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【Objective】Efficient irrigation management is critical for optimizing soil nitrogen dynamics and its uptake by rice in paddy fields. This paper investigates the effects of irrigation methods on the dynamics of ammonium nitrogen (NH4⁺-N), nitrate nitrogen (NO3--N) and alkali-hydrolysable nitrogen (AN) across the soil profiles, in attempts to provide an optimal irrigation strategy to sustain rice production in paddy fields.【Method】The field experiment compared three irrigation methods: shallow irrigation (QS) keeping a thin water layer on the soil surface; shallow irrigation with the root-zone soil water content being controlled at 80% of saturated water content (QSG), and deep irrigation keeping a deep water layer on the soil surface with the root-zone soil water content controlled at 80% of saturated water content (SSG). During the experiment, we measured the contents and transformation of NH4+-N, NO3--N and AN at different growing stages along the soil profile. Further measurements were made 1, 3, 5 and 7 days after nitrogen fertilization.【Result】Nitrogen content decreased as crop grew and soil deepened in all three irrigation methods. Compared with other treatments, QSG significantly increased NH4+-N, NO3--N, and AN in the 0-20 cm soil layer. Compared with QS and SSG, QSG increased the contents of NH4+-N, NO3--N and AN in the 0-10 cm soil layer by 13.91%-133.26%, 26.11%-273.75% and 2.8%-13.9%, respectively. Applying yellow humic acid significantly increased NH4+-N in the topsoil initially. However, the subsequent leaching of NH4+-N increased NO3--N content in the subsoil. The change in AN in nitrogen transformation provides a nitrogen source to the crop.【Conclusion】Shallow irrigation combined with the root-zone soil water content controlled at 80% of the saturated water content is the optimal irrigation strategy for paddy fields. Controlling the upper and lower irrigation limits can increase nitrogen retention. This will help optimize fertilizer management, sustainably improve rice yield in paddy fields.

The non-treated wastewater from residential areas contains high concentrations of ammonium-nitrogen (NH4+-N). When discharged into the drainage water system, it deteriorates the water quality in urban rivers. This study used two types of materials to form eco-bags, using activated zeolite bead (AZB) and alkaline pretreated straw (APS), in geotextile bags for easy recovery and reuse. The AZB and APS provided the breeding habitat for the microorganisms that promoted biofilm formation on their surface. The immobilization of engineered denitrification microorganisms facilitated the removal of NH4+-N from the urban river water. The NH4+-N removal in the AZB and APS bags were in the range of 64–73%, and 56–61%, respectively, while the chemical oxygen demand (COD) removal in the AZB and APS bags ranged from 33–36%, and 30–31%, respectively. In addition, as evident from DNA and microbial community analysis, the microorganisms demonstrated a greater proclivity to grow and proliferate on the surface of AZB and APS and improved the water quality of urban rivers.

The functionalized biochar was assembled on modified zeolite to synthesize a novel modified composite adsorbent. The latter was applied to simultaneous adsorption of ammonium and nitrate. The Box–Behnken design (BBD) in response surface methodology (RSM) was applied to optimize the parameters, which included ratio of raw materials, adsorbent dose, pH, and temperature. The chemical functional groups were determined by Fourier transform infrared adsorption (FT-IR). Stronger absorption peaks of amine groups indicated that the functionalized adsorbent could enhance the adsorption of contaminants. The composite adsorbent effectively increased NH4+ and NO3− adsorption capacity by porous structure recombination, change of surface morphology and further exposure of surface functional groups. The kinetic results indicate that the adsorption of both NH4+ and NO3− follows a pseudo-second-order nonlinear model. The Langmuir isotherm model fitted well the experimental data with a maximum adsorption capacity of 24.45 mg/g for nitrate and 24.63 mg/g for ammonium at 25°C. Nitrate was absorbed by electrostatic interactions with grafted amine groups and, in contrast, the ammonium adsorption was mainly related to ion exchange with Na+. The adsorption process of both nitrate and ammonium were spontaneous and exothermic. The adsorbents can be regenerated effectively in NaCl and NaOH mixed solutions, and the desorbed adsorbents are of high reusability and can be applied effectively at least for five cycles. Therefore, it has a great potential for nitrate and ammonium simultaneous removal from water environment.

