Effects of Ferrous Sulfate and Calcium Superphosphate on Nitrogen Loss and Humification During Co-Composting of Cattle Manure With Straw

Effects of calcium superphosphate (SP, 4.4% dry weight) and ferrous sulfate (LF, 4.1% dry weight) on nitrogen loss and humification were studied during co-composting of cattle manure with straw. Changes in temperature during composting, the chemical properties and humus compositions of the compost products were characterized. The results show that SP and LF groups both met the maturity requirements after 55 days of composting. The C/N ratios of compost products were 11.61 and 13.71, E4/E6 ratios were 1.96 and 1.57, and NH₄⁺-N contents were 34.19 and 35.74 mg·kg^-1, the seed germination indices were 143% and 144%, respectively. The addition of calcium superphosphate and ferrous sulfate had no adverse effect on the phytotoxicity of compost products. The addition of ferrous sulfate had a good nitrogen retention effect (the nitrogen loss of the control group and the LF group were 40.78% and 25.18%, respectively), while the addition of calcium superphosphate had no obvious nitrogen retention effect. It was found that the degradation of organic matter was inhibited in the presence of calcium superphosphate and ferrous sulfate, the loss of organic matter in the control group, SP and LF groups were 58.59%, 49.44% and 34.67%, respectively. The addition of calcium superphosphate and ferrous sulfate could improve the quality of humus. The percentages of humic acid in SP and LF groups were 45.23% and 51.60%, respectively, which were higher than 36.85% in the control group. Therefore, the addition of ferrous sulfate can significantly reduce the nitrogen loss during co-composting of cattle manure with straw, and improve the humus quality of the compost effectively.