Effect Of Main Meteorological Factors On Maize Grain Dehydration

The development of mechanical grain harvest technology is restricted by the high grain moisture content when harvesting maize(Zea Mays L.)in China.It is essential for maize production to investigate the effect of meteorological factors on grain dehydration,and fully use local climate condition to drydown in filed.And it can also greatly improve the quality of maize harvest and production efficiency.The experiment was conducted from 2015 to 2017 in the Xinxiang Experimental Station of the Chinese Academy of Agricultural Sciences,Henan Province,China(35°10′ N,113°47′ E).The process of grain drying-down of several local maize hybrids was continuously tested,and the removing trend method was used to analyze the effect of meteorological factors on grain dehydration.Otherwise,in 2017 and 2018,some maize hybrids and three different sowing dates were selected to determine the grain moisture content for a long time.The theory and model of equilibrium moisture content were adopted to explore the relationship between maize grain moisture content at late stage and meteorological factors.In addition,based on the results of the equilibrium moisture content model in Huang-huai-hai maize ecological area,the GAB model and meteorological data for many years were used to analyze the basic differences of grain dehydration based on environmental conditions in various maize ecological areas in China.The main results are as follows: 1.The Logistic Power model was adopted to fit the process of maize grain dehydration.The actual moisture content of maize grain was divided into trend moisture content,meteorological moisture content,and random error,and the main meteorological factors affecting grain dehydration before and after physiological maturity of maize grain were screened out by stepwise regression and path analysis methods.The results showed that the meteorological moisture content of maize grain had significant correlation with most meteorological factors.The average temperature,average wind speed and evaporation(PETPM)were selected before physiological maturity,and evaporation played a major role,while temperature and wind speed had an indirect effect through evaporation.After physiological maturity,average temperature and average relative humidity were chosen and all had direct effects,but the effect of average relative humidity was slightly greater than that of average temperature.2.A stable state of grain moisture content was built in different maize hybrids and sowing date after a long time drying in field after physiological maturity,which was similar with the equilibrium moisture content influenced by temperature and relative humidity.Equilibrium moisture content is the moisture content when the moisture in grain reaches a dynamic equilibrium with the water vapor pressure in the external environment at a constant temperature and humidity.The time to reach the stable state varied but seemed to be no obviously relationship with the hybrids and sowing date.Based on previous researches,the Guggenheim–Anderson–de Boer(GAB)model,whose variables were daily average temperature and daily relative humidity,was adopted to describe the daily change of equilibrium moisture content.According to the supplementary test result of grain moisture content at different temperature,some data in stable state were revised in the experiment.The revised data matched well with the equilibrium moisture content,and synchronism was found in them.However,the synchronism did not occur immediately,which had “hysteresis” and “convergence”,and in other words,the maize grain moisture content always lagged behind the equilibrium moisture content,and had only a slight fluctuation compared with the extremum of one.Nevertheless,the equilibrium moisture content calculated by the GAB model still generally matched well with the grain moisture content of the stable state.3.The equilibrium moisture content in field had significant difference in different maize ecological areas in China,which showed a decreasing trend from south to north and from coastal areas to inland or highaltitude areas.There were higher equilibrium moisture content in Southwest China maize ecological area and Southern China maize ecological area,followed by Huang-huai-hai China maize ecological area,while the lowest equilibrium moisture content was observed in the Northern China maize ecological area,Qinghai–Tibet Plateau maize ecological area and Northwest China maize ecological area,but most of the equilibrium moisture content were about in the range of 10 %–17 %.When only considering equilibrium moisture content(temperature and relative humidity in air),in the range of 10 %–17 %,it took 11–18 days to dry from physiological maturity of maize(about 30 %)to a moisture content of 25 %,while it would be 25–52 days when drying to 20 %.Difference in climate type is likely to be the key reason for the observed regional differences in equilibrium moisture content.Areas with warmer temperatures and abundant precipitation contribute to the higher equilibrium moisture content,which result in the lower drying rate and longer drying time in field.Therefore,the difference in equilibrium moisture content between regions can be considered to be an important indicator to inform the selection the suitable variety and harvest management type and also the key factor to balance maize yield with comprehensive benefits in China.