Interactive effects of straw management, tillage, and a cover crop on nitrous oxide emissions and nitrate leaching from a sandy loam soil.

Minimum tillage, residue recycling and the use of cover crops are key elements of conservation agriculture that play important roles in soil carbon (C) and nitrogen (N) dynamics. This study determined the long-term effects of tillage practice (conventional ploughing vs. direct seeding), straw management (retained vs. removed), and the presence of a cover crop (CC; fodder radish in this study) on nitrous oxide (N ₂ O) emissions, nitrate (NO ₃ ^- ) leaching, and soil mineral N dynamics between October 2019 and June 2020. In the factorial experiment with eight treatment combinations, cumulative N ₂ O emissions ranged from 0.04 to 0.8 kg N ha ^-1 , whereas NO ₃ ^- leaching varied between 4 and 28 kg N ha ^-1 . The study did not find effects of straw retention on NO ₃ ^- leaching or N ₂ O emissions. No-till reduced N ₂ O emissions by on average 46% compared to ploughing. Fodder radish reduced NO ₃ ^- leaching by 80-84%, and there was little N ₂ O emission in the presence of the cover crop; however, after termination in spring there was a flush of N ₂ O, cumulative N ₂ O-N averaged 0.1 and 0.5 kg N ha ^-1 without and with a cover crop. With information about long-term soil C retention from straw and fodder radish, an overall greenhouse (GHG) balance was calculated for each system. Without straw retention after harvest, there was always a positive net GHG emission, and the indirect N ₂ O emission from NO ₃ ^- leaching was similar to, or greater than direct N ₂ O emissions. However, in the presence of fodder radish, the direct N ₂ O emissions after termination were much more important than indirect emissions, and negated the C input from fodder radish. Direct seeding, straw retention and the use of a cover crop showed positive effects on N retention and/or GHG balance and could substantially improve the carbon footprint of agroecosystems on sandy soil in a wet temperate climate.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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