Dairy Manure and Nitrogen Fertilizer Effects on Residual Nitrate and Phosphate, and Wheat Yield in a Sandy Clay Loam Soil

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Dairy manure (DM) rates of [0 (DM0), 30 (DM30)), 60 (DM60) Mg ha−1] and three nitrogen (N) rates [0 (N0), 125 (N125), 250 (N250) kg ha−1] were tested in a sandy clay loam, to evaluate their effects on growth and yield of wheat crop (Triticum aestivum L.), residual nitrate nitrogen (NO3-N) and phosphorus (P) concentrations in the surface soil, and selected soil physical measurements [saturated hydraulic conductivity (Ksat), and bulk density (BD)]. Increasing N and DM rates gave higher wheat yields, increased concentrations of residual NO3-N and P in the surface soil and improved Ksat and BD. Highest grain yield of 3.8 Mg ha−1 (70.3% more than the control) was observed in DM60 × N250 treatment. Residual accumulation of N-NO3 and P in the surface soil at high N and/or DM application rates suggests the need to carefully manage N and DM inputs on farm fields to avoid environmental contamination.