No-till only increases NO emissions in poorly-aerated soils

摘要

Denitrification rates are often greater in no-till than in tilled soils and net soil-surface greenhouse gas emissions could be increased by enhanced soil NO emissions following adoption of no-till. The objective of this study was to summarize published experimental results to assess whether the response of soil NO fluxes to the adoption of no-till is influenced by soil aeration. A total of 25 field studies presenting direct comparisons between conventional tillage and no-till (approximately 45 site-years of data) were reviewed and grouped according to soil aeration status estimated using drainage class and precipitation during the growing season. The summary showed that no-till generally increased NO emissions in poorly-aerated soils but was neutral in soils with good and medium aeration. On average, soil NO emissions under no-till were 0.06kgNhap# lower, 0.12kgNhap# higher and 2.00kgNhap# higher than under tilled soils with good, medium and poor aeration, respectively. Our results therefore suggest that the impact of no-till on NO emissions is small in well-aerated soils but most often positive in soils where aeration is reduced by conditions or properties restricting drainage. Considering typical soil C gains following adoption of no-till, we conclude that increased NO losses may result in a negative greenhouse gas balance for many poorly-drained fine-textured agricultural soils under no-till located in regions with a humid climate.