Effect of drip irrigation intensity on soybean seed yield and quality in the semi arid Harran plain, Turkey

Abstract

Soybean (Glycine max. L.) crops were grown in 2003 and 2004 to determine effect of different water stress levels on growth, some physiological variables and seed composition under semi‑arid climatic conditions of Harran plain, Sanlıurfa, Turkey. Irrigation water treatments included 0 (I₀), 25 (I₂₅), 50 (I₅₀), 75 (I₇₅), and 100% (I₁₀₀) of full irrigation amounts with a 4 day irrigation interval. Water stress resulted in reduced vegetative growth, leaf relative water content and leaf chlorophyll content. In 2003 and 2004 seed yields ranged from 322 (I₀) to 3684 kg ha^-1 (I₁₀₀), and from 267 (I₀) to 3952 kg ha^-1 (I₁₀₀), respectively. Compared to I₁₀₀, the two-year average seed yield reduction for I₀, I₂₅, I₅₀ and I₇₅ were 92, 76, 50 and 25%, respectively. Water stress significantly decreased fatty acid content of C18:0, C18:1, C18:2, and C18:3 but not C16:00. I₁₀₀ produced the highest protein value (39.60% in 2003 and 39.00% in 2004), while I₀ yielded the lowest values (35.41% in 2003 and 36.11% in 2004). A negative correlation between evapotranspiration (ET) and oil content and ET and protein content in both years was determined. Leaf chlorophyll content, leaf relative water content, leaf area index, number of branch per plant, number of node per plant and plant diameter correlated positively with seed protein content and negatively with oil content.