Relations between organic acids generated by rice bran application on the paddy soil and the rice growth

Abstract

In organic cultivation of rice, application of rice bran to the surface of the paddy soil at the time of transplanting is adopted as one of the weeding techniques. In this study, we examined the effect of rice bran application for weeding on the growth of rice in relation to the formation of organic acid by rice bran application. Large-quantity application of bran (500g/m²; RB500) strongly reduced the redox potential in the soil and produced high concentrations of acetic acid and butyric acid in the soil compared to conventional-quantity application (100g/m²). RB500 delayed rooting and leaf age development, and suppressed the increase in stem number. The number of stems, which is a factor that greatly affects the yield, was strongly suppressed particularly in early- planting culture (May 11) compared to normal-planting culture (June 13), and the tendency of this result was not due to the age of seedlings used (young seedling with 3.2 leaf stage and middle seedling with 5.0 leaf stage). In the early- planting culture that the temperature was low at the time of transplanting, it was thought that the decomposition of rice bran was slow, and the presence of long-term harmful concentrations of organic acids affected the growth. From the view point of safe and stable rice production, we concluded that rice bran weeding combined with normal- planting culture is desirable.