The relationship between number of nitrogen-fixing rhizobacteria and growth pattern of rice varieties.

This study was conducted to evaluate the adaptability of rice varieties to nature farming. Nature farming refers to sustainable agriculture without the use of agricultural chemicals, including fertilizers. Four rice varieties were grown in fields under nature and conventional (control) farming conditions. The number of N 2 -fixing rhizobacteria, dry matter content, and nitrogen content of the plants were measured in each growth stage. In both farming conditions, the number of N 2 -fixing rhizobacteria was found to be associated with the growth stage of rice in relation to a change in dry matter and N content of the plants. The number of N 2 -fixing rhizobacteria in nature farming was higher than that in conventional farming. In nature farming, varieties with a higher number of N 2 fixing rhizobacteria in the late growth stages showed higher grain yields than in conventional farming. We suggest that varieties with a higher number of N 2 -fixing rhizobacteria in the late growth stages be used for breeding highyielding varieties under nature farming. The Japanese native J195 line used in this experiment may be a useful material for this purpose.