EVOLUTION DES NITRATES DANS QUELQUES SYSTEMES SOL–EAU DU QUEBEC

Abstract

Soil and water table nitrate concentrations were followed in test plots and fields seeded to corn (Zea mays L.) located in southwest Quebec, during 1971–73. Soil samples were taken to a depth of 150 cm in 25-cm intervals. Although there were few sites where nitrate concentrations exceeding 10 ppm were found in mineral soils, they were as high as 70 ppm in organic soils. Nitrate accumulation observed in 1972 changed to a near disappearance in 1973. This effect was ascribed to changes in climatic conditions. Nitrogen fertilization levels ranged from 50 to 300 kg N/ha, and reached a maximum of 600 kg N/ha over 2 yr. These had a significant influence on soil nitrate concentrations. However, the observed soil nitrate concentration did not exceed 40 ppm with the 200 kg N/ha rates in 1971. Nitrogen fertilization did not contribute significantly to ground water nitrate concentrations, and mean nitrogen levels (NO₃ + NO₂) were 4.5 mg/liter in the spring, 12.7 in July and 0.8 in September 1973. Nitrogen levels greater than 10 mg/liter were found only once in two soils. It was concluded that soil nitrate concentrations were low because of the approximately 112 kg N/ha nitrogen levels as used by corn growers.