Effect of land use on soil quality in Rivers Nyando and Yala catchments of Lake Victoria Basin, Western Kenya

Abstract

Soil, as a major subsystem of land, is rapidly changing with time as a result of changes in its’ environment or management. Periodic soil quality assessment is thus vital in evaluating agro-ecosystem sustainability, soil degradation, and identifying sustainable land management practices. This study assessed the impact of land use on soil quality in Rivers Nyando and Yala watersheds of Lake Victoria Basin, Western Kenya on three land use types namely: grazing fields, agricultural land and mixed farming. Surface (0-20cm) and subsurface (20-50cm) soil samples were collected at four different points within the 30mx30m plot and composite sample for each point packed in 4 different polythene bags for analysis. The soils were analyzed for soil organic carbon, nitrogen, phosphorus, pH, calcium, magnesium and potassium. Both descriptive and inferential statistics including Pearson Correlation Coefficient and Analysis of Variance (ANOVA) were carried out on the soil data. Findings showed that mean organic carbon and nitrogen levels varied significantly between land use types (p<0.0001). Mean potassium levels were significantly lower in grazing fields and higher in agricultural lands. The mean soil pH, phosphorus, calcium and magnesium were significantly higher in grazing fields compared to other two land use types. All parameters studied varied significantly between River Nyando and Yala catchments (P<0.05), with soils from River Nyando watershed having significantly higher mean phosphorus, calcium, magnesium and pH levels while those from River Yala catchment had significantly higher mean organic carbon, nitrogen and potassium levels. Soil organic carbon in composite samples showed significant negative correlation with pH (r=-0.295**), magnesium (r=- 0.553) and calcium (r=-0.388), but a positive correlation with potassium (r=0.518**), phosphorus (r=0.199*) and nitrogen (r=0.804**) at P<0.01. Grazing fields had lower soil organic carbon and total nitrogen while agricultural land had lower soil exchangeable bases, pH and carbon to nitrogen ratio