To remove the extra ammonium-nitrogen (NH 3 -N) and phosphorus (P) from contaminated water, a novel granular adsorbent (GAZCA) was fabricated with zeolite powders and Al–Mn binary oxide (AMBO) via the compression method. The SEM-EDS and mapping and XRD results illustrated the microstructure of GAZCA: the homogeneous aggregation of zeolite and AMBO nanoparticles with their crystal integrity and the uniform distribution of Al/Mn/Si/O elements on the adsorbent surface. FTIR and XPS results demonstrated the existence of impregnated sodium cations and hydroxyl groups, which were responsible for the removal of NH 3 -N and P, respectively. The results of BET analysis and compression tests exhibited a high surface area (14.4 m 2 /g) and a satisfactory mechanical strength of GAZCA. Kinetic adsorption results showed a fast adsorption rate for NH 3 -N and P, and mutual inference was not observed between the adsorption kinetics of NH 3 -N and P in the bi-component system. The adsorption isotherm results demonstrated that the maximum adsorption capacities of NH 3 -N and P were calculated as 12.9 mg/g and 9.3 mg/g via the Langmuir model, respectively. In the bi-component system, the adsorption capacities of NH 3 -N and P were maintained at low and moderate concentrations and decreased at high concentrations due to the blockage effects of NH 4 MnPO 4 ·H 2 O precipitates. The removal efficiency of NH 3 -N could be maintained in a wide pH range of 4~10, while P adsorption was inhibited at alkali conditions. The solution of sodium bicarbonate (0.4 M) was used for the regeneration of saturated adsorbents, which permitted GAZCA to keep 98% and 78% of its adsorption capacity for NH 3 -N and P even after three regeneration and reuse cycles. Dynamic experiments illustrated that a satisfactory performance was obtained for the in situ treatment of simulated N- and P-contaminated water by using a column reactor packed with GAZCA, thus further confirming its great potential for the control of eutrophication.

The origin of ammonium-nitrogen in Indonesian coastal groundwater has not been intensively examined, meanwhile the elevated concentration remains a concern. This research aims at tracing the potential sources of ammonium-nitrogen in the groundwater of Indramayu, Indonesia where groundwater is vital for livelihood. From results, a combined examination of nitrogen isotope, coliform bacteria, land-use, and geology confirmed the natural and anthropogenic origins of ammonium-nitrogen in the groundwater. In the brackish-water aquaculture region, groundwater has δ15NNH4 values from +1.8 to +4.8‰ signifying that ammonium-nitrogen is derived from mineralization of organic nitrogen to ammonium. Furthermore, ammonium has a significantly positive relationship with sodium indicating the exchangeable ammonium is mobilized to groundwater via cation exchange. Meanwhile ammonium-nitrogen from anthropogenic waste was detected in agricultural and residential region. The groundwater has more varied δ15NNH4 values, from −2.9 to +16.1‰, which implies attenuation of ammonium-nitrogen from several sources namely manure, mineral fertilizer, sewage, and pit latrines. Also, the presence of E. coli confirms the indication of human and animal waste contamination. However, since ammonium has no relationship with sodium, cation exchange is not feasible and ammonium-nitrogen flows into the groundwater from anthropogenic sources along with liquid wastes.

This study investigated the effects of nitrogen form on root activity and nitrogen uptake kinetics of Camellia oleifera Abel. seedlings, providing a scientific basis for improving nitrogen use efficiency and scientific fertilization in C. oleifera production. Taking one-year-old C. oleifera cultivar ‘Xianglin 27’ seedlings as subjects, 8 mmol·L−1 of nitrogen in varied forms (NO3−:NH4+ = 0:0, 10:0, 7:3, 5:5, 3:7, 0:10) was applied in this study as the treatment conditions to investigate the effects of different nitrogen forms on root activity and nitrogen uptake kinetics in C. oleifera seedlings. Comparing the performance of nutrient solutions with different NO3−:NH4+ ratios, the results showed that a mixed nitrogen source improved the root activity of C. oleifera seedlings based on total absorption area, active absorption area, active absorption area ratio, specific surface area, and active specific surface area. When NO3−:NH4+ = 5:5, the total absorption area and active absorption area of the seedling roots reached the maximum. The results of uptake kinetic parameters showed that Vmax NH4+ > Vmax NO3− and Km NO3− > Km NH4+, indicating that the uptake potential of ammonium–nitrogen by C. oleifera seedlings is greater than that of nitrate–nitrogen. The conclusion was that compared to either ammonium– or nitrate–nitrogen, the mixed nitrogen source was better for promoting the root activity of C. oleifera seedlings, and the best nitrate/ammonium ratio was 5:5.

The decrease in the rate of inflow and outflow of water—and thereby the uptake of plant nutrients as the result of Huanglongbing (HLB or citrus greening)—leads to a decline in overall tree growth and the development of nutrient deficiencies in HLB-affected citrus trees. This study was conducted at the University of Florida, Southwest Florida Research and Education Center (SWFREC) near Immokalee, FL from January 2017 through December 2019. The objective of the study was to determine the effect of rootstocks, nutrient type, rate, and frequency of applications on leaf area index (LAI), water relations (stomatal conductance [gs], stem water potential [Ψw], and sap flow), soil nutrient accumulation, and dynamics under HLB-affected citrus trees. The experiment was arranged in a split-split plot design that consisted of two types of rootstocks, three nitrogen (N) rates, three soil-applied secondary macronutrients, and an untreated control replicated four times. LAI significantly increased in response to the secondary macronutrients compared with uncontrolled trees. A significantly greater gs, and thus a decline in Ψw, was a manifestation of higher sap flow per unit LA (leaf area) and moisture stress for trees budded on Swingle (Swc) than Cleopatra (Cleo) rootstocks, respectively. The hourly sap flow showed significantly less water consumption per unit LA for trees that received a full dose of Ca or Mg nutrition than Ca + Mg treated and untreated control trees. The soil nutrient concentrations were consistently higher in the topmost soil depth (0–15 cm) than the two lower soil depths (15–30 cm, 30–45 cm). Mobile nutrients: soil nitrate–nitrogen (NO3-N) and Mg2+ Mg2+, Mn2+, Zn2+, and B leached to the lower soil (15–30 cm) depth during the summer season. However, the multiple split applications of N as Best Management Practices (BMPs) and optimum irrigation scheduling based on reference evapotranspiration (ETo) maintained soil available N (ammonium nitrogen [NH4-N] and NO3-N) below 4.0 mg kg−1, which was a magnitude 2.0–4.0× less than the conventional N applications. Soil NH4-N and NO3-N leached to the two lower soil depths during the rainy summer season only when trees received the highest N rate (280 kg ha−1), suggesting a lower citrus N requirement. Therefore, 224 kg ha−1 N coupled with a full Ca or Mg dose could be the recommended rate for HLB-affected citrus trees.

