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1. Wastewater‐recovered struvite evaluation as a fertilizer‐phosphorus source for corn in eastern Arkansas

   https://doi.org/10.1002/agj2.21162  

   Omidire, Niyi S.; Brye, Kristofor R.; English, Leah; Popp, Jennie; Kekedy‐Nagy, Laszlo; Greenlee, Lauren; Roberts, Trenton L.; Gbur, Edward E. (July 2022, Agronomy Journal)

   The perception of wastewater as a resource rather than a pollutant has not been well emphasized. Phosphorus (P) can be precipitated from wastewaters as the mineral struvite (MgNH4PO4·6H2O), which can be a potential sustainable alternative to the limited, rock phosphate (RP)-dependent, traditional fertilizer-P sources for agricultural production. This field study evaluated the effects of electrochemically precipitated struvite (ECST) and chemically precipitated struvite (CPST) compared to other conventional fertilizer-P materials [monoammonium phosphate (MAP), diammonium phosphate (DAP), triple superphosphate (TSP), and RP] on corn (Zea mays L.) response in two consecutive growing seasons in a P-deficient, silt-loam soil (Aquic Fraglossudalfs) in eastern Arkansas. Averaged across years, corn yield was numerically largest from ECST (12.9 Mg ha–1), which differed (P < 0.05) from all other treatments and was numerically smallest from DAP (10.1 Mg ha–1), which was similar to MAP (10.7 Mg ha–1), CPST (10.3 Mg ha–1), and RP (10.3 Mg ha–1). Corn yield and kernel P uptake from ECST were at least 1.2 times greater (P < 0.05) than from CPST, TSP, DAP, and RP. Yield from ECST was 1.2 times greater (P < 0.05) than from MAP. A partial budget analysis showed that, across both years, fertilizer-P treatment net revenues for ECST were greater than those associated with the other fertilizer-P sources. Results demonstrated that wastewater-recovered struvite materials have the potential to be a sustainable source of P for corn production in P-deficient, silt-loam soil from both a technical and economic perspective. 

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2. Assessment of Struvite as an Alternative Sources of Fertilizer-Phosphorus for Flood-Irrigated Rice

   https://doi.org/10.3390/su14159621  

   Brye, Kristofor R.; Omidire, Niyi S.; English, Leah; Parajuli, Ranjan; Kekedy-Nagy, Laszlo; Sultana, Ruhi; Popp, Jennie; Thoma, Greg; Roberts, Trenton L.; Greenlee, Lauren F. (August 2022, Sustainability)

   Phosphorus (P) recovery from wastewaters as struvite (MgNH4PO4·6H2O) may be a viable alternative fertilizer-P source for agriculture. The objective of this study was to evaluate the economic and environmental implications of struvite as a fertilizer-P source for flood-irrigated rice (Oryza sativa) relative to other commonly used commercially available fertilizer-P sources. A field study was conducted in 2019 and 2020 to evaluate the effects of wastewater-recovered struvite (chemically precipitated struvite (CPST) and electrochemically precipitated struvite (ECST)) on rice yield response in a P-deficient, silt–loam soil in eastern Arkansas relative to triple superphosphate, monoammonium and diammonium phosphate, and rock phosphate. A life cycle assessment methodology was used to estimate the global warming potentials associated with rice produced with the various fertilizer-P sources. Life cycle inventory data were based on the field trials conducted with and without struvite application for both years. A partial budget analysis showed that, across both years, net revenues for ECST and CPST were 1.4 to 26.8% lower than those associated with the other fertilizer-P sources. The estimated greenhouse gas emissions varied between 0.58 and 0.70 kg CO2 eq kg rice−1 from CPST and between 0.56 and 0.81 kg CO2 eq kg rice−1 from ECST in 2019 and 2020, respectively, which were numerically similar to those for the other fertilizer-P sources in 2019 and 2020. The similar rice responses compared to commercially available fertilizer-P sources suggest that wastewater-recovered struvite materials might be an alternative fertilizer-P-source option for flood-irrigated rice production if struvite can become price-competitive to other fertilizer-P sources. 

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3. Phosphorus budgets of intensively managed row crops at a long‐term agroecosystem research site in the upper US Midwest

   https://doi.org/10.1002/jeq2.70000  

   Hussain, Mir_Zaman; Hamilton, Stephen_K; Basso, Bruno; Robertson, G_Philip (February 2025, Journal of Environmental Quality)

