Determination of soybean water stress index (CWSI) for irrigation management for maximum yield and water productivity

Depending on land and water resourses avilibility, on-farm water management is usually aimed to maximize yeild or water productivity. The crop water stress index (CWSI) shows the plant's available water status well and therefore used as an appropriate tool for irrigation management in the field. The purpose of this study was determination of crop water stress index to soybean at different stages of growth in order to irrigation planing to achieve maximum yield and irrigation water productivity. For this purpose, soybean was cultivated with four irrigation regimes at the research farm of Lorestan University Agriculture faculty in the summer of 2016. The Irrigation levels were I1, I2, I3 and I4 with 100, 80, 60 and 40 percentof full water requirement, respectively. According to the results, the effect of irrigation levels on yield and soybean water productivity was significant at 1% probability level. The highest and the lowest values of CWSI were observed in I4 and I1, respectively in different growth stages. Also, the correlation of between CWSI and soil moisture content was significant at 1% probability level. The maximum yield was observed in I1 (1765.4 kg/ha) and The maximumwater productivity was 0.26 kg/m3 in I2. The values of CWSI for treatments ofI1 and I2were considered as the basis for irrigation scheduling to achieve maximum yield and water productivity. Finally, the CWSI values were obtained equal to 0.42, 0.37 and 0.29 for the maximum water productivity for the growth and development, middle and final stages of plant growth.