Enhancing the phosphorus content of layered double hydroxide fertilizers by intercalating polymeric phosphate instead of orthophosphate: A feasibility study.

HYPOTHESIS: Layered double hydroxide (LDH) loaded with orthophosphate (PO4) are suggested as slow-release P fertilizers. However, PO4-LDHs have a low maximal P content, related to high charge HPO42-/PO43- anions occupying the anion exchange capacity (AEC) of LDHs. We postulate that the P content of LDHs can be enhanced by exchanging them with polymeric-P (i.e. trimetaphosphate, P3O9), which has a lower molar charge/P ratio than its monomer. EXPERIMENTS: Adsorption capacities were compared between PO4 and P3O9 for as-synthesized and calcined MgAl LDHs with Mg/Al ratio of 2, 3, or 4; the P-LDHs were characterized (XRD, FTIR). Dialysis and soil incubation experiments were performed with PO4-LDHs, P3O9-LDHs, and corresponding soluble fertilizers to compare their P release and P solubility (CaCl2 extract). FINDINGS: The P adsorption capacities were 1.25-1.60 fold larger for P3O9 compared to PO4, yet the high theoretical P contents with P3O9 were not achieved (incomplete loading, P3O9 depolymerization). P3O9-Mg3Al released polymeric-P whereas P3O9-Mg2Al released depolymerized PO4, and P release from P3O9-LDHs was slower than that of PO4-LDHs. With soil incubation, soluble P from P3O9-LDH was initially lower but later converged to that of PO4-LDH as result of continued hydrolysis, yet did not exceed that of the soluble P3O9 and PO4 fertilizers.

Development of an organomineral fertiliser formulation that improves tomato growth and sustains arbuscular mycorrhizal colonisation.

Achieving sustainable agricultural development requires the efficient use of nutrient resources for crop production. Recovering nutrients from animal manures may play a key role in achieving this. Animal manures typically have low nutrient concentrations, and in ratios that are often not ideal for balanced crop nutrition. Here, combinations of organic and inorganic phosphorus (P) were formulated as granular products (organomineral fertilisers) with granule size suitable for transport and spreading. The fertilisers were produced by granulating powdered chicken litter with MAP and urea powders making the following formulations: 0:4, 1:3, 2:2, 3:1, 4:0. The kinetics of NH4+-N and P release from the fertilisers, and the effects on tomato growth and nutrition, as well as arbuscular mycorrhizal formation in roots following fertiliser application, were determined. Cumulative NH4+-N release ceased within 12 h, and was lower in the formulations with higher proportions of chicken litter. The cumulative P released reached approximately 80% of total P in all formulations, and the time to obtain maximum P dissolution was 19 days in the formulation that contained only chicken litter. The organomineral fertilisers increased tomato shoot growth by 15-28% compared to the chicken litter only, MAP only and MAP/urea formulations. Reasonable levels of mycorrhizal colonisation of tomato roots was achieved with the organomineral fertilisers. The results demonstrated that optimum plant growth does not depend solely on immediately available P, and that timing of nutrient supply to match plant demand is important. The combination of chicken litter with MAP sustained nutrient supply and improved plant growth. Taken together, organomineral fertiliser formulations are potential alternatives to inorganic P fertilisers that can improve crop growth and nutrition, while provide a sustainable use for animal production wastes.

Screening fertilizers for their phosphorus runoff risk using laboratory methods.

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.

Author Correction: Improving the efficacy of selenium fertilizers for wheat biofortification.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Improving the efficacy of selenium fertilizers for wheat biofortification.

Increasing the selenium (Se) concentration of staple crops by fertilization is a valuable pathway to increase Se in the human diet, thus preventing Se deficiency. A pot trial was set up to investigate whether the application of 3.33 µg kg-1 of Se (equivalent to 10 g ha-1) to wheat can be made more efficient by its co-application with macronutrient carriers, either to the soil or to the leaves. In the soil, Se was applied either on its own (selenate only) or as a granular, Se-enriched macronutrient fertilizer supplying nitrogen, phosphorus, potassium or sulfur. Selenium was also applied to leaves at head emergence with, or without, 2% w/v N fertilizers. With grain Se concentrations varying from 0.13-0.84 mg kg-1, soil application of selenate-only was 2-15 times more effective than granular Se-enriched macronutrient fertilizers in raising grain Se concentrations. Co-application of foliar Se with an N carrier doubled the Se concentration in wheat grains compared to the application of foliar Se on its own, the majority of which was in the highly bioavailable selenomethionine fraction. Results from this study demonstrate the possibility of improving the efficacy of Se fertilizers, which could enrich crops with Se without additional application costs in the field.

Sulfur and Zinc Availability from Co-granulated Zn-Enriched Elemental Sulfur Fertilizers.

Acidification by oxidation of elemental sulfur (ES) can solubilize ZnO, providing slow release of both sulfur (S) and zinc (Zn) in soil. For this study, a new granular fertilizer with ES and ZnO was produced and evaluated. The effect of incorporating microorganisms or a carbon source in the granule was also evaluated. Four granulated ES-Zn fertilizers with and without S-oxidizing microorganisms, a commercial ES pastille, ZnSO4, and ZnO were applied to the center of Petri dishes containing two contrasting pH soils. Soil pH, CaCl2-extractable S and Zn, and remaining ES were evaluated at 30 and 60 days in two soil sections (0-5 and 5-9 mm from the fertilizer application site). A visualization test was performed to evaluate Zn diffusion over time. A significant pH decrease was observed in the acidic soil for all ES-Zn fertilizer treatments and in the alkaline soil for the Acidithiobacillus thiooxidans-inoculated treatment only. In agreement with Zn visualization tests, extractable-Zn concentrations were higher from the point of application in the acidic (62.9 mg dm-3) compared to the alkaline soil (5.5 mg dm-3). Elemental S oxidation was greater in the acidic soil (20.9%) than slightly alkaline soil (12%). The ES-Zn granular fertilizers increased S and Zn concentrations in soil and can provide a strategically slow release of nutrients to the soil.