Dehydration Characteristics Of Maize Kernels In Ningxia And Prediction Of Mechanical Grain Harvest Period

[Objective]The moisture content of maize grain is an important factor affecting mechanical grain harvest.The grain moisture content that suitable for mechanical harvesting is closely related to the characteristics of cultivars and local climatic conditions.In this study,the optimal estimation values of the parameters in the regression model of grain dehydration for 38 maize cultivars in Ningxia were obtained,and the corresponding equations were established.Based on the dehydration characteristics of different types of cultivars,comprehensive characters and yield,the allocation of mechanical harvest that suitable for cultivars was designed,which is of great significance for popularize of mechanical grain harvesting technology in the region of Ningxia.[Methods]The Logistic Power nonlinear growth model was used to simulate the grain dehydration process.The model was performed by using the nonlinear curve fitting function of Curve Expert Professional 2.2software,with the accumulated temperature as the independent variable and grain moisture content as the dependent variable,to estimate the optimal parameters of each cultivar.The optimal estimation values of parameters b and c in different regression models were obtained,and the grain dehydration equations of maize cultivars were established.The applicability of the dehydration model was tested by the grain moisture content of 11 maize cultivars in the two-years'mechanical grain harvest in this region.Based on the 10-years?2008-2017?meteorological data,the dates of mechanical grain harvest of different maize cultivars were predicted.We divided the 38 cultivars into 4 types based on the average accumulated temperature of 3274.3?·d and the average grain moisture content of 30.1%at physiological maturity.The four types were as follows:late maturity with high moisture content?I?,early maturity with high moisture content?II?,early maturity with low moisture content?III?,late maturity with low moisture content?IV?.[Results]The accumulated temperatures during the whole growth period of the four types were 3276.2-3542.7?·d for type I,3025.9-3237.6?·d for type II,2720.5-3273.6?·d for type III and3277.4-3456.6?·d for type I,respectively.The moisture contents at physiological maturity were30.7%-35.7%,30.3%-31.8%,26.6%-29.5%,and 26.0%-30.0%for each type,respectively.The relationship between yield and accumulated temperature during the whole growth period is y=6.945x–6016.2,R²=0.4711^**,where y is the yield?kg/hm²?,x is the accumulated temperature demand??·d?,indicating that the accumulated temperature increases 1?·d and the yield increase by 6.945 kg/hm².The applicability test result of the dehydration model showed that it could be used in this region.According to the prediction results,the time when moisture content reduced to a same level was different between the type I and the type IV in the three sowing dates,the difference is 13d to 28d.The difference of the same type between different regions was greater than 40d.Under the sowing date 1,the type I cultivars could not reduce to 28%moisture content in the southern mountainous areas?Guyuan City,Xiji County,Haiyuan County?,but not for the other three types.Under the sowing date 1,all types could reduce to 16%moisture content in the northern plains?Huinong Station,Taole County,Yinchuan City,Zhongning County and Zhongwei City?except for Type I;in Central Region?Tongxin County,Yanchi County?only type 3could reduce to 16%moisture content?in Tongxin County,where the heat is relatively abundant,some Type II cultivars and some Type IV cultivars can also reduce to?,and in the southern mountainous areas all types cannot reduce to 16%moisture content.Under sowing date 3,Type III could be harvested starting from later September when moisture content was 28%,and this harvest time gradually delayed from the northern plain to the southern mountainous area.Under the same sowing date,parts hybrids of Type II,III and IV could reduce to 16%moisture content in the northern plains,but the time is after October.[Conclusion]The accumulated temperature required for the growth of maize kept stable during years,but not for regions and may be because of the characteristic of cultivars.We proposed a planting design of cultivar considering the mechanical grain harvesting,the yield,the characteristics of different types of cultivars and the actual environmental conditions in regions.Late-maturing and high-yield cultivars can be planted in the central and northern parts of Ningxia,noting that the high moisture content cultivars should be sown in advance in the central region.In the southern mountainous areas,cultivars of early maturing with low moisture content should be planted and sowing date should be as early as possible to realize the requirements of mechanical grain harvesting.