DOI: 10.5061/dryad.vx0k6djz7
title: Integrating perennial biomass crops into crop rotations: How to remove miscanthus and switchgrass without glyphosate

description: Perennial energy grasses have gained attention in recent years as a
 promising resource for the bioeconomy because of their benign
 environmental profile, high stress tolerance, high biomass yields and low
 input requirements. Currently, strong breeding efforts are being made to
 extend the range of commercially available miscanthus and switchgrass
 genotypes. In order to foster farmers’ acceptance of these crops, and
 especially of novel hybrids, more information is required about how they
 can be efficiently integrated into cropping rotations, how they can be
 removed at the end of their productive lifespan, and what effect they have
 on subsequently grown crops. Farmers in Europe are meanwhile increasingly
 constrained in the methods available to them to remove these crops, and
 there is a risk that the herbicide glyphosate, which has been used in many
 studies to remove them, will be banned in coming years. This study looks
 at the removal of  seven-year-old stands of miscanthus and
 switchgrass over one year at an experimental site in Southern-Germany.
 Three novel miscanthus genotypes were studied, alongside one variety of
 switchgrass, and the impact of each crop’s removal on the yield of maize
 grown as a follow-on crop was examined.  A combination of soil
 tillage and grass herbicides for maize cultivation was successful in
 controlling miscanthus regrowth, such that yields of maize grown after
 miscanthus did not differ significantly from yields of maize grown in
 monoculture rotation (18.1 t dry biomass ha-1). Yields of maize grown
 after switchgrass (14.4 t dry biomass ha-1) were significantly lower than
 maize in monoculture rotation caused by insufficient control of
 switchgrass regrowth by the applied maize herbicide. Although some
 regrowth of miscanthus and switchgrass was observed in the follow-on crop
 maize, complete eradication of both crops was achieved by subsequent
 winter wheat cultivation.
description: In
 order to test the effect of miscanthus and switchgrass removal on
 subsequent maize cropping, a field trial including three different
 miscanthus hybrids, switchgrass and maize was removed and the land resown
 with an annual crop, maize. The field trial was located at Ihinger Hof, a
 research station belonging to the University of Hohenheim in
 Southern-Germany. The field trial was established in 2013 as part of the
 EU project ‘OPTIMISC’ (Grant Agreement no. 289159) to assess the methane
 yield potential of three miscanthus hybrids and switchgrass by anaerobic
 digestion. Miscanthus and switchgrass were established at a planting
 density of 2 and 6 plants m<sup>-2</sup> respectively and
 grown alongside maize (annually sown at 10 seeds
 m<sup>-2</sup>) in a randomized split-block design with 4
 replicates (plot size 5 m x 15 m) of each genotype/crop. Miscanthus and
 switchgrass were harvested in three different harvest regimes (double cut
 in July and October, early single cut in August and late single cut in
 October). In the original field trial (2013-2018), the miscanthus and
 switchgrass plots were split according to the harvest regime (split plot
 size 5 m x 5 m). To avoid the harvest date treatment impacting the
 research performed in this study, the crop was allowed two seasons to
 regenerate in 2018 and 2019. All miscanthus and switchgrass plots were
 harvested in late October each year, resulting in uniform and vigorous
 crops by the end of 2019 growing season. Maize cultivation was continued
 in the plots from the initial experiment so that maize was continually
 grown on these plots since 2014. In 2019 all miscanthus, switchgrass, and
 maize plots were fertilized the day after sowing with 150 kg N (ha
 a)<sup>-1 </sup>given as calcium ammonium nitrate. After the
 final green harvest in late October 2019, the field was cultivated by
 ploughing on November 22<sup>nd</sup> 2019 to a depth of
 approx. 22 cm. In Table 1, the crop treatments in the initial field trial
 and the follow-on crop maize established after recultivation of the field
 are briefly characterized.<br><br>In April 2020 all plots were
 power-harrowed and maize ‘Kilomeris’ (KWS SAAT SE & Co. KGaA,
 Einbeck, Germany) was sown on April 27<sup>th</sup> 2020 at a
 density of 9.3 seeds m<sup>-2</sup> with a row distance of 75
 cm. Each plot of the recultivated field trial was sown with 6 rows of
 maize, resulting in 4.5 m x 15m maize plots. The crop protection strategy
 included two herbicide applications: The first treatment was carried out
 one week after sowing by application of a tank-mixture of soil active
 herbicides pendimethalin (1,365 g ha<sup>-1</sup>, Stomp
 Aqua®, BASF SE, Ludwigshafen, Germany) and Dimethenamid-P (900 g
 ha<sup>-1</sup>, Spektrum®, BASF SE, Ludwigshafen, Germany). 
