Phosphorus is noted as the limiting factor of eutrophication. We investigated the impact of different agricultural land use (mixed cropping, horticultural garden and fallow land) on the phosphorus loading of a reservoir. Soil samples were analysed for pH, particle size distribution, organic matter, available P and erodibility index calculated. Water samples analysed for biological oxygen demand (BOD5), dissolved oxygen, phosphate, organic matter and pH. The result shows available phosphorus in the order: fallow land > mixed cropping > horticultural garden. The results suggest that the PO43-in the reservoir maybe due to the effect of the cultivated land around the reservoir. The soil organic matter and available P shows significant patterns of seasonal and profile variations. To prevent runoff from agricultural land to the reservoir, the idea of zero cropping should be encouraged.
Keywords: phosphorus, erosion, reservoirs, land use, agricultural activities, agriculture, streams, Nigeria, water pollution, mixed cropping, horticultural gardens, fallow land, eutrophication, organic matter, soil contamination, runoff, zero cropping