The Selection Erosion of Plant Nutrients in Runoff

Abstract The enrichment of several P forms (Bray I, labile, inorganic, and organic), N, C, and K in runoff sediment was investigated for six soils of varying physical and chemical composition, using simulated rainfall (60 and 120 mm h −1 ). Differing enrichment ratios (ER) for C, N, and organic P (2.00, 1.61, and 1.47 avg for the six soils) indicate that erosion may reduce the C/N/organic P ratio of the remaining surface soil. Average ERs, for Bray I (2.45) and labile P (2.89) were significantly greater than for the other P forms (1.48). This was attributed to less aggregation of sediment compared to source soil for the major proportion (70%) of the runoff events studied. Phosphorus desorption‐sorption characteristics, buffer capacity (1.49), sorption index (1.56), equilibrium P concentration (1.80), and exchangeable K (2.46) were also enriched in runoff sediment compared to source soil. The logarithm of ER for each P form, N, C, and K was related to the logarithm of soil loss, which ranged from 10 to 800 kg ha −1 . Statistically significant differences between regression equations for each nutrient indicate that more than one equation is needed to estimate different nutrient ERs. Nutrient ER was related to clay and specific surface area ER of the sediment. This is to be expected as the nutrients described are chemically associated with clay‐sized particles. The potential use of ERs in estimating the effect of erosion on soil fertility is discussed.