Ammonia volatilization from nitric-acid-treated cattle slurry surface applied to grassland

The reduction in NH3 loss from HNO3 treated cattle slurry, surface applied to grassland, was measured on different soil types throughout the Netherlands from 1989 to 1992. Thirteen micro-meteorological mass balance and 10 small wind tunnel experiments were carried out. Amounts varying between 7-17 and 10-30 m-3 ha-1 were applied, resp. and measurements were performed for 4 and 10 days, resp. The pH of treated slurry ranged from 3.9 to 6.6. A mean total of 60% (range: 29-98%) of the NH4-N from untreated slurry was volatilized in the mass balance experiments. A reduction in NH3 volatilization of 85, 72 and 55% was achieved for acidified slurry with a respective pH of c. 4.5, 5.0 and 6.0. Approx 55% (range: 7-91%) of the total loss from acidified slurry was measured on the day of application. A mean total of 66% (range: 21-90%) of NH4-N from untreated slurry volatilized in the tunnel experiments. The reduction in NH3 volatilization was 73% for slurry with pH 4.5. Approx 27% (range: 6-91%) of the total loss from acidified slurry was measured on the first day. The smaller reduction and the different pattern in NH3 volatilization observed in the wind tunnel experiments might be the consequence of different climatic conditions in and outside the tunnels or they might be related to the higher rates of slurry application in these experiments. Regression analysis indicated that high temperature, slurry pH, potential water evaporation and NH4+ concn stimulated NH3 loss in the mass balance experiments (Rsuperscript 2 = 87%). It is suggested that the results obtained with acidified slurry were independent of the grassland soil type at the application levels employed.