Towards sustainable rye cultivation : soil carbon and yield modelling for crop rotations with rye

Sammanfattning: Using the Introductory Carbon Balance Model, ICBM, five different crop rotations with rye 1. Rye-Ley-Ley-Rye-Beans-Rye 2. Rye-Rye-Rapeseed-Rapeseed 3. Rye-Ley-Ley-Rye-Potatoes-Rye 4. Rye-Rye-Potatoes-Wheat 5. Rye-Rye-Potatoes-Beans-Wheat-Rye-Potatoes-Rapeseed were tested theoretically in four different cultivation scenarios • Straw left on the field, biogas digestate added as fertilizer. Labelled “+straw+BD”. • Straw left on the field, only synthetic fertilizer. Labelled “+straw-BD”. • Straw harvested, biogas digestate added as fertilizer. Labelled “-straw+BD”. • Straw harvested, only synthetic fertilizer. Labelled “-straw-BD”. on clay soil with 1 %, 2 % or 2.5 % carbon in top soil at start of the simulation. The term biogas digestate refers (in this case) to the slurry that remains after organic material, primarily food waste or animal manure, has been used for biogas production. For rotations with ley, a case where ley was used for biogas production and the resulting digestate was spread on the fields was also tested with all scenarios. Simulations were run over 48 years, and the results compared with respect to soil carbon effects and crop yield (by mass of total solids, energy and protein yield, as well as straw and bio fuel potential to replace fossil fuels), weighted to find the best performing crop rotation with rye, and the best cultivation methods. As expected, use of biogas digestate had a strong positive effect on soil carbon. Crop rotations with ley could not be shown to be more beneficial than those without in this study, especially not when crop yield was considered, unless the ley was used for biogas production and the digestate spread on the field. Straw harvest did, as expected, lower soil carbon stocks but given the potential reduction of greenhouse gas emissions when straw replaces oil as a fuel for heating, harvesting straw can still be recommended. The emission reduction is approximately five times larger than the potential carbon sink effect of the soil when straw is tilled back into the field, due to rapid degradation of fresh plant material in soil. The best rotation, in terms of yield relative to carbon effects, was found to be Rye-Rye-Potatoes-Wheat, highly productive (high yield of total solids, energy and protein, low yield of straw, no biofuels) and with a mostly neutral carbon effect on normal, healthy soils. The best rotation from a soil carbon perspective was found to be Rye-Ley-Ley-Rye-Potatoes-Rye with ley used for biogas production. The yield of food crops from this rotation was relatively low. The spreadsheet model used for simulations in this study is described in the report and can easily be modified and used for other studies, or for getting a rough idea of the yield and carbon effects of other crop rotations.