Yield and Quality Characteristics of Drip-Irrigated Soybean under Different Irrigation Levels

This study was conducted to determine the effects of deficit irrigation levels on the yield and quality of soybean [Glycine max (L.) Merr.]. Five different irrigation applications designated as full irrigation (I-100) with no water stress and slight (I-75), mild (I-50), severe water stress (I-25) and no irrigation (I-0) treatments based on the amount of evaporation measured by a Class A pan. The results showed that irrigation levels applied has statistically significant effect on yield and yield components. Water deficit stress significantly (P < 0.01) increased oil content while it decreased protein content. The highest water use obtained in I-100 treatment, while the lowest was found in I-0 treatment in both years. The maximum yield was obtained from under I-100, I-75, I-50, I-25 and I-0 treatments as much as 4.01, 3.95, 3.57, 2.83 and 1.92 t ha(-1) in 2014 and 4.11, 3.60, 3.24, 2.61 and 1.81 t ha(-1) in 2015, respectively. Compared with I-100, the 2-yr average yield reduction for I-0, I-25, I-50, and I-75 were 54, 32, 17, and 8%, respectively. The water use efficiency varied from 5.2 to 8.7 kg ha(-1) mm(-1) in the first year and from 5.6 to 8.3 kg ha(-1) mm(-1) in the second year, respectively. Based on the results of this study, soybean can be irrigated as much as 100% of Class A pan evaporation in regions with no water scarcity. Under deficit irrigation conditions, as an option, soybean can be irrigated as much as 75% of pan evaporation under Western Mediterranean conditions of Turkey.