Regulation of winter soil mineral nitrogen and N2O emissions by cover crop termination timing

Abstract

Cover crops (CCs) are widely promoted for reducing nitrate leaching and enhancing soil fertility, yet their role in regulating winter nitrous oxide (N 2 O) emissions remains poorly understood. This field study assessed how termination timing of oil radish ( Raphanus sativus ) influenced soil mineral nitrogen (SMN) dynamics and winter N 2 O emissions across five site-years in a humid temperate climate (Germany) on contrasting soil textures (loamy and sandy). Treatments included autumn termination, spring termination, and fallow. Although CCs reduced SMN by ~ 65% compared to fallow by December, this did not lead to lower winter N 2 O emissions. Instead, cumulative emissions over a standardized 100-day winter period were highest under autumn termination (1.23 ± 0.11 kg N 2 O–N ha −1 ), followed by spring termination (0.65 ± 0.06 kg N 2 O–N ha −1 ) and fallow (0.12 ± 0.01 kg N 2 O–N ha −1 ). Emissions were higher in 2019 than 2020, associated with warmer and wetter conditions. Autumn termination also increased spring SMN levels relative to spring termination in loamy soils, but not in sandy soils, where nitrate leaching may have occurred. While microbial gene abundances indicated greater nitrification and denitrification potential under autumn termination, they did not correlate with actual N 2 O fluxes. These findings suggest that autumn termination can enhance winter emissions, whereas delayed termination may shift emissions to spring, particularly under fertilized conditions. Site-specific CC management that considers termination timing, soil texture, and climatic context is essential to balance nitrogen retention with N 2 O mitigation.

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