Effect of planting density on lodging change of spring maize after physiological maturity

Heat resources are abundant in the Jinzhong Basin and can be used for dehydration in the late growth stage of spring maize. Lodging resistance is the key limiting factor for direct mechanical grain harvesting in this region. High planting density and harvest delay are important factors for the development and popularization of mechanical grain harvesting technology, but lodging in the late growth stage of maize limits the increase in planting density. One problem with implementing spring maize mechanical grain harvesting technology in the Jinzhong Basin is the selection of an appropriate planting density with high yield and lodging resistance. A field experiment was conducted in the Dongyang Experiment and Demonstration Base of Shanxi Academy of Agricultural Sciences from 2017 to 2019, with three planting densities (6.0×10⁴, 7.5×10⁴, and 9.0×10⁴ plants·hm^-2) and 29 maize cultivars. Changes in lodging at three planting densities were analyzed after the spring maize matured physiologically. The results showed that the average lodging rate for three planting densities at physiological maturity was 0.4% (6.0×10⁴ plants·hm^-2), 1.2% (7.5×10⁴ plants·hm^-2), and 2.5% (9.0×10⁴ plants·hm^-2). After physiological maturity, the average lodging rate increased significantly (P < 0.05). For every 10 days of delay, the lodging rate for three planting densities increased by 0.2 (6.0×10⁴ plants·hm^-2), 0.7 (7.5×10⁴ plants·hm^-2) and 1.5 (9.0×10⁴ plants·hm^-2) percentage points. The national standard GB/T 21962-2008 mentions that the lodging rate of maize should be less than 5% under mechanical grain harvesting conditions. According to the fitting equation, the lodging rate for the 9.0×10⁴ plants·hm^-2 density was higher than 5% after October 2. However, the lodging rates for the 6.0×10⁴ plants·hm^-2 and 7.5×10⁴ plants·hm^-2 densities were less than 5% until November. Therefore, maize grown at 6.0×10⁴ plants·hm^-2 and 7.5×10⁴ plants·hm^-2 could make full use of the local accumulated temperature for dehydration. According to the two-way average method with yield and lodging rate of the harvest period, the varieties and densities with high yield and lodging resistance in three years were always 'Jinkeyu3306' (7.5×10⁴ plants·hm^-2), 'Jinkeyu3306' (9.0×10⁴ plants·hm^-2), 'Dika517' (7.5×10⁴ plants·hm^-2), and 'Huanong887' (7.5×10⁴ plants·hm^-2). The average yield was 14 091.8 kg·hm^-2, and the average lodging rate was 1.7%. These varieties and densities of spring maize were suitable for mechanical grain harvesting in the region. The planting densities of 6.0×10⁴ plants·hm^-2 or 7.5×10⁴ plants·hm^-2 were suitable according to the annual precipitation, irrigation conditions, and the density tolerance of the varieties to achieve high yield and lodging resistance.