Effect of continuous use of poultry manure on urban vegetable farming soil properties

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Soil fertility, one of the important determinants of agricultural productivity, is generally thought to be supplemented with nutrients from poultry manure application. The residual effect of the poultry manure which could sometimes pose major environmental problems such as surface and groundwater contamination is generally ignored. In this study, the long-term impact of poultry manure (PM) on vertical distribution of soil macronutrients (N, P, K, Ca and Mg) was determined. In addition, change in other soil fertility indicators such as pH, organic matter (OM) and cation exchange capacity (CEC) levels were assessed in the cultivated soil profile at four depth intervals from 0 to 120 cm in urban (Gyenyase site) and peri-urban (Deduako site ) Kumasi, Ghana. The treatments were plots under cultivation while the control, adjacent uncultivated plots. Poultry manure was estimated to be applied at the rate of 100 t/ha per year at both sites with Gyenyase and Deduako sites cultivated for ten (10) years and four (4) years respectively. Soil samples from four depths (0-15, 15-30, 30-60, and 60-120 cm) from the two « sites were analyzed for total N, Bray no. 1 (available P), exchangeable K, Ca, and Mg, pH, OM and CEC. The soil types for Gyenyase and Deduako sites were sandy loam and loamy sand respectively. With the exception of N and OM which showed no significant differences between the two locations, levels of P, K, Ca, Mg and pH were significantly higher (p < 0.05) at Gyenyase site than the Deduako site, probably due to several years of cultivation. Cultivating vegetables with poultry manure as soil amendment caused significant increases in all selected soil properties (N, P, K.Ca, Mg, OM, CEC, and pH) at Gyenyase site compared with the uncultivated soil. Data from Deduako site also showed similar results except pH. Significant changes (p < 0.05) were recorded in the soil profile for N, P, K, OM and pH during wet season. During the dry season, only N, P and OM showed these changes. When the nutrient levels in cultivated and uncultivated sites were compared at the different depths, N, Ca, Mg, OM and CEC were observed to be significantly higher (p<0.05) in the cultivated soils. Potassium, Phosphorus and pH showed no consistent differences with depth. This result reflects crop removal, leaching, mineralization, erosion and pedogenic processes. The data also revealed that the levels of N and P were high at depths 15, 30 and 60 cm indicating sustainable nutrient reserve for plants but which could potentially pollute groundwater and surface water.
A thesis submitted to the Department of Teoretical and Applied Biology, College of Science Kwame Nkrumah University of Science and Technology, Kumasi in partial fulfilment of the requirements for the award of Masters degree in Environmental Science, 4950