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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%. Reduced Mo solubility after MC treatment, compared to the initial Mo source, was obtained with the MoO3 source and these composites were used for co-compaction with macronutrient fertilizers. Macronutrient pellets with 0.2% Mo were compacted using the 4% Mo and 36% Mo (characterized as ZnMoO4) compounds. A column dissolution test showed that the 4% Mo compound in a macronutrient carrier (DAP and MAP) only released around 40% of the total Mo compared to 80% for a non-MC treated control over 72 h. Column leaching using two soils revealed that the release behavior of Mo was strongly related to the pH of the leachate, which was affected by both the soil pH and the macronutrient carrier. More Mo was released when the MC-treated compound was co-compacted with diammonium phosphate (DAP) compared to monoammonium phosphate (MAP). The MC-treated compound with 4% Mo showed significantly less leaching than the control without ball milling when co-compacted with both MAP and DAP. In a pot trial with simulated leaching, the uptake of Mo was greater for the MC-treated 4% Mo compound co-compacted into DAP than for the other Mo sources. Overall, our results indicate that MC-treated MoO3–ZnO could be used as a slow-release Mo source in high-rainfall areas. [ABSTRACT FROM AUTHOR]

The application of pure boron (B) fertilisers, independent of other macronutrients, is impractical due to the increased cost of dual handling and spreading. Bulk blending of B with other micronutrients is also an unattractive option as the relatively low rates of B required results in poor nutrient distribution in the field. Co-granulating B with other macronutrients such as mono-ammonium phosphate (MAP) may overcome these problems. Five B sources (boron phosphate (BP[O.sub.4]) synthesised at 500 and 800°C for 1 h, colemanite, ulexite and borax) were co-granulated with MAP to targeted B contents of 0.5, 1.0 and 2.0%. The co-granulated BP[O.sub.4] had lower water solubility than co-granulated colemanite, ulexite and borax. Boron released from co-granulated borax, ulexite and colemanite was remarkably greater than co-granulated BP[O.sub.4] products. Over a 4-week soil incubation period with weekly leaching of one pore volume of water, the cumulative B release from co-granulated ulexite, borax and colemanite was 97, 75 and 58%, respectively, but only 16 and 4% for the co-granulated BP[O.sub.4] synthesised at 500 and 800°C, respectively. Co-granulated BP[O.sub.4] products have potential as a high quality fertiliser to increase crop yield with slow B release. Additional keywords: boron phosphate, dissolution, leaching, nutrient release., Introduction Boron (B) is one of the essential micronutrients required for normal plant growth and cell development (Gupta 1979). Deficiencies as well as toxicities of B result in many anatomical [...]

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. [ABSTRACT FROM AUTHOR]

Boron (B) is essential for plant growth and the use of soluble b fertilizers is common, but leaching can result in poor fertilizer use efficiency in highrainfall areas. We assessed the response of canola (Brassica napus l.) in two consecutive crops to the application of co-granulated slow-release b fertilizer under simulated leaching conditions. The slow-release b sources were boron phosphate (BPO4) synthesized at 500 or at 800°C for 1 h. For comparison, the more soluble b sources borax, ulexite, and colemanite were also included. all b sources were co-granulated with monoammonium phosphate (MAP) at a nominal concentration of 1.0% (w/w) b. The pure B sources, not co-granulated with map, were also included (first crop only). in the first crop, B concentrations in shoots were in the toxic range when b was supplied with the more soluble B sources, and dry matter yield was reduced for the treatments with borax and ulexite. The dry matter yields were lower and B concentrations in the shoot were higher in the treatments with pure B sources than in those with the co-granulated B sources. in the second crop, B concentrations in shoots were in the deficient range for the treatments with borax and ulexite and the plants showed B visual deficiency symptoms, although dry matter yield was not significantly affected. in contrast, the B supply for the treatments with BPO4 was adequate across both crops. The cumulative leaching loss of b for the treatments with co-granulated BPO4 was low compared with that for the more soluble B sources. These results indicate that BPO4 co-granulated products have potential as slow-release B fertilizers in high-rainfall areas. [ABSTRACT FROM AUTHOR]

We investigated the use of boron phosphate (BPO4) as a slow-release boron (B) source. Boron phosphate compounds were synthesized by mixing boric acid (H3BO3) and phosphoric acid (H3PO4) and heating at temperatures of 25 to 1000°C for 1 or 24 h. X-ray diffraction (XRD) patterns and chemical analysis confirmed the formation of BPO4. The crystallinity of these compounds increased with increasing temperature and heating time. The compounds synthesized at 300°C or less were hygroscopic and clumped together, while those synthesized at 500 to 1000°C were non-hygroscopic and free-flowing. The solubility of these compounds was assessed at different pH and P concentrations, and compared to the solubility of ulexite and colemanite. The solubility of the BPO4 compounds decreased with increasing synthesis temperature and with decreasing pH. The solubility and the kinetics of B release from BPO4 compounds synthesized at 500 and 800°C were slower than for most commonly used B sources. Given their slow dissolution, the BPO4 compounds may have potential to continuously supply B to crops in environments where B leaching is a problem. The compounds synthesized at 500 and 800°C show potential for co-granulation with macronutrient fertilizers such as mono-ammonium phosphate to produce slow-release B-enriched granules. [ABSTRACT FROM AUTHOR]

Losses of phosphorus (P) from fertilized fields may result in degradation of water quality. Various initiatives are under evaluation to minimize water contamination, including the adoption of less soluble or coated P fertilizer formulations aiming to mitigate losses of P in runoff. Field-based rainfall simulators are traditionally used to evaluate P runoff, but using these is time consuming, labor intensive, and costly given the complex apparatus and analyses involved. We hypothesized that laboratory-based methods could be useful to evaluate the risk of P runoff from fertilizers. In order to identify a rapid, inexpensive, and efficient screening process, we compared two laboratory-scale measurements, one in water (based on electrical conductivity measurements) and one in soil (based on visualization of P diffusion in soil), with runoff results from field-, glasshouse-, and laboratory-based rainfall simulators, using coated soluble phosphate fertilizers. The laboratory-based methods assessing the P release rate in water and in soil correlated closely (r ≥ .96) with the losses of P obtained in the three rainfall simulators regardless of the type of coating or solubility of the fertilizer. The faster and inexpensive electrical conductivity and diffusion visualization methodologies were useful to rank the fertilizers by P release to runoff. Hence, these tools may be useful for screening fertilizer formulations with respect to their runoff risk., (© 2021 The Authors. Journal of Environmental Quality published by Wiley Periodicals LLC on behalf of American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)