Decomposition Studies on Fine Roots of Gliricidia Sepium, Leucaena Leucocephala and Senna Siamea

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Nutrient composition, rate of decomposition and nutrient release pattern of fine roots (≤ 2mm) of Leucaena leucocephala, Gliricidia sepium and Senna siamea buried within 15cm and 30cm soil depths were studied biweekly under field conditions using litter pot method over an 84 day period. Generally, Gliricidia sepium had significantly higher (P < 0.05) initial levels of nutrients among species and could be described as high quality litter, Leucaena Leucocephala of moderate quality litter and Senna siamea of low quality litter. Gliricidia sepium fine roots showed the most rapid root weight loss within both 15cm and 30cm soil depths, followed by Leucaena leucocephala and then Senna siamea. Mean decomposition rate constants (Kd) was significantly higher for Gliricidia sepium and similar for Leucaena leucocephala and Senna siamea within both 15 and 30cm soil depths. The different decomposition rate could be related to litter quality (initial nitrogen, lignin and lignin/nitrogen ratio). Depths of placement did not significantly influence decomposition of fine roots. Nutrient release followed the order K > P > Mg > N > Ca > C for Gliricidia sepium, K > Ca > P > N > Mg > C for Leucaena leucocephala and K > P > Ca > Mg > C = N for Senna siamea within 15cm soil depth and K > P > Ca > Mg = N > C for Gliricidia sepium, K > Ca > P > N > Mg > C for Leucaena leucocephala, K > P >Ca > Mg > N = C for Senna siamea within 30cm soil depth. Nutrient release could be related to initial nutrient and lignin levels in fine roots. Depths of placement significantly influenced the release of potassium and magnesium and this could be attributed to leaching as the predominant mode for the release of potassium and magnesium.
A Thesis Submitted To the Department Of Agroforestry, Kwame Nkrumah University of Science and Technology in Partial Fulfillment of the Requirements for The Degree of Master of Science in Agroforestry