Since hydrothermal aqueous phase (HAP) contains abundant nutrients and humic-like substances, it is developed as nitrogen (N) fertilizer to improve plant growth and soil quality. However, significant NH 3 volatilization is a major drawback in dryland soil. To solve this problem, a compound fertilizer of HAP and urea was modified with various dosage (0.25 % - 5.0 %) of urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT). The NH 3 , N loss, and lettuce growth were evaluated in parallel soil column and pot experiments. Results showed that increasing NBPT dosage increased soil dissolved organic N (DON) and ON while decreased NH 4 -N, NH 3 , N loss, urease activity, and ureC . NBPT successfully inhibited ammonification. Increasing NBPT dosage increased NO 3 -N but decreased PAO and AOA . The utilization rate of metabolic substrate (NH 4 -N) was more important for forming NO 3 -N, as evidenced by the negative correlation of NO 3 -N and NH 3 . The DON from HAP included N-heterocyclic compounds, which are toxic for nitrifiers. The toxic DON also significantly decreased root dry weight by 22.31 % when 5.0 % NBPT was added. The optimal additive dosages were 0.5 % and 2.0 % in the column and pot experiments, respectively, which decreased NH 3 and N loss by 45.38 % and 32.08 %. Further increasing NBPT dosage no longer decreased N loss but did harm to plant root. Therefore, this study demonstrated that an appropriate addition of NBPT to HAP fertilizer can effectively reduce ammonia volatilization and N loss. The innovative technique would promote the utilization of HAP resource within the context of sustainable dryland agriculture.
Clay-hydrochar composites (CHCs) are of great significance in ammonium (NH 4 + ) adsorption and have the potential to be applied to paddy fields to prevent ammonia (NH 3 ) volatilization. In this study, three CHCs were produced by infusing different clays to poplar-sawdust-derived hydrochar , including a bentonite hydrochar composite (BTHC), montmorillonite hydrochar composite (MTHC), and kaolinite hydrochar composite (KTHC). These three CHCs were applied to a paddy soil column system growing rice. The temporal variations in NH 3 volatilization and NH 4 + loss in floodwater were monitored after three fertilization dates. The results showed that among the three CHCs, only the BTHC significantly reduced cumulative NH 3 volatilization (by 41.8%), compared to that of the unamended control (without addition of hydrochar or clay-hydrochar-composite). In the unamended control, NH 3 volatilization loss accounted for 31.4% of the applied N fertilizer; with the BTHC amendment, NH 3 volatilization loss accounted for 17.4% of the applied N fertilizer. The reduced N loss via the BTHC amendment resulted in an increased N supply and further improved the N use efficiency and yield by 37.36% and 18.8% compared to that of the control, respectively. The inhibited NH 3 volatilization was mainly attributed to the increased soil NH 4 + retention as a result of BTHC's larger pore volume and specific surface area. In addition, the BTHC treatment significantly reduced the abundance of archaeal amoA genes ( AOA ), which possibly inhibited nitrification and increased soil NH 4 + retention. This study, for the first time, screened BTHC as an excellent material for mitigating NH 3 volatilization from paddy fields. The reduced NH 3 volatilization loss might contribute to increased soil N retention and plant N use efficiency.
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