Adding Phosphate Fertilizer and Apple Waste to Pig Manure during Composting Mitigates Nitrogen Gas Emissions and Improves Compost Quality

Calcium superphosphate and apple (Malus pumila Mill.) waste can be used for controlling N loss and improving compost quality during composting, whereas integrated addition of the two additives on composting process remains unexplored. Therefore, this study was conducted to investigate the effects of combined use of calcium superphosphate and apple waste on NH3 and N2O emissions and compost quality during pig manure and wheat (Triticum aestivum L.) straw composting. Mixtures of pig manure and wheat straw were combined with 6% phosphate fertilizer (PF), 15% apple waste (AW), 3% phosphate fertilizer + 7.5% apple waste (PA1), or 1.8% phosphate fertilizer + 10.5% apple waste (PA2) based on dry weight of the initial mixtures; a treatment with no additives served as a control (CK). The PF treatment took 3 d longer to reach thermophilic phase than the CK, PA1, and PA2 treatments. The treatments of PF and PA1 reduced NH3 and N2O emissions by 67 and 45%, respectively. Moreover, N loss in PF and PA1 treatments (31.8 and 30.1%, respectively) was significantly less than in the CK. A pot experiment showed that application of the compost with PA1 treatment could increase plant height and dried biomass of Chinese pakchoi (Brassica campestris L. ssp.). We recommend adding 3% phosphate fertilizer and 7.5% apple waste to pig manure during composting.