Irrigation Effects on Quantity and Quality of High-Oleic Soybean.

The success of high-oleic soybean requires fatty acid stability across a range of growing conditions and management practices. Oil extracted from these varieties improves oxidative stability, thus eliminating the trans fats produced during hydrogenation. Irrigating soybean during reproductive growth offers a valuable opportunity to retain yield potential under water-deficient environments. The influence of irrigation on the fatty acid profile of high-oleic soybean has been inconclusive and particularly lacking evaluations in the Midwestern United States. The objective of this research was to investigate the effects of irrigation on grain yield and oil composition of high-oleic and standard varieties. Field studies were conducted in 2015 near Wanatah, Indiana. The field was split in half to compare dryland and irrigated soybean. Six high-oleic and two standard cultivars were planted in a RCBD within each water regime (dryland vs. irrigation) and replicated four times. A lateral irrigation system maintained a water supply of at least 25.4 mm (1”) in combination with rainfall on a weekly basis. This irrigation schedule was initiated when soybean reached R3 (first pod) and continued until R7 (first signs of physiological maturity). Standard varieties yielded more than high-oleic varieties under both dryland (4277 kg/ha vs. 4075 kg/ha) and irrigated conditions (4950 kg/ha vs. 4667 kg/ha). High-oleic seeds were larger than standard seeds regardless of water regime. Seeds were larger under irrigation as expected. The increase of seed size in high oleic soybean was more than double the increase of standard varieties (1.4 g/100 seeds vs. 0.6 g/100 seeds). Under the irrigation regime, oleic composition decreased slightly for high oleic varieties and increased slightly for standard varieties. While changes in oleic acid concentration between irrigated and dryland conditions were small, the current research suggest that water availability has the potential to alter fatty acid seed composition directly or indirectly (e.g., canopy temperature).