Studies On The Growth And Development Characteristics Of Maize Suitable For Grain Mechanical Harvesting And Its Harvesting Performance In Hebei Province

Hebei Province is an important grain base in China and one of the largest maize producing areas.At present,maize varieties widely cultivated in production have the problems of high stalk,late maturity and high grain moisture content at harvest,which seriously affects the application and promotion of mechanical harvesting of maize grain.This experiment was conducted in Qingyuan Experimental Station of Hebei Agricultural University during 2019-2020.Eight maize varieties were used as experimental materials,and three planting densities were set:60,000,75,000 and 90,000 plants/hm2.The yield and daily yield,growth period and accumulated temperature,grain filling and dehydration characteristics,moisture content of adjacent organs of ear,lodging resistance and other traits of maize varieties were systematically observed.The main results were as follows:(1)The increase of grain filling rate(GFR)and grain weight showed a"slow-fast-slow" trend with the growth period,and the duration of rapid growth period and grain weight increment were the largest.The GFR showed rapid growth period>gradual growth period>slow growth period.The ultimate growth,maximum growth rate and average GFR of Jingnongke 728(JNK728)were the largest among the eight maize varieties,and the maximum GFR of ZH1632 was the largest.The maximum growth day and filling active period of Lishou 1(L1)were the largest.The grain dehydration rate(GDR)showed a ’fast-slow ’ trend with the growth period,and the GDR of JNK728 and MC812 was significantly higher than that of other varieties at 54 days after silking(DAS).It can be seen that the GDR of short growth period varieties is faster than that of long growth period varieties in the late filling stage,and it is easier to achieve grain mechanical harvest.(2)With the increase of planting density,the plant height,ear height,ear ratio,internode length and lodging rate of each variety increased significantly,while the stem diameter,puncture strength,crushing strength,brace root layers,root number and root quality decreased significantly,and the stalk bending strength increased first and then decreased with the increase of planting density.At different growth stages,there were significant differences in stem strength among varieties.The puncture strength,crushing strength of the basal internode and stem bending resistance of each variety increased first and then decreased,and reached the maximum at the grain filling stage.(3)The grain moisture content(GMC)of varieties was extremely significantly positively correlated with the moisture content of stems,leaves,husks,ear stems and cobs.The dehydration rates of husks and ear stems showed a "slow-fast" trend with the growth period,while the dehydration rates of cob and grain showed a " fast-slow" trend,indicating that the dehydration rates of husks and ear stems were higher than those of cobs and grain at the late growth stage.The GMCt had a linear regression relationship with crushing rate and husk fluffiness,and had a significant positive correlation with crushing rate,and had a significant negative correlation with husk fluffiness.The GMC of MC812 and JNK728 were 28.4%and 26.9%at harvest time,which were suitable for mechanical harvesting of maize grain.(4)With the increase of density,the yield and daily yield of each variety increased first and then decreased.The yield reached the maximum at the density of 75,000 plants/hm2,and the yield and daily average increment of each variety increased by 8.6%and 8.7%,respectively,from 60,000 to 75,000 plants/hm2.The yield and daily yield of MC812 were the highest,which were 19.4%and 31.6%higher than those of Zhengdan 958(ZD958),respectively.The LAI of MC812 and JNK728 were larger under different densities,while Xiangyu 269(XY269)was relatively small.To sum up,due to the small temperature difference between day and night,cloudy and lack of light and heat resources in summer maize area of Hebei Province,the mechanical grain harvest level of maize in this area is very low.Therefore,varieties with short growth period and fast dehydration at late growth stage were selected to reduce the GMC at harvest stage.Increase production by increasing planting density;By selecting varieties with high stalk bending resistance and good root traits to reduce yield loss caused by lodging,it is the only way to realize direct grain harvest of maize.