Tillage effects on phosphorus losses from sludge-amended soils

The impact of sludge application method and rate on the quality of runoff from no-till and conventionally tilled fields was investigated on replicated plots using simulated rainfall. Anaerobically digested sewage sludge was applied at rates sufficient to supply 0, 75, and 150 kg/ha of available nitrogen (N) (0, 67, and 134 pounds/acre) to the field plots. These rates resulted in the application of 0, 115, and 230 kg/ha phosphorus (P) (0, 103, and 206 pounds/acre), respectively. Sludge was surface-applied to the no-till plots. On conventional tillage plots, sludge was either sugace-applied or incorporated to a depth of 10 to 15 cm (4–6 inches). A total of 90 mm (3.5 inches) of rainfall at an intensity of 45 mm/hr (1.8 inches/hour) was applied to the sixteen 0.01-ha (0.025-acre) plots. Runoff samples were collected at plot discharges and analyzed for sediment and P contents. No-till practices greatly reduced runoff and sediment yields. Runoff and sediment yields decreased as sludge application rates increased for both tillage systems. Surface application of sludge resulted in higher concentrations and yields of P relative to incorporation. Sediment-bound and total-P yields were less from sludge-treated plots than from control treatments because of reduced erosion and runoff as a result of sludge addition.