Soil Test Phosphorus as an Indicator of Nitrate-Nitrogen Leaching Risk in Tile Drainage Water

A 2 year tile drainage study of 39 fields in Nova Scotia, Canada was conducted. Weekly nitrate-nitrogen (NO3-N) concentrations were highest in spring and fall during high flow. Fields receiving poultry or swine manure had elevated drainage NO3-N and soil test phosphorus. Water quality guidelines for NO3-N (10 mg L-1) were exceeded on 90% of rotations (corn-grass or corn-grain) and 13% of long-term cover fields. A significant correlation between NO3-N and soil test P (r (2) = 0.42; p < 0.001) was found. The 10 mg L-1 guideline was exceeded at 100% of fields with soil test phosphorus > 200 mg kg(-1) and 60% overall.