   Abstract Phosphorus (P) budgets for cropping systems provide insights for keeping soil P at optimal levels for crops while avoiding excess inputs. We quantified 12 years of P inputs (fertilizer and atmospheric deposition) and outputs (harvest and leaching losses) for replicated maize (Zea maysL.)—soybean (Glycine maxL.)—wheat (Triticum aestivum) crop rotations under conventional, no‐till, reduced input, and biologically based (organic without compost or manure) management systems at the Kellogg Biological Station LTAR site in southwest Michigan. Conventional, no‐till, and reduced input systems were fertilized between 13 and 50 kg P ha⁻¹depending on year. Soil test phosphorus (STP) was measured at 0‐ to 25‐cm depth every autumn. Leached P was measured as dissolved P in the soil solution sampled beneath the rooting depth and combined with modeled percolation. Fertilization and harvest were the predominant P fluxes in the fertilized systems, whereas only harvest dominated P flux in the unfertilized organic system. Leaching losses were minor terms in the budgets, but leachate concentrations were nevertheless close to the range of concern for downstream eutrophication. Over the 12‐year study period, the organic system exhibited a negative P balance (−82.0 kg P ha⁻¹), coinciding with suboptimal STP levels, suggesting a need for P supplementation. In contrast, the fertilized systems showed positive P balances (mean: 70.1 kg P ha⁻¹) with STP levels well above agronomic optima. Results underscore the importance of tailored P management strategies to sustain crop productivity while mitigating environmental impacts. 

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4. Cotton Response to Foliar Potassium Application in South Texas Dryland

   https://doi.org/10.3390/agronomy14102422  

   Kommineni, Varshith; Bhandari, Ammar B; Schuster, Greta; Nelson, Shad D (October 2024, Agronomy)

   Potassium (K) deficiency is common in cotton (Gossypium hirsutum L.)-growing areas. This study aims to investigate the effects of different rates of foliar K fertilizer application on three cotton varieties: NG 5711 B3XF (V1), PHY 480 W3FE (V2), and FM 1953GLTP (V3). Potassium fertilizer was dissolved in water and was foliar-applied at 34, 50, and 67 kg ha−1. Cotton plant height (CH) and canopy width (CW) were monitored throughout the growing season. The results showed that foliar K fertilizer application significantly impacted the CH and CW in dry years. Although insignificant, the cotton lint yield increased by 15% and 20% with 34 and 50 kg ha−1 in 2020 and by 9% and 7% with 50 and 67 kg ha−1 in 2021, indicating the potential for improved lint yield with foliar K application in rainfed production systems. Similarly, variety V3 had significantly greater lint and seed yields than V1 in 2020. The average lint yield among the varieties was 32%, and the seed yield was 27% greater in 2020 than in 2021. The cotton fiber color grade was significantly greater at 50 kg ha−1 in 2020 and 67 kg ha−1 in 2021. Cotton variety significantly affected color grade, uniformity, staple length, Col, RD, and Col-b contents in 2020 and 2021. The results suggest that foliar K application can enhance cotton production in rainfed production systems. However, more research is required to quantify varietal and foliar K application rates for improved lint yield and quality. 

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5. Recovery of struvite for organic production: Mineral-based magnesium supplementation and pH elevation

   https://doi.org/10.1016/j.jclepro.2024.142244  

   Iftikhar, Aysha; Tao, Wendong (May 2024, Journal of Cleaner Production)

   Phosphate in wastewater can be recovered in the form of struvite crystals for use as slow-release fertilizer. Currently, struvite recovery often requires supplementing magnesium ions and raising pH with chemicals, making the recovered struvite unfavorable for organic production. In an effort for cleaner production, this study developed a versatile approach employing two mineral products in variable combinations for optimal supplementation of magnesium and elevation of pH. Magnesite, a mineral of MgCO3, was ground and calcined without use of any catalysts. The magnesite calcined under the optimum conditions (800 ◦C for 30 min) can be dissolved in near-neutral filtrate of sludge digestate to supplement magnesium and raise pH for effective struvite formation. The OMRI-listed Epsom salts (MgSO4•7H2O), mineral-based water-soluble commercial products, can be used to supplement magnesium without changing pH of alkaline wastewater. Six-hour batch operation of an airlift crystallizer removed 85.7% and 94.7% of phosphate in hydrolyzed human urine when magnesium was amended to 1.2 × molar concentration of phosphate with calcined magnesite and an OMRI-listed Epsom salt, respectively. More than 98% of phosphate was removed from filtrate of sludge digestate in 3-h batch operation using calcined magnesite to raise pH to 8.5 and the Epsom salt for further magnesium supplementation. Struvite accounted for 85.7%, 90.5%, and 81.5% of the crystals recovered from urine with calcined magnesite, urine with Epsom salt, and filtrate with both mineral products, respectively. The material and energy costs of this green process were estimated to be $0.16/kg struvite from urine with calcined magnesite, $1.37/kg struvite from urine with Epsom salt, and $0.94/kg struvite from filtrate with both mineral products. This study proved the technical and economic feasibility of chemical-free magnesium supplementation and pH elevation, making the recovered struvite potentially certifiable for organic production. 

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