Abstract Selecting the most effective phosphorus (P) fertilizer source is essential for maximizing crop yields. However, there is little information to guide the choice between the widely used soluble granular sources: ammonium phosphates and superphosphates. The aims of this study were to examine whether there are differences in wheat ( Triticum aestivum L.) grain yield response to ammonium phosphate and superphosphate fertilizers in field conditions, and if these differences relate to diffusion of P from fertilizer granules. Two field experiments were conducted on acidic gravelly soils in Western Australia where P deficiency occurs to compare wheat growth response to P applied as monoammonium phosphate (MAP), diammonium phosphate (DAP), single superphosphate (SSP) or double superphosphate (DSP). A diffusion study was conducted to quantify the effect of P source on P diffusion from the fertilizer granules. Grain yield with MAP was up to 18% higher than SSP at one field experiment, and 10% higher than DSP at the other. The extent of P diffusion around the granules in the diffusion study showed the same order as the wheat growth response in the field experiments. The difference among P sources is attributed to greater precipitation or adsorption of phosphate near the granule with superphosphates, likely due to the presence of calcium (Ca) in the fertilizer. Our results reinforce the continued use of MAP as a source of P for crops grown on the acidic, gravelly, P responsive soils in Western Australia.

This study explores a mechanochemical (MC) technique to synthesize a slow-release fertilizer containing zinc (Zn), molybdenum (Mo) and minor amounts of sulfur (S). The reactants ZnO, MoO3, and ZnSO4.7H2O were milled in a ball mill with a two-step operation. The two metal oxide reactants were initially milled for 1 h to activate the oxides followed by milling with ZnSO4.7H2O or minor water for another 2 or 4 h to accelerate the formation of layered zinc molybdenum oxide-sulfate. The products were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA), confirming the successful synthesis of a product with low Mo solubility containing mostly Zn and Mo. The product milled with ZnSO4.7H2O formed a clear layered structure which further slowed the release of Mo. The slow-release character of the product with 1 h + 2 h milling was observed in a column dissolution study; the solubility of Mo was less than half the product made without the second milling step. Column dissolution studies demonstrate the material's biphasic release behaviour, highlighting its potential for sustainable agriculture as a slow-release fertilizer. Furthermore, the products maintained lower solubility across a wider pH range compared to the reactants.

The use of petroleum-based coatings in controlled-release fertilizers (CRFs) raises environmental concerns and it is unclear if, and to what extent, CRFs can improve P use efficiency. This study explored the synthesis of bio-based polyurethane (PU) fertilizer coatings from castor oil and liquefied wheat stover and their effect on P use efficiency. The castor oil-based PU effectively delayed P release, achieving a 75 % release time (longevity) of 209 d at a 6 % coating rate on monoammonium phosphate (MAP). In contrast, wheat stover-based PU was less effective, likely due to incomplete polymerization. Three coated MAPs with longevities of 7, 37 and 209 d (7d-, 37d-, and 209d-MAP) were tested in an incubation trial using three contrasting soils and in a pot trial using two of those soils. The 37d-MAP reduced P fixation and increased wheat P uptake by 50 % compared to uncoated MAP in a highly P-fixing Oxisol, but had no effect on biomass, likely due to early P deficiency. The CRFs did not reduce P fixation in the other two soils with lower P-fixing capacities, and no improvement in P uptake was observed. The 209d-MAP performed poorly in both soils in the pot trial, as most P was still retained in the granule after 70 d. Overall, these results indicate that CRFs with suitable release rate can enhance P fertilizer efficiency in highly P-fixing soils, but effects are likely to be small or non-existent in most other soils.

