Abstract
Classification of soil potential productivity, the classification criteria, and standards for evaluating the soil fertility in Japan are introduced in this chapter. Increasing the carbon sequestration in soil during the process of biomass production is of great importance to improve the soil fertility for producing more biomass. The modified Rothamsted Carbon model that has been improved for evaluating major arable soils in Japan, i.e. Andosols and paddy soils, will also be included. Soil microbes play crucial roles in soil functions, especially nutrient cycling, and thus contribute significantly to sustainable crop production. General aspects of soil microbes are discussed in order to provide an understanding of the role that soil microbes play in crop production. Because soils with higher nitrogen-supplying capacity, expressed as the rate of microbial mineralization of soil organic matter, are considered to have higher soil fertility; microbial mediation to enhance soil fertility is also discussed.