ECONOMIC-ANALYSIS OF IRRIGATION AND DEEP TILLAGE IN SOYBEAN PRODUCTION SYSTEMS ON CLAY SOIL

A 5-year study ( 1 987-199 1 ) was conducted on a Tunica clay (clayey over loamy, montmorillonitic, non-acid, thermic Vertic Haplaquept) to determine effects of irrigation and deep tillage on soybean yields and economic returns. Irrigation increased average yield of the conventional check treatment (disked) by 57% (3020 vs. 1924 kg ha-1 ). Under irrigation, yields from all deep-tilled treatments and the conventional check treatment were similar and averaged 3066 kg ha-1. Under non-irrigated conditions, yields from all deep-tilled treatments were similar, averaged 2829 kg ha-1, and were higher than the conventional check treatment that averaged 1924 kg ha-1. Average yields from the non-irrigated deep-tilled treatments were 92% as high as yields from comparable treatments with irrigation. Irrigation increased the average net returns of the conventional check treatment 75% ($206 vs. $118 ha-1). Over the 5-year study, average net returns to all irrigated treatments were similar and ranged from $ 194 to $206 ha-1. Net returns to the non-irrigated deep-tilled treatments averaged 156% higher than returns from the non-irrigated conventional check treatment ($302 vs. $118 ha-1) and was attributed to the higher yields of the deep-tilled treatments (2829 vs. 1924 kg ha-1). Net returns to the non-irrigated deep-tilled treatments also averaged 47% higher than returns from the irrigated conventional check treatment ($302 vs. $206 ha-1). This difference was attributed to the similarity of yields (2829 vs. 3020 kg ha-1) and the sizeable difference in specified costs of production ($335 vs. $481 ha-1) that favored non-irrigated production of soybean with deep-tillage.