Effect of phosphate additive on the nitrogen transformation during pig manure composting.

Previous studies revealed that phosphate, as an additive to composting, could significantly reduce NH emission and nitrogen loss through change of pH and nitrogen fixation to form ammonium phosphate. However, few studies have explored the influence of pH change and phosphate additive on NO -N, NH-N, NH, and NO, which are dominate forms of nitrogen in composting. In this study, the equimolar HPO, HSO, and KHPO were added into pig manure composting to evaluate the effect of H and PO on nitrogen transformation. As a result, we reached the conclusion that pH displays significant influence on adsorption from PO to NH. The NH-N concentration in HPO treatment kept over 3 g kgDM (dry matter) which is obviously higher than that in HSO treatment, and NH-N concentration in KHPO treatment (pH>8.5) is lower than 0.5 g kgDM because adsorption capacity of PO is greatly weakened and NH-N rapidly transformed to NH-N influenced by high pH value. The NO emission of composting is significantly correlated with incomplete denitrification of NO -N, and PO addition could raise NO -N contents to restrict denitrification and further to promote NO emission. The study reveals the influence mechanism of phosphate additive to nitrogen transformation during composting, presents theoretical basis for additive selection in nitrogen fixation, and lays foundation for study about nitrogen circulation mechanism during composting.