The Nutrient Status of the Soils in Shenchong Basin and the Effects of Soil Erosion

Abstract

The nutrient status of the soils in Shenchong Basin and the effects of soil erosion were examined during the summer of 1987. Eight raingauges and two thermographs provided meteorological data. Soil samples were collected from different land use categories in the uplands and lowlands, including agricultural areas. Water and sediment samples were collected from 1) surface discharge from the upland slope, rills and a gully during storms and 2) surface and ground waters during dry weather. Analysis was carried out on water samples to determine ammonia-nitrogen, nitrate-nitrogen, orthophosphate, soluble iron, calcium and potassium concentrations. The soil and sediment samples were analyzed for nitrate-nitrogen, available phosphorus, exchangeable potassium, calcium, magnesium and iron. Concentrations of nitrate and orthophosphate in the water samples were very low. Potassium showed the highest concentrations. Ammonia was the dominant inorganic nitrogen species in water and possibly the soils. The soils were highly acidic (pH < 5) and the soluble iron concentrations were high in the upland soils. Total aluminum concentrations were also high. Potassium concentrations were high in soils from vegetated areas. The higher levels of calcium and magnesium in the agricultural soils were were related to lime additions. Available phosphorus concentrations were very low. Nitrate showed no spatial trend except for the high concentration in the cassava field which was attributed to the peanut plants that were previously planted there. In general, nutrient concentrations were low compared to other tropical areas in the world.