Skip to main content
Open Access Publications from the University of California

Department of Plant Sciences

UC Davis

Nitrogen mineralization of green manure legume residues in different soil types


Understanding nitrogen (N) mineralization patterns of green manure legume residues is crucial in the synchronization of N release from plant residue and uptake by plants. A laboratory incubation experiment was conducted over a 16-week period to determine N mineralization of three green manure legumes [(Mucuna (Mucuna pruriens), Lablab (Lablab purpureus cv. Rongai) and Sunhemp (Crotalaria juncea)] in three soils with varying clay contents (62, 20 and 12% clay) from South Africa. The amount of N mineralized from the residues was determined at 2, 4, 8 and 16 weeks from the onset of incubation. Nitrogen release pattern of the three legume residues followed a similar pattern in all the three soils, with sunhemp treated soil having the highest amount of mineral N after 16 weeks of incubation in all the three soils, followed by lablab and then mucuna. The amount of mineral N ranged from 121 to170, 96 to 134 and 92 to 108 mg kg-1 in the sunhemp, lablab and mucuna treated soils, respectively. The cumulative amounts of N from the legume residues mineralized recovered as mineral N in soil after 16 weeks of incubation ranged from 21-41% (92-121 mg kg-1), 30-68% (108-170 mg kg-1) and 26-60% (93-147 mg kg-1) of the initial added N contained in the residues in the soils with 62, 20 and 12% clay contents, respectively. Less than 50% of the initial added N was mineralized in the high clay content soil. Mineralization rate constant, k, was significantly linearly related to the residue N content, net mineralized N, C/N ratio and Lignin/N ratio. Results from this study indicate that all the three legumes can contribute significant amounts of N for uptake by plants, with sunhemp tending to release N at a faster rate, followed by lablab and then mucuna. High clay content in soil slowed down N mineralization.

Main Content
For improved accessibility of PDF content, download the file to your device.
Current View