Decomposition Rates of Biomass Obtained from Six Month-Old Tephrosia vogelii, Tithonia diversifolia and Natural Fallow Vegetation at Maseno, Kenya

Abstract

Organic residues incorporated into soil release their nutrients through decomposition. This process may be slow or rapid depending on the biomass quality and environmental conditions. For a period of 8 months, an incubation study with litterbags was carried out in field conditions to determine the decomposition rate of Tephrosia vogelii Hook F., Tithonia diversifolia (Hemsley) A. Gray and natural vegetation fallows. Leaves, stems and roots of Tephrosia, Tithonia and natural fallow had high decomposition rates and less than 30% of the biomass remained undecomposed after 8 months of incubation. Tithonia leaves decayed within 1 month after incubation and Tithonia mixture released most of its N in mineral form during the first month. Tephrosia roots and leaves had a half-life (t50) of about 2 months, which is lower than that for Tithonia roots. Tephrosia stems and natural fallow roots were both low in N and decomposed slowly. Decomposition and nutrient release patterns were influenced by the quality of the material, in particular the N content, lignin and polyphenols.