A wide view of no-tillage practices and soil organic carbon sequestration

Many believe that conservation tillage practices could increase the sequestration of atmospheric carbon dioxide into agricultural soils and this sequestered carbon may partially offset the greenhouse gas effect and thus reduce the impact of global warming. Recent advances in soil carbon (C) and greenhouse gas analysis have made it possible to evaluate the impacts of conservation tillage on C sequestration from various perspectives. Although conservation tillage favors soil and water conservation, there are biased estimates of C sequestration associated with conservation tillage, and it is particularly an issue for a "pure" no-tillage (NT) system. Accordingly, this paper presents an overview of the progress achieved in evaluating C sequestration in no-till (the extreme type of conservation tillage) and conventional tillage production systems. In addition to extended discussion of how soil sampling and calculations could influence the estimates of C gains or losses in no-till versus conventional tilled soil, this review will also focus on following aspects, including (1) the impact of NT on crop yields which governs organic C inputs to soil from crop residue, (2) the impact of NT on soil organic C mineralization which is a major pathway of soil C output, and (3) the roles of the initial levels of C stocks and soil erosion rates which are crucial for estimating soil C sequestration under different tillage systems. Many soil C studies have indicated that the impacts of NT on soil C sequestration are compounded by many factors and should not be generalized.