Effects of application of organic fertilizer under different planting densities on dry matter production and yield formation of summer maize

A 2-year field experiment was conducted during summer maize seasons at Wuqiao Experimental Station, Hebei Province. In the experiment, different amounts of organic fertilizers were continuous applied for 2 years of 2011 and 2012 during summer maize seasons based on plant densities. The aim of the experiment was to analyze the effects of organic fertilizer on dry matter production and yield formation of summer maize at low planting density in order to reduce lodging while achieving stable and/or high yield. The randomized block design was used with two factors (plant density and amount of organic fertilizer). Three planting densities - 90 000 plants·hm^-2 (D1), 75 000 plants·hm^-2 (D2) and 60 000 plants·hm^-2 (D3) were set in the experiment. While one amount of organic fertilizer of 30 m³·hm^-2 (O1) was applied under D1 and D2, three amounts of organic fertilizer of 0 m³·hm^-2 (O0), 30 m³·hm^-2 (O1), 45 m³·hm^-2 (O2) were applied under D3. The results showed that the application of organic fertilizer effectively improved soil fertility. The application of organic fertilizer in 2011 improved dry matter production, crop growth rate and crop yield under D3. However, the improvements in these crop variables were not significant. In the second year of organic fertilization (which was in 2012), senescence delayed and leaf area index together with relative chlorophyll content at late growth stage maintained high values under 60 000 plants·hm ^-2 planting density. Total dry matter production at maturity stage under 60 000 plants·hm ^-2 planting density significantly improved to almost similar levels to that under 75 000 plants·hm^-2 and 90 000 plants·hm^-2 planting densities. In addition, dry matter production and crop growth rate under planting density of 60 000 plants·hm^-2 both improved after anthesis by organic fertilization. Both the crop parameters maintained high levels similar to those under planting densities of 75 000 plants·hm^-2 and 90 000 plants·hm^-2. Both kernel number per ear and thousand kernel weight under planting density of 60 000 plants·hm^-2 significantly increased by the application of organic fertilizer, which effectively compensated for low ear number at low planting density. Crop yield under low density (60 000 plant·hm^-2) plus 45 m³·hm^-2 organic fertilizer (D3O2) was 10 838 kg·hm^-2, which was similar to that under planting densities of 75 000 plants·hm^-2 and 90 000 plants·hm^-2 (11 080 kg·hm^-2 and 11 202 kg·hm^-2). It was concluded that low planting density in combination with the application of organic fertilizer effectively regulated both pre-anthesis and post-anthesis dry matter production, delayed leaf senescence, increased dry matter production after anthesis, suppressed excessive growth and increased crop yield.