Possibility of No-Input Farming in Lowland Rice Fields in Japan from the Viewpoint of Sustaining Soil Fertility

Abstract

In Japan, the area of low-input rice production is gradually increasing with a growing public interest in the quality and safety of our staple food. In an extreme case, rice has been grown over years without using any chemical fertilizers and agrochemicals. However, it is uncertain how much and how long such no-input farming can sustain rice yield and soil fertility. To better understand the sustainability of no-input rice farming in Japan, I briefly review previous results obtained from the long-term field experiments. The topics are (1) rice yield and soil fertility under no-input farming, (2) the environmental factors affecting rice growth and soil fertility under no-input farming, and (3) the dynamics of soil K under continuous rice cropping. The corresponding conclusions are as follows: (1) rice yield and soil fertility under no-input farming in Japan were influenced by various environmental and management factors operating at regional and field scales; (2) the input of K through irrigation and the high-clay content in soil were considered the key environmental factors that enable to sustain no-input farming; and (3) soil K depletion caused by long-term exhaustive cropping should be assessed by monitoring the decrease of soil nonexchangeable K rather than that of exchangeable K.