Adding an appropriate proportion of phosphogypsum ensured rice husk and urea composting to promote the compost as substrate utilization

[Display omitted] •Urea instead of chicken manure as nitrogen source can significantly reduce the EC value of compost products.•Adding phosphogypsum can reduce the N loss and maintain a suitable C/N ratio in the initial stage of composting.•After adding phosphogypsum (10%∼20%) in the rice husk + urea composting system, the total N loss (85.2%∼89.2%) is similar to the rice husk + chicken manure composting system.•Adding 10%∼20% of phosphogypsum can promote the substrate utilization of rice husk + urea compost product. To explore the effectiveness of urea replacing poultry manure as the nitrogen source in the rice husk composting system, and to promote the utilization of compost products as substrates, 0%, 10%, 20%, and 30% of phosphogypsum were added respectively in the urea composting system, and were compared with the chicken manure composting (RCP0). Finally, the fermentation and maturation of RCP0 were achieved, but high EC value limited the utilization of compost products as the substrate. Urea, as an N source, could lower the EC value, but the C/N ratio was uncoordinated during the initial stage of composting. Adding an appropriate proportion of phosphogypsum could ensure a proper C/N ratio to promote smooth fermentation and enable the products to be ideal substrates. When the added proportion was 30%, the thermophilic stage was shortened significantly but this may increase heavy metals. 10%-20% were concluded to be the recommended proportion.