Molybdenum (Mo) is an essential plant micronutrient, required only in small amounts. Nonetheless, Mo deficiencies in crop production are not uncommon, and to avoid yield loss, fertilizers enriched with soluble Mo compounds are often supplied. However, the application of soluble Mo compounds is linked to low Mo use efficiencies due to fast Mo fixation in acid soils and leaching in sandy soils. This study explored sparingly soluble powellite (CaMoO4) in Mo-enriched granular fertilizers to regulate the release of Mo over time and supply available Mo throughout a crop's growth period. Powellite was prepared via a simple precipitation reaction, and macronutrient carriers were cocompacted to pellets with either powellite or conventional soluble ammonium molybdate (amMo). In column dissolution experiments, powellite-based fertilizers consistently released Mo more slowly than corresponding amMo-based fertilizers, with the slow release notably more pronounced for powellite embedded in carriers with high content and solubility of Ca. A pot trial with chickpea demonstrated that powellite-based fertilizers can minimize Mo leaching in well-drained conditions in comparison with amMo-based fertilizers, while still acting as an adequate Mo source for crops. These results demonstrate how a desired Mo release can be obtained by selecting a suitable powellite macronutrient carrier, highlighting the potential of powellite-based Mo fertilizers for more efficient Mo use in crop production.

Widespread per- and poly-fluoroalkyl substances (PFAS) contamination in water, sediments and soils has driven demand for scalable and cost-effective treatments suitable for application across a range of ∑PFAS concentrations from ng/L to mg/L. One promising class of treatment technology is based on PFAS accumulation at the surface of air bubbles. In this study, hydrodynamic cavitation induced by high shear mixing generated colloidal gas aphrons (CGAs) made of different surfactants (cationic, anionic and non-ionic) to facilitate separation of PFAS differing in carbon–fluorine chain length, head group and charge. Separation efficiency was evaluated for a 600 µg/L ∑PFAS mixture of 6 PFAS each at 100 µg/L, and also for a solution spiked to 1 mg/L ∑PFAS with an aqueous film forming foam (AFFF) mixture. The choice of surfactant produced CGAs with different bubble sizes and surface properties; the non-ionic surfactant produced significantly smaller bubbles, while the cationic and anionic surfactant varied principally by charge. The ∑PFAS separation efficiency varied from < 30 % to 86 % using different surfactants after a 30 s process. The non-ionic surfactant was most effective overall, and the cationic surfactant was most efficient for short-chain PFAS, and those with the carboxylic head group due to surface charge compatibility. Zwitterionic precursor PFAS and perfluoroalkyl sulfonic acids species tested in this study were removed with > 90 % efficiency when anionic and non-ionic surfactants formed the CGAs, while short-chain perfluoroalkyl acids PFAA were removed similarly effectively by cationic surfactant-derived CGAs. While separation efficiencies were lower than the > 95 % ∑PFAS reductions reported elsewhere, the effect was achieved with a treatment time of 30 s, in contrast to the significantly longer treatment cycles applied in other studies.

Molybdenum (Mo) is an essential micronutrient required for plant growth but is prone to leaching from neutral and alkaline soils. The use of slow-release Mo sources could potentially reduce leaching losses from soils and increase crop yields. In this study, we assessed mechanochemistry as a green method to produce slow-release Mo sources. Molybdenum compounds (MoO3 or (NH4)6Mo7O24·4H2O) were mechanochemically (MC) treated with ZnO to synthesize compounds with a Mo content of 1–36

Per- and poly-fluoroalkyl substances (PFASs) are contaminants of emerging concern, yet the understanding of factors that control their leaching and release from contaminated soils remains limited. This study aimed to investigate the impact of dissolved organic carbon (DOC) on the release of PFASs—specifically, perfluorohexane sulfonate (PFHxS), perfluorooctane sulfonate (PFOS), and perfluorooctanoic acid (PFOA)—from soils contaminated by aqueous film forming foam (AFFF)-. Batch aqueous leaching experiments were conducted on AFFF-contaminated soils under alkaline solution conditions (pH 9.5, 10.5, and 12) as it enhances leaching of both PFAS and DOC. Leaching of PFOS was significantly increased under alkaline conditions. Although the leaching of PFAS generally increased with pH, PFOS appeared to be more retained under the very alkaline pH conditions used in this study. At the same solution pH, leaching of PFOS and DOC was less in Ca(OH)2 than in NaOH. The retention of PFOS under these conditions may be attributable to the shielding of the negative charge of the soil components and colloids (e.g., DOC and clay minerals) in the leachates and/or the screening of negative charges on head groups of PFOS due to the high concentration of divalent cations. Solution chemistry affected desorption of PFOS more than PFHxS and PFOA. The study highlights that the influence of DOC on PFAS leaching and transport can be very complex, and depends on leachate chemistry (e.g., pH and cation type), PFAS chemistry, the magnitude of PFAS contamination and factors that influence the solid:liquid partitioning of organic carbon in soil.

