Effects Of Sowing Date On Growth Period, Yield And Quality Of Japonica Rice In Different Ecological Regions

This study was conducted to investigate the effects of sowing date on the growth process, yield, grain quality and utilization of temperature and light of indica and japonica rice in the main rice planting ecological regions of Hubei province, which was in order to provide a reference for the transformation of indica to japonica rice and high-yield cultivation of japonica rice in Hubei province. Field experiments with six sowing dates and four varieties of middle rice including Yongyou4949, Nanjing9108, Yangliangyou6 hao and Huanghuazhan were conducted in six counties including Xiangzhou, Suixian, Shayang, Yiling, Gongan, Wuxue between 2014 and 2015. Through determining the paddy growth process, yield and grain qualities of each ecological region combined with the regional meteorological data, the effects of different sowing dates on growth period, yield, grain quality and utilizing traits of temperature and light in different ecological regions were comparatively analyzed. The main results were as follows:1. As the latitude decreased, the whole growth period showed a tendency to shorten. With 1° decrease of latitude, the growth period shortened by 16.5 days(2014) and 9.7 days(2015). These differences were mainly due to the differences in the duration of filling stage, which shortened by 13.4 days(2014) and 10.4 days(2015) with 1° decrease of latitude. As the sowing date was delayed, the whole growth period shortened. With 10 days delay of sowing date, the growth period shortened by 2.39 days, which was mainly caused by the changes of vegetative stage. The vegetative stage shortened by 2.4 days with every 10 days delay of sowing date. The growth period of Huanghuazhan lasted about 131 days, which was relatively short and stable. The growth period of Nanjing9108 lasted longer as 146 days, which tended to vary. The growth period of Yongyou4949 and Yangliangyou6 hao were respectively 140 days and 147 days, which were moderately stable. The filling stage of japonica rice was 50.3 days, which was longer than that of indica rice as 41.5 days.2. As the latitude decreases, the utilization of effective accumulated temperature of all the varieties throughout the growth period also decreases. Compared with thoses at Xiangzhou site, the utilization of effective accumulated temperature of Yongyou4949, Nanjing9108, Yangliangyou6 and Huanghuazhan in Wuxue respectively decreased by 9.65%, 7.05%, 6.75% and 7.07% in 2014. Compared with those at Suixian site, the utilization of effective accumulated temperature of Yongyou4949, Nanjing9108, Yangliangyou6 and Huanghuazhan in Gong’an decreased by 4.78%, 3.49%, 3.34% and 3.5%, respectively in 2015. As the latitude decreased, the sunshine duration and radiation use efficiency throughout the growth period also decreased. Compared with those at Xiangzhou site, the utilization of effective accumulated temperature of Yongyou4949, Nanjing9108, Yangliangyou6 and Huanghuazhan in Wuxue decreased by 9.31%, 6.67%, 6.7% and 5.64%, respectively in 2014. And compared with those at Suixian site, the utilization of effective accumulated temperature of Yongyou4949, Nanjing 9108, Yangliangyou6 and Huanghuazhan in Gongan decreased by 6.47%, 9.25%, 1.8% and 2.74%, respectively in 2015. As the sowing date was delayed, the utilization efficiency of temperature and sunlight of all the varieties reduced. For instance, the utilization efficiency of temperature and sunlight of rice seeded on June 4th was lower than that of rice seeded on April 15 th by 6.2%. As the sowing date was postponed, the sunshine duration and radiation use efficiency both increased first then decreased and reached the maximum when the rice was seeded on April 25 th. The utilization efficiency of temperature and sunlight throughout the growth period of Yangliangyou6 and Nanjing9108 was the highest, with that of Yongyou4949 lower and that of Huanghuazhan the lowest. The differences among them were significant. The utilization efficiency of temperature and sunlight of Yangliangyou6 was high due to the high use efficiency during vegetative stage and vegetative-reproductive stage, and the high utilization efficiency of temperature and sunlight of Nanjing9108 was mainly because of the high use efficiency during filling stage and vegetative stage.3. As the sowing date was postponed, the yield increased first then decreased. The highest yield in 2014 appeared when the rice was seeded on May 5th and May 15 th, which was 10.4 t/hm2 in average. The highest yield in 2015 appeared when the rice was seeded on May 15 th and May 25 th, which was 11.35 t/hm2 in average. The changes in yield was mainly affected by the number of grains per panicle and seed setting rate. The yield at Suixian site were respectively 11.6 t/hm2 and 12.5 t/hm2 in 2014 and 2015, which was significantly higher than that at other sites. The yield of Yongyou4949 was respectively 11.6 t/hm2 and 12.6 t/hm2 in 2014 and 2015, which was significantly higher than that of other varieties. At Suixian site, the highest yield of Yongyou4949(seeded on May 5th) was 14.9 t/hm2 in 2014 and the highest yield of Yongyou4949(seeded on May 15th) was 14.9 t/hm2 in 2015.4. As the sowing date was delayed in a certain range, the rice processing quality and appearance quality was gradually improved, and the quality of rice seeded on June 4th was the best. The rice planted at Shayang and Suixian sites was more of advantage to obtain better quality. The processing quality and appearance quality of Huanghuazhan was the best, with that of Yongyou4949 and Yangliangyou6 lower. The processing quality of Nanjing9108 was relatively good, but its appearance quality was the lowest. The chalky rice rate of Nanjing9108 was 91.1% with 50.4% of chalkiness, which showed that the processing quality of Nanjing9108 was not at advantage at all of the sites.