Optimization of Plant Density and Nitrogen Use in Corn (Zea mays L.) by Central Composite Design

Response Surface Methodology (RSM) is a statistical tool for modelling and optimization of multiple factors which determine optimum process conditions by combining experimental designs with interpolation by first- or second degree polynomial equations in a sequential testing format. Nitrogen (N) and plant density are two factors crucial to the successful implementation of crop management practices used in corn production systems. Numerous studies have reported the effects of N fertilization on yield of corn. The optimum resource level in agro-ecosystems should be determined to decrease production costs, conserve resources and reduce environmental pollution which occurs as a result of excessive use of these resources. In this work, optimization of nitrogen fertilizer and plant density of corn using central composite design for RSM was done.
An experiment was conducted using central composite design with 13 treatments and two replications at the Research Field of Ferdowsi University of Mashhad during the growing season of 2015-2016. The treatments were allocated based on low and high levels of plant density (7 and 10 plants m-2, respectively) and nitrogen (0 and 300 kgN ha-1, respectively). Biological yield, grain yield, N utilization efficiency, N recovery and N use efficiency were calculated as independent variables and changes of these variables were evaluated by a regression model. Optimum levels of nitrogen and plant density were proposed to obtain the expected level of these traits based on economic, environmental and economic-environmental scenarios.
The results showed that the effect of linear component was significant on biological and grain yield and nitrogen efficiency indices of corn. Effect of square component was significant on all studied traits except for biological yield and N recovery. Interaction effect of full quadratic was significant on biological yield and N recovery. Lack of fit test had no significant effect on the studied traits except for NUE. The highest observed and predicted values of grain yield were obtained in 7 plants.m-2 with 150 kg N per ha (11.71 ton ha-1) and 10 plants m-2 with 300 kg N per ha (12.22 ton ha-1), respectively. The maximum observed and predicted values of N recovery were obtained in 10 plants.m-2 with 300 kg N per ha (86.45%) and 10 plants.m-2 with 300 kgN ha-1 (90.14%), respectively. The optimum levels of nitrogen fertilizer and density were 8.12 plants.m-2 with 225.27 kg N per ha, 7 plants.m-2 with 46.95 kg N per ha and 7 plants.m-2 with 69.42 kg N per ha for economic, environmental economic-environmental scenarios, respectively.
Increasing nitrogen fertilizer led to an increase in grain yield and a decrease in nitrogen use efficiency whereas increasing density caused an increase in grain yield and nitrogen use efficiency.