factorial experiment.

## Method

The experimental factor “soil type” was realized by taking advantage of a unique open-air facility featuring three different soils with contrasting soil texture (loamy sand, silt loam, sandy clay loam). The facility was established south of Berlin in 1972 where average annual precipitation sum is 500 mm yr⁻¹ and the mean annual temperature is 9.8 °C. In this facility, cauliflower was grown according to common agricultural practice (protective nets, irrigation) and fertilized inorganically according to soil mineral N target values and expected N uptake. The crop residues were removed fresh, immediately slashed, and applied at rates equivalent to 154 kg N ha⁻¹. The experimental factor “residue placement” comprised four levels: complete removal of residues after harvest (“control”), surface application of residues and incorporation three weeks later (“mulch”), incorporation of residues by mixing (“mix”), incorporation of residues by plowing (“plow”). Emission sums of N₂O and NH₃ were derived from linearly interpolated gas flux measurements. Flux measurements of N₂O were obtained by applying the closed-chamber technique in combination with gas chromatography (4 samples per measurement). For NH₃, a passive filter trap method was used in combination with the ventilated closed chambers. The experimental duration lasted for 7.5-months, starting with cauliflower harvest.

## Results

The addition of cauliflower crop residues generally increased both N₂O and NH₃ emissions as compared to the control for a period of 1-2 months. The N₂O emission sums (7.5 months) induced by residue application, i.e. after subtraction of the soil-specific control emission sums, were significantly affected only by residue placement, not however by soil type or the interaction of the two factors. The results suggest that cauliflower residues incorporated by plowing always cause higher N₂O emissions (2.3-3.4 kg N₂O-N ha⁻¹) than after surface application (0.4-0.9 kg N₂O-N ha⁻¹) or incorporation by mixing (0.7-1.3 kg N₂O-N ha⁻¹), irrespective of the soil type. This can be explained by the concentration of water and nutrients in a layer of burrowed crop residues after plowing, which most strongly supports the formation of anaerobic denitrification hot-spots. Apparently, this may also be true in a well-aerated soil, such as the loamy sand, which exhibited soil bulk water contents around 30 % water-filled pore space. Here, fresh patches of nutrient-rich residues can presumably create microsites that are at least temporarily independent of the abiotic conditions in the bulk soil. Yet, it cannot be ruled out that other source processes contributed significantly to N₂O emissions, especially in the loamy sand. In contrast, NH₃ emission sums induced by crop residues were significantly affected by residue placement, soil type, and the interaction of the two factors. Multiple comparisons revealed that this translated into significant differences among residue placement treatments in the loamy sand but not in the silt loam or sandy clay loam. In the loamy sand, the emissions increased in the order plow < mix < mulch (0.2 < 1.0 < 1.9 kg NH₃-N ha⁻¹). These results principally corroborate findings of other studies in that incorporation generally reduces NH₃ emissions substantially in comparison with surface-application. As far as
the soil-type specific effect of residue placement is concerned, the results suggest that NH₃ emissions can be expected to be low in fine-textured soils with high cation exchange capacity, even when residues are surface-applied. In contrast, in coarse-textured soils with low cation exchange capacity the technique of residue application has a decisive impact on NH₃ emissions, which decrease with the deepness of incorporation. This result may be limited to situations where plant sap can be easily leached from the surface layer of residues to the upper mineral soil. In this context, the preparation of crop residues, viz. slashing in the present study, is presumably of particular importance.

## Conclusions

Incorporating fresh and slashed cauliflower crop residues by plowing appears to produce the highest N₂O emissions in a range of soils whereas surface-application may primarily increase NH₃ emissions in coarse-textured soils with low cation exchange capacity. Future studies can be focused on testing the assumption of local and temporal independence of crop residue patches in terms of abiotic conditions or the contribution of different soil depth intervals to gaseous N emissions after application of crop residues.
LOW USE OF NITROGEN IN THE COLUMBIAN INDUSTRY OF SUBSTRATE GROWN CUT FLOWERS

Carlos A. Gómez Gómez¹, Nathalia R. Casas Ortíz², Martha Cristina Bustos López³, Nicolás Hernández Guarín⁴, Víctor Julio Flórez Roncancio⁵, Carlos Alberto González Murillo⁶

¹Universidad Nacional de Colombia, Bogotá, Colombia, ²Universidad Nacional de Colombia, Bogotá, Colombia, ³Universidad Nacional de Colombia, Bogotá, Colombia, ⁴Universidad Nacional de Colombia, Bogotá, Colombia, ⁵Universidad Nacional de Colombia, Bogotá, Colombia, ⁶Universidad Nacional de Colombia, Bogotá, Colombia

Objectives

1. Evaluating nitrogen content adjustment in the fertirrigation formula used for substrate grown minicarnations *cv*. Rony in the Bogota plateau.

2. Determining nitrogen content in substrate, foliar tissue and leachate at different phenological stages of minicarnation *cv*. Rony

3. Proposing and evaluating an alternative nitrogen content for the fertirrigation formula of minicarnation *cv*. Rony.

Method

The trial was carried out in the facilities of *Marengo Agrarian Center*, which belongs to *Universidad Nacional de Colombia*, is located in the municipality of Mosquera (14 km from Bogota) and makes part of the Bogotá campus. A weighing lysimeter was employed as supporting tool for fertirrigation decision making.
Minicarnation plants (*Dianthus caryophyllus* L.) *cv*. Rony were grown in a substrate made up of re-used rice husk, new rice husk and plant residue compost in percentages of 60, 30 and 10%, respectively, at a planting density of 24.7 plants.m⁻² of greenhouse area. The irrigation system consisted of two 14 mm driplinesper bed, equipped with self-compensating emitters at 15 cm spacing and flow rate of 1.1 L.h⁻¹.

The experimental design was a repeated measures one with three between subjects factors (lixiviate, plant tissue and substrate), and a single within-subject factor (time). Three samples of lixiviate, three of substrate and three of total plant tissue were taken every seven weeks. The experiment was monitored for a period of 28 weeks. Statistical differences among treatments were identified in SAS 9.2.

Two treatments were applied: Treatment 1 (T1), which followed commercial growing criteria, and Treatment 2, with a modified formula. From planting to week 16, T1 contained the following compound formula (mg.L⁻¹): N, 220; P, 30; K, 130; Ca, 120; Mg, 40; Fe, 2.5; Cu, 1; Zn, 0.5; B, 2; Mo, 0.1. This formula was adapted from weeks 17 to 28 as follows: N, 165; P, 25; K, 190; Fe, 3; Zn, 1 and B, 1.5. In T2, the conventional formula was modified in its N content. During the vegetative phase, it contained (mg.L⁻¹): N, 110; P, 30; K, 130; Ca, 120; Mg, 40; Fe, 2.5; Cu, 1; Zn, 0.5; B, 2; and Mo, 0.1. During the productive phase, modifications for T2 were: N, 90; P, 25; K, 190; S, 127; Fe, 3; Zn, 1; and B, 1.5, with no variation in all other elements. Both treatments were daily applied through 3 to 4 irrigation pulses per bed, each of which poured 70 to 80 L, depending on climate conditions.

Results

Under both treatments, N content was observed to increase during the first seven weeks of the experiment, reaching values that ranged between 3.2 and 3.6%, which can be considered normal according to foliar tissue reports by Ortega [1]. Later on, these values decreased until week 28, with average values of 2.4% for T1, and 2% for T2. Under both treatments, and according to usual standards, the crop's N assimilation values obtained during this period, which were found to be below 3%, would indicate deficiency of this nutrient. However, no deficiency symptoms (such as plant color changes) were observed.

According to Vélez [2], carnations grown in burnt rice husk show decreased N percentages in plant tissues, with values ranging between 1.89 and 2.67%, which are similar to those reported in the current work for T1 and T2. This, coupled to the fact that the plants were not affected by the N drop observed along plant growth, demonstrates that said reduction was due to age and concomitant needs.
As to substrate measurements, significant differences in nitrogen content were found during week 1 under both treatments, when no nutrient solution had been applied. Thereafter, and except for significant differences recorded on week 28, no additional ones were found for the substrate-time interaction.

