Studies on Full Heading and Safe Sowing Date for Different Maturing-type Japonica Rice Cultivars of Jiangsu Province

To know heading dates corresponding to sowing dates of four maturing-type japonica rice cultivars in regions from north to south of Jiangsu Province and to establish the theoretical basis for sowing date arrangement for direct seeding and mechanical transplanting of rice by ascertaining the critical safe sowing dates,we directly seeded five japonica cultivars including Lianjing 4(mid-maturing and mid-season rice),Huaidao 10(late-maturing and mid-season rice),Yangjing 4038(early-maturing and late-season rice),Nanjing 44(early maturing and late-season rice),and Nanjing 46(mid-maturing and late-season rice) in Lianyungang(34°83' N),Huai’an(33°34' N),Yangzhou(32°25' N) and Suzhou(31°18' N) at an interval of ten days from May 10 to July 20.A model y = a + b 1 x 1 + b 2 x 2 was used to fit the virtual sowing dates and heading dates.Based on the results from four experimental locations and five cultivars,we obtained 20 sets of data,and 20 prediction equations with good fitting degrees of which the values of R 2 ranged from 0.9927 to 0.9998 were produced.On the basis of annually daily average temperatures and corresponding safe full heading dates of japonica rice during past 25 years,the sowing date for safe full heading was deduced by means of iterating repeatedly,then,a set of safe sowing dates with 90% assurance were evaluated,and the application of the safe sowing dates in various locations was finally analyzed.The results showed that,in a wheat-rice double cropping system of Lianyungang,the earliest sowing or transplanting date was June 15,which was suitable for mid-maturing and mid-season japonica rice cultivars with a safe sowing date of June 21 for direct-seeding;but other maturing-type varieties should have earlier sowing dates and could not be used for direct-seeding.In the south of Huai’an with a rice-wheat cropping system,the earliest date for sowing or transplanting was about June 12,and the safe sowing date was July 4 for mid-maturing and mid-season cultivars and June 22 for late-maturing and mid-season cultivars,and these cultivars could be used for direct-seeding.The safe sowing date was June 17 or 18 for early-maturing and late-season japonica rice cultivars,with a risk of direct-seeding because of a short growing period;the sowing date for safe full-heading of mid-maturing and late-season japonica rice cultivars was June 8,and such cultivars could not be used for direct-seeding.The earliest sowing or transplanting date in the south of central Jiangsu was June 8–11,and the safe sowing date was July 12,July 3,and June 25–28,respectively,for mid-maturing and mid-season,late-maturing and mid-season,and early-maturing and late-season cultivars,and these cultivars could be used for direct-seeding in this district;the safe sowing date of a mid-maturing and late-season cultivar was June 11,and this type of cultivars could not be used for direct-seeding owing to a too short growing period.In the south of Jiangsu,the earliest sowing or transplanting date was June 5,and the safe sowing date was July 18,July 13,July 9–10,and July 3,respectively,for the above four types of cultivars,and all cultivars could be used for direct-seeding if only considering a safe full-heading stage.However,the grain yield could not be high for mid-season cultivars with direct-seeding because they had short growing period.