The diversity, persistence, bioaccumulation potential and mobility of per- or polyfluoroalkyl substances (PFASs) make these contaminants particularly formidable when determining their environmental fate and behaviour.

The susceptibility of surface soil to drying when rainfall is scarce has prompted evaluation of deeper placement (20 cm) of fertilizers within the profile to where soil moisture is more likely to be stored. However, concerns arise regarding potential chemical challenges to P availability in the subsurface. This study examined differences in chemical conditions between the soil surface (0-10 cm) and subsurface (15-25 cm), and investigated the effect on the diffusion and extractability of banded P. Analysis of surface and subsurface samples from 15 sites revealed substantial differences in characteristics that influence P behavior between depths. The phosphorus buffering index (PBI) was largely explained by concentrations of amorphous Al and Fe (hydr)oxides and CaCO3. The measured diffusion distance of P from monoammonium phosphate (MAP) granules was found to be inversely related to PBI. Consequently, significant differences in diffusion distances were typically observed between soil layers characterized by marked PBI variations. The measured diffusion radii were used to calculate the mean P concentrations of surface-banded and deep-banded MAP in a field scenario, which were replicated in a 4-week laboratory incubation. The resulting lability of applied P was determined through isotopic exchange, and although significantly higher P recoveries were measured from the subsurface at two sites where large pH differences existed between depths, no significant differences were measured between depths at all other sites. Hence, the subsurface is not a more hostile zone for deep-placed P. Subsurface fertilizer placement is being tested to improve crop access to fertilizer P. Soil characteristics that influence the behavior of P can differ between the surface and subsurface. Large differences in soil characteristics between depths can affect the distance of P diffusion from granules. The availability of P applied to the subsurface was not consistently different from that applied to the surface. Differences in fixation of added P between depths were only observed at sites with a large difference in pH.

Purpose The application of magnesium (Mg) fertilizer to alleviate Mg deficiency and improve crop yield has gained wide recognition. However, high Mg leaching loss is a growing concern in high rainfall areas, especially in acidic soils. Developing Mg fertilizer with less risk of leaching and adequate Mg supply to crops in a convenient way is worth considering in agricultural production. Methods In this study, five Mg-fortified mono-ammonium phosphate (MAP) fertilizers were produced with anhydrous magnesium sulfate (MgSO 4 ) and dolomite (CaMg(CO 3 ) 2 ) in various ratios. Nutrient solubility, Mg nutrient release, Mg leaching, and agronomic effectiveness under rainfall conditions in an acidic soil were evaluated. Results Addition of the Mg sources to the MAP fertilizer did not affect P solubility of the fertilizer. The MAP fertilizers fortified with both MgSO 4 and dolomite showed an initially fast release of Mg followed by slower release. In a pot experiment with simulated rainfall, the amount of Mg leached significantly decreased with increasing proportion of dolomite in the Mg-fortified fertilizers, which varied from 19.1% for the MgSO 4 treatment to 3.8% for the dolomite treatment. Shoot dry matter yield and Mg concentration of soybean were higher for treatments with Mg-fortified MAP than for MAP-only. Conclusions The use of dual-release Mg sources in macronutrient fertilizers could be a promising strategy to better meet crop Mg demands and effectively reduce Mg leaching losses, especially in sandy soils of high rainfall areas.

