Soybean yield and nutrition after tropical forage grasses

In tropical agroecosystems, intercropping crops and including perennial forages can increase crop system diversity and sustainability. However, adequate management of cash crops in crop rotation under no-till requires an understanding of the release of nutrients by surface mulch. This study evaluated the effects of two sowing times and nitrogen (N) management of palisade grass [Urochloa brizantha (A. Rich.) Stapf Marandu] and guinea grass [Megathyrsus maximus (Jacq.) B.K. Simon & S.W.L. Jacobs Tanzania] on forage production, nutrient accumulation, and decomposition rates; soybean [Glycine max (L.) Merrill] yield; and soil chemical properties over three growing seasons. Palisade and guinea grasses were sown for intercropping with sorghum [Sorghum bicolor (L.) Moench] in the growing season or after sorghum silage harvest (hereafter succession) and subjected to N fertilization management (urea − 0 and 70 kg N ha−1 cut−1, totalling 210 kg N ha−1 per season) during the off-season. Nitrogen fertilization increased nutrient accumulation in surface mulch in all cropping systems. Regardless of cropping system, N rates, or growing season, palisade and guinea grass provided an adequate plant biomass production, soil cover throughout the year, soybean nutrient use efficiency, and soil quality. Soybean was positively influenced by N fertilization of grasses sown in succession to sorghum. Guinea grass had the greatest effect on soybean grain yield, with an improvement of 0.8 Mg ha−1. Sowing grasses in succession to sorghum positively affected soil pH, Ca, Mg, and base saturation.