Substrate N content remained steady from weeks 7 to 21. In analyzing this nutrient across phenological stages, Botero and Flórez [3] report that it shows relatively lower levels during the first weeks, after which it goes up, to decrease during the final weeks before cutting. While T1 exhibited this behavior, T2 determined regular N levels all along the experiment. In this respect, Vélez [2] has observed that in all phenological stages, N percentages are inversely correlated with burnt rice husk proportion.

Maximizing crop productivity requires precision in N supply. This not only implies an optimal application of this mineral, but an optimal ammonia - nitrate - urea ratio in irrigation water as well. In greenhouse flower production, wherein irrigation results in a rapid flow through the radical zone, only $NH_4^+$ and $NO_3^-$ are usually applied, their ratio being used to balance rhizospherepH over time [4].

## Conclusions

The N content modification treatments did not affect growth rate or stem length. Optimal exportation quality (99.63 cm stem length) was obtained under T1. Nonetheless, T2 allows reaching national market quality and 10% exportation quality.

A variable $NO_3^+$ concentration was observed under T1. In contrast, nitrate leaching under T2 showed stable behavior. This indicates that N concentration can be modified without affecting plant development. In this way, nitrate dumping in superficial and underground waters can be reduced.

In sum, N concentration reduction as applied in T2 constitutes a feasible option in carnations.

## Acknowledgements

The authors want to express their gratitude to Colciencias, Asocolflores and Ceniflores for financial support granted to the present research work.

## References

[1] Ortega R., D. 1997. Fertirrigación en cultivos de flores. In: Silva M., F. (ed.) Fertirrigación, Sociedad Colombiana de Ciencia del Suelo, Colombia. p.136-147.

[2] Carvajal, N. A. V., Roncancio, V. J. F., and Rivera, A. F. 2014. Comportamiento de Variables Químicas en un Sistema de Cultivo sin Suelo para Clavel en la Sabana de Bogotá. Rev. Fac. nal. Agr. Medellín, 67(2), 7281-7290.

[3] Botero, A. y Flórez V. 2012. Cambios en la composición química de los sustratos en el cultivo de clavel. In: Avances sobre fertirriego en la floricultura Colombiana. Universidad Nacional de Colombia. Bogotá. p. 124-132.

[4] Bar-Yosef, B., Mattson, N.S. and Lieth, H.J. 2009. Effects of $NH_4^+$: $NO_3^-$ urea ratio on cut roses yield, leaf nutrients content and proton efflux by roots in closed hydroponic system. ScientiaHorticulturae, 122(4), 610-619.
# EFFECT OF WOOD ASH AND ROCKDUST ON CLOVER GROWTH AND DINITROGEN FIXATION

Sigrun Dahlin¹, Maria Stenberg²,³

¹Swedish University of Agricultural Sciences, Uppsala, Sweden, ²Swedish Board of Agriculture, Skara, Sweden, ³Swedish University of Agricultural Sciences, Skara, Sweden

## Objectives

Bioenergy production with recycling of nutrient-rich by-products for agricultural or forest production can contribute to a circular economy. Wood ash not only contains high concentrations of nutrients (and potential pollutants) but also is a liming agent. Basaltic rockdusts are by-products from quarries and are sold and promoted as soil amendments. This study aimed to investigate if application of wood ash or basaltic rockdust can increase N₂ fixation by red clover (Trifolium pratense L.) grown in mixture with perennial ryegrass (Lolium perenne L.) on an inherently acid and nutrient-poor soil.

## Method

A fully randomised pot experiment (4 replicates) testing amendment with by-products was revisited. Samples from treatments with bottom ash derived from mixed deciduous wood or basaltic rockdust, and a non-amended control were selected for analysis.

Topsoil was used from a postglacial silt loam which originated from mainly granitic and sandstone bedrock and had semi-natural grassland vegetation. The soil was sieved through 8×18mm mesh and homogenised before use. Portions of 6 kg dry weight were weighed to each pot and the amendments added after which all soil portions were homogenised. The ash was applied at 0.14 kg m⁻² conforming to the maximum allowable 7-year application rates for trace elements as stated by the Swedish Environmental Protection Agency. Application rates for the rockdust surpassed these limits on the assumption that element availability was low; application thus followed the supplier's recommendation (5.0 kg m⁻²).

A mixture of red clover (cv. Nancy) and perennial ryegrass (cv. Helmer) was sown and thinned to 10 plants of each species per pot *ca* 2 weeks after emergence. Pots were also sown with pure ryegrass to serve as reference plants. The pots were kept in a fenced outdoor area and irrigated with deionised water to complement precipitation during the growing season and subsequently over-wintered at 0°C. Pots were returned to the outdoor area in April and harvested 15 June, 20 July and 20 August 2010. The clover was between the stem elongation and early flowering stage at all three harvests. Shoot material was force-dried at 50°C in perforated plastic bags, weighed, milled in a Grindomix GM 200 cutting mill and dry matter content determined on subsamples. Care was taken at all stages to prevent sample contamination. Samples were analysed for total N (LECO CN2000) and ¹⁵N abundance. N₂ fixation was estimated by the ¹⁵N natural abundance method [1] using the ryegrass in pure stands as reference crop and the lowest determined delta ¹⁵N value as B value [2].

## Results

Clover dry weight at the first cut was significantly highest on the ash amended soil (218 g m⁻²), lower in the rockdust amended soil (145 g m⁻²) and lowest on the control soil (85 g m⁻²). Differences were significant also at the second cut. However, there were no significant differences at the third cut. This growth period had hot and dry weather which induced water stress in the pots, and most so in the ash amended treatment which had the highest electrical conductivity (not shown).

The ash amended crop accumulated significantly more total N (5.5 g m⁻²) than the control (2.7 g m⁻²) at the first cut, while the rockdust amended crop was intermediate (3.9 g m⁻²) and not significantly different from the control. However, the total N concentration in the clover was higher in the control treatment (3.2% and 3.6%) than in the rockdust (2.7% and 2.9%) and wood ash (2.5% and 2.1%) treatments during the first and second cuts, respectively. The higher N concentration in the control treatment with its low biomass and lower concentration in the amended treatments suggests an N dilution effect caused by the increased biomass
accumulation [3]. Dahlin *et al.* [4] found that Mg and Mo most likely limited clover growth on this soil, and this limitation was apparently alleviated by the application of ash and to some degree by the rockdust application. Other factors may also have contributed, though, such as differences in leaf:stem ratio and low numbers of rhizobia limiting N₂ fixation.

The percentage of clover N derived from air ranged 74-78% at the first cut and increased slightly to 87-91% at the third cut, with no significant differences between the treatments. The amount of fixed N in clover in the first cut was thus significantly higher in the ash amended clover (3.8 g m⁻²) than in the control (1.7 g m⁻²), with the rockdust-amended clover intermediate (2.7 g m⁻²) and not significantly different from the control. The second cut showed the same trend, but differences were non-significant. Soil N used by the clover was significantly higher in the ash-amended plants (1.3 g m⁻²) than in the control (0.6 g m⁻²) with the rockdust amended clover intermediate (0.9 g m⁻²). This suggests that increased mineralisation of soil N due to increased pH decreased the need for fixed N which may have contributed to the no-effect on the percentage N derived from air despite increased total N accumulation. The results confirm earlier work that N₂ fixation is generally driven by plant N demand as determined by biomass accumulation and availability of soil N.

## Conclusions

The ash amendment increased N fixation and plant growth strongly in the clover. Plant growth increased to a lower degree on rockdust amended soil, but the N fixation was not significantly higher than in the control.

The study suggests wood ash high in nutrients but low in pollutants can be successfully used as a multi-element soil amendment to enhance clover growth on low-fertility soils. However, further studies including field experiments are required.

## Acknowledgements

¹⁵N analyses and data evaluation was funded by Intendent CL Behms fond för baljväxtodling.

## References

[1] Jarrell, W.M., Beverly, R.B. 1981. Advances in Agronomy 34, 197-224.

[2] Dahlin, A.S., Edwards, A.C., Lindström, B.E.M., Ramezanian, A., Shand, C.A., Walker, R.L., Watson, C.A., Öborn, I. 2012. European Journal of Agronomy 43, 33-39.