Zinc (Zn) is the most commonly found deficient micronutient in agricultural soils worldwide, limiting crop yield and reducing food quality. Zinc-enriched fertilizers have been successfully used to tackle crop Zn deficiency. However, Zn solubility is reduced after addition to phosphate fertilizers due to the formation of sparingly soluble precipitates, decreasing Zn availability to crops. We hypothesized that the availability of Zn in the fertilizer to plants is related to its speciation in the fertilizer. We evaluated a range of ammonium phosphate fertilizers using X-ray absorption near-edge structure and assessed the water-solubility of Zn in the formulations. Four Zn species were identified in these fertilizers, with zinc ammonium phosphate the most abundant one. The speciation of Zn in the fertilizer had little relationship with the water solubility of Zn in the final product. Zinc solubility was driven by fertilizer pH, with lower pH resulting in higher solubility. We concluded that added Zn reacts with the fertilizer matrix to form mainly zinc (ammonium) phosphates, and when the fertilizer is dissolved in water, hopeite controls the solubility. Based on these findings, we tested whether a barrier coating between the P granule and the Zn compound could prevent reaction between Zn and P and thus enhance Zn availability. Indeed, higher Zn uptake was observed in an isotopically labeled fertilizer growth trial when a barrier coating physically separated Zn and P in the fertilizer. In summary, Zn availability to crops can be maximized by decreasing fertilizer pH and separating P and Zn in the granule. Water-soluble Zn content affects the effectiveness of Zn fertilizers. Zn speciation is not a reliable predictor of fertilizer Zn solubility. Zn water solubility is maximized by decreasing granule pH. A coated barrier between the P matrix and Zn coating improved plant Zn uptake.

Per- and poly-fluoroalkyl substances (PFAS) are prevalent environmental contaminants detected in materials such as soils, biosolids, and wastes. Understanding PFAS leaching is crucial for assessing risks associated with leaving impacted material in place, reuse, or disposal. However, there is limited guidance on laboratory methods to measure extent and rate of leaching. This review aims to identify the best methods for assessing PFAS leaching that are reflective of relevant release scenarios. Various methods have been applied to assess PFAS leaching from contaminated materials. The most common are batch leaching methods that simulate particular conditions (e.g. rainfall, landfill), with the intention of providing conservative estimates (worst-case scenarios) of cumulative PFAS release over time. Columns, static leaching, and rainfall simulators are also used to simulate less aggressive field-like conditions. While less common, pan and suction lysimeters have been used to measure PFAS leaching in situ. Most methods use saturated conditions that do not account for the possible influence of air–water interface accumulation and wetting–drying cycles on leaching. A notable gap is the scarcity of data benchmarking laboratory-leached concentrations with real-world PFAS concentrations. Establishing this relationship is crucial for reliable laboratory protocols. This article reviews methods for estimating leaching of PFAS from contaminated materials. Given the variety of methods, selecting those that best simulate assessment objectives is essential. Specific scenarios requiring PFAS leaching assessment, such as leaving materials in place, reuse, and disposal, are discussed. The knowledge gaps presented could be used to improve existing leaching methods for better predictions and understanding of PFAS leachability.

With nearly five decades of per- and polyfluoroalkyl substances (PFASs) being associated with firefighting and industrial activities, these compounds inevitably accumulate in both ground and surface water. PFAS contamination in water has emerged as a significant environmental and public health concern, particularly perfluorooctanesulfonic acid (PFOS), which is often found in higher concentrations compared to other PFAS and has more pronounced adverse health effects. Addressing PFAS contamination requires treating large volumes of water, making technologies that rapidly separate and concentrate PFASs highly favoured. The strong surface activity of PFAS, such as PFOS, enables them to generate colloidal gas aphrons (CGAs) during high shear mixing of their aqueous solutions, where PFASs can be separated and collected as foam. This study aims to evaluate the effectiveness of high shear mixing in separating PFOS from solution, leveraging its accumulation at air-water interfaces. High shear-assisted PFOS separation was tested by varying parameters like rotational speed (4000 to 10,000 rpm), mixing time (30 s to 30 min), and the effect of electrolytes. Results showed greater PFOS separation in the presence of electrolytes, particularly monovalent cations like Na+, compared to divalent cations such as Ca2+, due to the creation of more stable CGAs with smaller sizes. At a mixing rate of 6000 rpm, 85 % of PFOS was removed in 30 s from a highly contaminated PFOS solution (10 mg/L), with over 95 % separation after 5 mixing cycles. While high-shear mixing was efficient in PFOS separation from highly contaminated solutions it was less efficient for low-level contaminated solutions (less than 1 mg/L). These results suggest that hydrodynamic cavitation induced by high-shear mixing seems promising for enhancing the separation of PFOS from heavily contaminated solutions. This technique could serve as a standalone method or be integrated with other PFAS removal technologies to enhance the overall efficiency of PFAS removal from polluted water sources.

