**5. Conclusions**

In this review, no-input rice farming in Japan was evaluated from the viewpoint of soil sustainability. It can be concluded that soil fertility under this farming system has been supported by various environmental and management factors, especially the input of K through irrigation, high-clay content in soil, and accumulation of fertilizer P applied previously to the soil. In the case of our no-input trial for 5 years, a significant depletion of mineralizable N and nonexchangeable K was observed after three cropping seasons, and rice growth was limited by soil K supply when the input of K by irrigation was restricted. These results highlight the importance of monitoring the dynamics of multiple soil nutrients for several years.
