Effects Of Sowing Dates And Seedling Age On The Utilizations Of Nutrient And Radiation And Temperature,Yield And Quality Of Late Season Japnica Rice

Due to its high yield potential and high rice quality,expanding the plantation of japonica rice becomes one of the important developmental trends in the rice production of China.The climate in the double-season rice region of Hubei Province is suitable for raising the late season japonica rice;however,the cultivation techniques for the late season japonica rice are remained to be studied in this region.Appropriate sowing date and suitable seedling age can make rice plants grow in the optimal climatic conditions,therefore,play important roles in the connection of crops,the yield formation and the effective utilization of resources in multiple cropping systems.In this study,Ejing 403,a main late season japonica cultivar in Hubei Province,was used as a material to study the effects of different sowing dates and seedling age on the growth progress,individual growth and development,population development,rice quality,and the utilizations of nutrient and temperature and radiation of transplanted late japonica rice through a two-year field experiment in 2017-2018.The main purpose of this study is expected to determine the appropriate sowing time and suitable seedling age for the production of late season japonica rice with high yield,high quality and high efficiency,and provide suitable scheme of farming arrangement for the late season japonica rice plantation in the double-season rice pattern of ?early indica-late japonica? in Hubei Province.The main results are as follows:1.Seedling age longer than 20 days was not conducive to the high yield formation of late japonica rice when sown on June 18 and 25.When sown on July 2,the yield decreased with the extension of seedling age in 2017.However,the yield was significantly lower when sown on July 2 than on June 25 in 2018 but no significant difference in the yield was detected among different seedling age treatments.Therefore,the appropriate sowing date is not later than June 25 and the suitable seedling age is about 20 days for the late japonica rice in the double-season rice region of Hubei Province.2.With the extension of seedling age,the LAI(leaf area index)at the jointing and full heading stages increased at first and then decreased with the highest being found in the treatment of 20 day seedling age.With the delay of sowing date,the LAI at the jointing and full heading decreased gradually.The econiomic yield as extremely significantly positively correlated with LAI at the jointing and full heading stages,respectively.The maximum LAI growth rate of the treatments with higher yield was 0.28-0.31/d,which occurred at 40-46 days after sowing(DAS).The mean rate in the fast LAI growth period was 0.22-0.27/d and the initial and terminal time of the fast LAI growth period occurred at 29-36 DAS and 51-56 DAS,respectively,and the fast LAI growth period lasted for 18-22 days for the treatments with higher yield.3.When sown on June 18 and 25,the dry matter yield above ground showed a decreasing trend with the extension of seedling age in the period from full heading to full maturity of Ejing 403.When sown on July 2,the dry matter yield at the full heading and full maturity increased initially and then decreased with the extension of seedling age,and the highest was found in the treatment that seedling age was 20 days.When the seedling age was longer than or equal to 20 days,the dry matter yield decreased in general in the period from the full heading to full maturity with the delay of sowing date.In the experiment of 2018,the dry matter yield at the late growth also decreased with the delay of sowing date when the seedling age was 15 days.The economic yield was extremely significantly positively correlated with the biomass yields at the full heading,milky and full maturity stage,respectively.For the populations with higher yield in 2018,the maximum rate of dry matter accumulation was 0.24-0.26 t/ha/d,which occurred at 60-69 DAS;the mean rate in the fast dry matter accumulation period was 0.20-0.23 t/ha/d,the initial and terminal time of the fast dry matter accumulation period occurred at 36-40 DAS and 84-98 DAS,respectively,and the fast dry matter accumulation period lasted for 48-58 days.4.When the seedling age was longer than or equal to 20 days,the brown rice rate increased with the delay of sowing date of Ejing 403.When sown on the same date,the polished rice rate was higher in the treatments with shorter seedling age than in that with longer seedling age.In the experiment of 2018,the chalky rice percentage and the chalkiness of rice decreased with the delay of sowing date.When sown on the same date,the chalky rice percentage and the chalkiness of rice were the lowest in the treatment with long seedling age(30 days).These indicated that the appropriate delay of sowing date and extension of seedling age are beneficial to improving the appearance quality of late japonica rice.5.With the delay of sowing date,the accumulative temperature of the whole growth period showed a decreasing trend.With the extension of seedling age,the accumulative temperature and sunshine hours in the whole growth period showed an increasing trend.When sown on June 25,the grain production efficiency of temperature was the highest when seedling age was 20 days.In the experiment of 2018,the grain production efficiencies of temperature and sunshine hours decreased with the delay of sowing date when the seedling age was not longer than 25 days.When sown on the same date and the seedling age was shorter than or equal to 20 days,the grain production efficiency of sunshine hours decreased with the extension of seedling age in the two-year experiment.6.When sown on June 25 and the seedling age was shorter than 25 days,the maximum rate and the mean rate in the period of fast nitrogen(N),phosphorus(P)and potassium(K)uptakes increased with the extension of seedling age.The maximum rate and the mean rate in the period of fast N,P and K uptakes decreased with the delay of sowing date when the seedling age was longer than 25 days.In the experiment of 2018,the economic yield was significantly positively correlated with the maximum rate and the mean rate in the period of fast P and K uptakes.For the treatments with higher yield,the maximum N uptake rate was 3.01-3.89 kg/ha/d,the mean uptake rate in the fast N uptake period was 2.66-3.35 kg/ha/d,and the fast N uptake period lasted for 25-31 days.The maximum P uptake rate was 0.80-0.81 kg/ha/d,the mean uptake rate in the fast P uptake period was 0.68-0.80 kg/ha/d,and the fast P uptake period lasted for 69-74 days.The maximum K uptake rate was 11.63-12.56 kg/ha/d,the mean uptake rate in the fast K uptake period was 10.20-11.01 kg/ha/d,and the fast K uptake period lasted for 14-15 days.