Quantification planting density based on heat resource for enhancing grain yield and heat utilization efficiency of grain mechanical harvesting maize

The selection and promotion of mechanical grain harvesting maize varieties that shorten the maturity period in exchange for sufficient dehydration time pose new challenges for increase in the yield of spring maize in the north and the full utilization of heat. The use of a synergistic mechanism can provide a theoretical basis for the high-yield and high-efficiency cultivation and large-scale promotion of mechanically grain-harvested varieties of maize. In this study, different types of maize varieties were used as the tested materials, and the density network tests were conducted in four ecological regions of Inner Mongolia with different thermal conditions in eastern Inner Mongolia, which belonged to heat limit area (where medium-early- and early-maturing maize varieties are planted) and heat sufficient area (where the medium-later- or late-maturing varieties are planted), respectively. The effects of planting density on stage development, yield formation, and heat use efficiency (HUE) of different types of maize varieties were analyzed, and their responses to heat resources were analyzed. The results showed that the maximum yield of mechanical grain-harvesting varieties was obtained under the condition that the accumulated temperature utilization rate of ≥10 ℃ reached 86.0%−89.3%. The maximum yield and corresponding density of mechanical grain-harvesting varieties in different regions were higher than those of the current farmers’ variety, especially the differences were obvious in the regions with limited heat. The density of the maximum yield of mechanical grain-harvesting varieties decreased linearly with the increase of the total amount of heat resources. The density increased by 1700 plants·hm⁻² for every 100 ℃ decrease of accumulated temperature in the region ≥10 ℃. The areas with limited heat (ecological areas dominated by early-maturing and medium-early-maturing varieties, in this paper, it is east region of Xing’an Mountain and south region of Xing’an Mountain), the proportion of growing days per-silking and post-silking, the proportion of accumulated temperature ≥10 ℃, and the proportion of biomass of mechanical grain-harvesting varieties all approached 5∶5. To achieve the maximum yield, it was necessary to increase the densification from 60 000 plants·hm⁻² to 88 000−91 000 plants·hm⁻². Increases the density after increasing yield of 11.1−12.7 t·hm⁻², yield increase 20.1%−23.3%, and HUE can be increased by 20.6%−30.1%; In areas with abundant heat (ecological areas mainly planted with mid-late maturity or late maturity varieties, this paper refers is the north region of Yanshan Mountain and west Liao River Plain), the ratio of growing days and accumulated temperature per-silking and post silking tended to be 4.5∶5.5, the ratio of biomass at per-silking and post silking was 4∶6, and the yield ranged from 15.4 to 16.9 t·hm⁻². The maximum yield needed to be densified from 60000 plant ·hm⁻² to 81 000-83 000 plant ·hm⁻². After densification, the yield can be increased by 6.1%−11.5%, and the HUE can be increased by 8.6%−17.5%. The effective matching of heat demand of varieties and regional heat resources is the premise to obtain high yield and fully tap the potential of regional yield. Quantitative dense planting based on the matching of heat resources is an effective way to achieve increased yield and efficient utilization of heat resources for mechanical grain-harvesting varieties of spring maize. In the area with limited heat resources, the balance of pre-silking and post-silking at resources and the full accumulation of pre-silking biomass were the key factors, and the suitable density was 88 000 to 92 000 plants·hm⁻². In the area with abundant heat, the production of post-silking matter was explored, and the suitable density population was constructed. The maize was to delay post-silking leaf senescence, and the suitable density was 81 000−83 000 plants·hm⁻².