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 NH3 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 x--N, NH4+-N, NH3, and N2O, which are dominate forms of nitrogen in composting. In this study, the equimolar H3PO4, H2SO4, and K2HPO4 were added into pig manure composting to evaluate the effect of H+ and PO43- on nitrogen transformation. As a result, we reached the conclusion that pH displays significant influence on adsorption from PO43- to NH4+. The NH4+-N concentration in H3PO4 treatment kept over 3 g kg-1DM (dry matter) which is obviously higher than that in H2SO4 treatment, and NH4+-N concentration in K2HPO4 treatment (pH>8.5) is lower than 0.5 g kg-1DM because adsorption capacity of PO43- is greatly weakened and NH4+-N rapidly transformed to NH3-N influenced by high pH value. The N2O emission of composting is significantly correlated with incomplete denitrification of NO x--N, and PO43- addition could raise NO x--N contents to restrict denitrification and further to promote N2O 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.