Decomposition, Nitrogen, and Phosphorus Mineralization from Residues of Summer-Grown Cover Crops and Suitability for a Smallholder Farming System in South Africa

Abstract

Cover crops, usually grown under conservation agriculture, may offer numerous benefits depending on the farming system. In this study the authors investigated residue decomposition, nitrogen (N) and phosphorus (P) release from mucuna (Mucuna pruriens) and sunhemp (Crotalaria juncea) as well as their uptake by maize in a farming system common in smallholder farms in South Africa. This was done through litterbag, laboratory incubation, and field studies. Sunhemp stems had 65% dry weight remaining after 132 days while just over 10% of mucuna and sunhemp leaves remained. There was no mineral contribution to maize growth by cover crops. However, in incubation studies, mucuna mineralized 60 mg N kg−1 and 3.2 mg P kg−1 and sunhemp mineralized 45 mg N kg−1 and 3.5 mg P kg−1. This suggested that weeds and/or leaching may have impacted negatively to nutrient flow from decaying cover crops species to maize during the long winter fallow period.