Tillage effects on runoff water quality from sludge-amended soils

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Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University

A rainfall simulator was used to study the effects of tillage system and sludge application method and rate on runoff, sediment, phosphorus (P), and nitrogen (N) losses from agricultural lands. Surface application and incorporation of sludge were studied. Anaerobically digested sewage sludge was applied at rates supplying 0, 75, and 150 kg/ha of plant-available N. These rates resulted in applications of 0, 115, and 230 kgP /ha, respectively. A total of 90 mm of rainfall, with an intensity of 40-45 mm/hr, was applied to sixteen 0.01 ha plots, on a silt loam soil. Runoff water samples were collected from plot discharge and later analyzed for sediment and nutrient contents.

No-till was found to be effective in reducing runoff and sediment losses. Runoff and sediment losses decreased as sludge application rates increased, regardless of the tillage system. The surface application of sludge was more effective in reducing sediment losses than sludge incorporation. Nutrient concentrations and yields were greater from conventional tillage plots than from no-till plots. Surface application of sludge to conventional tillage plots resulted in higher concentrations and yields of most forms of P and N, relative to incorporated sludge treatments. Sediment-bound and total-P yields were less from sludgetreated plots than from the control treatments due to decreased erosion and runoff as a result of sludge application. With respect to sediment and nutrient yields in surface runoff, no-till appears to be a safer alternative for disposal of sewage sludge than conventional tillage. The structural characteristics of the soil under the two tillage systems are also discussed.