Effect of Application of Rice Straw to Paddy Field : I. Effects of Application Methods of Rice Straw and Nitrogen Fertilizer

Field experiments on the effects of application methods of rice straw and nitrogen fertilizer to a growth and yield of rice were carried out in the paddy fields of Yamaguchi Agricultural Experiment Station and Faculty of Agriculture, Yamaguchi University during 1976 to 1980. Results obtained are summarized as follows : 1) In a well-drained and sandy paddy field of Yamaguchi Agricultural Experiment Station, the application of rice straw (ca. 70kg/a) in last autumn or the current spring to paddy was harmless to the growth of rice, although the early growth was slightly repressd. A rice yield increased with the application of rice straw in both applocation times. The treatment having resulted in the highest yield of rice was “November : broadcast of rice straw-April : their incorporation-end May : fertilization, incorporation and submerging-early June : transplanting”, and about 9 per cent of the yield increased as compared with without-rice straw-treatment. 2) In a clayey paddy field of Yamaguchi University, worse drained than Yamaguchi Agricultural Experiment Station, the application of rice straw (ca. 60kg/a) in last autumn of the current spring to paddy was also harmless to the growth of rice. The effect of nitrogen fertilizer applied with rice straw in last autumn on the rice yield was very low. 3) It was observed that the disease tolerance of rice plant increased with the application of rice straw in both experimental sites. 4) It is suggested that the effective application method of rice straw and nitrogen fertilizer in Yamaguchi area be as follows : Rice straw (ca. 60-70kg/a) which was cut and broadcasted automatically by a combined harbester in last autumn is incorporated into the soil until early April. An increasing amout of basal nitrogen fertilizer (extra 20 to 30 per cent) is applied and incorporated agein until early June and then the field is submerged before transplanting.