Application of liquid fraction of digestates and biochar in winter wheat: nitrous oxide emissions and yield response

Abstract Digestate from anaerobic digestion is used for fertilizer application, but the efficiency is not always very high, and it may lead to significant emissions of nitrous oxide. In this two-year field study, we tested differently treated liquid fraction of digestate (LF) to investigate N 2 O emissions and crop yield. The treatments included biochar amendment, acidification and sedicanter separation followed by post-digestion (SLF). The response of the treatments was tested as second fertilizer application in winter wheat ( Triticum aestivum L.) and compared with mineral fertilizer. The N 2 O emissions were measured using static chambers from April to June in 2023 and 2024. The bulk of N 2 O emissions occurred within two weeks after application in both years. Biochar-amended and acidified LF and SLF did not have a significant effect on cumulative N 2 O emissions in either of the two years. Biochar resulted in significantly lower cumulative and yield-scaled emissions in 2023 (but not in 2024) in the treatment with mineral N likely due to dry soil conditions in the first year. Yield was not significantly different among treatments receiving 150 kg N ha −1 . The fertilizer value of treated and untreated liquid fractions of digestates ranged between 56–77% of total N in both years. In conclusion, N 2 O emissions could not be reduced with acidification, biochar amendment, or SLF and were all similar to mineral N application. In addition, biochar N 2 O mitigation in treatments with mineral N fertilizer in dry years may be outweighed by increased emissions in years with high rainfall.