Nitrogen and phosphorus transfer in soil erosion processes.

This study deals with the transfer of nitrogen and phosphorus in surface runoff from eroding upland fields in Japan, Universal Soil Loss Equation (USLE) standard plots were installed in the upland fields, and differing amounts of fertilizer were spread on each plot. The supernatant was obtained from each sample by centrifugal separation. Total nitrogen and total phosphorus in the eroded suspension and supernatant were separately analysed by means of absorption spectrophotometry. Additionally, the supernatant was analysed for ammonium, nitrate and nitrite nitrogen. The results indicate that the total nitrogen and phosphorus concentrations in the eroded suspension were higher than in the supernatant. Total nitrogen and phosphorus concentrations in the eroded suspension tended to increase with an increase in the concentration of eroded material indicating that the soil particles and organic matter dominantly transported nitrogen and phosphorus components. Although there was poor agreement between inorganic nitrogen concentration and suspended solids, the amount of nitrogen and phosphorus transfer increased with soil losses. Nitrogen and phosphorus losses in the plots with the highest fertilizer application were larger than in the less fertilized plots. The results indicated that nitrogen and phosphorus losses in surface runoff increase with soil loss and level of fertilizer application.