Residual Effects of Compost and Fertilizer Applications on Nutrients in Runoff

The application of compost or fertilizer at rates that exceed crop nutrient requirements can result in phosphorus (P) and nitrogen (N) accumulation in soil. This study was conducted to determine the influence of soil P and N contents on the concentrations and total amounts of P and N transported in runoff. Composted beef cattle feedlot manure or inorganic fertilizer were added from 1992 to 1995 to a Sharpsburg silty clay loam soil at rates sufficient to meet P or N requirements for corn and incorporated following application. After four years of corn production following the last compost application, P concentration, EC, and pH of the surface soils on the N–based compost treatments were significantly greater than the check plots. Simulated rainfall was applied to the experimental site in 2000. Concentrations and total amounts of P and N in runoff were similar on the compost and inorganic fertilizer plots. The application of corn residue at a rate of 6 Mg ha–1 did not significantly affect the nutrient concentration of runoff or total nutrient transport when compared to a no–residue condition for a study site with a slope varying from 0.15% to 2.70%. On an adjoining field, compost or inorganic fertilizer were applied at rates in excess of crop P and N requirements to increase soil test P levels. For Bray and Kurtz No. 1 soil test P levels ranging from 42 to 267 mg kg–1 and water–soluble soil test P values varying from 5 to 61 mg kg–1, the dissolved P (DP) concentration of runoff did not correlate well with soil test P. Thus, factors other than soil test P appear to influence P loss in runoff for the bare soil used in this investigation.