Modified crop rotations for a sustainable intensification? A case study in a high-yielding environment with recurrent nitrogen surplus

Agriculture is a major contributor to nitrate groundwater contamination. Hence, farmers are demanded to reduce the environmental impact but simultaneously must provide sufficient food products. One important building block for this "sustainable intensification" are appropriate cropping strategies. The potential of modified crop rotations was evaluated in a high-yielding environment in Northern Germany. Therefore, in five consecutive growing seasons (2016/2017 - 2020/2021) three crop rotations were grown in a field trial and compared with respect to agronomic (cereal unit), economic (gross margin) and environmental (N surplus) parameters. A standard crop rotation, typical for the region of the study, was compared with rearranged and augmented crop rotations. Therefore, crops with a high autumnal N uptake (winter oilseed rape and catch crops) were grown after crops with typically high soil mineral N (SMN) amounts after harvest (faba bean and winter oilseed rape). Due to the change of preceding and subsequent crops, an increased N transfer was supposed to prevent N from leaching and a lower N fertilizer demand of the subsequent crop was expected. On average, the modified crop rotations achieved significantly higher cereal units (9.3 and 10.8 t center dot ha -1) compared to the local crop rotation (8.5 t center dot ha -1). The gross margin of the local crop rotation was 1474 euro center dot ha- 1 and the other crop rotations maintained (1443 euro center dot ha -1) or significantly increased (1572 euro center dot ha -1) this value, respectively. The local crop rotation had a N surplus of 47 kg N center dot ha -1. In contrast, the N surplus of the modified crop rotations was significantly lower (10 and 28 kg N center dot ha -1). In summary, the results showed that a thoughtful rearrangement of crop rotations is an appropriate measure to simultaneously improve yields and gross margins with less unfavorable environmental impacts.