THE RHODE RIVER WATERSHED - PHOSPHORUS DISTRIBUTION AND EXPORT IN FOREST AND AGRICULTURAL SOILS

To evaluate the effects of land use on P transport and transformation in the Atlantic coastal plain, we examined the distribution and fractionation of P in forested and agricultural soils of the Rhode River watershed and their export rates. Nearly 70% of P in forest soils was bound in organic forms. Fractionation studies reveal that cultivation and fertilizer P application increased total and inorganic P content and decreased organic P content of the soils. About half of the increase in the inorganic P content of the agricultural soils is due to the mineralization of organic P during cultivation and the rest is probably due to fertilizer P application. The inorganic phosphates in the forest and agricultural soils are chiefly associated with Fe either as iron phosphates or as phosphates adsorbed on the iron oxide surfaces. The agricultural watershed had a higher P export (46.3 g P ha-1 wk-1) compared to the forested watershed (5.% g P ha-1 wk-1). Particulate P dominated the P export from both watersheds. Variations in the P flux from the watersheds was correlated to changes in water discharge. The discharge pattern of organic and inorganic P forms from the watersheds are highly related to their soil P composition.