Ammonia volatilization from artificial dung and urine patches measured by the equilibrium concentration technique (JTI method)

The aim of this study was to investigate the dynamics of ammonia (NH3) volatilization from intensively managed pastures on a soil type typical of the dairy production area in Finland and to clarify the effect of rainfall on NH3 volatilization. The study included two experiments. In Experiment 1 the total amount of NH3–N emitted was calculated based on the annual surface coverage of dung (4%) and urine (17%). The application rate of total N in the simulated dung and urine patches was approximately 47 g N m−2 and 113 g N m−2, respectively. In Experiment 1 the general level of NH3 emissions from the urine patches was high and the peak volatilization rate was 0.54 g NH3–N m−2 h−1. As expected, emissions from the dung pats were clearly lower with a maximum rate of 0.10 g NH3–N m−2 h−1. The total emission calculated for the whole pasture area (stocking rate four cows ha−1 y−1, urine coverage 17% and dung coverage 4%) was 16.1 kg NH3–N ha−1. Approximately 96% of the total emission originated from urine. In Experiment 2 we measured the emissions from urine only and the treatments on the urine patches were: (1) no irrigation, (2) 5+5 mm and (3) 20 mm irrigation. The peak emission rates were 0.13, 0.09 and 0.04 g NH3–N m−2 h−1 and the total emissions were 6.9, 3.0 and 1.7 kg NH3–N ha−1, for treatments (1), (2) and (3), respectively. In both measurements over 80% of the total emission occurred during the first 48 h and there was a clear diurnal rhythm. Increasing rainfall markedly decreased NH3 emission. Volatilization was highest with dry and warm soil. The JTI method appeared to be suitable for measuring NH3 volatilization in this kind of experiment. According to our results, the importance of pastures as a source of NH3 emission in Finland is minor.