Effect of separation and acidification of cattle slurry on ammonia volatilization and on the efficiency of slurry nitrogen for herbage production

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Abstract
During the growing season of 1988 at the Agricultural Research Institute, Hillsborough, cattle slurry was kept whole or was separated through screens with mesh sizes of 5 mm, 3 mm, 0·25 mm and 0·015 mm. The resulting slurry liquids were either left unacidified or were acidified to pH 5.5 with 5M-H2SO4 prior to application at 75 kg NH+4-N/ha to perennial ryegrass in the field. Volatilization of ammonia was measured using ventilated enclosures. Plots treated with a range of rates of inorganic fertilizer N were used to construct response curves to assess the efficiency of N in slurry for herbage production compared with equinitrogenous inorganic fertilizer.On average over the season, acidification of cattle slurry decreased ammonia volatilization to < 15% of that from unacidified whole slurry. Compared with inorganic fertilizer N, the overall efficiency of NH+4-N was 96% in acidified slurries and 36% in unacidified whole slurry. Ammonia volatilization from separated slurries decreased with decreasing mesh size to 39% of that from whole slurry for a 0·015 mm mesh. The overall efficiency of NH4+-N in slurry separated through a 0·015 mm mesh was 76%. A highly significant linear relationship was found between NH3-N volatilized from all slurry treatments and N offtake in herbage at all three harvests.