Simulation of corn yield loss in nitrogen levels under Pigweed densities

ABSTRACT: In order to simulate corn yield loss per unit area at different levels of nitrogen under different weed densities, two experiments in split plot based on completely randomized blocks with three replications were conducted in 2010 and 2011 at the Islamic Azad University of Astara. Nitrogen in four levels of 0 (control), 100 (recommended nitrogen amount in the), 160 and 220 kg N.ha was the major factor; and the sub factor was density of redroot pigweed at four levels (0 (monoculture corn), 5, 10 and 20 plants per square meter). The results showed that the effect of red root pigweed density on corn seed yield loss per unit area was gained by three parametric Gompertz sigmoidal equation. In this equation the coefficient (a) that showed the maximum loss of corn yield, has the most appropriate accordance with quadratic polynomial equation. Therefore, the integration of these two equations, equations of corn yield loss at different levels of nitrogen and different red root pigweed density, was simulating as the following model: f=(a+b*x+c*x^2)*exp(-exp(-(y-yo)/d)In this equation; f: Corn yield loss (percentage), a: maximum asymptotic value, yo: turning point of the curve, x: amount of nitrogen, y: pigweed density, and b, c, d are the coefficients of equation.The result showed that the density of 10.5 weed plant per square meter can reduce corn yield in non-consumption of nitrogen 20%, and by consuming 220 kg N.ha reduce it 40%, in comparison with control.