AMMONIUM, NITRITE AND NITRATE ACCUMULATION IN THREE MANITOBA SOILS AS INFLUENCED BY ADDED AMMONIUM SULFATE AND UREA

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Abstract
Samples of the Ap horizons of three Chernozemic Black soils of acid, neutral and alkaline pH were incubated with the addition of ammonium sulfate and urea in order to trace the formation and/or disappearance of ammonium, nitrite and nitrate. A nitrogen concentration of 50 ppm N (air-dry basis) resulted in little difference of nitrification rate in 12 days between ammonium sulfate and urea, although considerable differences existed between soils. At high nitrogen concentrations (200, 400, and 800 ppm N), urea led to high nitrite concentrations in the neutral Wellwood soil, as well as showing a higher rate of ammonium oxidation in all soils, particularly the acid Holland soil. Expressed as the difference between initial total mineral N and total mineral N after incubation, nitrogen showed a loss at the higher fertilizer rates with the Wellwood and Holland soils. This was greatest in the ammonium sulfate treatment with the initially most acid soil.