Abstract
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.
Highlights
Plant residue returned to the soil is the primary source of the soil organic matter (SOM)
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
What we seek in this study is to develop and test a simple relationship for predicting the decomposition of residues of diverse composition under varying soil water conditions, especially for tropical conditions, where there is often data paucity, or where only routinely determined plant residue and soil properties are often available
Summary
Plant residue returned to the soil is the primary source of the soil organic matter (SOM). In low- input agricultural systems, the SOM is the main repository of plant nutrients (Bandaranayake et al, 2003) and apart, other soil properties such as soil structure, porosity, and water holding capacity are enhanced with increasing SOM (Skjemstad et al, 1996). Whether the SOM will increase or not depends largely on the quantities of residue input, as well as the rate at which the residue decomposes. A major challenge is how to manage residues to minimize losses during the fallow period. This requires an understanding of the factors that affect residue loss, and the prediction of
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