EFFECTS OF SEPARATION, DILUTION, WASHING AND ACIDIFICATION ON AMMONIA VOLATILIZATION FROM SURFACE-APPLIED CATTLE SLURRY

Treatments 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.