# Usefulness of nitrogen application in heavy soils compared to more favourable land in Ireland – utilisation of the Moorepark Grass Growth model

Luc Delaby, D Hennessy

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Luc Delaby, D Hennessy. Usefulness of nitrogen application in heavy soils compared to more favourable land in Ireland – utilisation of the Moorepark Grass Growth model. 19. Symposium of the European Grassland Federation (EGF), May 2017, Alghero, Italy. hal-01603795

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# Usefulness of nitrogen application in heavy soils compared to more favourable land in Ireland – utilisation of the Moorepark Grass Growth model

Ruelle E.<fnref n="1" />, Delaby L.<fnref n="2" /> and Hennessy D.<fnref n="1" />

## Abstract

Ireland's temperate climate is favourable for grass growth, and efficiently grazed grass is the cheapest feed available on most dairy farms. In heavy soils, grass growth conditions and utilisation of grazed grass are less favourable than in free draining soils and will affect the dairy farm performance. The Moorepark Grass Growth model was used to compare the impact of weather, soil type and nitrogen (N) application on grass growth, number of grazing events and N leaching. Weather data (from the year 2015) and soil from two locations, Moorepark (free draining soil) and Athea (heavy soil), were used. Overall, the soil type and weather conditions for the heavy soil farm are limitations to grass growth.

**Keywords:** model, heavy soil, grass growth, nitrogen fertilisation

## Introduction

Since the removal of the EU milk quotas, in Ireland new dairy enterprises are developing outside of the existing traditional milk production regions to more marginal soil types. In Ireland, the economic performance of dairy farms depends, to a large extent, on the efficient conversion of grazed grass to milk. Heavy soils can retain three to five times more water than well drained soils (Shalloo et al., 2004). However, heavy soils have a low capacity to absorb rainfall due to poor soil structure and low porosity. In this study the Moorepark Grass Growth model (MGGm) (Ruelle and Delaby, 2016) was parameterised using weather and soil type data from a highly productive area (Moorepark (site M)) and from a heavy soil area (Athea (site A)) at different nitrogen (N) fertiliser application levels.

## Materials and methods

The MGGm is a dynamic model developed in C++ describing the grass growth and the N fluxes of a paddock at a 2 m<fnref n="2" /> level. The model is run with a daily time step simulating soil N mineralisation/ immobilisation and water fluxes, grass growth, N uptake and grass N content. The core model functions are described in Ruelle and Delaby (2016). The MGGm was used to compare the impact of the climate and soil type at two contrasting sites in Ireland: a free draining soil type – Moorepark (site M) (52.17N; 8.27W) and a heavy soil type – Athea (site A) (52.461N; 9.29W). Nitrogen fertiliser application was 0, 120, 240 or 360 kg N ha⁻<fnref n="1" />. The 2015 weather data and the soil types of each site are described in Table 1.

The initial soil mineral N content for the first day of the simulation was set at 80 kg N ha⁻<fnref n="1" /> for both sites. A grazing event occurred as soon as the grass height reached 9 cm. The post-grazing sward height

<table><caption>Table 1. Description of the soil types and weather conditions for the Moorepark (M) and Athea (A) sites.</caption><thead><tr><td>Site</td><td>Clay (%)</td><td>Sand (%)</td><td>Organic matter (%)</td><td>Rain (mm)</td><td>Average temperature (°C)</td><td>Average solar radiation (J cm<sup>-2</sup>)</td></tr></thead><tbody><tr><td>Moorepark</td><td>26</td><td>22</td><td>7.0</td><td>1,209</td><td>9.9</td><td>947</td></tr><tr><td>Athea</td><td>47</td><td>13</td><td>2.3</td><td>1,653</td><td>9.1</td><td>975</td></tr></tbody></table>

<footnote n="1">¹Animal & Grassland Research and Innovation Centre, Teagasc, Moorepark, Fermoy, Co. Cork, Ireland;</footnote>

<footnote n="2">²INRA, AgroCampus Ouest, UMR 1348, Physiologie, Environnement et Génétique pour l'Animal et les Systèmes d'Elevage, 35590 Saint-Gilles, France</footnote>
was set at 3.5 cm for the first grazing event of the year and 4 cm thereafter. Residency time for each grazing event was 2 days. The number of animals grazing was calculated by the model using the biomass disappearing each day of the grazing event and assuming an intake of 16 kg dry matter (DM) cow⁻¹ day⁻¹. The simulation was run for 10 years with repetitive use of the 2015 weather data to provide model stability. To further understand the impact of weather and soil type the site M weather data were applied to the site M soil and the site A soil type, and the site A weather data were also applied to both soil types. The result of the last year of the simulation are presented.

## Results and discussion

Results are presented in Table 2 and Figure 1. Average grass growth across all N fertiliser application rates was of 11,120 kg DM ha⁻¹ for the site M soil with the site M weather; 9,730 kg DM ha⁻¹ for the site M soil with the site A weather; 8,151 kg DM ha⁻¹ for the site A soil with the site M weather and 7,340 kg DM ha⁻¹ for the site A soil with the site A weather. On average for the four N-fertiliser rates and the two sets of weather data, the site A soil type had less grass growth (-2,680 kg DM ha⁻¹) than the site M soil type. Similarly, on average for the four N-fertiliser rates and the two soils the weather from site A resulted in less grass growth (-1,100 kg DM ha⁻¹) compared to the site M weather.

