Prevention of Lodging by Mixed Planting of Rice Varieties : IV. Effects of seed-blends row seeding on lodging and yield

摘要

The effects of seed-blends row seeding on lodging and yield were examined at five nitrogen levels with direct sowing on well drained paddy field. Two varieties "Koshihikari", tall and lodging-susceptible, and 'Kanto 100', short-statured and lodging-resistant, were used. The two varieties were sown in different mixing rate, including the pure stands. Results of the experiment can be summarized as as follows: 1. Compared on the same nitrogen level, the higher the relative mixing rate of Kanto 100, the less the lodging of community and the more the lodging resistance of Koshihikari in itself. The lodging resistance of Koshihikari was increased in the mixtures by means of the shortening in culm length and the increase in breaking resistance, while that of Kanto 100 was decreased. The less the rate of variety in the mixtures, the more the changes in characteristics of the variety. 2. The positive effect of mixed planting on yield increase was observed in plot of medium fertility level where Kanto 100 successfully prevented Koshihikari from lodging, but no effects were observed in low fertility plots with no occurrence of lodging, nor in too fertile plot where Kanto 100 faild to prevent lodging. 3. Koshihikari had more the percentage of ripened grains and the yield when grown in the mixtures than when grown in the pure stand. Therefore Koshihikari showed the strong competitor in these characters in mixed planting the same as previously in alternate rows planting. However, the panicles and the spikelets number of Kanto 100 increased, while those of Koshihikari tended to decrease in the mixtures especially in low fertility level. These results suggested that the relative competitive ability of variety was reversed during growth process. 4. The lodging of community was highly and positively correlated with the lodging index. Multiple regressions where applied to estimate the lodging index (I) and the yield (y) using the following equations : I = a + bx1 - cx2 + dx22 y = e + fx1 + gz - hz2 where x1 is The fertility level, x2 is the percentage of Kanto 100 in the mixtures, z is the degree of lodging at 30 days after heading and the characters from a to h are all positive coefficients.