Maize (Zea mays L.) kernel moisture content at physiological maturity significantly differs among hybrids and is affected by the environment. Nonetheless, 35% was previously reported and is widely accepted as the moisture content at physiological maturity. To verify whether the 35% moisture content could be applied to various hybrids and regions, a multi‐area, multi‐year trial was conducted from 2015 to 2018 in six locations in different maize‐planting regions of China. Time‐series kernel moisture contents and kernel dry weights were investigated for 156 hybrids in total to ascertain the growth pattern of the percentage maximum kernel dry weight as a function of kernel moisture content. The growth patterns were fitted with a tri‐linear model with a plateau, and at the point at which the percentage maximum kernel dry weight first reached its maximum (physiological maturity), the kernel moisture contents were 32% for summer maize, 34% for spring maize, and 38% for Daqing (a special spring maize region). We found that regional variation existed in kernel moisture content at physiological maturity. The regional average moisture content at physiological maturity could thus be used as an indicator to determine physiological maturity for most hybrids in the region. In addition, varietal differences in moisture content could be accounted for when using the regional average value.

The grain impurity rate is an important index for assessing the quality of mechanical maize harvesting. Therefore, it is of great significance to clarify the current situation of maize impurity rate and study the factors that affect the impurity rate in order to promote the development of mechanical maize harvesting technology. From 2012 to 2019, a total of 2504 maize impurity rate measurements were obtained. The results showed that the average impurity rate at maize harvest was 1.18% in China, in which the Huang-Huai-Hai summer maize area was 1.68%, which was significantly higher than the 0.65% in the Northwest spring maize area and 0.77% in the North China spring maize area. There was a significant positive correlation between the impurity rate and the moisture content of the maize harvest. The average moisture content of maize at harvest in Huang-Huai-Hai summer maize area was the highest at 27.55%, which was the main reason for the high impurity rate in this area. When harvesting different varieties with the same moisture content, there were significant differences in the impurity rate between different varieties. The cob hardness of the variety may also affect the impurity rate of maize. Different harvesters and weather conditions during harvesting are also important factors affecting the impurity rate. Therefore, by breeding fast dehydrated varieties and harvesting maize in time, the impurity rate of maize during mechanical harvesting can be effectively reduced.

How to allocate heat resources during yield formation and grains drying in the field to ensure food security while reducing the grain moisture content (GMC) is an important issue in maize (Zea mays L.) production in China. In this study, we established three production scenarios (traditional production (TPS, GMC > 30% at harvest), mid-moisture grain harvest (MMHS, GMC ≤ 25% at harvest), and low-moisture grain harvest (LMHS, GMC ≤ 20% at harvest)). Five varieties (DMY1, FK139, DK159, XY335, and JK968) were selected as model varieties to establish a grain drying prediction model, and the model prediction accuracy was good (RMSE = 2.96-4.04%, R 2 = .408-.733). Results revealed that the production loss of the LMHS was 23.7% compared to the TPS, while the MMHS had a production loss of 6.5%. By replacing new varieties with high yield potential and fast grain drying rate, even small production increases can be achieved in MMHS. By adjusting the layout, it was possible to achieve 25% GMC in Inner Mongolia, which can promote the mechanical grain harvesting. However, the conditions for further reducing GMC (20%) at harvest are not yet available, and this requires more detailed future research.