Effect of water-retaining agent on nitrogen conversion in cattle manure composting process

To mitigate the environmental pollution caused by ammonia volatilization during livestock manure composting, this study investigated the effects of different dosages of water-retaining agent (CK: 0 g/m³; T1: 100 g/m³; T2: 200 g/m³; T3: 300 g/m³; T4: 400 g/m³; T5: 500 g/m³) on nitrogen transformation and ammonia emissions in cattle manure windrow composting. The results showed that the water-retaining agent exhibited a significant dosage-dependent effect: appropriate dosages (T1-T3) could retain water, stabilize the microenvironment for nitrifying bacteria, promote the conversion of ammonium nitrogen to nitrate nitrogen, and reduce ammonia volatilization. Among these treatments, the T3 treatment achieved the optimal effect; compared with CK, the final moisture content increased by 16.97%, the nitrate nitrogen content increased by 22.03%, the ammonia volatilization decreased by 15.06%, and the total nitrogen loss rate decreased by 10.32%. In contrast, excessive dosages (T4-T5) prolonged the thermophilic phase of composting, inhibited the activity of nitrifying bacteria, leading to increased ammonia volatilization (12.61% and 38.72% higher than CK, respectively) and intensified total nitrogen loss. This study clarified the water-retention and nitrogen-fixation mechanism of the water-retaining agent, identified its optimal dosage, and provided a theoretical basis and technical support for the clean composting of livestock manure and efficient nitrogen retention.