This paper develops and tests a simple relationship for predicting the decomposition of plant residues of diverse composition under varying soil water conditions. Known weights of four plants samples comprising of groundnut (Gn), mucuna (Mc), maize (Mz) and bush fallow (Bf), were put in nylon bags and randomly buried in three plots with varying soil moisture conditions (viz: W1 = 60% field capacity (FC); W2 = 75% FC and W3 = FC) and the weight losses of the samples in the bags determined at different time intervals. At the field capacity state, plant residue composition was the major controlling factor on decomposition rate constants (kd), with Gn (0.032 d-1) and Mc (0.022 d-1) having significantly higher kd than Mz (0.019 d-1) and Bf (0.016 d-1).Decreasing soil water reduced the kd values of the plant residues. Using a modified first order decay equation that included C/N ratio and soil water content, the patterns of plant residue decomposition of diverse composition under varying soil water conditions were adequately simulated (R2 = 0.95 and RMSE = 8.84). We conclude that plant residue decomposition patterns can be described using simple relationships that required knowledge of the routinely determined C/N ratio of the residues and the soil water content only.
Key words: C/N ratio, soil water content, field capacity, plant residue, decomposition rate constant.
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