Characterization Of Maize Grain In-field Drydown And Its Relation To Grain Filling

In modern maize(Zea mays L.)production,mechanical grain harvesting is adopted and grain moisture content at harvest thus becomes an important economic indicator.For high yield,traditional maize production mainly focuses on yield formation and grain filling while modern maize production must take into account both of grain filling and drying in field,however,little is known about the grain dehydration in China.Centering on grain dry-down and grain filling,the multi-site and-year trial(2014?2019)and the multi-sowing date trial(2018?2019)were carried out to continuously investigate grain's dynamics of moisture concentration(%),moisture content(g)and dry weight(g),of which the objectives of clarifying the characteristics of grain dehydration in field,explaining the relationship between grain drying and filling,and optimizing cultivars'selection in conformity with heat resources in various areas.The research results mainly included the following three aspects:1)Characterization of grain dehydrationThere were significant differences in grain moisture loss rate no matter before or after physiological maturity of maize cultivars,on average,which were 1.43?1.81%/d and 0.35?0.83%/d for all cultivars,respectively.The environment affected grain moisture loss rate,but the genotype was the main factor.Generally,cultivars with high moisture loss rate before maturity declined moisture quickly after maturity,while existing noticeable cases of particular cultivars.According to grain moisture dynamic,the model M=90/[1+(T/a)~b]was developed based on the relationship between the thermal time(T)from silking and the time-series moisture concentration(M).By denoting the moisture loss rate,the parameters a and b in the model could be used as the indicators for selecting the fast-drying cultivars,that is,the smaller parameter a and the larger parameter b mean the faster grain drying.On a regional scale,this model could accurately predict the moisture concentration,thereby guiding the decision-making during harvest.Also,at present,the thermal time from sowing to 25%moisture could be used as the maturity indicator for selecting and breeding cultivars for mechanical grain harvesting.2)Relationship between grain drying and grain fillingThe correlation coefficient between moisture loss rate and grain filling rate was 0.240**,while theirpartial correlation coefficient was-0.192*.Variety diversity was observed in the rate of grain filling and drying.There were cultivars with fast filling and fast drying,indicating that grain filling and moisture drying could be coordinated.Additionally,the maximum moisture content was positively correlated with the final grain weight(r=0.766**).Moreover,the growth process of relative grain weight converged with the decreasing grain moisture concentration,disregarding varietal and environmental differences.Furthermore,when the grain dry weight reaches its maximum,the moisture concentration differed significantly among regions,which was 32%for summer maize and 34%for spring maize.This moisture value could be used to determine the time of physiological maturity.3)Cultivars'lay-out for mechanical grain harvestingIn Huanghuaihai Plain,the thermal times of summer maize cultivars from sowing to black layer,to 25%moisture,and to 20%moisture were 2960(2551?3209)°C·d,3070(2644?3394)°C·d,and 3206(2788?3470)°C·d,respectively.After the black layer,on average,113°C·d and 250 were required for grain drying to 25%and 20%moisture.Under double-cropping system,the heat resource for summer maize season in Huanghuaihai Plain was 3615?1839°C·d,decreasing from south to north.Based on the heat resource and the thermal times of cultivars,Huanghuaihai Plain could be divided into three zones,thus optimizing the cultivars'lay-out for achieving mechanical grain harvesting on a strategy.Conclusively,this paper researched the characteristics of grain dehydration,the relationship between grain drying and grain filling,the moisture model,the indicators for selecting and breeding of fast-drying cultivars,the optimization of cultivars in conformity with local heat resources,and the cultivars'lay-out for mechanical grain harvesting in Huanghuaihai Plain.The above findings would provide theoretical foundation and technical support for reducing grain moisture during harvesting period,potentially,which is also conductive to enhancing the competitiveness of maize industry and ensuring food security in China by propelling modern maize production.