Dehydration of maize grains in the field can reduce costs associated with drying after harvest. A delayed harvest approach after physiological maturity, in which plants stand in the field to allow the stems to dry, has been widely adopted in maize production. However, it remains unclear how harvesting at different time points during the dehydration stage may affect grain yield and quality. In the present study, experiments were conducted in the Ningxia Irrigation Area of northwest China from 2019 to 2022, we continuously observed and used a linear-plateau model to analyze the changes in grain weight and quality traits (such as bulk density and levels of starch, protein, oil, fiber, and free fatty acids) during the field dehydration period of maize hybrids with differing maturity times. Harvesting at a grain moisture content of >31.0% was shown to affect grain weight, whereas harvesting at a moisture content of <25.9% did not affect grain weight or yield. The stable period for grain weight occurred during the physiological maturity stage for an early-maturing hybrid and 5–12 days before physiological maturity for the mid–late-maturing hybrids. When the field grain moisture content was <37%, harvesting did not affect the grain bulk density. Grain bulk density tended to stabilize one to two weeks earlier than grain weight and two to three weeks before the physiological maturity period. The protein, oil, fiber, and free fatty acid contents in maize kernels at 30 days after silking were not affected by the harvesting period, and the starch contents were unaffected in maize kernels harvested at any time later than 50 days after silking. Overall, maize grain should be harvested during field dehydration and delayed harvesting after physiological maturity with relatively low moisture content to get a better yield with superior quality.; delayed harvesting is therefore an important technical approach to improve the efficient production of high-quality maize.

The stalk strength of maize (Zea mays L.) has a significant effect on stalk lodging and harvesting loss, and the cob mechanical strength affects the grain broken rate in mechanical grain harvesting. Clarifying the relationship between maize stalk strength and cob mechanical strength could provide a theoretical basis for the selection of cultivars with high lodging resistance and high suitability for mechanical grain harvesting. In 2017 and 2018, 64 maize cultivars were planted in four locations to investigate the changes in the bending strength of stalks and cobs using the three-point bending method during the late growth stage. The results showed that, in the late growth stage, with increasing number of days after physiological maturity, the stalk bending strength (SBS) of the fifth internode above the soil gradually decreased, the cob bending strength (CBS) decreased first and then increased, and it was lowest at about six to eight days after physiological maturity. In the same experimental site and sampling period, there was no significant correlation between the SBS and the CBS of different maize cultivars. Cluster analysis showed that most of the investigated maize cultivars showed low stalk strength during the late growth stage. However, a few of the maize cultivars were suitable for mechanical grain harvesting due to their characteristics of high stalk bending strength and moderate cob bending strength during the late growth stage.

The reasonable assessment of maize varieties in different ecological regions can allow temperature resources to be fully exploited and reach the goal of high yield and efficiency and is thus an important direction of modern maize development in China. In this study, a logistic power nonlinear growth model was used to simulate the accumulated temperature required for kernel dehydration to moisture contents of 25%, 20%, and 16% for various maize cultivar, which were divided into six types based on the accumulated temperature required for kernel dehydration to a moisture content of 25%. The relationship between the yield of maize cultivars and the accumulated temperature required for kernel dehydration to a moisture content of 25% was found to follow a unary function model. Changing the planted maize variety was found to increase economic returns by more than 7000 RMB/hm2 in Ningxia, Northwest China. Under the conditions of mechanical grain harvesting, economic benefits can be further increased by means of selecting high yields and fast-dehydrating varieties, selling when the grain dehydration is below 16%. A better way to achieve grain dehydration to a moisture content below 16% is to postpone the harvest date as much as possible rather than drying after the harvest at physiological maturity. The areas of various types of maize varieties can be dehydrated to moisture contents of 25%, 20%, and 16% were marked. Based on the distribution of heat resources in different regions of Ningxia from the normal sowing date to October 31 before winter irrigation, the appropriate cultivars for various regions in the province were determined based on production benefits. Therefore, in different areas of Ningxia, selecting suitable maize varieties according to temperature resources can reach a high yield and mechanical kernel harvesting, and ultimately obtain higher economic benefits. Keywords: maize, dehydration, grain yield, economic return, mechanical kernel harvesting DOI: 10.25165/j.ijabe.20201401.6035 Citation: Li H Y, Wang Y H, Xue J, Xie R Z, Wang K R, Zhao R L, et al. Allocation of maize varieties according to temperature for use in mechanical kernel harvesting in Ningxia, China. Int J Agric & Biol Eng, 2021; 14(1): 20–28.