Latitudinal Difference of Rice Varieties Productivity in the Lower Yangtze and Huai Valleys and Its Rational Utilization

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Rice grain yield is affected significantly by the latitudinal environment factors. However, little is known about the latitudinal difference of prolificacy and stability of grain productivity in rice varieties with different growth durations in the downstream of Yangtze River and Huai River Valleys. In this study, under the condition of rice-wheat cropping rotation, a field experiment with five seeding dates using 11 rice varieties with different growth durations in Jiangsu Province was conducted to investigate the latitudinal difference of prolificacy and stability of grain productivity and the rational distribution of the varieties in Peixian(34.7° N), Donghai(34.5° N), Suyu(34.0° N), Jianhu(33.4° N), Yangzhou(32.4° N), and Kunshan(31.3° N) of Jiangsu Province in 1997–2000. Results showed that there was a highly significant difference in grain yield of rice varieties with different growth durations and different seeding dates in different latitudinal sites. The equation Y = at2+bt+c was used to describe the relationship between grain yield and seeding date for all varieties, according to the change of values a and b there were three types of parabola which might be transformed between each other due to the change of sites or years. Compared with other rice varieties the prolificacy and stability of grain productivity of late-maturity medium japonica rice varieties were better, thereby their suitable planting zones were wider. But with the mature date prolonging unceasingly, the prolificacy index(Pi) decreased and the stability index(Si) increased in late-maturity japonica rice varieties, so the yield prolificacy and stability became poor. The prolificacy of Liangyoupeijiu(hybrid mid-maturity indica rice variety) was only less than that of late-maturity medium japonica rice varieties but better than that of other rice varieties, while its yield stability was just better than that of early-maturity medium japonica rice varieties. Compared with the early-maturity rice varieties, the late-maturity rice varieties had significantly better prolificacy and stability than other varieties. Based on the prolificacy and stability of varieties with different growth durations and the conditions of annual temperature and light in Jiangsu, we rationally regionalized planting area into suitable region, sub-suitable region, possible region and unsuitable region to confirm the distribution of rice varieties. Medium-maturity medium japonica rice varieties, late-maturity medium japonica rice varieties and early-maturity late japonica rice varieties were the main varieties suitable to plant in Subei, Suzhong and Sunan regions, also some varieties with closer growth duration could be planted as a supplement. However, hybrid mid-maturity indica rice varieties were only suitable to be planted in western hilly land of Jiangsu Province. In northern Huai River zone appropriately otherwise, earlier sowing was available and in Suzhong and Sunan regions the seeding date had to be suitable, otherwise, earlier or later sowing was not available to increase grain yield. On the premise of safely maturity accomplished, it is beneficial for increasing rice productivity to select partial late maturing varieties and plant more japonica rice varieties in the indica-japonica region.