[3] Cole, C.V., Heil, R.D. [SD2] 1981. In: Clark, F.E., Rosswall, T. (eds) Terrestrial Nitrogen Cycles, Ecological Bulletins, 33, 363-374.
# GUIDING FARMERS TOWARDS SMART FERTILIZATION AND A BETTER SOIL QUALITY IN BELGIUM AND THE NETHERLANDS

G. Verlinden¹, S. De Neve², R. Postma³, D. Germey¹, S. Sleutel², M. Hanegraaf³, K. Cochez¹, J. Dewaele², S. Steyaert¹

¹Flemish Land Agency, Ghent, Belgium, ²Ghent University, Ghent, Belgium, ³Nutrient Management Institute, Wageningen, The Netherlands

## Objectives

The LIFE-Demeter project (project partners: Flemish Land Agency (B), Ghent University (B), Nutrient Management Institute (NL)) wanted to develop an integrated approach to tackle the environmental problems (low soil quality, polluted water) caused by unsustainable soil management in Flanders and the Netherlands.

### Specific objectives:

- increasing awareness amongst all agricultural stakeholders about the benefits and principles of a sustainable soil and nutrient management in daily farm practices.

- developing a decision support tool at field level integrating the major aspects of sustainable soil management: soil organic matter optimization and N and P fertilization. The tool will translate results of scientific research into practical recommendations to farmers. The more farmers will use the tool and implement the tool's advices, the more the considered environmental problems (soil quality, polluted water) are improving.

- training farmers and advisors in the use of the tool. This will facilitate adoption of the tool and increase sustainable environmental results.

## Method

The EU LIFE Demeter project created a unique integrated approach to improve both soil and water quality.

### Development of the decision support tool, named Demetertool

The Demetertool operates as an online open-ended tool, whereby input can be specifically adjusted for each farm. The tool works with limited input and a user-friendly interface to enhance its success.

The Demetertool consists of an organic matter module (carbon evolution in the soil, using the Roth-C model) and a nutrient module (N and P balances) and operates on the field level. Following input of basic management and soil information of the field, the Demetertool offers farmers a soil balance-based N fertilizer advice, a long-term prediction of soil organic carbon stock evolution as well as a simple P-balance for a given crop rotation. These practical recommendations aim at a more integrated sustainable management of both nutrients and soil organic matter on an individual plot scale.

To maximize its usefulness, the tool was tested by experts, by 80 Flemish and Dutch farmers and 20 farm advisors of the Flemish Land Agency.

### Validation of the decision support tool - field monitoring study

The Demetertool was validated with a group of 80 farmers in Flanders and the Netherlands. For each of the participating farms, the farm and soil management was studied. Two fields per farm were extensively monitored during 3 years. For each field soil analyses were performed (%C, pH, plant-available P, K and Mg, mineral N in the soil profile) and applied manure was analysed. Based on the soil analyses a fertilization advice was generated with the Demetertool. At the end of the growing season the applied fertilization was compared to the given advice and crop yield and residual nitrate in the soil profile were measured and discussed with the farmer.

### Farm guidance

During the project Flemish farmers were visited and guided by the counselors of the Flemish Land Agency
individually. During these visits, the counsellors advised the farmers about a more environmentally friendly farm management. Dutch farmers visited study group meetings, in which measures to improve their management were discussed.

## Results

A decision support tool for sustainable soil management was developed and validated in Flanders and the Netherlands. Farmers were trained in using the webtool and about the principles of sustainable soil and nutrient management. To support this, information sheets were developed. Out of these methods came forth a set of results.

Since 2015, the decision support tool (Demetertool) is online. The freely available tool offers farmers a hands-on report about both the organic matter evolution and the nutrient management (nitrogen and phosphate) on their land. Moreover, farmers can change their inputs in the tool all the time and thus make simulations to calculate how much they can improve their soil quality significantly even by taking simple measures s.a. green crops, changing rotations and manure types,...

The Demetertool may be considered as a successful tool, appreciated by farmers and advisors as proven by the high number of active accounts (>500) since the tool was launched online.

The participating fields in the monitoring study had a loamy, sandy loam or sandy texture in Flanders and a sandy texture in the Netherlands. In Flanders soil organic matter content was low in the loamy and sandy loam soils: 63 and 50% of these fields had an OM content lower than 2% OM, respectively. In the Netherlands, 6% of the participating fields had an OM content lower than 2% OM and 59% below 3% OM. On 36% of the participating fields the applied N by the farmer was in accordance with the advice generated by the Demetertool. 33% of those fields had a residual nitrate content in autumn above the limit of 90 kg nitrate-N/ha. On 34% and 30% of the participating fields the farmers applied more or less N than the recommended dose, respectively. This resulted in a residual nitrate content above the limit in 39% and 19% of the fields, respectively.

The field monitoring study and guidance of the farmers resulted in a list of frequently asked questions most farmers have. Based on these questions, key topics were selected to create practical information sheets. This resulted in the information package: "A successful harvest on a healthy soil".

Until now, this package contains information sheets about 15 topics: Green crops, Soil acidity, Plant nutrients, Working with the Demetertool, Soil structure and compaction, Crop rotation, Organic matter, ...

This information package is freely available in both a digital as a paper version and is used frequently by farmers and by advisors as teaching material. In 2016, also students in agricultural studies and new farmers will be addressed to work with both the Demetertool and the information package.

## Conclusions

The Demeter project has delivered a decision support system that can help farmers to optimize nutrient and soil organic matter management simultaneously at field level. Calculations illustrate the potential of the DST as a unique and valuable tool for fertilizer recommendations and management of soil organic matter.

The information package "A successful harvest on a healthy soil" developed during the project is a useful and practical tool for farmers and students to learn more about sustainable soil and nutrient management.

The project results and products were mainly launched in 2015, as the Demeter project ended in 2016. To maximize the practical use of the project results, the three complementary partners cooperating in the Demeter project will consolidate these results in the long term. These partners are the Flemish Land Agency (BE), the Nutrient Management Institute (NL) and Ghent University, Department of Soil Management (BE).
The partnership created a long term action plan to guarantee awareness raising and maintaining the use of the Demetertool and information sheets after the projects end. Part of this plan is a set of communication actions s.a. social media, news messages, event communication, ... but also a maintained farm guidance in the form of group sessions and teaching sessions amongst students. The project partners will promote replication of the Demetertool in other European regions and countries.

## Acknowledgements

Demeter is a LIFE+ project. The EU LIFE+ programme finances projects that contribute to the development and implementation of environmental policy and legislation.
PARAMETRIC CONSTRAINTS ACROSS PROCESS-BASED MODELS IN SIMULATING
NITROUS OXIDE EMISSIONS FROM ARABLE FIELDS

M. I. Khalil¹, B. Osborne¹, M. Abdalla², G. Lanigan³, M. Williams⁴, C. Mueller¹,⁵

¹University College Dublin, Dublin 4, Ireland, ²University of Aberdeen, Aberdeen, UK, ³Teagasc, Johnstown Castle, Wexford, Ireland, ⁴Trinity College Dublin, Dublin 2, Ireland, ⁵Justus-Liebig-University Giessen, Giesen, Germany

Objectives

The development and selection of process-based models requiring a limited number of readily available input parameters for accurate quantification of agricultural greenhouse gas (GHG) emissions and the identification of mitigation options is a significant objective. Of particular importance is the quantification of the fluxes of nitrous oxide (N₂O), a potent and stratospheric reactant having a large emission uncertainty. Several models are currently used to predict a GHG emissions in different ecosystems, DNDC [1], DailyDayCent [2] and ECOSSE [3]. In Ireland, some models have been tested/validated but the results have not been sufficiently robust for use in the inventory process. The availability of multi-year N₂O flux data and input parameters measured at field scale facilitated model comparison exercises. The main objectives were to simulate daily N₂O emissions using common input parameters, evaluate their seasonal/annual fluxes and emission factors (EF) together with an examination of differences between model outputs and measured datasets.

