Target growth and evaluation of topdressing determined based on growth diagnosis in organically grown rice

Abstract

Target growth of organically grown rice was to produce yields of 550–600 g m–2. After clarifying the nitrogen uptake rate and nitrogen mineralization characteristics of organic fertilizer, we examined the influence that topdressing had on yield determined based on the growth diagnosis. The tiller number of organically grown rice was smaller than that of conventionally grown rice throughout the growth period. However, the percentage of productive tillers in organically grown rice was higher than that in conventionally grown rice. The panicle number in organically grown rice was almost the same as that in conventionally grown rice. Furthermore, as compared with conventionally grown rice, the leaf color score of organically grown rice was lower until the beginning of July and was higher after the panicle formation stage. Rate of nitrogen uptake from five types of organic fertilizers ranged from 40 to 80%, with an average of 69%. Kinetics analysis showed that the nitrogen mineralization rate of organic fertilizer was 20 to 60%, and the rate showed a significant positive correlation with the nitrogen uptake rate. Topdressing based on the growth diagnosis produced the target number of panicles and color score in organically grown rice to obtain the target yield of 550–600 g m–2. Thus, the target grain yield can be obtained by topdressing determined based on the growth diagnosis in organically grown rice.