Contribution of Nitrogen and Phosphorus to Subsurface Drainage Water from Intensively Cropped Mineral and Organic Soils in Ontario

Abstract Nutrient content of tile drainage water was measured continuously from six mineral soil sites during 1972 and 1973 and from three organic soil sites during 1972 to 1975. The sites ranged in size from 5 to 113 ha and varied in cropping and fertilization practices. Average weekly concentrations of NO 3 ‐N in drainage water from mineral soils which were fertilized at or below recommended rates seldom exceeded 10 mg/liter, whereas those from sites fertilized at rates greater than recommended were seldom below 10 mg/liter. Annual NO 3 ‐N contribution ranged from 4 to 64 kg/ha with the larger amounts associated with those sites fertilized at rates greater than recommended. Average annual concentrations of NO 3 ‐N in drainage water from organic soils ranged from 14.8 to 42.7 mg/liter and the average annual contribution ranged from 37 to 245 kg/ha. The PO 4 ‐P concentrations in drainage water from the organic sites increased markedly during the course of the study and averaged 18.2 mg/liter on one site for the 1974/1975 drainage period. Laboratory leaching studies indicated that the high PO 4 ‐P concentrations could be attributed to fertilizer use. Laboratory studies also indicated that the P‐adsorption capacity of organic soils in southern Ontario varied widely depending on the total Fe and Al contents of the samples. It is suggested that the P‐adsorption capacity should be considered before organic soil areas are developed for crop production.