Abstract: The aim of this research was to explore the potential to achieve increased yield of maize variety Zhenghong No. 6 through high plant density under normal fertilisation rates. Field trials were set up in Zhongjiang County in the central hilly region of Sichuan. Five planting densities were set up: 5.25 (CK, actual production density), 6.00, 6.75, 7.50 and 8.25×10⁴ plants·ha^-1, and the growth, lodging and yield of Zhenghong No.6 compared under the different planting densities. It was found that as planting density increased, plant height, cob length, and leaf area index all increased, while stem diameter decreased. With each stepwise increase in plant density of 750 plants·ha^-1, plant height increased on average by 6.47 cm and cob height from the ground by 2.13 cm, while the maximum leaf area index increased by 0.46, and stem diameter decreased by 0.46 mm. With greater plant density, single-plant dry weight decreased (CK, 231.5 g·plant^-1; 8.25×10⁴ plants·ha^-1, 185.1 g·plant^-1) but the crop biomass increased (CK 12153 kg·ha^-1; 8.25×10⁴ plants·ha^-1, 15271 kg·ha^-1). Across the range of tested plant densities, with increasing density, the percentage dry matter allocation to leaves and stem sheaths increased, while the allocation to stem initially increased and then decreased. Within-plant dry matter allocation was grain (~55%)>stem (~15%)>leaf (~10%)>cob>leaf sheaths>bract leaves, and proportions of each responded differently to increasing density. A calculation of % dry matter translocation at grain-fill crop development stage showed that leaf ‘translocation ratio' reduced from 18.67% to 15.04% across the tested plant density range, while stem sheath translocation ratio was greatest (20.52%) at 6.75×10⁴ plants·ha^-1. With increase in planting density, the incidence of lodging and stalk-folding increased significantly, while the incidence of empty ears, drooping ears, and double ears decreased; the ear number per ha^-1 increased significantly; ear length, ear diameter, ear grain number, 1000-kernel weight and the harvest index showed a downward trend, and bare tip length tended to increase. The grain yield was highest at 7.50×10⁴ plants·ha^-1 (10419 kg·ha^-1 and 38.02% greater than the control). Thus, it can be seen that dense planting of maize increases the risk of stalk lodging and folding, and within a certain density range, the increase in the dry matter productivity of the population more than compensates for for the decrease in productivity per plant, resulting in higher yield. Based on simulation modelling, the optimal planting density for spring maize variety Zhenghong No. 6 in the hilly region of central Sichuan under the conditions of this experiment is 7.94×10⁴ plants·ha^-1.

Key words: maize, Zhenghong No. 6, densification, grain yield, dense planting effect