Win-win for monosodium glutamate industry and paddy agriculture: Replacing chemical nitrogen with liquid organic fertilizer from wastewater mitigates reactive nitrogen losses while sustaining yields

Recycling nutrients from the monosodium glutamate (MSG) wastewater as a low-cost fertilizer is a cleaner practice in the MSG industry. However, the potential of liquid organic fertilizer (LOF) recovered from MSG wastewater serving as a substitute for chemical fertilizer, improving crop yields, and mitigating reactive nitrogen emissions, has not been investigated. In a two-year paddy field experiment, the LOF recovered from the MSG wastewater was used as top dressing, following a multi-splits fertigation way, to evaluate its effects on rice yield, nitrogen use efficiency (NUE), NH3 volatilization and nitrogen leaching losses. For top-dressed N, with local traditional top-dressing strategy (broadcast urea in three splits) as control (CF), LOF fertigated in seven splits (LOF160, totally 160 kg N ha−1) was set in 2017, and another two reduced N levels for LOF top-dressing (LOF130 and LOF100) were included in 2018. Compared with CF, the LOF160, LOF130 and LOF100 achieved similar rice yields and showed significant improvements in NUE (19.4%, 25.5% and 34.4%, respectively). Furthermore, due to the specific N forms and the implementation practice of more splits and low split-dosage, the LOF fertigation significantly decreased the cumulative NH3 volatilization by 41.2%–67.7% and cumulative TDN leaching losses by 19.5%–44.1%. Although additional fertigation equipment investment is required, the LOF fertigation still improved the net economic benefits (NEB) by 10.4%–18.9% and the net economic and ecological benefit (NEEB) by 34.0%–54.9%, which primarily attributes to labor and fertilizer savings and the mitigation in environmental damage cost. This indicates that the use of recycled LOF as a substitute for chemical fertilizer can offer a promising option for delivering environmental and economic benefits of reduced chemical fertilizer use and industrial-agricultural pollution.