Effect of plant growth and form of nitrogen fertilizer on denitrification from four South Australian soils

Abstract

In measuring losses of volatile nitrogen in sealed growth chambers, four major wheat-growing soils were used, namely, a mallisol, a red-brown earth, a calcareous sand, and a grey-brown soil of heavy texture. The rate of loss varied from 1 to 15 mg nitrogen/(kg soil/week) when nitrate nitrogen was applied to the soil; when ammonium nitrogen was used, losses were 1-4 mg nitrogen/(kg soil/week) over a 6-week period. The major component of these losses was nitrogen gas with lesser quantities of nitrous oxide. Both gases were produced by biological denitrification of soil nitrate. This was confirmed with an incubation experiment which used a portion of the same samples of soil. When nitrate nitrogen was applied to the soil, denitrification was increased by increasing soil water content and plant growth. These effects were greatest in the heavy textured soils. The application of ammonium nitrogen to the red-brown earth, mallisol, and grey-brown soil of heavy texture reduced the losses of soil nitrogen as nitrogen gas and nitrous oxide. Considerable losses of soil nitrogen were recorded for the calcareous sand when ammonium nitrogen was applied. Plant growth did not affect the losses of soil nitrogen from those soils receiving ammonium nitrogen.