Measurements and modelling of fertilizer concentrations in subsurface drain flow from a potato field

A 4.87 hectare potato field at St. Leonard d'Aston, Quebec was instrumented to measure surface runoff and tile drain flow over the 2 year growing season period, 1989-1990. The soil type was a Ste. Jude sandy loam. Several soil and water parameters and NPK concentrations in runoff were measured. The CREAMS (Chemicals, Runoff and Erosion from Agricultural Management Systems) computer simulation model was validated for the study site.Observed N concentrations in tile drain flow exceeded the Canadian water quality guideline of 10 mg/L. Observed P concentrations were less than 0.01 mg/L; and K concentrations, for the most part, exceeded 10 mg/L.CREAMS overpredicted event surface runoff depths, and underpredicted event percolation depths. However, total monthly surface runoff and percolation depths closely matched observed values.CREAMS overpredicted event nitrate concentrations in tile drain flow. There was a poor match between predicted and observed event nitrate concentrations in tile drain flow (coefficient of predictability, CP$ sb{ rm A}$ = 104.95). However, predicted total monthly nitrate load closely matched observed values (CP$ sb{ rm A}$ = 0.84). Total monthly and seasonal nitrate loads in tile drain flow were underpredicted