 Both soil active herbicides are a standard treatment in maize cultivation
 and are known to also be suitable for miscanthus cultivation. For this
 reason, volunteer miscanthus and switchgrass regrowth appeared and needed
 to be suppressed with a second application of a leaf-active herbicide on
 May 26<sup>th</sup> 2020 containing 63 g
 ha<sup>-1</sup> Foramsulfuron, 2 g ha<sup>-1</sup>
 Iodosulfuron, 20 g ha<sup>-1</sup> Thiencarbazone and 30 g
 ha<sup>-1</sup> Cyprosulfamide (MaisTer® power, Bayer Crop
 Science Deutschland GmbH, Monheim, Germany). For fertilization, 198 kg N
 ha<sup>-1</sup> was applied as stabilised Urea including
 Dicyandiamid und 1H-1,2,4 Triazol as a nitrification inhibitor (Alzon 46,
 SKW Stickstoffwerke Piesteritz GmbH, Wittenberg, Germany) in one
 application directly after sowing.<br> <strong>Physical measurements of crop
 growth</strong> To
 assess the development of the maize crop, plant measurements were taken
 during the vegetation period on May 15<sup>th</sup> 2020, June
 5<sup>th</sup> 2020 and August 6<sup>th</sup>
 2020. The measurements included number of maize plants
 m<sup>-2</sup>, volunteer miscanthus and switchgrass shoots
 m<sup>-2</sup>, and average canopy height of the maize crop
 and volunteer miscanthus and switchgrass regrowth. The number of maize
 plants and miscanthus and
 switchgrass shoots was measured in the centre of the maize plot over an
 area of approx. 1 m<sup>2</sup> (0.75 m x 1.33 m). The average canopy height of
 maize and volunteer miscanthus and switchgrass was estimated by using a
 measuring stick and was measured from the ground to the highest fully
 developed leaf. During these plant measurements the plots were also
 checked for volunteer growth of other weeds (i.e. neither miscanthus nor
 switchgrass), but due to the effective chemical weed management no
 significant quantity of
 weeds was found.
 <br><br>Weather data were collected from a weather
 station managed by the LTZ located at Ihinger Hof.<br> <strong>Yield and mineral offtake data collection<br></strong>Two methods were used to assess the yield of maize and regrowing miscanthus and switchgrass. Total harvestable fresh biomass yield was estimated on September 17<sup>th</sup> 2020 using a BAURAL SF 2000 (Zürn Harvesting GmbH & Co. KG, Schöntal-Westernhausen, Germany) self-propelled plot forage harvester. The third and fourth maize rows, in the centre of the plot, were harvested at a cutting height of approx. 20 cm and along 13.6 m stretch resulting in a sampling area of 20.4 m<sup>2</sup>. The harvested biomass was weighed during harvest by the harvester to assess the fresh biomass yield and a sample was taken for dry matter content analysis. Volunteer miscanthus and switchgrass biomass was not removed prior to harvesting with the forage harvester, but due to poor regrowth, their contribution to the overall yield was only minor. Yield calculated from this harvest was called harvestable yield, and reflected yields as they would be achieved in praxis.<br><br>A second yield determination was carried out by harvesting maize plants and regrowth by hand. A 1m<sup>2 </sup>area (0.75 m x 1.33 m) was harvested manually in the fifth maize row at a cutting height of approx. 5 cm. During the hand harvest, maize and volunteer miscanthus and switchgrass biomass was collected separately and the fresh weight of the biomass samples was assessed by weighing on a scale. After weighing, the fresh biomass was chipped using a laboratory chipper and a representative sample was taken for further chemical analysis. This was called potential yield as it represented the amount of biomass that could potentially be taken from the field. Potential yield was calculated for maize and for switchgrass and miscanthus regrowth.