The response to N fertiliser was variable. On the site M soil type, the response decreased as N fertiliser application increased (average response between 0 and 120 was 26 kg DM ha⁻¹ per kg N; average response between 240 and 360 was 13 kg DM ha⁻¹ per kg N). On the site A soil type the highest response to fertiliser was always the response between 120 and 240 kg N ha⁻¹, average 20 kg DM ha⁻¹ per kg N, while average response between 0 and 120 kg N ha⁻¹ was 11 kg DM ha⁻¹ per kg N. This was due to the low soil mineral N content in site A over the years leading to a poor grass growth at the first level of fertilisation. The N-fertiliser responses were comparable to results from previously published research (e.g. Hennessy et al., 2008). The site M weather permitted a greater number of grazing events (average of 0.75 events

<table><caption>Table 2. Impact of soil type, weather and N fertiliser application on the number of grazing days, number of grazing events, grass growth, final soil N mineral content and annual N leaching.</caption><thead><tr><th>Soil type</th><th>Weather source</th><th>N fertiliser application rate (kg N ha<sup>-1</sup>)</th><th>Grazing days (days ha<sup>-1</sup>)</th><th>Grazing events</th><th>Grass growth (kg DM ha<sup>-1</sup>)</th><th>N min end year (kg N ha<sup>-1</sup>)</th><th>Leaching (kg N ha<sup>-1</sup>)</th></tr></thead><tbody><tr><td rowspan="4">M</td><td rowspan="4">M</td><td>0</td><td>486</td><td>5</td><td>7,364</td><td>72</td><td>87</td></tr><tr><td>120</td><td>687</td><td>7</td><td>10,479</td><td>86</td><td>104</td></tr><tr><td>240</td><td>790</td><td>8</td><td>12,635</td><td>104</td><td>131</td></tr><tr><td>360</td><td>881</td><td>9</td><td>14,001</td><td>133</td><td>168</td></tr><tr><td rowspan="4">A</td><td rowspan="4">A</td><td>0</td><td>389</td><td>4</td><td>5,884</td><td>56</td><td>94</td></tr><tr><td>120</td><td>579</td><td>6</td><td>8,960</td><td>67</td><td>119</td></tr><tr><td>240</td><td>680</td><td>7</td><td>11,207</td><td>75</td><td>143</td></tr><tr><td>360</td><td>793</td><td>8</td><td>12,870</td><td>90</td><td>175</td></tr><tr><td rowspan="4">A</td><td rowspan="4">M</td><td>0</td><td>296</td><td>3</td><td>4,440</td><td>24</td><td>33</td></tr><tr><td>120</td><td>393</td><td>4</td><td>6,367</td><td>43</td><td>63</td></tr><tr><td>240</td><td>585</td><td>6</td><td>9,694</td><td>56</td><td>84</td></tr><tr><td>360</td><td>787</td><td>8</td><td>12,101</td><td>76</td><td>109</td></tr><tr><td rowspan="4">A</td><td rowspan="4">A</td><td>0</td><td>298</td><td>3</td><td>4,764</td><td>17</td><td>32</td></tr><tr><td>120</td><td>390</td><td>4</td><td>5,443</td><td>33</td><td>70</td></tr><tr><td>240</td><td>492</td><td>5</td><td>8,402</td><td>41</td><td>96</td></tr><tr><td>360</td><td>681</td><td>7</td><td>10,749</td><td>54</td><td>124</td></tr></tbody></table>

DM = dry matter; M = free draining soil type (Moorepark); A = heavy soil type (Althea).
<figure><img src="image_2.png" /><figcaption>Figure 1. Average grass growth (kg dry matter ha⁻¹) using the Moorepark (black) and the Athea (grey) weather on either the Moorepark (plain line) or the Athea (dotted line) soil type.</figcaption></figure>

more) and grazing days (average of +75 days). N leaching was greater on the site M soil type (+51 kg N on average) and with the site A weather (+9.25 kg N on average).

## Conclusions

The heavy soil site was less favourable for grass growth and grazing due to its high clay content and low soil organic matter. Even if less important, the weather in that area was also a limitation to the grass growth. N leaching was lower on the heavy soil area, leading to a good response to fertiliser with less environmental impact.

## Acknowledgements

The authors acknowledge Patrick Tuohy and James O'Loughlin for their help in collecting the site A data. This work was funded by Research Stimulus Fund 2011 administered by the Department of Agriculture, Fisheries and Food (Project 11/S/132).

## References

- Hennessy D., O'Donovan M., French P. and Laidlaw A.S. (2008) Manipulation of herbage production by altering the pattern of applying nitrogen fertilizer. *Grass and Forage Science* 63, 152-166.

- Ruelle E. and Delaby L. (2016) The Moorepark Grass Growth Model – application in grazing systems. *Grassland Science in Europe* 21, 409-411.

- Shalloo L., Dillon P., O'Loughlin J., Rath M. and Wallace M. (2004) Comparison of a pasture-based system of milk production on a high rainfall, heavy-clay soil with that on a lower rainfall, free-draining soil. *Grass and Forage Science* 59, 157-168.