The Spatio-temporal Characteristics Of Winter Wheat Phenology Changes In My Country And The Appraisal Of The Suitability Of The Sowing Period Based On APSIM Model

Winter wheat is one of the most important food crops in China.It is widely planted in Huang Huai Hai Plain,Loess Plateau,Southwest China and Xinjiang.Its yield ranks second in China,next only to rice.The effects of climate change on the phenological period and growth season length of winter wheat have been widely concerned and deeply studied in the past decades.Climate change leads to the change of winter wheat phenology,which changes the water and heat resources obtained in the growing season,and then affects the yield.Winter wheat sowing time,that is,sowing date,is one of the most important agricultural activities,which can be controlled independently in agricultural production.It is one of the important but unsolved scientific problems in the research of climate change and agricultural production to adjust the sowing date to deal with the change of water and heat resources in growing season caused by climate change.Based on the winter wheat phenological data of the main winter wheat producing areas in China,the change trend of winter wheat phenological period from1993 to 2013 was analyzed.Based on the SPEI(Standard Precipitation Evapotranspiration Index)and winter wheat yield data,the key water and heat periods affecting crop yield were determined.The crop growth model APSIM(agricultural production systems simulator)was used to carry out simulation experiments on different sowing dates.The optimal sowing date of different winter wheat production areas was determined with yield as evaluation index.Furthermore,the difference between the actual sowing date and the optimum sowing date of Winter Wheat in different regions of China was analyzed,and the influence potential of sowing date adjustment on winter wheat yield was studied.The main conclusions are as follows:(1)In terms of spatial distribution characteristics,the phenological period distribution of winter wheat at most stations in the study area has a latitudinal zonality,and the phenological period gradually changes in the north-south direction.The specific performance is that the high latitude area sows early but the phenological period is late,and the low latitude area sows late but the phenological period is early.In terms of temporal variation characteristics,the phenological period of Winter Wheat in each region had significant changes,especially the sowing date and turning green stage of winter wheat.In the study area,63.3%of the stations delayed the sowing date,with an average of 3.5 days per decade;79.6%of the sites delayed the rejuvenation period,with an average of 4.9 days per decade;53.1%of the stations delayed the jointing stage,with an average delay of 4.3 days per decade;56%of the stations advanced the heading date,with an average of 3.6 days per decade;50.3%of the stations showed an advance trend,with an average advance of 2.6 days per decade;and 65.7%of the sites showed an average advance trend of 2.6 days per decade The growth season was shortened by an average of 3.9 days per decade.The phenological period of winter wheat has different characteristics in time and space.By calculating the correlation coefficient between sowing date and each phenological period and yield,the effect of sowing date on phenological period and yield of winter wheat was reflected.The results showed that there was a strong correlation between sowing date and phenological period and yield of winter wheat.If the sowing date of winter wheat was changed,other phenological periods and yield would be changed.(2)SPEI index was used as the index of dry and wet changes during the growth period of winter wheat.The results showed that the drying trend of winter wheat appeared at seedling stage,overwintering stage,turning green stage and jointing stage.The spatial characteristics of SPEI index in winter wheat growth period were analyzed by EOF(Empirical Orthogonal Function)method.The results showed that the dry wet trend was consistent in Huang Huai Hai Plain,Loess Plateau and Xinjiang except for southwest China in the first mode.The second mode and the third mode showed the differences in north-south and east-west directions,reflecting the influence of longitude and latitude on SPEI index.The multiple regression equation between SPEI and climatic yield of winter wheat was established;the results showed that 45.4%of the variation of winter wheat yield could be explained by the change of SPEI.The time when the water and heat conditions affected the yield of winter wheat were November,January,February,March and May.(3)The results showed that the phenological period and yield simulated by the localized APSIM model were consistent with the measured phenological period and wheat yield.The average value of R~2 was more than 0.9.The RMSE of seedling and maturity stages was within 5 days,and the RMSE of simulated yield was less than500kg.Taking the yield as the evaluation index,the suitable sowing date of Winter Wheat in Huang Huai Hai Plain and southwest China based on APSIM model was later than the actual sowing date,and the suitable sowing date of Winter Wheat in Loess Plateau and Xinjiang was earlier than the actual sowing date.The difference between actual sowing date and suitable sowing date in Huang Huai Hai Plain and Xinjiang reached 0.01 significant level,indicating that Huang Huai Hai Plain and Xinjiang were not actively adjust the sowing date of winter wheat to deal with the warming of winter temperature.The sowing date can be postponed by 3 to 6 days in the north of Huang Huai Hai Plain,and 7 to 10 days in the southern region.The sowing date of winter wheat can be advanced 6 to 8 days in the western region and 3 to 5 days in the eastern region of Xinjiang to obtain higher yield.The adjustment of sowing date had a positive effect on winter wheat yeld in all regions,with the largest increase in Huang Huai Hai Plain and Xinjiang,which increased by 8.5%and 7.9%respectively on the basis of actual yield.For Huang Huai Hai Plain,the yield of winter wheat can be increased by428.7 kg/ha by adjusting the sowing date to the optimum sowing date.The yield of winter wheat could be increased by 416.8kg/ha if the sowing date of winter wheat was adjusted to the suitable sowing date in Xinjiang.The change of sowing date has little effect on winter wheat yield in the Loess Plateau and southwest China,but it has a certain improvement under the suitable sowing date.The increase of winter wheat yield in Loess Plateau is 75.8.kg/ha,and that in southwest China is 54.6 kg/ha.By analyzing the distribution and change trend of accumulated temperature of winter wheat before winter,the rationality of suitable sowing date based on APSIM model in Huang Huai Hai Plain and Xinjiang was verified.The essence of the change of winter wheat sowing date is to make the accumulated temperature before winter reach the optimum condition for winter wheat,ensure the safety of winter wheat and ensure the high and stable yield of winter wheat.By analyzing the distribution and change trend of accumulated temperature of winter wheat before winter,the rationality of suitable sowing date based on APSIM model in Huang Huai Hai Plain and Xinjiang was verified.The essence of the change of winter wheat sowing date is to make the accumulated temperature before winter reach the optimum condition for winter wheat,ensure the safety of winter wheat and ensure the high and stable yield of winter wheat.