<br><br>In both harvests, biomass samples were dried at 80 °C to a constant weight in a drying cupboard. The dry weight was then used to calculate the dry matter yield. Winter wheat was sown following the maize harvest, though data about the yield and growth of this crop was not collected. <strong>Chemical analysis of harvested biomass </strong> The dried subsample of pure maize, miscanthus or switchgrass was then milled in a cutting mill SM 200 (Retsch, Haan, Germany) using a 1-mm sieve. The milled subsample was then used for analysis of ash, nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg) and calcium (Ca) content. The nitrogen content was analyzed using a Vario Macro Cube (Elementar Analysensysteme GmbH, Hanau, Germany) in which the samples are completely incinerated with oxygen and content of nitrogen compounds in the resulting off-gas was measured by a thermal conductivity detector. The P, K, Mg and Ca content was measured by microwave digestion of the biomass, followed by analysis of the extract using ICP-OES. For this analysis, 0.5 g of each sample was diluted with 8 ml HNO<sub>3</sub> and 6 ml H<sub>2</sub>O and digested in an ETHOS.lab microwave (MLS GmbH, Leutkirch, Germany). The ICP-OES analysis of the extract was performed by Core Facility Hohenheim, which is the central laboratory of the University of Hohenheim. <strong>Soil sampling </strong> Soil samples were taken on four dates to examine the nutrient dynamics in the soil during the vegetation periods. On the first date, April 15<sup>th</sup>, multiple samples were taken from the field and combined to use as a baseline for further calculations. Samples were then taken on May 18<sup>th</sup>, June 24<sup>th</sup> and after the harvest on September 22<sup>nd</sup> 2020. Soil samples were taken with an auger to a depth of 90 cm and divided into three fractions (0-30 cm; 30-60 cm; 60-90cm) which were then analysed separately. Directly after extraction from the soil, the soil samples were cooled to avoid ammonium losses and stored frozen until analysis. Following extraction stones and other debris were removed from soil samples. Plant available nitrogen in fresh soil (NO<sub>3</sub> and NH<sub>4</sub>; referred to as N<sub>min</sub>) was determined using a CaCl<sub>2</sub> extraction and FIA (flow-injection analysis) measurement (DIN ISO 14255:1998-11). The amount of plant available phosphorus and potassium was then analysed in dried soil via CAL-extraction followed by measurement with a flame photometer or FIA respectively (OENORM L 1087:2012-12-01).  Soil pH was determined with a glass electrode after CaCl2 extraction (DIN ISO 10390:2005).<br><br><strong>Nitrogen balance in the soil<br></strong>Soil samples taken from the beginning of the vegetation period until after maize was harvested were used to calculate a nitrogen balance. A mixed probe was used for the first value, hence for all treatments initial soil nitrogen is given as 18.15 kg ha<sup>-1</sup>. Mineral offtake calculated from harvest data was compared with measured soil nitrogen.  <strong>Statistical analysis</strong> Statistical analysis was conducted in R (R Core Team 2020) and RStudio (Version 2022.02.3). The program ‘agricolae’ was used to perform an ANOVA and Tukey’s test using the following model. Where:             y = yield of maize or regrowth of miscanthus or switchgrass μ = general mean effect prev = effect of the previous crop B = effect of block    = residual error Homogeneity of variance was assessed visually. The effects were tested at a level of probability of <em>α </em>= 0.05.
