Measurements of mineralization, nitrification and denitrification in laboratory incubations of soil from a semi-arid natural grassland

Abstract

Experiments were done to compare three incubation methods after it was found that prolonged incubation of soil in sealed preserving jars resulted in the exhaustion of head- space oxygen and anaerobiosis in the soil. Nitrate added to soil from the 0–50 or 200–400 -mm layers from a natural permanent pasture at 2% water content and incubated at 37°C in sealed preserving jars was recovered without the formation of ammonium or nitrite. At 12% or 22% water content, nitrate was lost from the 0–50 -mm layer and partly replaced by ammonium and nitrite. Nitrate added to the 0–50, 50–200 or 200–400 -mm layers and incubated under water in sealed tubes with no headspace at 27°, 37° or 44°C for 7, 14 or 21 days was lost with the transient appearance of nitrite whereas most of the ammonium added was recovered. Nitrate added to the same soils in Stanford-Smith columns, saturated with water and incubated at 27° or 37°C for periods of up to 63 days was recovered by elution after incubation. Small amounts of nitrite and of ammonium appeared during some incubations. Measurements of net mineralization by the three methods agreed better for the 200–400 mm layer than for the 0–50 -mm layer. None of these three incubation methods was entirely satisfactory for measuring the effects of temperature and water content on the mineralization of nitrogen in soil. © 1993 Taylor & Francis Group, LLC.