Bioacidification of animal slurry has proven to be a good alternative to traditional acidification with sulfuric acid for reducing ammonia emissions. However, the
fertiliser value of the bioacidified slurry is yet to be determined before a whole-system assessment can be made. The N fertiliser value of pig slurry either untreated or
bioacidified with glucose and/or fermented brown juice (BJ) was investigated in a pot experiment with maize (Zea mays L.) grown in a greenhouse. The slurry
treatments were either pre-acidified with sulfuric acid to pH 6.5 or 5.5 before bioacidification, or bioacidified without pre-acidification. Plant growth was good in all
treatments, but the bioacidified treatments showed a lower mineral fertiliser equivalence (MFE) value than the non-bioacidified treatments. Average MFE values
were 71 %, 62 %, 59 % and 41 % for the non-bioacidified (noC), glucose (glu), glucose and brown juice (glu + BJ20) and brown juice (BJ50) treatments respectively.
This reduction was most likely caused by immobilisation of N due to the addition of easily available C from the substrates. The fertiliser value was not affected by the
pH, C/N ratio and C content of the treatments, while a positive correlation was found with NH4 + -N content. Pre-acidification positively affected MFE, probably due
to higher nutrient availability. Further studies on the effect of different inclusion rates of substrates for bioacidification and the effect of application method on the
fertiliser value, as well as studies under field conditions, are needed before recommendations can be made about bioacidification as an alternative to traditional
acidification.