In this study, the date when the kernel moisture content of different types of maize variety dehydrates to a suitable level for mechanical grain harvesting was predicted for different sowing dates in the Ningxia Hui Autonomous Region of China, in order to provide a basis for the variety selection at the regional scale, the determination of a suitable harvest period, and the development of the mechanical harvesting of maize varieties with a low moisture content.

Using the average kernel moisture content at physiological maturity (30.1%) and the average accumulated temperature (3 274.3 °C·d) required for sowing to physiological maturity ≥0 ℃·d as indicators, 38 common maize varieties were classified into four types by the two-way average method: type I varieties were characterized by late maturity and slow dehydration; Type II were characterized by early maturity and slow dehydration; type III varieties were characterized by early maturity and fast dehydration; type IV varieties were characterized by late maturity and fast dehydration. According to the production practice in Ningxia, the varieties with medium kernel moisture content and accumulated temperature requirement at physiological maturity stage were selected as the representative variety of each type. Then, the Logistic Power nonlinear growth model was used to predict the dehydration of the 38 maize varieties base on 10 years of recent meteorological data (2008-2017). Based on these data, the kernel moisture characteristics of each type of variety were predicted for various regions of Ningxia with different heat resources for three different sowing dates (initial sowing, peak sowing, and initial sowing).

The results showed that, initial sowing could obtain an accumulated temperature of 162.2-229.8 °C·d in crop growth more than that of final sowing. The accumulated temperatures required for kernel dehydration to a moisture content of 25% from sowing for Type I, Type II, Type III, and Type IV cultivars were 3 615.2, 3 290.6, 3 138.0, and 3 426.6 °C·d, respectively. In northern and central Ningxia, all types of varieties could meet the requirement that the kernel moisture content be reduced to 25%, while in the southern regions, Type III varieties could meet the requirement that the kernel moisture content be reduced to 25% for sowing at the initial and peak sowing times. The predicted accumulated temperatures from sowing to dehydration required for kernel dehydration to a moisture content of 16% for Type I, Type II, Type III, and Type IV cultivars were 4 320.6, 3 816.4, 3 632.9, and 4 023.6 °C·d, respectively. For the Type III varieties, in northern Ningxia on the initial sowing date and final sowing date, the kernel moisture content of both could be reduced to 16%; in the central region on the initial sowing date and peak sowing date, the accumulated temperature required for dehydration to 16% could be satisfied.

The heat resources of Ningxia could be used rationally through the selection of maize varieties with appropriate dehydration characteristics and early planting, thereby help to achieve high-quality mechanical maize kernel harvesting in this region. In northern and central Ningxia, it was recommended to select early-maturing, fast-dehydrating (Type III) varieties in order to achieve the mechanical harvesting of maize with a low kernel moisture content and thus convert regional heat resources into economic benefits.