Method

Data on inputs and management practices were collected from field experiments conducted at the Teagasc, Oak Park, Carlow Research Station (Sandy loam-loam in texture, free draining, Euteric Cambisol). The experiments consisted of conventionally-tilled spring barley crops receiving N fertilizer (CAN) at 135-159 kg N ha⁻¹yr⁻¹ and crop residues at 3 t ha⁻¹yr⁻¹ over 8 years. Sampling of N₂O fluxes were carried out using static chambers at 0, 30 and 60 min intervals between 9 and 11 AM every week and more intensively (twice weekly) following fertilizer application, and measured using gas chromatography with an ECD. Simulations using three dynamic models (ECOSSE v5+, DNDC v9.4 and DailyDayCent) were performed and the comparative performance was evaluated against the effect of the measured variables on N₂O emissions. The datasets were collated and compiled to prepare a list of common input parameters with respect to site characteristics and management practice and either default or module-based datasets, including 30 year meteorological data (1982-2011) to initiate the models. Detailed site characteristics and input parameters can be found elsewhere [4,5,6].

The models were run (with initialization of soil C pool at steady state equilibrium values with crop residue inputs and N as NO₃⁻ concentration measured immediately before the start of the experiments) using the common input parameters. The outputs were collated and converted into standard units for comparison with measured datasets. The simulated values of N₂O were compared and validated quantitatively with measured and/or outsourced values. An evaluation of the consistency of seasonal (crop growing period)/annual N emissions with simulated values was carried out. Equal weights on all simulated values were placed to test the model fits for all data points. Seasonal and annual EFs over the simulation period were calculated by subtracting cumulative measured and model outputs of unfertilized controls from that of the fertilized treatments and dividing by the respective N inputs. Where applicable, an analysis of variance for significance at *p*<0.05 was performed and the exact 95% confidence intervals calculated using both SAS v. 9.3 (SAS Inc.) and MODEVAL.

Results

The maximum N₂O fluxes measured over 8 years was 17.6 g N ha⁻¹d⁻¹ (except one i.e. 56.0 g N ha⁻¹d⁻¹) and a minimum of -8.0 g N ha⁻¹d⁻¹ for the fertilized, and 6.6 versus -10.4 g N ha⁻¹d⁻¹ for the unfertilized fields. The simulated N₂O fluxes varied largely between the fertilized (80.0-100.9 g N ha⁻¹d⁻¹) and unfertilized (24.5-56.5 g N ha⁻¹d⁻¹) fields, with the highest peaks coming from DailyDayCent. Regardless of the models, the simulated N₂O fluxes were consistent over the years but none of the models predicted fluxes less than zero or
captured the daily N₂O fluxes for the unfertilized field. The results contrast with the measured values, where a sink of N₂O occurred under conditions of high moisture and low nitrate level. The total bias and error differences for N₂O fluxes were within their 95% confidence levels indicate the quite high predictive potential of the models. However, only the ECOSSE-simulated values showed a significant relationship (R²=0.33, *p*<0.05) with the measured ones under fertilized conditions. These findings are in line with some previous reports [e.g., 2,5,7] although the overall performance depended mainly on the daily fluxes.

Based on an 8-year average, the DNDC-simulated total N₂O fluxes for the fertilized (207 kg N ha⁻¹) and unfertilized (81 kg N ha⁻¹) fields were 2-15 times lower than the estimates using the other 2 models. The variations among the model estimates and their relationship with key driving forces (e.g., soil water and NO₃⁻) are assumed to be limited by functions that produce and release N₂O. However, results using ECOSSE are in broad agreement with the literature values for total N₂O emissions measured from crop fields (0.7-3.5 kg N ha⁻¹yr⁻¹) [8].

The DNDC and DailyDayCent models significantly (*p*<0.01) underestimated seasonal/annual N₂O fluxes compared to ECOSSE and the corresponding EFs were 0.09, 0.31 and 0.52%. Similar overall underestimations, particularly using the earlier versions of DNDC, have been reported [4,5]. The DailyDayCent model also underestimated the N₂O EF (44%), with similar findings using DayCent (~25%), when compared with the default annual value [9]. This may be attributed to the limited number of field measurements, as this could result in associated large uncertainties, and use of default values for both DNDC and DailyDayCent. In contrast, the ECOSSE model, on average, increased the EF by 35%, but was within a closer range of the measured estimate. This is in line with estimates made using the previous version of ECOSSE [10] although lower than the IPCC default value (1%). Overall, the estimation of EFs using simulated values is constrained by total flux differences between the fertilized and unfertilized fields. This indicates the need for adoption of an appropriate methodological compromise and consideration of other factors controlling N₂O emissions.

## Conclusions

Both DNDC and DailyDayCent underestimated daily and total N₂O fluxes compared to ECOSSE. The ECOSSE provided an improved prediction of fertilizer-induced N₂O fluxes and thereby EFs. There are clear constraints in terms of the processes and driving forces (e.g. growth parameters, soil moisture) to predict precise N emissions. Further refinement and validation of all models, including sensitivity tests of site characteristics, land use and management, and climate are recommended. This will provide improved agricultural GHG estimates for upscaling to the national level and for identification of mitigation options.

## Acknowledgements

The Irish Environmental Protection Agency (EPA) for funding this project through STRIVE/NDP (2007-2013).

## References

[1] Li, C., Frolking, S., Harriss, R. 1994. Gloabl Biogeochemical Cycles 8, 237-254.

[2] Del Grosso, S.J., Ojima, D.S., Parton, W.J., et al. 2002. Environmental Pollution 116(S1), S75-S83.

[3] Smith J.U., Gottschalk, P., Bellarby, P.J., et al., 2010. Climate Research 45, 179-192.

[4] Abdalla, M., Wattenbach, M., Smith, P., et al. 2009. Geoderma 151, 327-337.

[5] Abdalla, M., Rueangritsarakul, K., Jones, M., et al. 2012. Water Air & Soil Pollution 223, 5155-5174.

[6] Khalil, M.I., Kiely, G., O'Brien P., Müller, C., 2013a. Geoderma. 193-194, 222-235.

[7] Bell, M.J., Jones, E., Smith, J., et al. 2012. Nutrient Cycling in Agroecosystems 92, 161-181.

[8] De Gryze, S., Wolf, A., Kaffka, S.R., et al. 2010. Ecological Applications 20, 1805-1819.

[9] Del Grosso, S.J., Mosier, A.R., Parton, W.J., Ojima, D.S. 2005. Soil & Tillage Research 83, 9-24.

[10] Khalil, M.I., Richards, M., Osborne, B., et al. 2013b. Atmospheric Environment 81, 616-624.
# SIMULATING SUSTAINABLE NITROGEN AND PHOSPORUS USE ON FARM LEVEL IN ACCORDANCE TO FERTILISING LIMITS IN FLANDERS

Peter Van Der Straeten, Koen Cochez, Greet Verlinden, Kevin Grauwels

Vlaamse Landmaatschappij, Brussels, Belgium

## Objectives

Council Directive 91/676/EEG concerning the protection of waters against pollution caused by nitrates from agricultural sources sets out that catchments of ground and surface waters that are at risk of being polluted should be designated as nitrate vulnerable zones. In these NVZ's an action programme should be outlined every four years implementing compulsory measures to decrease losses of nutrients to the aquatic environment.

A key measure in action programmes is the limitation of fertilizer application rates. In consecutive action programmes, Flanders has decreased nitrogen fertilization limits to reach equilibrium between fertilisation and crop requirement. To further improve water quality, Flanders' 5th action programme (2015-2018) differentiates nutrient management measures between regions and farms according to their regional and individual impact on water quality. This further increased the complexity of the legislation which further enhanced the need for a decision support tool. Since 2008 the Flemish Land Agency offers a Balance Simulator.

## Method

The decision support tool (DST) Balance Simulator is developed by the Flemish Land Agency and was made available for use by farmers for the first time in 2008. The aim is to support farmers in reaching a better nutrient use efficiency and at the same time help them to adopt legislation after each review of the action programme. To enhance the use of this DST by the individual farmers, this tool is developed in Microsoft Excel and can easily be downloaded from the website of the Flemish Land Agency (www.vlm.be). The Balance Simulator runs on the farmer's computer, which ensures full confidentiality of the data that are filled in to make simulations. The programme is updated annually to implement changes in legislation, correct flaws in the programme and improve the performance.