description: Excel
description: # Integrating perennial biomass crops into crop rotations: how to remove
 miscanthus and switchgrass without glyphosate. Maize was grown following
 miscanthus,maize and switchgrass. At the end of 2020 maize was harvested
 using a forrage harvester (baural) and by hand. Regrowth of miscanthus and
 switchgrass was harvested as well. Data from these three harvests was
 collected. Biomass from these three harvests was analysed to determine
 mineral content. Physical measurements of plant height and stem and plant
 density were taken. Soil samples were taken in 2020 to determine what
 impact crop removal and maize cultivation had on the soil. ## Description
 of the Data and file structure **Where data is missing a "."
 symbol is placed.** **V122\_soil\_probe\_data**- This data set contains
 soil probes taken on four dates in 2020. The first data was a mixed probe
 and is thus the same for all plots. The columns represent NO3 and NH4
 (mineral nitrogen content), elemental P, and elemental K in the soil. The
 final column represents the total Nmin in 0-0-90cm. Previous Crop
 represents the crop grown before maize ie. whether it was maize,
 Switchgrasss or one of the three miscanthus genotypes: OPM16, OPM17,
 OPM77. Depth respresnts the soil fraction being examined **Physical
 measurements of maize and miscanthus-** This data set contains field
 measurements taken in 2020 of maize plants and regrowing miscanthus and
 switchgrass plants. Previous crop represents the last crop grown before
 maize, if it was maize, switchgrass or miscanthus (OPM16,OPM17,OPM77). The
 date represents the date the measurement was taken. Maize\_plant\_no is
 the number of maize plants per square metre. Regrowth stems is the number
 of miscanthus or switchgrass stems per square metre. Regrowth height is
 the height of the regrowing miscanthus or switchgrass plants and maize is
 the height of the maize plant . The first measurement shows 5.5cm for
 maize, as the maize regrowth was extremely homogenous this was generalised
 for all measurements at that date. <br> **V122\_offtake\_data- this
 dataset contains the calculated offtake of N,P,K,Ca,and Mg in harvested
 biomass, and in regrowth.** "This data set contains the nutrient
 offtake data. Baural yield and nutrient content data refers to the harvest
 carried out using a forrage harvester. "Hand "refers to the
 harvest carried out where maize plants were harvested by hand. Regrowth
 yield refers to the harvest carried out where regrowing miscnathus and
 switchgrass was harvested by hand. Baural data is thus a mix of maize
 plants and regrowing switchgrass and maize. Hand is purely maize. Regrowth
 is pure switchgrass or miscanthus. For each the N,P,K,Ca,C,H, and Mg
 offtake was determined and is given in kg ha-1" **yield\_and\_biomass
 contents-** This data set contains the yield data and nutrient content
 data. Baural yield and nutrient content data refers to the harvest carried
 out using a forrage harvester. "Hand "refers to the harvest
 carried out where maize plants were harvested by hand. Regrowth yield
 refers to the harvest carried out where regrowing miscnathus and
 switchgrass was harvested by hand. Baural data is thus a mix of maize
 plants and regrowing switchgrass and maize. Hand is purely maize. Regrowth
 is pure switchgrass or miscanthus. For each the N,P,K,Ca, Mg ,C and H
 content was determined, as well as the ash content. Yield data is in
 tonnes per hectare, content data is in mg/g and ash in %.
 **weather\_data\_2020\_and\_longterm-** is the weather data used to
 construct figure 1 collected from the weather station at Ihinger Hof
 managed by the Landwirtschaftliche Technologie Zentrum. map of experiment-
 is a map of the experimental site and experimental plots. ##
 Sharing/access Information All data was derived from experimentation.
 Weather data was collected from the Ihinger Hof weather station operated
 by Landwirtschaftliche Technologie Zentrum Augustenberg- The agricultural
 technology centre Augustenberg. This is available at
 https://www.wetter-bw.de/Internet/AM/NotesBwAM.nsf/(XP\_StationABC\_All)/095e00fe589ba5d7c1257ca8002cc942?OpenDocument&TableRow=3.9