IOP journal sustainability science and technology (sus sci tech) in 2024 and beyond: equitable publishing aligned with United Nations' sustainable development goals (SDGs), Jonas Baltrusaitis, Bhavik Bakashi, Katarzyna Chojnacka, Christopher Chuck, Marc-Olivier Coppens, Jacqueline Sophie Edge, Gavin Harper, Benjamin Hsiao, Hao Li, Mark Mba-Wright, Michael McLaughlin, Arpita Nandy, Shu-Yuan Pan (潘述元), Zhe Qiang, Cauê Ribeiro de Oliveira, Malgorzata Swadzba-Kwasny, Meng Wang, Yizhi Xiang, Lizhi Zhang

Micronutrient availability in agriculturalsoils is an importantdriver for crop production, and for mobile micronutrients, slow-releasefertilizers can more efficiently enhance crop nutrition. In this study,for the first time, layered transition metal molybdates (LTMs) areproposed as slow-release fertilizer compounds for the micronutrientsmolybdenum (Mo), zinc (Zn), and copper (Cu). A series of LTMs weresuccessfully prepared in varying synthesis conditions, characterized(inductively coupled plasma optical emission spectrometry, X-ray diffraction,Fourier transform infrared, and scanning electron microscopy), andtested for solubility in water. For three selected LTMs (Zn-Mo,Cu-Mo, and Zn-Cu-Mo), the solubility as a functionof solution pH was determined. The LTMs showed limited stability inacidic conditions. Therefore, co-compaction of LTMs with pH neutralor alkaline macronutrient carriers [muriate of potash (MOP), limestone,rock phosphate] was explored. A Zn-based LTM co-compacted in a MOPcarrier showed a useful slow and almost constant release rate of bothMo and Zn in a column dissolution test (Mo release reaching 32% after72 h), while a reference compacted MOP fertilizer with soluble Moreleased 90% of Mo after 4 h. Hence, a Zn-LTM could prove useful asa slow-release fertilizer or raw material to incorporate into non-acidicmacronutrient fertilizers.

This paper aims to describe the performance of a soil washing plant (SWP) for remediating a per-and poly-fluoroalkyl substances (PFASs)-contaminated soil with a high clay content (61%). The SWP used both physical and chemical processes; fractionation of the soil particles by size and partitioning of PFASs into the aqueous phase to remove PFASs from the soil. Contaminated water was treated in series with granulated activated carbon (GAC) and ion-exchange resin and reused within the SWP. Approximately 2200 t (dry weight) of PFAS-contaminated soil was treated in 25 batches of 90 t each, with a throughput of approximately 11 t soil/hr. Ef-ficiency of the SWP was measured by observed decreases in total and leachable concentrations of PFASs in the soil. Average removal efficiencies (RE) were up to 97.1% for perfluorocarboxylic acids and 94.9% for per-fluorosulfonic acids. REs varied among different PFASs depending on their chemistry (functional head group, carbon chain length) and were independent of the total PFAS concentrations in each soil batch. Mass balance analysis found approximately 90% of the PFAS mass in the soil was transferred to the wash solution and > 99.9% of the PFAS mass in the wash solution was transferred onto the GAC without any breakthrough.

Potatoes are one of the staple food crops known to accumulate Cd in tubers from soil. Therefore, various countries around the world established maximum levels (MLs) for Cd in potatoes (and other foodstuff), taking into account the typical dietary intake of their populations. In Europe, there are several regions with high soil Cd concentrations, and the dominant source appears to be geogenic. However, no soil risk assessment tool has been developed to date to ascertain the likelihood of produce compliance with the ML, prior to sowing. In this study, we developed a predictive model for Cd concentration in potato tubers based on one soil extraction with 0.1M CaCl2, and subsequent determination of six elements (Cd, K, Mg, Mn, P and Zn) in the extracted solution by ICP-OES. This predictive model accounted for 74% of the observed tuber-Cd variance and was developed using 304 paired tuber-soil samples covering field conditions and incorporating climatic, agronomic and management variability across Ireland. Uncertainty in the model was used to calculate the probability of tuber-Cd exceeding the current European ML (0.1 mg Cd/kg FW) at each predicted tuber Cd concentration.

