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Phosphorus (P) is limiting nutrient in soil system. The P availability in soil strongly depend on Iron (Fe) speciation. Colloidal iron phosphate (FePO4coll) is an important phosphorus (P) fraction in soil solution that carry P from soil to water bodies. This study tested the hypothesis that phytate exudation by Pteris vittata (P. vittata) can dissolve FePO4coll that leads to release of P and Fe. The phytate exudation in P. vittata increased from 434−2136 mg kg−1 as the FePO4coll concentration increased from 0−300 mM. The total P in P. vittata tissue increased from 2.88 to 8.28 g kg−1, the trichloroacetic acid P fractions (TCA fractions) were: inorganic P (0.86–5.10 mg g−1), soluble organic P (0.25–0.87 mg g−1), and insoluble organic P (0.16–2.03 mg g−1) which leads to higher biomass as FePO4coll increased from 0−300 mM. The linear regression analysis showed that FePO4 solubilizing activity has a positive correlation with TP, TCA P fractions in P. vittata, TP in growth media, and root exudates. This study shows that phytate exudation dissolved the FePO4coll due to the chelation effect of phytic acid on Fe, and due to the high Fe–P solubilizing activity in root exudates of P. vittata.

Background Rice paddy wetlands may serve as a nutrient source or sink in agricultural ecosystems. However, the pattern of nutrient loss on a watershed scale is not clear. A year-round on-site observation study based on 6-h intervals was conducted. Rainfall, temperature, runoff nutrient concentrations, and adjacent stream water samples were automatically monitored to uncover the temporal changes in the runoff losses of the predominant nutrient proxies (total N and total P) from a typical rice-planting area (120 ha) in the Yangtze river delta region of China. Results A high total N concentration in the rice-planting area was observed during the rice-planting season; however, significant fluctuation in the total P was evident throughout the year. The Δtotal N (drainage minus stream) parameter showed negative values with a mean of −0.25 mg L−1, while Δtotal P showed positive values with a mean of 0.06 mg L−1. The annual average N and P runoff from paddy field were 11.6 kg ha−1 and 1.5 kg ha−1, respectively. The window phases for the total N loss were mainly concentrated in the rice-growing season. However, the window phase for the total P loss was more dispersive throughout the year. No apparent relationships were found between rainfall and N and P concentrations by self-organizing map analysis. Conclusions The high-resolution monitoring, in this study, suggested that nutrient loss loading rather than nutrient concentration was strongly related to surface runoff Therefore, fertilization before high-intensity rainfall should be avoided to mitigate the nutrient runoff losses and maintain the rice wetland eco-function.

Background Trace amounts of nitrogen and phosphorus can easily trigger eutrophication damage in surface water, while cost-effective adsorption treatment is in prospect for clearing these pollutants simultaneously and efficiently. In this study, engineered adsorbents decorated with ZnFe-LDH by alkaline coprecipitation (3-6 mm, with modified ceramsite as CZF and modified volcanic rock as VZF) were prepared for NH 4 + and H 2 PO 4 - co-adsorption from aqueous solutions.Results Coexisting ions showed great effects on phosphate adsorption, especially Ca 2+ and CO 3 2- , and humic acid exhibited only a limited shielding impact on co-adsorption properties. Though comprehensive tests presented that the maximum captured amount of ammonium and phosphate occurred at pH 7, the isotherm and kinetic results suggest that two adsorbents preferentially adsorbed each pollutant. Specifically, the maximum uptake quantity of NH 4 + (15.55 mg-N g -1 ) and H 2 PO 4 - (11.21 mg-P g -1 ) were achieved by VZF and CZF, respectively, and controlled by physisorption and chemisorption distinctively, revealing that contaminants were cleared in disparate ways. Performances of seven consecutive adsorption/desorption cycles using 5% NaOH regenerant suggested that CZF retained 71.9% of PO 4 - removal efficiency, and VZF retained 47.9% of the NH 4 + adsorption rate, implying the strong reusability of ZnFe-LDH-modified adsorbents. A dynamic study has assessed that with 1 kg of combined modified adsorbents, approximately 527 L of polluted runoff flow could be continuously treated to below the National limits within one adsorption cycle.Conclusion Comparing with other parallel adsorbents, ZnFe-LDH-modified adsorbent is promising in eliminating eutrophication due to their superior capacity, stability, renewability, and non-toxicity.

We are still challenged to fully understand to what extent controlling irrigation inputs is important for limiting phosphorus (P) losses from paddy soils and how this affects the contribution of dissolved P (DP), particulate P (PP), and colloidal P (Pcoll) fractions in P losses. For this investigation, an internet-based smart irrigation system was developed to precisely implement different irrigation scenarios––flooding irrigation (FI) and two water-saving irrigation (WSI) scenarios of intermittent (II) and controlled irrigation (CI). A simulation experiment was conducted and the concentrations of total P (TP), DP, PP, and Pcoll released to floodwater (FW) and leachate (LW) were determined during a rice season after the addition of different P forms (chemical fertilizer (CP), biogas slurry (BP), and manure (MP)) at a rate of 40 kg P·ha−1. The results revealed that the CI scenario effectively decreased P losses in FW (∼51%) and LW (∼63%) with a positive WSI ratio (39.1%), while II reduced it in FW by ∼11% and in LW by ∼27% with a WSI ratio of 11.0% compared with FI. The BP and MP additions caused a higher risk of P losses than CP under FI, with lower risk under WSI. DP largely contributed to P losses (FW: 30%–71%; LW: 42%–66%); however, more PP was released to FW under II (37%–54% of TP). The Pcoll (FW: 5%–23% and LW: 6%–24%) was more sensitive to release at initial periods after fertilization on account PP. This work provides a promising approach to timely control irrigation inputs, which could limit P losses from paddy soil; however, there remains a need to assess and generalize our initial evidence at field scales.

Modified ceramsite has been widely reported as a P adsorbent in wastewater treatments; however, its performance in removing P from agricultural runoff is unclear. A new low-cost ceramsite is modified in this study applying Zn/Fe-layered double hydroxides (LDHs; CZF) to investigate its practicality in treating P-polluted agricultural runoff. The results revealed that the CZF has a theoretical maximum P-adsorption capacity of 11.2 mg-P g−1. Various factors in P-adsorption performance followed the order of pH value (−22.6) > Ca2+ (21.5) > Mg2+ (19.9) > CO32− (−14.5) > SO42− (−13.3) > humic acid (−10.7) > NO3− (−5.57) > Cl− (−2.93) > Na+ (0.32) > NH4+ (0.19). Through iterant adsorption/regeneration, CZF cyclically reduced P concentration in agricultural runoff from 0.58 mg-P L−1 to below 0.1 mg-P L−1 under the preferred parameters of 20 g L−1 dosage, 2 h adsorption time at pH 7.2, and 1 h desorption time at pH 13.0. The treated water has low luminescence toxicity as well as low leaching risks of embedded Zn and adsorbed P in the spent CZF. Additionally, the CZF packing module significantly decreased P in agricultural runoff within four weeks. The CZF dosage and hydraulic retention time (HRT) prolonged the effective operating time (EOT) for P removal, whereas the total organic carbon (TOC) concentration had a negative impact. The cost of CZF for removing P from agricultural runoff was as low as 0.45 ¥ m−3. Overall, this research indicates that using CZF as the adsorption substrate in a ditch purification system is an effective approach for mitigating P pollution in agricultural runoff.