In a first stage, the farmer needs to answer several questions about his farm management (crop or livestock production), the objectives of using the balance simulator (use as a fertiliser plan and fertilisation account in function of the legislation) and the simulations he wants to make, leading to a customised DST tailored to the farm. In a second step the farmer needs to provide data at both the farm and the parcel level. At farm level information is requested on livestock production, manure production and transport from and to the farm, inputs of mineral and other organic fertilizers. At parcel level the farmer supplies the crop type, acreage, soil type.

## Results

Based on the production and inputs of nutrients in the farm as well as the different crops and their acreage, the farmer distributes the available nutrients between the parcels of the farm in order to obtain a sustainable fertilisation plan. This will result in a real-time calculation of farm gate balances and parcel level balances.

With this information the farmer can make decisions or simulations to improve the farm nutrient management: how much manure needs to be exported off the farm, which nutrient flow is out of balance, what is the effect of derogation on the farm, what if manure of other farmers is accepted, what are the possibilities of manure treatment techniques, is there space for expansion of the farm, etc.

The Flemish Land Agency uses different methods to enhance the use of the Balance Simulator by farmers. The simulator is free for download from the website www.vlm.be. In winter period sessions are held where farmers can practise the use of the programme. In spring the advisory service of the Flemish Land Agency starts with the assistance of individual farmers who have to deal with restrictions due to bad practices: mean-
while the possibilities of the programme are shown.

In the period 2008-2015 2,056 farmers were reached through practical sessions. The winter period 2015-2016 has not yet come to an end, but already 531 farmers (27 January) were reached. In the period 2008-2014 4,476 downloads were registered, but some of them are counted twice with the sessions. On the other hand many downloads are on account of (private) suppliers of farmers: in these cases it is not known for how many farmers the programme is used. In 2015 there were 859 downloads due to the starting of the new action programme.

From 2016 on, other pathways will be explored to spread the use of the programme more efficiently: e.g. asking suppliers of farmers to persuade farmers to practise the use of the programme in groups.

## Conclusions

The differentiation between farms and regions, for measures to improve nutrient management which was introduced in Flanders' fifth action programme in execution of the Nitrates Directive, has increased the complexity of the legislation which further enhanced the need for a decision support tool. The Balance Simulator helps farmers to overview the consequences of new legislation and how to deal with it.

The use of Balance Simulator by the individual farmers is increasing and will be further enhanced following several strategies.
# NITROGEN LEACHING OF AUSTRIAN'S ARABLE AREAS UNDER THE PERSPECTIVE OF GREENHOUSE GASES EMISSIONS

Alexander Eder, Guenther Schmid, Lisa Huber, Peter Strauss

Institute for Land and Water Management Research, Petzenkirchen, Austria

## Objectives

Agricultural production causes greenhouse gases emissions, which have to be evaluated and reported annually at national scale according to IPCC guidelines. The guidelines require the estimation of indirect nitrogen soil emissions via leaching and runoff. The ratio of these nitrogen emissions and the sum of total nitrogen inputs and mineralization potential of crop residues is termed factor $Frac_{LEACH}$. Without better information a $Frac_{LEACH}$ of 0.3 has to be used for the national inventory reports. In this study a country specific $Frac_{LEACH}$ value for arable land in Austria was calculated, considering typical crop rotations, management practices and different soil qualities at the main intensively used agricultural areas.

## Method

The IPCC $Frac_{LEACH}$ value can be calculated by dividing the nitrogen losses by the sum of all nitrogen inputs and mineralization potential of crop residues. Therefore, we used the physical based SIMWASER/STOTRA-SIM model to calculate the nitrogen losses through leaching and the crop mass which is the basis for the amount of residues left on the field. Nitrogen inputs via mineral and organic fertilizers were taken as proposed in the Austrian fertilization guideline. There are eight major agricultural production areas in Austria, which can be subdivided into 87 minor agricultural production areas (MAPAs). The delineation of these areas was based on landscape and climatic characteristics and typical farm characteristics (size, type of farm, etc.). The simulations were done for the 17 MAPAs with the highest contribution of arable land (coverage of 65 % of total arable land). Within each of these 17 MAPAs three soil qualities (poor, mean and good = 10%, 50% and 90%-percent quantile of the distribution of effective field capacity) were investigated. Soil information was obtained from the Austrian Soil map which provides information on soil type including layering, layer depth, textural composition and organic carbon content. This basic soil information was converted from maps into quantitative parameter sets within SIMWASER using a large soil database that was established during SIMWASER development. Typical crop rotations, land management practices and fertilization practices, especially the type of fertilizer and the time of application, were obtained from the Austrian agricultural chamber for each of the 17 MAPAs. A total of 35 crop rotations were analysed. Combined with three soil qualities, this resulted in 105 simulation runs. Annual harvest data for the relevant crops provided by the Austrian Statistical Office where used for the model calibration.

## Results

Concerning the effect of soil quality as reflected by the simulation runs of 'poor', 'medium' and 'good' soil qualities, overall the 'poor' soils exhibit 36 % higher nitrogen loss through leaching compared to 'medium' soils, while the 'good' soils release 13 % less nitrogen to groundwater.

In our simulations, all 'medium' and 'good' soil scenarios resulted in lower $Frac_{LEACH}$ values than the IPCC default of 0.3. With a few exceptions, also the 'poor' soil conditions gave lower $Frac_{LEACH}$ values than proposed by the IPCC. For the 'poor' soil conditions, the mean $Frac_{LEACH}$ was estimated as 0.21 with a standard deviation of 0.09. Smaller values of $Frac_{LEACH}$ were simulated for the 'medium' and 'good' soil conditions with 0.14 and 0.12, and standard deviations of 0.07 and 0.06, respectively.

Only in four MAPAs, and in those only for the 'poor' soil conditions, the IPCC default value was exceeded. These MAPAs are already in the focus of public efforts to reduce nitrate concentrations in the groundwater, which underpins the validity of the model simulations. The highest values for $Frac_{LEACH}$ (between 0.33 and 0.36) were simulated in MAPAs with very high groundwater recharge either because of high annual rainfall and/or low effective field capacity.
However, low effective field capacity alone does not necessarily cause high values of $Frac_{LEACH}$. For instance in two MAPAs with low effective field capacity (50 - 70 mm · m⁻¹) $Frac_{LEACH}$ values are only 0.13 to 0.18. This is caused by a direct effect of the crop rotation, which included forage crops for one third of the six years lasting crop rotation for these MAPAs. As is known from previous studies nitrogen losses and therefore $Frac_{LEACH}$ is much lower for grassland than for arable land. Therefore, considering the whole crop rotation, the long term mean for $Frac_{LEACH}$ is balanced although higher losses might occur during the years of maize or cereals growing.

In general there is a positive correlation (r = 0.61, spearman correlation) between $Frac_{LEACH}$ and groundwater recharge and a negative correlation (r = -0.58) between $Frac_{LEACH}$ and effective field capacity. Fertilization had the lowest impact on the $Frac_{LEACH}$ value (r = 0.33) although the impact is stronger for the individual soil classes. A surprisingly high negative correlation exists between $Frac_{LEACH}$ and the crop residues (r = -0.71). An explanation could be that crop rotations with higher share of catch crops which are usually not harvested show reduced nitrogen losses through leaching but increase amount of crop residues left on the field. Additionally, straw from cereals remaining on the soil has a wide carbon-nitrogen relation (~100:1), which immobilizes inorganic nitrogen and decreases nitrogen leaching.

## Conclusions

Consideration of the areal contribution of each simulated MAPA and including different soil qualities within each MAPA leads to a weighted average of $Frac_{LEACH}$ on arable land in Austria of 0.16. If one accounts for nitrogen losses through lateral pathways by a 30% increase the value for Austrians arable land increases to 0.20. Including grassland (share of 51 %) leads to an overall $Frac_{LEACH}$ of 0.11 for all agricultural land.