Background Precipitation of Zn phosphates may limit Zn availability in cogranulated P fertilizers. We assessed whether the Zn availability of Zn could be improved by post-granulation acid treatment. Methods Uncoated Zn-fortified monoammonium phosphate granules were compared with sulfuric acid-coated granules in which Zn was either cogranulated or dissolved in the acid coating. Spatially resolved XRF and XANES was used to assess the distribution and speciation of Zn in the granules (before and after incubation in soil) and in the exposed soil. The amount of Zn remaining in the granule was determined after incubation in various soils. The effect of acid coating rate on corn yield was determined in a highly Zn-deficient soil in a pot trial. Results The speciation of Zn in the untreated granules was dominated by Zn phosphates. In the sulfuric acid treatments, sulfate species accounted for ~ 45% (if cogranulated) or ~ 80% (if coated) of the Zn. After one week incubation in soil, 10–86% of the added Zn remained in the residual granule, mostly as sparingly soluble compounds. The Zn speciation in the soil near the granule was dominated by Zn phosphates irrespective of treatment, but Zn moved further away from the application site in the acid treatments, as more Zn was released from the granule. In the pot trial, the dry matter yield increased by 70% at a coating rate of 0.75% H 2 SO 4 compared to the uncoated control. Conclusions Post-granulation acid treatment of Zn-fortified P fertilizers is an effective way to enhance the phytoavailability of fertilizer Zn.

Purpose Boron (B) is an essential micronutrient required throughout the growth cycle of plants so effectively supplying crops with B using fertilizers is challenging. The purpose of this study was to assess the agronomic effectiveness of mechanochemically synthesized zinc borate as a slow release B source and compare it to commonly used B sources after incorporation with different macronutrient carriers. Methods Zinc borate synthesized using a green mechanochemical method as well as commercial B sources (borax, colemanite, and commercial zinc borate) were incorporated with various macronutrient fertilizers (monoammonium phosphate – MAP, muriate of potash – MOP and urea). The fertilizers were evaluated by a) assessing the solubility behaviour of these products; and b) comparing potential leaching losses, plant growth, and plant uptake through a greenhouse study. Results The mechanochemically synthesized zinc borate, commercial zinc borate, and colemanite had similar dissolution rates when MAP was the carrier, but both zinc borates dissolved more B than colemanite when MOP and urea were the carriers. In the pot trial, high losses of B in leachates resulted in low B uptake by plants fertilized with soluble sodium tetraborate. All the slow-release B sources showed less B leaching and greater B uptake compared to the soluble B treatment, but more B was leached for the mechanochemically synthesized than for the commercial zinc borate. Conclusions Our study indicates that mechanochemically synthesized zinc borate could be effective in matching plant demand for B and reducing leaching losses in high rainfall environments, particularly with urea as the carrier, while providing the benefit of lower waste stream production compared to commercial zinc borate sources.

Globally, fertilizer agglomeration (caking) during transport and storage leads to irreversible breakdown, dust, equipment blockages and inconsistent field application. Coatings which are hydrophobic reduce moisture uptake at high humidity and reduce caking but still need to release plant nutrients. Here, natural and synthetic waxes coated onto fertilizer granules with powders to impart surface roughness reduced contact between condensed water droplets and the surface, lowering moisture ingress. The adhesive strength of the coatings and rate of nutrient release are shown with degree of roughness quantified using laser surface microscopy. The wax-only coatings on potassium chloride fertilizer (MOP, 50% K) reduced moisture uptake by up to 30%, while for coatings with wax and roughener reductions were between 56% and 80%. Beeswax with micronutrient rougheners reduced moisture uptake by over 65% whilst maintaining uninterrupted nutrient supply. Thus, these hydrophobic coatings can improve physical characteristics of fertilizer without compromising the kinetics of nutrient release.