Ruzigrass root persistence and soybean root growth

Abstract

Cropping systems using forage grasses as cover crops have been effective in soil conservation and nutrient cycling, but root persistence of ruzigrass (Urochloa ruziziensis) is significant, and may impair root growth of the next crop. However, it is unknown how this would interfere with soybean root growth and yield under field conditions. Ruzigrass root persistence during soybean development, and its effects on soybean yield were studied under field conditions. Ruzigrass and soybean were grown alone or in rotation, and roots were sampled every 30 days and evaluated using carbon isotope discrimination. Despite temporary impairment of soybean root growth in the uppermost soil layer, there was no effect of ruzigrass on soybean yield. The ruzigrass root decay rate was high in the first 30 days after desiccation, and then it slowed down. Soybean roots grew slowly up to 30 days after planting (DAP, V7) and then peaked at 90 DAP (R5). Soybean root growth and yield are not affected by decaying ruzigrass roots. Around 50% of the ruzigrass roots are mineralized before soybean flowering. However, by soybean harvest there are still from 25 to 28% of non-decomposed ruzigrass roots up to the soil depth of 0.20 m.