Comparison of Water-Yield Relations, Water Deficit Index, and Crop Water Stress Index in Silage Maize (Zea mays L.) and Sorghum (Sorghum bicolor L.)

In this study, water-yield relations, Crop Water Stress Index (CWSI), which is one of the commonly used crops stress indicators, and the Water Deficit Index (WDI), which is a new approach, were compared by applying deficit irrigation in 2018-2019 growing period in Kahramanmaraş, Turkey. Five irrigation levels were applied to silage maize and sorghum plants. According to the results, yield was higher in silage maize than in silage sorghum both in full irrigation (100%) and in water-deficit irrigation (treatment where 80%, 60%, 40%, 20% meeting water requirement of plant). However, when average yield values of both years were examined, maize showed a decrease of 49 and 46%, respectively, while sorghum showed a decrease of 33%, compared to treatment with 40 and 20% irrigation, respectively. Similarly, there was a decrease of 66-54% in maize for 20% treatment, while there was a decrease of 45-46% in sorghum. This showed that sorghum maintained its yield potential better than maize in conditions of 60% or more water constraint. When the average CWSI and WDI indices were examined mutually, it was observed that rate of increase in stress and amount of decrease in productivity gave more consistent results in WDI than in CWSI. It has been understood that CWSI, one of crop stress determiners, is insufficient in determining stress compared to WDI, and WDI gives more accurate results. Accordingly, complete and accurate results of WDI have been obtained despite the shortcomings of CWSI method, which has been used in stress determination until now. It is suggested to use WDI for crop water stress index.