Estimating ammonia volatilization from unsaturated urea fertilized and urine affected soils by an indirect method

Abstract

An indirect method for evaluating the emission of ammonia from urea-fertilized upland crops or urine-affected pastures, without affecting the plant's environment, was evaluated at Yanco, N.S.W., Australia and near Lincoln University, New Zealand. The parameters measured were the ammoniacal nitrogen concentration, pH and temperature in the aqueous phase at the soil's surface, and windspeed at a reference height. The combined effect of these influences on volatilization rate were incorporated into a linear relationship of the form F =k u _z ρ0, where F is the vertical flux of ammonia, determined by a micrometeorological method,u _z is the wind speed at some reference height above the soil,ρ0 is the ammonia concentration in equilibrium with the liquid phase (calculated from the ammoniacal nitrogen concentration, pH and temperature) andk is a proportionality constant. Strong linear relationships of this kind were found for the data sets from both experiments. The respective correlation coefficients for the relationships at the two sites were 0.870 and 0.879, and the respective k values were 6.3 × 10⁻⁵ and 7.5 × 10⁻⁵. The field measurements require little in the way of specialized equipment (e.g. flat - surface pH electrode, ammonia electrode, anemometer) and are comparatively easy to carry out. The results suggest that with some further refinement, this technique could achieve application in the calculation of ammonia losses from small plots in the field.