● Column experiments with an inclined slope were applied to simulate NH 4-N transport. ● The transport of NH 4-N was simulated via HYDRUS-2D. ● The chemical non-equilibrium model well described the transport process. ● The lateral flow led to the preferential loss of surface NH 4-N. ● Flow rate and rainfall intensity affected the adsorption and leaching of NH 4-N. Ion-absorbed rare earth mines, leached in situ, retain a large amount of ammonium nitrogen (NH 4-N) that continuously releases into the surrounding environments. However, quantitative descriptions and predictions of the transport of NH 4-N across mining area with hill slopes are not fully established. Here, laboratory column experiments were designed with an inclined slope (a sand box) to examine the spatial temporal transport of NH 4-N in soils collected from the ionic rare earth elements (REE) mining area. An HYDRUS-2D model simulation of the experimental data over time showed that soils had a strong adsorption capacity toward NH 4-N. Chemical non-equilibrium model (CNEM) could well simulate the transport of NH 4-N through the soil-packed columns. The simulation of the transport-adsorption processes at three flow rates of leaching agents revealed that low flow rate enabled a longer residence time and an increased NH 4-N adsorption, but reduced the extraction efficiency for REE. During the subsequent rainwater washing process, the presence of slope resulted in the leaching of NH 4-N on the surface of the slope, while the leaching of NH 4-N deep inside the column was inhibited. Furthermore, the high-intensity rainfall significantly increased the leaching, highlighting the importance of considering the impact of extreme weather conditions during the leaching process. Overall, our study advances the understanding of the transport of NH 4-N in mining area with hills, the impact of flow rates of leaching agents and precipitation intensities, and presents as a feasible modeling method to evaluate the environmental risks of NH 4-N pollution during and post REE in situ mining activities.

Purpose Both an optimization statistical model and a chemical thermodynamic equilibrium computer model were proposed to develop, improve, and optimize struvite precipitation process. Methods and result The NH 4 -N in synthetically prepared wastewater was removed using struvite precipitation technology. A quadratic statistical modeling, response surface methodology (RSM), was applied to investigate the improvement availability for high-level removal of ammonium-nitrogen by struvite precipitation. Then, a chemical equilibrium model, Visual MINTEQ, was used to calculate the equilibrium speciation and saturation index in aqueous solution and solid phases. In addition, the availability of Mg 2+ , NH 4 + , and PO 4 3− ions as a function of pH was modeled. The predicted and experimental data indicated that the two models might describe the experiments well. The results showed that pH was an important parameter in ammonium-nitrogen removals at low initial NH 4 -N concentration. P/N molar ratio was a limiting factor on struvite precipitation at high initial NH 4 -N concentration. Conclusion Within the ranges of the investigated factors, Visual MINTEQ program can be proposed to predetermine the concentration of ammonium precipitated by struvite, and RSM can be used to predict total NH 4 -N removal by both struvite precipitation and ammonia volatilization from our investigated system operated at high pH and opened to the atmosphere.

Coagulation can effectively recover substances from wastewater; however, there is a lack of efficient coagulants for simultaneous recovery of organic matter, nitrogen, and phosphorus. We prepared a composite polysilicate metal (CSM) flocculant by combining Fe3+ and Mg2+ ions in polysilicic acid (PSiA). According to the results of scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR), the CSM exhibited a larger amorphous phase along with new compounds, including Mg3Fe2(SiO4)3 and hydroxyl metals. The CSM demonstrated a higher coagulation efficiency than PSiA and polymeric ferric sulfate, particularly for PO43−-P and NH4+-N removal. The metal/silicate molar ratio substantially influenced the structure and composition of the CSM, along with the coagulation efficiency, with an optimal ratio of 3:1. Additionally, we proposed a novel preparation strategy to achieve an optimum CSM basicity (B*) for coagulation by adjusting the initial pH of PSiA (pHInitial) without adding an alkali agent. The results demonstrated that the optimum B* can be obtained by adjusting pHInitial to 0.5 or 1. The overall optimum coagulation performance for the simultaneous removal of organic matter, PO43−P, and NH4+-N from wastewater was 68.5%, 99%, and 17.5%, respectively. This study provides a feasible approach for synchronous pollutant recovery from wastewater.