Reducing gaseous losses of nitrogen from cattle slurry applied to grassland by the use of additives

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Abstract
Losses of nitrogen (N) through ammonia (NH3) volatilisation and denitrification were determined following the application of cattle slurry to grassland in autumn or spring. Denitrification was examined on two contrasting soils. A system of small wind tunnels was used to measure NH3loss and an acetylene inhibition technique for denitrification. Between 31 and 84% of the ammonium N (NH‐N) applied in slurry was lost through NH3volatilisation. Acidifying the slurry to pH c 5.5 prior to application reduced these losses to between 14 and 57%. On a freely drained loam soil, denitrification from unacidified slurry applied in the autumn at 80 m3ha−1was continuous throughout the winter, with the maximum rate of 0.91 kg N ha−1day−1occurring a few weeks after slurry application. The total denitrification losses were equivalent to about 29% of the NH‐N applied for this treatment and 41% for the acidified slurry. The nitrification inhibitor dicyandiamide reduced the amount of N lost through denitrification by 70% when applied with the slurry at 25 kg ha−1, by 55% at 20 kg ha−1and by 30% at 15 kg ha−1. The nitrification inhibitor nitrapyrin did not appreciably reduce denitrification. Denitrification losses were consistently small from slurry applied to the freely drained loam soil in spring, or to a poorly drained, silty clay in autumn or spring. Neither nitrification inhibitor was of benefit in these situations.