Economic optimization of crop yield with determination critical period of weed control (CPWC) on corn

Studying the weed’s effect during period of plant growth is needed for economical and useful programming. In this paper two groups of treatments have been used. In the first group, weed and plant had competition form the beginning of growth period and then weeds were controlled at the certain time. In the second group, weeds were controlled from the beginning of growth period and at the certain time, were competed with the plant. At the end of growth period, the crop yield of both treatments have been measured and the variations of relative crop yield of treatments during growth period have been investigated, using Logistic and Gompertz functions. These functions describe the relationship between time and related yield, continuously. The independent variable in Logistic and Gompertz methods is end of control period and beginning of control period respectively. Critical point of weed control has been determined with calibration and parameter estimate of these two models. In all of past studies, CPWC has determined by accept of certain percent (5%) for allowable relative crop yield decrease. In this research, CPWC has been calculated based on economic decrease of crop yield. Therefore, this period has named as Economic Period of Weed Control (EPWC). EPWC, which is a function of income from one percent of crop yield to cost of one day of weed control in unit area, is calculated using dynamic programming. EPWC is annually updated, according to value of crop yield and cost of weed control for unit area. The results of this study show that the length of intersection point of Logistic and Gompertz curves is 27 days after planting of corn and critical point of weed control.