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Journal of Biological Sciences

Year: 2007 | Volume: 7 | Issue: 4 | Page No.: 632-637
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Authors

M. Fosu

Ronald F. Kuhne

Paul L.G. Vlek

Keywords

Research Article

Mineralization and Microbial Biomass Dynamics During Decomposition of Four Leguminous Residues

M. Fosu, Ronald F. Kuhne and Paul L.G. Vlek
Decomposition of Sunn hemp (Crotalaria juncea), Devil bean (Crotalaria retusa), Calopo (Calopogonium mucunoides) and Velvet bean (Mucuna pruriens) in litterbag field incubation experiment was compared with mineralization of the same leguminous cover crops in a laboratory incubation study to assess N release and synchrony. Initial rapid N release followed by slower and curvilinear release was observed with the litterbag approach. The laboratory incubation approach however, showed a significant initial N immobilization in all cover crop amended soils, particularly with devil bean. The highest immobilization occurred four days after residue incorporation and coincided with the highest microbial biomass-N flush of 250% above the un-amended soil. Residues with higher quality in terms of lower percentage cellulose and lower Lignin/N ratio mineralized faster with lower N immobilization. Legumes with C/N ratio less than 20 and percent N above 1.7 may immobilize N. High N immobilization particularly in devil bean and mucuna may result in poor synchrony between N release and cereal N requirements and could result in low initial stimulation of succeeding cereal crop and lower yields. Cover crops left to mature and dry should thus be incorporated at least 2 weeks at the beginning of the following season before planting the cereal. Care must be taken in interpreting N release data using litterbag approach.
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