In general, the Austrian fertilization guideline provides suitable thresholds for fertilizer application. However, within sensitive regions with low effective field capacities and/or high groundwater recharges, high nitrogen losses may occur. An overall maximum long term nitrate concentration of seepage water from the simulations would be 27 mg l⁻¹ which is below the threshold for drinking water of 0.50 mg · l⁻¹. However, it should be noted that in some years, higher nitrate contributions to the groundwater occurs. These might be compensated by low contributions in other years, but may lead to concerns for drinking water supply. Further, irrigation was not included in the analyses but might increase nitrogen losses to the groundwater. Choice or adjustments of the crop rotation, e.g. the integration of forage crops, are able to significantly lower the long term $Frac_{LEACH}$ values and nitrogen losses. During the growth period, the crops directly control nitrogen consumption. Beneficial effects also occur when residues are left on the field after harvest.
# OPTIMIZING N-TRANSFER IN WINTER-WHEAT CROPPING SYSTEMS THROUGH MICROBIAL N-IMMOBILIZATION

Steffen Rothardt, Ingo Pahlmann, Henning Kage

Christian-Albrechts-University, Kiel, Germany

## Objectives

N-leaching is a serious issue in respect of groundwater pollution, indirect GHG emission and energy balance. Several studies showed the possible impact of tillage intensity and crop residue composition [1]. But there is a lack of information about options to reduce N-leaching by actively manipulating microbial immobilization with respect to its total amount and timing. Microbial activity is strongly connected to the availability and C/N ratio of the soils organic biomass [2]. Therefore we tested approaches to manipulate the soil conditions in a field experiment by application of different organic materials. The focus has been set on crops with problematic high N-contents after harvest i.e. oilseed rape (WOSR) and faba beans (FB). Followed by winter-wheat these crops cause a high risk of nitrate leaching. In parallel we strive to simulate the mineralization, leaching and N-uptake processes after harvest using the obtained experimental data for parametrization and validation.

## Method

The field experiment consists of two local common crop compositions (WOSR - wheat - barley and FB - wheat - barley). Organic biomass is applied with four substrates differing in their C/N ratios (straw of the preceding crop, wheat straw, saw dust and complete straw removal). The following winter-wheat is fertilized with four different N-levels (from none to more than optimum) allowing to determine the effect of biomass application on optimum N-rates and thereby N-transfer effects. After harvest of WOSR and FB, during the fallow period and during parts of the winter-wheat growth period effects of biomass application on nitrogen turnover will be observed by recording of GHG emissions (closed-chamber method, [3]) and Nmin contents.

## Results

First data obtained in autumn 2015 suggest different turnover rates in dependency of the substrate treatment. Wheat straw incorporation shows the strongest effects on N2O-emission rates and Nmin retention, which could be signs of immobilization.

## Conclusions

During the growth period 2016 the leaf area index and thereby N-uptake dynamics will be observed. Together with the yield data the results will be statistically analyzed and used for the evaluation of a soil-plant model. If indicated the experimental design will be adjusted before the next post-harvest period.

## References

[1] Henke, J., Böttcher, U., Neukam, D., Sieling, K., Kage, H., 2008. Evaluation of different agronomic strategies to reduce nitrate leaching after winter oilseed rape (Brassica napus L.) using a simulation model. Nutr. Cycl. Agroecosystems 82, 299-314. doi:10.1007/s10705-008-9192-0

[2] Abiven, S., Recous, S., Reyes, V., Oliver, R., 2005. Mineralisation of C and N from root, stem and leaf residues in soil and role of their biochemical quality. Biol. Fertil. Soils 42, 119-128. doi:10.1007/s00374-005-0006-0

[3] Lapitan, R.L., Wanninkhof, R., Mosier, A.R., 1999. Methods for stable gas flux determination in aquatic and terrestrial systems, in: Bouwman, A.F. (Ed.), Developments in Atmospheric Science, Approaches to Scaling of Trace Gas Fluxes in Ecosystems. Elsevier, pp. 29-66.
EFFECT OF A NITRIFICATION INHIBITOR ON NITROUS OXIDE AND AMMONIA
EMISSIONS FROM A MAIZE CROP

Jaime Recio-Huetos¹, Alberto Sanz-Cobeña¹, Julia Le Noé², Sonia Garcia-Marco¹, Gemma Andreu¹, Jose
Manuel Alvarez¹, Antonio Vallejo¹

¹Technical University of Madrid (UPM), Madrid, Spain, ²Pierre and Marie Curie University, Paris, France

Objectives

Improving the Nitrogen Use Efficiency (NUE) of N fertilized cropping systems is a crucial issue both from economic and environmental points of view. For that purpose, one of the potential technological strategies is the use of nitrification inhibitor (NI) which inhibits the ammonium oxidation into nitrate Nitrification gives rise to N losses via both nitrate (NO3-) leaching and the greenhouse gas nitrous oxide (N2O) emissions. In this way the DMPP (NI) provide an opportunity to act against N losses from agro-ecosystems. The objective of this study was to assess the use of DMPP (3,4-dimethyl pyrazole phosphate) and DMPSA (3,4-dimethyl- ylpyrazol succinate) (NI) under Mediterranean conditions in order to reduce N2O emissions from agricul- tural fields. We also aimed to investigate the potential effect of using NI on NH3 emissions from an irrigated maize crop fertilized with pig slurry (PS) and Calcium Ammonium Nitrate (CAN) in split application.

Method

The experiment was conducted in “la Chimenea” field station located in the central Tajo river basin near Aranjuez, (Madrid, Central Spain). The soil type is a silty clay loam (Typic Calcixerpt), calcareous and rich in organic matter and basic pH (8.2). Four plots (40 m × 40 m) were selected and arranged, according to treatments, in a randomized complete block design with two replicates per treatment. Since each plot was 1.600 m2, the settlement of more than 2 replicates per treatment could not be performed [1]. The application of fertilizers was adjusted to provide 200 kg total N ha-1 for all treatments in split application.

The first fertilization comprised two different treatments: (i) pig slurry (PS); (ii) pig slurry mixed with the ni-
trification inhibitor DMPP (provided by EuroChemAgro) with a weight-based proportion of inhibitor in the
mixture of 0.81 % (i.e., 5 kg DMPP ha-1) (PSNI). Pig slurry was homogeneously applied by surface spread-
ing and subsequently incorporated up to 10 cm on 20th April 2015 at a rate of 50 kg N ha-1 and maize was
sown on 30th April 2015 at a density of 75.000 seeds ha-1.

At the second fertilization (23rd June 2015), CAN (calcium ammonium nitrate) synthetic fertilizer was ap-
plied to the soil surface in granular form by hand at a rate of 150 kg ha-1 with and without the nitrification
inhibitor DMPSA (provided by EuroChemAgro) in the PS and PSNI treated plots, respectively. A control
treatment (C) was used as semi-control as no N fertilizer was applied in these plots. Irrigation started on
May 28th (25.9 mm) and finished on the 2nd September. Total water applied to the crop through sprinklers
was c. 900 mm

Results

The application of DMPP with PS (PSNI) in the first fertilization had a non-significant difference with C treatment. Oppositely, significantly higher N2O fluxes were measured in plots without DMPP. All the treatments became of the same order of magnitude 16 days following the first fertilization. On the other hand, as a result of the second fertilization (23rd June 2015), N2O emissions were surprisingly higher in plots where the NI had been applied. This was thought to be associated to favoured denitrifying conditions due to intense irrigation. In any case, differences between cumulative fluxes from PS and PSNI at the end of the measurement period were not significantly different.

For both treatments, the highest daily losses of NH3 occurred one day after the application of the fertilizers,
afterwards, almost no NH3 losses were measured in the 28 following days. The use of NIs did not affect
significantly cumulative NH3 emission The average NH3 cumulated emission from PSNI and from PS plots
amounted to 3.0 and 3.1 kgN-NH3 ha-1, respectively. At the end of the experiment, NH3 losses from PS
only reached 5.5% of the TAN applied, while losses from PS+DMPP amounted to 5.1%. . Absence of sig-
nificant differences was attributed to the implementation of NH3 abatement application practices for both organic (mechanical incorporation) and synthetic (incorporation with irrigation water) fertilizers [2].

