Irrigation, tillage and mulching effects on soybean yield and water productivity in relation to soil texture

Depleting groundwater resources in Indian Punjab call for diversifying from rice to crops with low evapo-transpiration needs and adopting water-saving technologies. Soybean offers a diversification option in coarse- to medium-textured soils. However, its productivity in these soils is constrained by high soil mechanical resistance and high soil temperature during early part of the growing season. These constraints can be alleviated through irrigation, deep tillage and straw mulching. This 3-years field study examines the individual and combined effects of irrigation, deep tillage, and straw mulching regimes on soybean yield and water productivity (WP) in relation to soil texture. Combinations of two irrigation regimes viz., full irrigation (If), and partial irrigation (Ip) in the main plot; two tillage regimes viz., conventional-till (CT)-soil stirring to 0.10 m depth, and deep tillage (DT)-chiseling down to 0.35 m depth followed by CT in the subplot; and two mulch rates viz., 0 (M0) and 6 t ha−1 (M) in the sub-subplot on two soils differing in available water capacity were evaluated. Seed yield was greater in the sandy loam than in the loamy sand reflecting the effects of available water capacity. Irrigation effects were greater on loamy sand (40%) than on sandy loam (5%) soil. Deep tillage benefits were also more on loamy sand (14%) compared to sandy loam (5%) soil. Yield gains with mulching were comparable on the two soils (19%). An evaluation of interaction effects showed that mulching response was slightly more in Ip (20%) than in If regimes (17%) in the sandy loam; while in the loamy sand, mulching gains were comparable (18-19%) in both irrigation regimes. Benefits of deep tillage in the loamy sand soil were more in Ip (20%) than in If regimes (17%). Deep tillage and straw mulching enhanced WP (ratio of seed yield/water use) from 1.39 to 1.97 kg ha−1 mm−1 in Ip regime, and from 1.87 to 2.33 kg ha−1 mm−1 in If regime in the loamy sand soil. These effects on WP were less in the sandy loam soil with greater available water capacity. Yield and WP gains are ascribed to deeper and denser rooting due to moderation of soil temperature and water conservation with straw mulching and tillage-induced reduction in soil mechanical resistance. Root mass in CTM0, CTM, DTM0 and DTM was 2.79, 5.88, 5.34 and 5.58 mg cm−2 at pod-filling in the loamy sand soil. Comparable yield responses to deep tillage or mulching in the loamy sand soil suggest that either of the options, depending on their cost and availability considerations, can be employed for improving soybean yield and water productivity.