[Impacts on N and P conservation during swine manure composting with different modified metal-salts addition]

Batch experiments were carried out by using mixed-level uniform design method U6 (692) x 3) to investigate the effect of the addition of different metal-salts at 20%, 40% and 60% of NT, respectively, including modified red-mud (MR) at pH 5.0 +/- 0.2 and 7.0 +/- 0.2, respectively, modified forsterite (MF) at pH 7.0 +/- 0.2, and MgSO4 on nitrogen and phosphorus conservation during swine manure composting. The results showed that the optimum effect of N saved occurred at No. 5 experiment (20%, MF, day 17) and No. 3 experiment (40%, MgSO4, day 10). Meanwhile, the P conservation of experiments with metal salts addition was better than that of the control, and the No. 6 experiment (20%, MR with pH =5, day 21) was the highest on TP conservation, with the lowest ratio of PO4(3-) -P/TP.