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TECHNICAL REPORTS

Waste Management

Nitrogen- vs. Phosphorus-based Dairy Manure Applications to Field Crops

Nitrate and Phosphorus Leaching and Soil Phosphorus Accumulation

Section for Animal Production Systems, School of Veterinary Medicine, Univ. of Pennsylvania, 382 West Street Rd., Kennett Square, PA 19348

^* Corresponding author (jdtoth{at}vet.upenn.edu)

Received for publication December 23, 2005. Management of animal manures to provide nutrients for crop growth has generally been based on crop N needs. However, because manures have a lower N/P ratio than most harvested crops, N-based manure management often oversupplies the crop-soil system with P, which can be lost into the environment and contribute to eutrophication of water bodies. We examined the effects of N- vs. P-based manure applications on N and P uptake by alfalfa (Medicago sativa L.), corn (Zea mays L.) for silage, and orchardgrass (Dactylis glomerata L.), leaching below the root zone, and accumulation of P in soil. Treatments included N- and P-based manure rates, with no nutrient input controls and inorganically fertilized plots for comparison. Nitrate concentrations in leachate from inorganic fertilizer or manure treatments averaged 14 mg NO₃–N L^–1, and did not differ by nutrient treatment. Average annual total P losses in leachate did not exceed 1 kg ha^–1. In the top 5 cm of soil in plots receiving the N-based manure treatment, soil test P increased by 47%, from 85 to 125 mg kg^–1. Nitrogen- and P-based manure applications did not differ in ability to supply nutrients for crop growth, or in losses of nitrate and total P in leachate. However, the N-based manure led to significantly greater accumulation of soil test P in the surface 5 cm of soil. Surface soil P accumulation has implications for increased risk of off-field P movement.

Abbreviations: STP, soil test phosphorus • GS, growing season • NGS, non-growing season • DPS, degree of phosphorus saturation