[Effect of magnesium salt addition on nutrients conservation during swine manure composting]

Experiments were carried out to investigate the effect of magnesium chloride addition on nutrients conservation in the thermophilic stage of swine manure composting. The results indicated that in the end of thermophilic stage of composting, the ammonia nitrogen loss of the pile with Mg-salt addition was 24.25 g, reduced by 58%, compared with 56.60 g of the control. And the total nitrogen (TN) concentration of the pile with magnesium chloride addition was higher by 18% than that of the control pile. Sequential extraction phosphorus results showed that the total phosphorus (TP) in both piles were similar (14.2 g/kg TP of the pile with Mg-salt addition and 12.0 g/kg TP of the control). However, the addition of Mg-salt is helpful for conserving phosphorus in swine compost because the percentage of the easily dissolved phosphorous forms such as H2O-P and NaHCO3-P in the control was increased from 30% of TP to 60% of TP, compared with that maintained at 30% of TP in the pile with Mg-salt addition. Crystal mixture which includes magnesium phosphate were found in the pile of adding magnesium chloride.