Soil NH4+ content varied significantly with time being driven by N application. Pig Slurry applied with DMPP delayed the NH4+ peak concentration by 10 days but induced a peak concentration about 3 times higher (highest values reached 64.55 mg N- NH4+ kg-1 dry soil) compared to PS alone (highest value reached 39.14 mg N- NH4+ kg-1 dry soil). After peaking, the gradual decline of NH4+ during the experiment could be due to nitrification, NH3 volatilization, N uptake by vegetation and microbial immobilization.

Total biomass was increased by fertilizers comparing to the control plots, no significant differences were detected between plots fertilized with and without DMPP

Yield scaled N2O emissions (considering grain yield) was higher in fertilized plots than in C. Although no significantly different, the application of DMPP led to higher yield scaled N2O emissions (17.4 and 16.4 mg N2O kg-1, for PSNI and PS, respectively).

Conclusions

Considering the two fertilizations separately, cumulative N2O fluxes appeared to be dropped by 58% relative to PS treatment in the pre-seeding treatment.

It is likely that Mediterranean climate enables optimal effects of DMPP over both N2O and NH3 emissions since hot and dry conditions enhance both nitrification and slurry infiltration. Accordingly, applying DMPP with PS could be an efficient option for mitigating N2O fluxes from crop fields in Mediterranean agro eco-systems but this should be done under dry conditions and slurry should be incorporated in order to avoid the probable increase of NH3 emissions associated to the use of DMPP.

When irrigation started, after fertilization with CAN, emissions of N2O were higher in the plots treated with CAN+DMPSA (PSNI) although differences were not significant comparing to CAN alone (PS). At the end of the cropping period, plots treated with NIs were associated with higher N2O emissions in comparison with PS+CAN plots although no significant differences were found. Emissions were low possible due to soil conditions (e.g. high soil moisture) favoured by irrigation and leading to denitrifying soil conditions. Emissions of NH3 were decreased by the application of NIs, without significant differences between N fertilized plots. This would have been associated to an application of the fertilizer following NH3-abatement strategies (e.g. incorporation of the slurry and CAN, physically and with irrigation, respectively).
# NITROGEN MINERALISATION AND GREENHOUSE GAS EMISSION FROM SOIL APPLICATION OF SLUDGE FROM SLUDGE TREATMENT REED BED SYSTEMS

Beatriz Gómez-Muñoz¹, Julie Larsen²,³, Georgios Bekiaris¹, Charlotte Scheutz², Sander Bruun¹, Steen Nielsen³, Lars S. Jensen¹

¹Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Frederiksberg C, Denmark, ²Department of Environmental Engineering, Technical University of Denmark, Kgs. Lyngby, Denmark, ³Orbicon A/S, Roskilde, Denmark

## Objectives

Sludge Treatment Reed Bed system (STRB) is a technology to dewater and stabilize sludge from wastewater treatment by simple gravity filtration and mineralisation. This creates a solid sludge residue of a quality that makes it suitable as fertiliser on agricultural land. However, there is little information about the main effects on N mineralisation and greenhouses gas (GHG) emissions in soil after the sludge residue application. In this work we evaluated the effect of treatment time (degree of stabilization) of sewage sludge residue in a vertical profile from three different STRBs on soil N mineralisation and GHG emissions after it is applied to soil.

## Method

Sludge residue was collected at three different STRB in Denmark: Helsinge STRB (Hel) Stenlille STRB (Ste) and Himmark STRB (Him). At the last day of the resting period (without input of sludge), eight sampling points were randomly chosen in each STRB. At Hel and Him, the cores were taken to a depth of 100 cm, whereas at Ste the cores were only 40 cm deep (the total depth of this STRB). Three cores from each point were taken. One from each point was mixed into homogeneous samples, whereas the two remaining cores were cut into depth fractions, each of 10-cm. Grounded and dried sludge samples were used to estimate total carbon (TC) and total nitrogen (TN) using an elemental analyser. Mixed and different depths samples were used in an incubation experiment. Sandy loam soil from the CRUCIAL field trial in Taastrup (Denmark) was amended with the different sludge samples at rate of 2% (dry weight). Water content was adjusted to reach pF 2 (24% water w/w and 60% Water filled pore space). On days 0, 1, 3, 7, 14, 42, 80 and 160 of the incubation, a destructive sample was analysed for ammonium and nitrate N (sum of these termed inorganic N (IN) in the following). On day 0, 1, 3, 5, 7, 21, 42, 80 and 160, a static chamber (kilner jars) was used to estimate CO₂ and N₂O emissions, taking gas samples after sealing (time 0) the jar and again after two hours of incubation. All the gas samples were analysed by gas chromatography.

## Results

Main properties of the sludge residue varied across the depth of the profile. In general, an increase of dry matter content from 20 to 27 % was observed in the deeper samples, suggesting that the STBR system is effective for sludge dewatering due to water drainage and evapotranspiration from the reed beds. However, a reduction in TN and TC content was found for the deeper samples, which could be due to the mineralisation of the sludge residue along the profile and plant uptake of mineralised N in the reeds. Similar results were reported by Nielsen and Bruun [1]. At the end of the incubation, the IN mineralised out of the TN applied was higher for the Hel and Him samples with 31 and 28 % of TN, respectively. In both, the IN production was significantly higher in the samples from the surface layers, reducing to around 16 % in Hel and 21 % of TN in Him in the deeper samplings. However, these differences were not observed in Ste, which was related with a higher C/N ratio in these samples. Yoshida et al. [2] observed a similar reduction in the N mineralisation in the samples from the deeper layers compared to the samples from the surface layers. These findings suggest that during the stabilization of the sludge, a significant part of N could be lost through volatilization, denitrification and leaching, but also that N uptake by reeds could be significant. At the same time, the C compounds in stabilized sludge have been reported to be more recalcitrant; furthermore, low N mineralisation in deeper layers can be expected. Correspondingly, for the samples from all three STRB plants lower CO₂ emissions from the deeper layers was observed. The highest CO₂ emissions were observed for the samples from the surface layers which could be related with the high content of labile organic matter and
nutrients in the fresh sludge, serving as substrates for microbial decomposition processes and increase gas emissions from microbial respiration. Nielsen et al. [3] found a decrease in the labile organic C in the deeper layers from STRB systems.

Soil N₂O emissions decreased significantly with the application of sludge from the deeper layers compared to the samples from the surface layers, indicating that the stabilization of the sludge reduced the amount of organic matter for the denitrification process. However, the fertilisation with samples from the surface layers, with low dry matter content and high TN and TC is a substrate source for denitrifiers and therefore higher N₂O emission could be expected. The mixed samples for the three different STRBs systems resulted in very low N₂O emissions and as low as the values of the sludge from deep part of the profiles.

## Conclusions

This study supports that STRB is an appropriated technology to stabilize sewage sludge, increasing the dry matter content and decreasing the availability of labile compounds. Application of less stabilized residue sampled in the surface part of the reed bed results in higher soil N mineralisation but also higher CO₂ and N₂O emissions. However, the combination between fresh (surface samples) and stabilized (deeper samples) is a good solution to reduce soil N₂O emissions, while still obtaining a high N availability in soil.

## Acknowledgements

This research was funded partly by the 'dNmark research alliance' (grant no. 12132421 from the Danish Council for Strategic Research).

## References

[1] Nielsen, S., Bruun, E. W. 2014. Environmental Science and Pollution Research 22, 12885-12891.

[2] Yoshida, H., Nielsen, M. P., Scheutz, C., Jensen, L. S., Christensen, T. H., Nielsen, S., Bruun, S. 2015. Acta Agriculturae Scandinavica, Section B - Plant Soil Science 65, 506-516.

[3] Nielsen, S., Peruzzi, E., Macci, C., Doni, S., Masciandaro, G. 2014. Water Science and Technology 69, 539-545.
# A PROPOSAL OF NITROGEN BALANCE IN A HIGH DENSITY OLIVE ORCHARD.

