Effect of acidification with sulphuric acid on the volatilization of ammonia from cow and pig slurries

SUMMARY Pig and cow slurries were applied to bare soil surfaces in the laboratory. Volatilization of NH 3 was measured using ventilated enclosures for 3·25 days after slurry application. Slurries were acidified to pH values between 7 and 4 with 5 M H 2 SO 4 . Lowering cow slurry pH to 5·5 decreased NH 2 volatilization by 95%, while lowering pig slurry pH to 6·0 decreased NH 3 volatilization by 82%. A field experiment, measuring the volatilization of NH 3 for 2 h after application to grassland stubble of slurry acidified to pH values between 7·5 and 5, gave similar results to the laboratory study. Titration curves were constructed within the pH range of 9 to 4 with cow and pig slurries. There was a significant ( P < 0·05) positive correlation between the NH 4 + -N content of the slurries and the volume of acid required to attain a target pH of 6·0 for pig slurries and a pH of 5·5 for cow slurries. One litre of slurry containing 2 g of NH 4 + -N required c . 20 ml of 5 M H 2 SO 4 for acidification.