Effects of sowing date and ecological points on yield and the temperature and radiation resources of semi-winter wheat

Exploring the effects of sowing date and ecological points on the yield of semi-winter wheat is of great significance. This study aims to reveal the effects of sowing date and ecological points on the climate resources associated with wheat yield in the Rice-Wheat Rotation System. With six sowing dates, the experiments were carried out in Donghai and Jianhu counties, Jiangsu Province, China using two semi-winter wheat varieties as the objects of this study. The basic seedlings of the first sowing date (S1) were planted at 300x104 plants ha-1, which was increased by 10% for each of the delayed sowing dates (S2-S6). The results showed that the delay of sowing date decreased the number of days, the effective accumulated temperature and the cumulative solar radiation in the whole growth period. The yields of S1 were higher than those of S2 to S6 by 0.22-0.31, 0.5-0.78, 0.86-0.98, 1.14-1.38, and 1.36-1.59 t ha-1, respectively. For a given sowing date, the growth days increased as the ecological point was moved north, while both mean daily temperature and effective accumulative temperature decreased, but the cumulative radiation increased. As a result, the yields at Donghai County were 0.01-0.39 t ha-1 lower than those of Jianhu County for the six sowing dates. The effective accumulative temperature and cumulative radiation both had significant positive correlations with yield. The average temperature was significantly negatively correlated with the yield. The decrease in grain yield was mainly due to the declines in grains per spike and 1 000-grain weight caused by the increase in the daily temperature and the decrease in the effective accumulative temperature.