Optimization of Irrigation and Plant Density of Corn (Zea mays L.) by Using Response-Surface Methodology

Introduction:

Water and plant density have a complex interaction. Determination of optimum density is an effective strategy to improve the efficiency of available resources usage and to increase the yield per unit area. Despite extensive research on the effects of different levels of irrigation and plant density for different crops, including corn, information on the optimization of these resources, using response-surface methodology (RSM) is scarce. Therefore, the objective of this study was to determine the optimal level of irrigation and plant density in corn production based on central composite design (CCD).

 An experiment was conducted by using response-surface methodology with the central composite design and two replications on corn at the Research Farm of Ferdowsi University of Mashhad, during the 2015 growing season. The experimental treatments were the highest and lowest levels of irrigation volume (6000 and 14000 m-3.ha-1) and plant density (5 and 9 plants.m-2). Grain yield (GY), biological yield (BY) and water use efficiency (WUE) were measured as response variables in a full quadratic polynomial model. Consumption rate of irrigation and density were optimized based on three scenarios: economic, environmental and eco-environmental. Grain yield of corn and WUE were considered as the main factors to determine the optimum level of treatments under the economical and environmental scenarios, respectively. In the eco-environmental scenario, the main factor was WUE and grain yield.

The results indicated that at low level of irrigation (6000 m3.ha-1) plant density and grain yield correlated with others as quadratic so that by increasing the density from 5 to 7 plants.m-2,grain yield first increased and then decreased with enhancing density to 9 plants.m-2.It seems that at low levels of irrigation, reduction and enhancement of plant density, respectively, as a result of increasing evaporation from soil surface and increasing competition in resource uptake (light and water) has reduced grain yield. Grain yield at high levels of irrigation showed a relatively linear relationship with incrementing plant density, and the highest grain yield with 1324.9 g.m-2was obtained from treatment of 14000 m3.ha-1 of water and density of 9 plants.m-2. Nevertheless, the results of model fitting showed that the highest grain yield with 1318.4 g.m-2 was attained from the density of 7 plants.m-2 and 14000 m3.ha-1 of water. Therefore, it seems that with the simultaneous enhancement in plant density and irrigation, vegetative growth due to lack of light has increased, as a result of grain yield than optimum densities (7 plants.m-2) has shown a decrease.The regression model could significantly indicate that impact of independent variables on the grain yield, biological yield and water use efficiency (dependent variable). In economic scenario with considering 8 plants.m-2 and irrigation of 14000 m3.ha-1 the maximum of economical yield with 1345.8 g.m-2 was achieved in which biological yield and water use efficiency were 4534.7 gr.m-2 and 0.98 kg.m-3 of water, respectively. In environmental scenario also the choice of the density of 7 plants.m-2 and irrigation of 7939 m3.ha-1 the highest water use efficiency (1.21 kg.m-3) was attained in which grain yield that was 988.6 g.m-2. Based on eco-environmental scenario with choice of the density of 7.5 plants.m-2 and irrigation of 10848.5 m3.ha-1 the maximum grain yield and water use efficiency was obtained in 1240.7 g.m-2 and 1.16 kg.m-3 of water, respectively.

Due to lack of water resources and environmental problems caused by the excessive use of water, applying appropriate management practices such as proper planting density to optimize these resources is essential. The best way to achieve the highest economic yield and water use efficiency and, to reach sustainable agriculture is the choice of eco-environmental scenario in which by application of the density of 7.5 plants.m-2 and irrigation level of 10848.5 m3.ha-1 the maximum grain yield and water use efficiency with 1240.7 g.m-2 and 1.16 kg.m-3 of water was obtained, respectively.