Short-term effects of soil amendment with tree legume biomass on carbon and nitrogen in particle size separates in central Togo
1998
Lehman, J. | Poidy, N. | Schroth, G. | Zech, W.
We examined the effects of adding different plant materials on short-term organic matter dynamics of a West African savanna soil. Leaves and roots from three alley-cropped tree legumes were added to soil and exposed in the field for 120 d using PVC cylinders. Particle size fractionation of the exposed soil separating particulate organic matter (POM, 20-2000 micrometers), silt (2-20 micrometers) and clay (< 2 micrometers) demonstrated that most of the C was stored in the silt and most of the N in the clay size separates. Adding Senna leaves to the soil led to an increase of the organic C content in the silt and clay fractions, and to an increase of the N content in the silt fraction. In Gliricida amended soil, the N content increased in silt and clay size separates. Roots of all three species had no effect on C or N contents in particle size fractions. The lignin content and the polyphenol-to-nitrogen ratio (PP-to-N ratio) decreased from coarser to finer particle size separates, while the acid-to-aldehyde ratio (Ac-to-Al ratio) increased. The addition of Senna leaves decreased the polyphenol content and the PP-to-N ratio in all particle size fractions. The lignin content was not affected. In the silt fraction, the alkyl-C content was decreased, the carboxyl- and amide-C content increased by the addition of Senna leaves indicating that it was not unaltered plant material but microbial metabolites which were responsible for the increase of C. The PP-to-N ratio of the added plant material seems to control the effects of soil amendment with tree legume biomass through its influence on decomposition processes and on the formation of organo-mineral complexes for both C and N.
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