Surface application of acidified cattle slurry compared to slurry injection: Impact on NH3, N2O, CO2 and CH4 emissions and crop uptake

- Surface application of acidified slurry and slurry injection gave similar N emissions and crop yield.
- Surface application of the non-acidified liquid fraction led to significant NH3 emissions
- Surface application of acidified slurry or acidified liquid fraction are good alternatives to slurry injection.
- Acidification affects the N2O emissions.

Intensive cattle production has a severe environmental impact due, partly, to ammonia (NH3) and greenhouse gas emissions resulting from handling of the large amounts of slurry (liquid manure) produced. The present study aimed to compare, in terms of NH3, N2O, CH4 and CO2 emissions and crop yield, slurry injection in soil (reference technique) and a combined approach of slurry (S) treatment (by separation and/or acidification) followed by surface application. A pot experiment was performed over 67 days with an oat forage crop amended with S or the separated liquid fraction (LF), with and without acidification to pH 5.5. Injection of S was compared with surface application of treated S followed or not by soil incorporation. Soil injection reduced NH3 emissions to insignificant levels and did not increase N2O emissions, while maintaining oat yields similar to those for the surface application of S. Surface application of acidified S or acidified LF led to NH3 emissions < 7% of applied NH4+-N, with no increase of N2O emissions relative to surface application of S. Furthermore, a stronger decrease of N losses can be achieved by surface application of acidified S followed by soil incorporation. However, surface application of LF without incorporation led to significant NH3 emissions and therefore is not recommended. Significantly lower (p < 0.05) CH4 emissions were observed with application of acidified slurry and LF, relative to the respective non-acidified treatments. These results show that surface application of acidified slurry is a good alternative to slurry injection when the latter technique cannot be used.