Selection of spring maize varieties suitable for high-density planting, high-yield and grain mechanical harvesting in Beijing-Tianjin-Hebei region of China

Abstract: Mechanical harvesting can significantly improve the technical efficiency, while reduce the production cost in maize farming. However, the evaluation system and maize variety are still lacking, particularly suitable for mechanical grain harvesting in the Beijing-Tianjin-Hebei region of China. Variety selection of maize has also limited the implementation of mechanical grain harvesting in modern agriculture. In this study, a 3-year experiment on the variety/density of spring maize, and 2-year experiment on mechanical grain harvesting were carried out in the Beijing-Tianjin-Hebei region, China. Three first-level evaluation indexes were set, including the suitability for mechanical grain harvesting, high-stable yield while high quality, and high Water Use Efficiency (WUE), according to the requirements of varieties, climate, and planting conditions in the mechanical grain harvesting for this region. The second-level evaluation indexes under the suitability for mechanical grain harvesting were the broken rate of kernel, impurity rate, and total loss rate. The relationship between the broken rate of kernel and impurity rate with the moisture content of kernel were in the parabolic and exponential form, respectively. The moisture contents of kernel were 3.6%~24.8% and ≤26.99%, when the broken rate of kernel ≤5% and impurity rate ≤3%. Therefore, the third-level evaluation indexes under the kernel broken rate and impurity rate was the moisture content of kernel at the 10th day after physiological maturity, where the criteria was ≤25%. The total loss rate represented the parabolic relationship with the moisture content of kernel, and the linear relationship with the lodging rate and standard deviation of ear height. Therefore, the third-level evaluation indexes under the total loss rate were the moisture content of kernel at the 10th day after physiological maturity(≤25%), lodging rate(≤5%), and standard deviation of ear height(≤5.93 cm). In 3-year experiment on the variety/density of spring maize, the average yield, WUE and ear rot rate were 10 889.64 kg/hm2, 2.28 kg/m3 and 1.75%, respectively. The average standard deviation of yield and WUE were 1 776.79 kg/hm2 and 0.43 kg/m3, respectively. The high and stable coefficient of yield and WUE were 0.53 and 0.46, respectively. According to the correlation analysis, the increasing ratio of yield and WUE with the density increasing by 15 000 plants/hm2 were 6.59% and 11.89%, whereas, the decreasing ratio of yield per plant with the density increasing by 15 000 plants/hm2 was 8.38. These values of yield, ear rot rate, and WUE can be used to set the second-level evaluation indexes under the high-stable yield while high quality, and high-stable WUE. The Analytic Hierarchy Process(AHP) and entropy weight method were selected to calculate the comprehensive weights of each evaluation index. The discrimination criteria of evaluation index can be used as the index values of distinguish variety, to avoid relying solely on sequencing for the selection of maize varieties. In 2-year experiment on mechanical harvest, Yufeng 98, Yudan 9953, and Jinkeyu 3306 were selected as spring maize varieties, due to their fast grain dry down rate, high and stable yield, increasing yield with high density, low ear rot rate, and high WUE. The evaluation system of suitable variety can contribute to the promotion of mechanical maize harvesting in the Beijing-Tianjin-Hebei region, providing for a certain reference for the selection of high-yield maize varieties suitable for high-density planting, and mechanical harvesting in other areas.