Soil Amelioration and Nutrient Export in Senna Siamea [Cassia Siamea], Gliricidia Sepium and Leucaena Leucqcephala stands at age four years.

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Soil amelioration potential was investigated for four- year-old stands of Senna siamea [Cassia siamea] , Gliricidia sepium and Luecaena leucocephala established at the IRNR Farm, University of Science and Technology (UST), Kumasi (06° 43’W, 01o 36’N) Soils under tree stands and an adjacent grass fallow were analysed for pH, CM, total N, available P and K, exchange cations and CEC at 0-15cm, 15-30cm and 30-60cm soil depths. AWC, equilibrium infiltration rate and bulk density were also determined for each stand. Trees were destructively sampled for biomass yield and tissue nutrient analysis. Data generated was subjected to Analysis of Variance in a Completely Randomized Design with four replicates of each treatment. Stands increased pH, CM and CEC by 24-26%, 9-31% and 44-110% respectively in the 0-15cm depth of profile. N and P levels declined by 38-49% and 80-89% respectively. Grass fallow had better chemical properties than tree stands in most parameters measured including pH, CM, N, P and CEC. These properties decreased in the order: Grass > Senna Leucaena > Gliricidia. Among trees, Senna had significantly higher (p < 0.01) above-ground biomass than Gliricidia and icaena. This resulted in higher nutrient accumulation for Senna in Kg/ha of 266 for N, 34 for P1 261 for K, 833 for Ca and 113 for Mg. Gliricidia had the lowest N and Mg accumulation while Leucaena had the lowest P, K and Ca. Low proportions of foliage biomass made estimates of nutrient export still, high even if foliage were retained on site at harvest. Regressions of total N, pH, CEC, available P and bulk density on OM are included to show the influence of GM on soil improvement. Estimates of nutrient-use efficiencies of the tree species are also included.
A Thesis presented to the Board of Postgraduate Studies, University of Science and Technology, Kumasi, in Partial Fulfilment of the Requirements for the Degree of Master of Science in Agroforestry,1995.