EFFECTS OF DRY-MATTER CONTENT AND TEMPERATURE ON AMMONIA LOSS FROM SURFACE-APPLIED CATTLE SLURRY

Effects of increasing dry matter content in slurry on NH3 loss was measured with a wind tunnel system, whereby parameters affecting the volatilization can be estimated under controlled conditions. The effect of dry matter content on NH3 loss was measured using a slurry adjusted to different contents of dry matter. The slurry was prepared by mixing the fibrous and liquid fractions of a mechanically separated cattle slurry. Slurry was applied to a 5 cm high grass ley (Lolium multiflorum Lam.) and to barley (Hordeum vulgare L.) at a rate of 3 L m-2. The content of dry matter varied from 0.9 to 22%, total N from 2.9 to 4.9 g N L-1, TAN (NH3 + NH4+) from 1.6 to 3.0 g N L-1 and pH from 7.0 to 7.9. The results indicated that NH3 volatilization increased with increasing slurry dry matter content. The accumulated 6-d loss ranged from 19 to 100% of applied TAN from slurries having a dry matter content of 0.9 and 15.6%, respectively. The accumulated NH3 loss after 6 h exposure was linearly related to dry matter content. In the periods of 6 to 12 h, 12 to 24 h and 24 h to 6 d the loss was nonlinearly related to dry matter content. If the results were adjusted for effects of pH and temperature, NH3 loss tended to be sigmoidally related to content of dry matter in all four periods. Therefore, changes in slurry dry matter content on NH3 loss seemed to be small if the dry matter content was higher than 12% or lower than 4%.