Acidification of pig slurry effects on ammonia and nitrous oxide emissions, nitrate leaching, and perennial ryegrass regrowth as estimated by N-urea flux.

OBJECTIVE

The present study aimed to assess the nitrogen (N) use efficiency of acidified pig slurry for regrowth yield and its environmental impacts on perennial ryegrass swards.

METHODS

The pH of digested pig slurry was adjusted to 5.0 or 7.0 by the addition of sulfuric acid and untreated as a control. The pig slurry urea of each treatment was labeled with N urea and applied at a rate of 200 kg N/ha immediately after cutting. Soil and herbage samples were collected at 7, 14, and 56 d of regrowth. The flux of pig slurry-N to regrowth yield and soil N mineralization were analyzed, and N losses via NH, NO emission and NO leaching were also estimated.

RESULTS

The pH level of the applied slurry did not have a significant effect on herbage yield or N content of herbage at the end of regrowth, whereas the amount of N derived from pig slurry urea (NdfSU) was higher in both herbage and soils in pH-controlled plots. The NH-N content and the amount of N derived from slurry urea into soil NH fraction (NdfSU-NH) was significantly higher in in the pH 5 plot, whereas NO and NdfSU-NO were lower than in control plots over the entire regrowth period. Nitrification of NH-N was delayed in soil amended with acidified slurry. Compared to non-pH-controlled pig slurry (i.e. control plots), application of acidified slurry reduced NH emissions by 78.1%, NO emissions by 78.9% and NO leaching by 17.81% over the course of the experiment.

CONCLUSION

Our results suggest that pig slurry acidification may represent an effective means of minimizing hazardous environmental impacts without depressing regrowth yield.