Determining water requirement and soybean crop coefficients in different growth stages

The main purpose of this study was to determine the parameters related to irrigation management in planting soybean in the field. This experiment took place based on randomized complete blocks design with three replications at the Tehran University in Karaj in 2008. Furrow surface irrigation treatments consisted of full irrigation (FI)، conventional deficit irrigation treatment at 75 and 50 percent soil moisture deficit compensation (DI75% and DI50%) and partial root drying treatment at fifty percent soil moisture deficit compensation (PRD50%). Results showed that soybean crop coefficients in four stages consisted of: initial (Kc ini)، developed (Kc adv)، middle (Kc mid) and also in final stage (Kc lat) during soybean growth stage was obtained 0. 34، 0. 7، 1 and 0. 44 respectively. Average stress coefficient (Ks) in DI75%، DI50% and PRD50% was estimated 0. 89، 0. 76 and 0. 7 respectively. These data show that although crop water requirement decreased for PRD50% treatment as compared with FI، DI75% and DI50% by 75%، 50% and 25%، respectively، but stress coefficients did not change at the same rate. This observation could be related to adaptability of crop under partial root drying scheme.