Grain Yield, Phenology and Water Use in Wheat-soybean Intercropping Compared to Sequential Crops and Cover Crop-soybean Systems

Abstract

Wheat-soybean intercropping would allow double annual cropping systems without delaying soybean planting as the sequen-tial double cropping does, while covering the soil during the winter period with a cash crop. We evaluate the effect of two seeding wheat-soybean intercrop structures, 50% of the soil surface seeded under wheat and 50% under soybean (Wt₅₀Sb₅₀), and 40% wheat-60% soybean (Wt₄₀Sb₆₀), on the available soil water (ASW) at soybean seedtime, crop phenology, soil water use and soybean yield, in relation to sequential double cropping (Wt₁₀₀Sb₁₀₀) and full season soybean (Sb). In order to quantify the delayed sowing date effect, a late seeding soybean date (Sjl) equal to Wt₁₀₀Sb₁₀₀ was evaluated. Intercropping wheat-soybean obtained smaller yield than Sb, but Wt₄₀Sb₆₀ obtained similar yield compared to Wt₁₀₀Sb₁₀₀ (3.06 Mg ha^-1 for Sb and Sbl against 2.1 and 1.78 Mg ha^-1 for Wt₄₀Sb₆₀ and Wt₁₀₀Sb₁₀₀ respectively, p≤0,05). Wheat consumed most of the ASW up to 60 cm depth both in intercropping and sequential cropping (Wt₁₀₀Sb₁₀₀). On the fraction of the soil planted with soybean ASW at sowing time was similar in Wt₄₀Sb₆₀ and Sb (57 and 41 mm respectively), but when averaged with SAW in the fraction of the surface under wheat (40%), it was reduced to 28 mm. The highest total production was obtained with Wt₁₀₀Sb₁₀₀, but if soybean yield is prioritized, a Wt₃₀Sb₇₀ seeding structure would maintain the soil covered during the winter, reserve ASW for the soybean crop, and not to lose soybean yield.