Effects of separation, dilution, washing and acidification on ammonia volatilization from surface-applied cattle slurry

Abstract

SUMMARYTreatments which lowered the rate of ammonia volatilization from surface-applied cattle slurry were evaluated in three field experiments during 1989/90 at the Agricultural Research Institute of Northern Ireland. The relative effects of separation, dilution with water before application and washing with a water spray after application, on ammonia volatilization rates were compared over 4 days using ventilated enclosures. As the loss rate of ammonia during the first 4 days after application was highly correlated with the loss rate over the first 4 hours after application, the loss rate in the first 4 hours was used as a rapid method to assess the efficacy of various combinations of separation, dilution and acidification. Ammonia volatilization loss rates from treatment combinations were compared to the loss rate from whole slurry.A 50% decrease in ammonia volatilization was achieved by separation through a 0·4 mm mesh, separation through a 10·0 mm mesh plus dilution with 86% by volume of water, or separation through a 2·0 mm mesh plus washing with 53% by volume of water.A 75% decrease in ammonia volatilization was achieved by acidification to pH 6·5, or combinations of separation and dilution, namely separation through a 0·4 mm mesh plus 50% dilution or separation through a 5·0 mm mesh plus 100% dilution.A 90% decrease in ammonia volatilization was achieved by acidification to pH 6·0, dilution by 50% plus acidification to pH 6·5, or separation through a 0·4 mm mesh plus acidification to pH 6·5.The effects of separation and acidification on ammonia volatilization were cumulative. There was a highly significant inverse linear relationship between ammonia volatilization rate and volume of nitric acid used. Adding 10 M nitric acid at 1·4% by volume lowered volatilization by 75% of that from whole slurry and increased the nitrogen content of the slurry by 2 g N/l, making it a more balanced NPK fertilizer for cut swards. Because the variable value of cattle slurry is due to loss of nitrogen as ammonia and smothering of the sward with slurry solids, a combination of separation or dilution to lower sward contamination and acidification with nitric acid to lower volatilization may be the best practical option for improving cattle slurry as a fertilizer for cut grass.