Ammonia volatilisation from pig slurry and ANS with DMPP applied to Westerwold ryegrass (Lolium multiflorum Lam., cv. Trinova) under Mediterranean conditions.

Ammonia volatilisation from agriculture represents an important nitrogen (N) loss which has both environmental and economic impacts. In regions where large amounts of manures are available, there is a need to find appropriate management strategies that help to reuse them without increasing ammonia volatilisation. A study was made of the effect on ammonia volatilisation and yield of fertilising ryegrass with pig slurry (PS) and ammonium nitrosulphate (ANS-26) alone and with the 3,4-dimethylpyrazol phosphate (DMPP) nitrification inhibitor added to them. The study was conducted under Mediterranean conditions at two different sites. The treatments (control, PS, PS + DMPP, ANS-26 and ENTEC®) were established in a randomised block design with three replicates. Ammonia was sampled daily after each fertilisation using semi-static volatilisation chambers. We hypothesised that PS could replace mineral fertiliser without substantially increasing ammonia volatilisation in the studied systems. Temperature positively correlated with ammonia emissions. On the whole, during the two years of the study, the PS treatments presented higher average cumulative ammonia volatilisation (25% of total ammonium nitrogen (TAN) applied at Site 1; 21% of TAN applied at Site 2) than the mineral ones (11% of TAN applied at Site 1; 10% of TAN applied at Site 2). At pre-sowing, ammonia volatilisation was significantly (p < .05) lower (51% at Site 1; 55% at Site 2) than after ryegrass cuts due to burying PS immediately after application. Overall, applying DMPP had no effect on ammonia volatilisation. There were no significant differences in average yield (from 13.7 to 15.8 kg ha^-1 at Site 1; from 11.6 to 13.5 kg ha^-1 at Site 2) between the fertilised treatments, though ENTEC® tended to increase it. Applying PS (pre-sowing fertilisation) in combination with mineral N or processed PS fractions after ryegrass cuts could be an interesting option for the recycling of this livestock by-product without increasing ammonia volatilisation while maintaining yields.