| 1. Safe full heading date of rice is very important for arranging sowing and replanting date. In this study, four representative regions (Ganyu, Huaian, Yangzhou, and Wuxian city), planted from north to south in Jiangsu province, were used to analysis their 50-years'(1958-2007) daily average temperature of May to October. According to the normal temperature indices of safe full heading date in Japonica rice with weaker and stronger cold tolerance, safe full heading dates of past 50 years, the first 25 years and the second 25 years from 1958 to 2007 in two Japonica rice varieties, with the guarantee rates of 50%, 80% and 90% respectively, are found; the safe full heading date of the second 25 years is significantly than that of the first ones (the delayed period is about 3-4 days); and the shifting range of the safe full heading dates in the four typical places is clearly enlarged. Therefore, the safe full heading dates of different places from north to south, are 18th September, 20th September, 24th September and 28th September respectively, 4-6 days later than the safe full heading dates which are customarily used in different places at present. Under the circumstance of the global warming, these results can be utilized as references for production in different rice-growing areas. In order to confirm the safe full heading dates of different varieties in the Japonica rice and exact sowing(planting) dates, more experiments should be carried out to observe cold tolerance, obtaining the safe full heading dates of mayor varieties so as to direct sowing and planting.2. In order to determine the safe sowing dates for Japonica rice varieties of different maturity types from north to south in Jiangsu province, an experiment of interval Sowing, every ten days per interval, starting from may 10, was carried out with five varieties, including Lianjing 4 (early-maturing medium Japonica), Huaidao 10 (late-maturing medium Japonica), Yangjing 4038 (early-maturing late Japonica), Nanjing 44 (early-maturing late Japonica) and Nanjing 46 (medium-maturing late Japonica), in four sites where prefecture-level cities of Lanyungang, Huai'an, Yangzhou, and Suzhou located. A forecasting equation y=a+b1x1+b2x2 was introduced to simulate the data from experiment, in the equation, y refers to days from sowing to full heading; a refers to standard days, namely the days from sowing to full heading in standard situation; b1 refers to temperature-sensitive index, that means difference of growth durations when the difference of daily average temperature reaches 1℃; x1 is the temperature difference, which refers to the difference between the average temperature and 30℃in growth period, it takes positive values in cases when the average temperature is lower than 30℃and 0 in other cases; b2 is the light-sensitive index,which refers to difference of growth duration when there's 1 day difference between two sowing dates; x2 is the sowing difference, namely the interval from sowing date to summer solstice, the positive value should be taken before the summer solstice, and the negative value should be taken after it accordingly. By compare with the real data from experiments, the 20 forecasting formulas of the five varieties in four regions, the results show that, the fitting degree are as high as 0.9927 to 0.9998, all reach the significant level, indicating that these models can describe the relationship between sowing date and full heading date accurately, providing a reliable basis for estimating full heading date and safe sowing date. On the basis of the 20 prediction formulas, perennial full heading dates(prediction) are obtained after several iteration by analyzing the average of past 25 years'daily average temperature, and then the perennial safe sowing dates and the safe sowing date with the guarantee rates of 80% are proposed. Analyzing the rotation and variety utilization of the double cropping system in the experimental sites with the results above, main conclusions are as follows: in Lianyungang, only medium-maturing medium Japonica varieties can be used for mechanical transplanting and direct-seeding, without delay; in huai'an, late-maturing medium Japonica varieties can be planted by machine before June 25, and directly seeded by the end of June; in Yangzhou, early-maturing late Japonica varieties and late-maturing medium Japonica varieties can both be utilized for mechanical transplanting or direct-seeding; in Suzhou, early-maturing late Japonica varieties and medium-maturing late Japonica varieties can be used for these two types of planting, and because of the long interval between two rotating crops, these Japonica rice should be planted as early as possible in order to extend growth period for higher yield.Compared with previous similar studies, this study, with more sowing dates and longer interval of sowing date, has more experimental sites and better geographical representation of latitude. The maturity types of the experimental varieties cover all the types of the Japonica rice planted in Jiangsu province. Moreover, the way by which full heading date and safe sowing date are determined accurately by prediction formulas with full heading date temperature and light, overcomes experiential deviation. In conclusion, the results of this study provide scientific basis for the sowing date of direct seeding rice and mechanical transplanting rice in Jiangsu province.
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