Soil Carbon Sequestration by Cropland Management and Mitigation of Climate Change

Abstract

Soil organic carbon（SOC）is a huge and important component of the global carbon cycle. Agricultural soils can be either a sink or a source of atmospheric CO₂, depending on the balance between the input of carbon（C）to soils and the output of C through decomposition. We can change this balance by changing agricultural soil management, understanding the mechanisms of SOC turnover. Not only the quantity but also the quality of input C affects SOC balance, and environmental conditions such as temperature and moisture of soils as well as inherent properties of soils such as texture affect the decomposition rate of SOC. Since there are many factors affecting SOC balance, SOC turnover models are very useful tools to evaluate the effect of management practices on SOC balance. The RothC model, one of leading SOC models in the world, was validated against long-term experiments in Japan and Thailand, and modified RothC models for paddy soils and for Andosols was developed. The country scale potential of soil carbon sequestration was estimated, then, by using the RothC model for Japanese arable lands. The use of LCA, which includes not only changes in SOC, but also CO₂ emissions from the use of fossil fuel in agricultural production processes, is effective and essential in evaluating the effects of agricultural management practices on climate change mitigation. It is important, too, to include other green house gases（CH₄ and N₂O）, other environmental impacts（e.g. nitrate nitrogen in soils and water）, and impacts on agricultural productivity, in evaluation of agricultural management practices.