Residue decomposition dynamics in mixed ratios of two warm‐season cover crops

Abstract

AbstractCover crop residue management has gained attention over the past few decades due to the potential of cover crop residues to provide soil cover and nutrient availability for subsequent crops. Nutrients released from cover crop residues depend on the nutrient composition of plant tissue and ensuing rates of mineralization. To evaluate the rate of carbon (C) and nitrogen (N) mineralization from cover crops, a field decomposition experiment was conducted in a humid subtropical agricultural field. Residues of two warm‐season cover crops, sunn hemp (Crotalaria juncea L.) and sorghum sudangrass (Sorghum bicolor L. × S. bicolor var. Sudanese), were placed in litterbags at various mixture ratios on the soil surface to quantify the amount of N and C released from the residues over 56 d. Residue biomass decomposition followed decay patterns that were similar despite treatment mixtures of cover crop ratios. The initial ratio of cover crop material in the litter mixture influenced early N release where ratios with increasing sunn hemp increased N decomposition. The majority of residue breakdown (50–75%), and C (50–75%) and N (65–75%) decomposition occurred during the first 7 d for all the treatments. A minor fraction of residue remained (10–14%) at Day 56, with 10–14% C and 7–25% N. The 25% N remained in the sole sorghum sudangrass treatment. These results indicate that N from legume cover crops may not be available to subsequent crops in humid subtropical soils lacking the capacity to retain nutrients leached out of cover crop residue, though small fractions of dry matter may remain.