Effects of Organic Maize Cropping Systems on Nitrogen Balances and Nitrous Oxide Emissions

Silage maize cultivation is gaining importance in organic farming, and thus its environmental and climate impacts. The effects of digestate fertilization in combination with different catch crops and tillage intensities in maize cultivation are investigated in a long-term field experiment in southern Germany. The tested variants are (a) maize after winter rye, plowed, unfertilized and (b) fertilized with biogas digestate, (c) maize after legume-rich cover crop mixture, mulch seeding, fertilized with digestate, and (d) maize in a white clover living mulch system, fertilized with digestate. Over three years (2019 to 2021), crop yields and N balance were analyzed, N2O emissions were measured in high temporal resolution using the closed chamber method, and soil moisture, ammonium, and nitrate contents were continuously determined. Maize dry matter yields ranged from 4.2 Mg ha−1 (variant a, 2021) to 24.4 Mg ha−1 (variant c, 2020) depending on cropping intensity and annual weather conditions. Despite relatively high nitrogen fertilization with digestate, the N balances were negative or nearly balanced; only in 2021 did the N surplus exceed 100 kg ha−1 (variant b and c) due to low yields. In maize cultivation, relatively low N2O-N emissions (1.0 to 3.2 kg ha−1) were measured in the unfertilized variant (a), and very high emissions in variant b (5.6 to 19.0 kg ha−1). The sometimes extremely high N2O emissions are also due to soil and climatic conditions (high denitrification potential). The experimental results show that cover crops, living mulch, and reduced tillage intensity in silage maize cultivation can reduce N2O emissions, improve nitrogen balance and increase maize yields.