Field evaluation of winter rye as a biological nitrification inhibitor to reduce nitrous oxide emissions

Agriculture is under increasing pressure to reduce greenhouse gas emissions as part of global efforts to mitigate climate change and ensure sustainable food production. Among these emissions, nitrous oxide (N₂O) is a particularly potent greenhouse gas, largely originating from agricultural soils, which makes effective mitigation strategies crucial. Winter rye has been identified as a potential biological nitrification inhibitor due to its release of the compound 6-methoxy-2-benzoxazolinone (MBOA) by the roots. This compound suppresses nitrifying bacteria, thereby reducing the conversion of ammonia to nitrate in soil systems and ultimately lowering N₂O emissions. Unlike chemical nitrification inhibitors, whose environmental side effects remain insufficiently understood, biological nitrification inhibitors occur naturally and offer a promising, sustainable alternative for reducing emissions in agricultural systems. We tested the nitrification inhibiting effect of MBOA in Danish fields under common Danish farming practices. The aim was to determine the degree of N₂O reduction by winter rye, compared to cereals without a biological nitrification function. If successful, winter rye could be a low-emission substitute for similar crops, providing farmers with a practical tool to reduce greenhouse gas emissions without compromising crop management, aligning with EU climate targets and sustainable agriculture goals. Three field trials were conducted in West Jutland, Denmark. Winter wheat was selected as a control species with no genes producing MBOA. To account for different N-demands in rye and wheat, both species received three different N-treatments: 0, 130 and 190 kg N ha^-1, respectively. We measured N₂O emissions 20 times during the growing season using the static chamber method along with soil N contents and -moisture. As expected, N₂O emissions increased with increasing N amounts applied in both species. Although variability was observed among trials, results indicated an overall trend toward lower N₂O emissions from winter rye compared to winter wheat under the high N application (p < 0.07). These findings suggest that winter rye can act as a biological nitrification inhibitor under field conditions, contributing to reduced N₂O emissions and supporting agricultural practices with lower carbon footprints. Further trials will assess the consistency of these effects across varying weather conditions, aiming to strengthen recommendations for large-scale implementation. If confirmed, this strategy could offer a scalable, low-cost approach to reducing agricultural greenhouse gas emissions without major changes to current farming systems.