Physico-chemical properties of soils under five different multipurpose trees and shrubs in the semi- deciduous zone of Ghana

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Efforts to overcome declining soil fertility and also minimize the reliance of farmers on the application of inorganic fertilizers are of concerns to stake holders in the agriculture sector. There is inadequate fertilizer use and farmers inability to apply adequate quantities that would supply the required nutrients to crop. There have been several studies that attempt reversing this trend by using organic inputs. Leaf biomass from Multipurpose Trees and shrubs (MPTs) like Senna siamea, Senna spectabilis, Leucaena leucocephala, Gliricidia sepium and Albizia lebbeck, are known to provide enormous amount of nutrient for crops when used in rotations and/ or fallow. A study was conducted on soil of Kumasi- Ofin – Nta compound association to investigate the effect of the five multipurpose tree species on some soil physical and chemical properties thirteen years after fallow. The field layout was a Completely Randomized Design which was made up of five MPTs species in three blocks. Soils were sampled from 0 – 10 cm, 10 – 20 cm and 20 – 30 cm soil depths. The samples were taken through physical and chemical laboratory analysis. The five MPTs leaves were also evaluated to determine their chemical properties. Further study was undertaken using the litter bag technique for the decomposition of the leaves and amounts of residual nutrient in biomass during decomposition. Data collected were subjected to analysis of variance (ANOVA). The soils under the five MPTs species showed no significant influence of the five MPTs on chemical properties (soil pH, nitrogen, phosphorus, potassium, Calcium and Magnesium). However there was significant influence of the MPTs on soil physical properties (bulk density and porosity). Analysis of the MPTs leaf showed significant differences in nutrient levels of the fallow species especially N, P, K, Ca, Mg and C: N ratio. Recorded values were within the sufficiency rate reported by Kang, (1980). N was moderate to high (3.08 – 4.76), P was low to moderate (0.16 – 0.23) and K was low to moderate (0.43 – 0.68). Applications of 5T/Ha biomass from these MPTs are expected to yield between 195 to 390 kg N Ha-1, 9.75 – 19.5 kg P Ha-1 and 27.8 – 55.5 Kg K Ha-1 to growing crops. Decomposition test carried out using the litterbag technique showed differences in the period degradability of the five MPTs. Gliricidia sepium, Leucaena leucocephalla and Senna spectabilis decomposed faster than Senna siamia and Albizia lebbeck.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the award of the Degree of Master of Science in Agroforestry, 2011