Effects of more plants per hill on population quality and yield of summer maize

It is important to get high maize yield by increasing planting density, but this could have some shortfalls (e.g., canopy closure) which limit further increase in planting density. In order to alleviate canopy closure of summer maize under high density and to improve population quality and yield, a 2-year field experiment was conducted at the Wuqiao Experimental Station of China Agricultural University. Three treatments were designed in the field, including one plant per hill (P1), two plants per hill (P2), and three plants per hill (P3) under planting density of 82 500 plant·hm2. Then the study estimated leaf area per plant, dry matter (DM), photosynthetic potential (PP), relative growth rate (RGR), net assimilation rate (NAR), crop growth rate (CGR), grain-leaf area ratio and grain yield. Leaf areas under P2 and P3 treatments at silking stage (R1) increased by 10.7%21.9% and 7.3%16.7%, respectively. At about 20 days after silking (DAS), leaf areas under P2 and P3 treatments increased by 13.5%21.9% and 9.4%12.7%, respectively, compared with P1 treatment. The DM of P2 and P3 treatments at R1 and physiological maturity stage (M) was significantly higher (P < 0.05) than that of P1 treatment. PP was improved at 6-leaf stage under P2 treatment, but decreased with increasing number of plants per hill. Compared with P1 treatment, RGR from DAS20 to M increased by 30.4%190.7% and 33.9%183.5%, NAR increased by 16.1%161.9% and 30.7%155.8%, respectively, under P2 and P3 treatments. Also CGR, grain-leaf area ratio and grain yield were enhanced under P2 and P3 treatments. Compared with P1 treatment, yield under P2 and P3 treatments increased by 5.8%23.5% and 4.9%18.9%, respectively. It was noted that ear number per hectare and grain number per ear under P2 treatment slightly increased and the thousand-grain weight increased obviously over that of P1 treatment. Analysis of ear number per hectare, grain number per ear and thousand-grain weight after two years of growth showed that ear number per hectare dropped slightly, grain number per ear increased slightly, and thousand-grain weight evidently increased under P3 treatment, compared with P1 treatment. Yield showed significant and positive linear correlation with grain weight/leaf area ratio (R² = 0.94****) and grain number/leaf area ratio (R² = 0.76***). Thus under high density conditions, more plants per hill improved the processes of leaf area and dry matter accumulation that in turn improved population quality. The increment in grain yield under more plants per hill was mainly due to the enhancements of thousand-grain weight and grain number per ear. In conclusion, population quality, yield and yield components were improved in two plants per hill treatment. Thus based on this study, two plants per hill planting pattern was recommended as the best performing planting pattern of maize.