Hemza Belguerri¹,², Josep M Villar², Miquel Pascual², Amadeu Arbonés¹, Josep Rufat¹

¹IRTA, Generalitat de Catalunya, Lleida/Catalunya, Spain, ²University of Lleida, Lleida/Catalunya, Spain

## Objectives

Fertilization of the olive tree (Olea europaea L.) is a cultural practice with the objective of covering nutrients exported by the plant [1]. One of the most essential nutrients for plant growth and production is nitrogen (N), which plays an important role and is usually the most consumed by the plant [2]. One of the tools used to program plant fertilization is the N balance, which considers the difference between inputs and outputs of this element. The objective of this experiment was to estimate the inputs and outputs of N in a very high density orchard related to tree response and soil conditions, particularly nitrogen availability.

## Method

The trial was conducted on a commercial very high density olive orchard (cv. Arbequina) in Torres de Segre (Lleida) in northeast Spain for three years, 2010, 2011 and 2012. The climate is continental Mediterranean. The average annual rainfall was 324 mm, irregularly distributed, and mean evapotranspiration (Peman-Monteith) was 1101 mm. The trees were planted in summer 2002 at 4.5 m × 2.2 m, (1010 trees ha-1) growing on a moderately deep soil. The soil was silty-loam textured and calcareous (pH = 8) with an organic matter content of 1.5%, and electrical conductivity (EC 1:5) of 1.4 dS m-1 (due to the presence of gypsum). Irrigation was based on water balance, applying 100% of the water needs of the plant throughout the growing season, according to the methodology of FAO [3]. To calculate the balance of nitrogen, two treatments of this element, N0 without N, and N50 with the application of 50 kg ha-1 of nitrogen with a N-32 (16% urea, 8% ammonium and 8% nitric) were weekly applied by fertigation. Statistical analysis of the results was performed using the JMP-SAS software (JMP, Version 12. SAS Institute Inc., Cary, NC, 1989-2014).

The nitrogen balance (kg ha-1) is expressed by the following equation [4]:

$$ \text{Nitrogen balance (kg ha-1) = N inputs - N outputs = N inorganic final - N inorganic initial = } \Delta N \text{ inorganic} $$

Inputs calculated were the mineralization of organic matter, irrigation and rainfall N supply and the amount of N fertilizer applied. Outputs were calculated from crop and pruning exportations and N losses by denitrification [5] and leaching.

## Results

Nitrogen exports by the crop and pruning material were 20 and 33 kg ha-1 year-1 respectively for N0, and 30 and 62 kg ha-1 year-1 for N50. This difference was due to a higher olive yield and nitrogen concentration in pruning material and fruits in N50 trees [6]. The amount of nitrogen lost by denitrification was negligible compared to other outputs, with values which did not exceed of 2 kg ha-1 year-1, and with higher values for N50 due to the presence of large quantities of nitrate in the soil [7], [8]. No leaching losses were recorded because of a low rainfall and high evapotranspiration. The average amount of nitrogen provided by irrigation water and rainfall was 8.8 and 6 kg ha-1 year-1, respectively. The mineralization of organic matter was 40 and 43 kg ha-1 year-1 for N0 and N50 respectively.

During the three years period, the average of nitrogen balance was positive with values of 19.6 kg ha-1 for N50 and 9.5 kg ha-1 for N0. Distortions of nitrogen balance may be due to other factors which are difficult to quantify and not directly mentioned in this work like, 1) the mineralization of the pruning material and mowed weeds (because pruning residues were chopped and left onto the orchard), 2) natural leaf abscission [9] and 3) rhizodeposition contribution [10].

## Conclusions
Nitrogen application significantly increases yield, vegetative growth and nutrient in plant tissues. The positive results for N balance can be explained as an adaptation of olive trees to different soil N availability conditions by equilibrating their vegetative growth and fruit yield.

## References

[1] Hidalgo and Pastor. 2002. Vida Rural. February, pp: 46-50.

[2] Fernández-Escobar et al. 2008. Environmental and Experimental Botany 64: 113 - 119.

[3] Allen et al. 1998. FAO Irrigation and drainage paper 56: 1-15.

[4] Fernández-Escobar et al. 2012. Scientia horticulturae 135: 219 - 226.

[5] Maris et al. 2015. Science of the Total Environment 538, 966-978.

[6] Rufat et al. 2014. Agricultural Water Management 144: 33-41.

[7] Germon and Couton. 1999. Courrier de l'environnement de l'INRA. 38: 67-74.

[8] Henault et al. 1998. Biology and Fertility Soils 26:199-207.

[9] Rapoport. 2008. In: El cultivo del olivo. Junta de Andalucía/ Mundi-Prensa, España.

[10] Scandellari et al. 2010. Agriculture, Ecosystems and Environment 136, 162-168.
# AMMONIA AND GHG EMISSIONS IN FRESH DIGESTATE LAGOONS IN SPAIN:
A COMPARATIVE ASSESSMENT BETWEEN COVERED AND UNCOVERED STORAGE

Eva Herrero Mallén¹, Marta Teresa Fernández¹, Haritz Arriaga Sasieta², Pilar Merino Pereda²

¹Sociedad Aragonesa de Gestión Agroambiental, S.L.U., Zaragoza, Aragon, Spain, ²NEIKER-Tecnalia, De-río, Basque Country, Spain

## Objectives

Future trends of EU policies, aimed at increasing the use of clean energy, foster the spreading of anaerobic digestion plants that process organic materials like manure. Thus, the digestate production is increasing across Europe, although its efficiency as organic fertilizer and environmental concerns has not been widely studied as in the case of raw manure.

Gaseous emissions from fresh digestate lagoons might differ from those of untreated slurry due to the differences in their physical-chemical properties, such as lower dry matter and higher mineralized nitrogen and pH, which may enhance NH₃ emissions.

The purpose of this study is the evaluation of NH₃, N₂O, CH₄ and CO₂ emissions in two fresh digestate storage lagoons: an uncovered lagoon of 950 m² and 2,500 m³, and a covered lagoon of 1,450 m² and 3,500 m³ of storage capacity. Two different techniques have been used: dynamic chambers and a located extraction system respectively.

## Method

The experiment took place in Almazán (Soria, Spain) from 30th June to 2nd July 2015. All measurements were performed at three time intervals: morning (10:00 - 11:30 a.m.), noon (1:00 - 2:30 p.m.) and afternoon (4:00 - 5:30 p.m.). The environmental conditions and the digestate temperature were monitored during the assay. The digestate from both lagoons was sampled and analysed in laboratory. The storages were at full capacity at the time of the trial and receiving approximately a flow rate of 100 m³/day of fresh digestate. Gas samples were analysed using a photoacoustic analyzer Bruel and Kjaer 1302, equipped to perform continuous measurements of NH₃, N₂O, CH₄, CO₂, and water vapour. The following sampling methodologies were used:

### Dynamic chamber methodology in the uncovered lagoon

The digestate was poured directly into this lagoon and the emitting source was the whole surface. The method followed was an adaptation of the methodology developed in IRSTEA [1].

Six rectangular chambers (60 x 34 x 40 cm) were distributed evenly on the surface. One was placed directly in the discharge zone (hot-spot), two in the nearby and the other three chambers were placed away from there.

A clean air flow was passed through the interior of the floating chambers, simulating a natural air flow of 2.5 l/min (3.3 m/s wind speed), via polyethylene tubes. The samples from each chamber (outlet) were brought to the photoacoustic through teflon tubes and analyzed.

### Located extraction system in the covered lagoon

10 safety valves (30 cm high - 13 cm diameter) evenly distributed around the perimeter of the lagoon represent the only emission points of the storage system. The stored gas was released freely without any forced draught.

Air flow rate in the valves was estimated measuring air speed with a hot-wire anemometer. The air samples were taken 40 cm above the base of the cover using a teflon tube. This tube was fixed in a PVC pipe also covered inside with teflon in order to avoid NH₃ adherence (1 m high - 16 cm diameter) and placed over the valves monitored. 5 measurements were performed over 8 hours.

## Results

During the sampling period, average temperatures were higher than usual in this region varying between 28 - 34 °C and the wind blew gusty along the three days.

The average values analysed in digestate samples of the uncovered lagoon were: N<sub>Kjeldahl</sub>: 3.10 kg/m³, N<sub>ammoniacal</sub>: 2.66 kg/m³, dry matter: 2.8% and volatile solids: 57.1%. In the case of the covered lagoon: N<sub>Kjeldahl</sub>: 2.37,