Rodrigo Coqui da Silva

The need to increase food production means that fertilizers will continue to play a key role in farming systems. However, current formulation and practices are increasingly being scrutinized due to the low efficiency of applied nutrients with negative economic and environmental consequences. Enhance nutrient use efficiency requires a comprehensive understanding of soil-fertilizer interactions. Here, we contend that this knowledge has been generated by 'bulk' soil approaches that, while providing useful information, oversimplify these interactions by neglecting the strong chemical gradients occurring in the soils around fertilizers (i.e., in the fertosphere). Progress in non-destructive, in situ, and spatially resolved analytical techniques now allow a paradigm shift in the investigation of fertilizer chemistry in soil. For instance, mapping of diffusive gradients in thin films (DGT) allows for nutrient availability to be quantified in 2D. Complementing DGT information with imaging X-ray absorption near-edge structure (XANES-imaging) provides an avenue to understand how chemical speciation along chemical gradients in the fertosphere controls nutrient availability. This information is essential to improve agronomic practices and for the development of novel fertilizers. This is particularly important in developing fertilizers from recycled materials and return nutrient cycles within, or at least closer to, their planetary boundaries.

N‐ ( n ‐Butyl) thiophosphoric triamide (NBPT) is the most widely adopted urease inhibitor, used to reduce ammonia (NH ₃ ) volatilization from urea. Micronutrients such as boron (B), zinc (Zn), nickel (Ni) and molybdenum (Mo) are also reported to inhibit urease, serving simultaneously as plant nutrients. However, there is little information on the potential synergistic or antagonistic effects of NBPT and micronutrients on urea protection. The aim of this study was to evaluate NH ₃ volatilization losses, soil pH and soil mineral nitrogen content (‐N and ‐N) after application of urea coated or granulated with the micronutrients B, Zn, Ni or Mo, individually. Thereafter, the fertilizers were applied combined and not associated with NBPT. Ammonia volatilization was measured in a closed static chamber under controlled conditions. Urea granulated with B and Zn reduced NH ₃ ‐N volatilization circa 30% compared with untreated urea, while Mo and Ni had no effect. NBPT stabilizer had the greatest effect on NH ₃ ‐N volatilization (44%–59% reduction), but was less effective (only 20%–34% reduction) when urea was coated with B, Zn or Mo. On the other hand, when B and Zn were incorporated via granulation, the efficiency of NBPT was not reduced, likely because of the physical separation. These findings demonstrate that granulating urea with B or Zn combined with an NBPT‐coating can be a valuable strategy to reduce NH ₃ volatilization losses while also supplying micronutrients and hence potentially increase yields in agricultural production systems.

Zinc (Zn) is the micronutrient commonly found deficient 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.

Chemical characterization of fertilizers, in terms of total nutrient content, is essential for quality control and definition of field-based rates. The Ministry of Agriculture, Livestock and Supply (MAPA) by IN/2007 recommends different methods for nutrient content extraction for fertilizers. These methods can have high analytical costs, be laborious, and generate large quantities of residues. Therefore, this work proposes a simple and more environmentally friendly extraction method by using nitric acid solution to extract total content of nutrients from fertilizers, which has the advantage of a cold extraction, less residue generation, and easier execution. The experiment was carried out using eight nutrient sources (tricalcium phosphate, monocalcium phosphate, potassium chloride, zinc oxide, copper oxide, manganese oxide, ulexite, and a mixture of soluble sources of these nutrients), four nitric acid concentrations (0.0, 1.0, 2.5, or 5.0 mol L⁻¹), and six shaking times (10, 20, 30, 40, 50, or 60 min). A completely randomized design with three replicates was used. These data indicated 2.5 mol L⁻¹ HNO₃ as suitable concentration to extract total nutrient content from the sources. In addition, as there was no shaking time effect on elements extraction; in a second trial, we compared the performance of HNO₃- at 2.5 mol L⁻¹ under a shaking time of 60 min across MAPA methods. The results evidenced that soluble contents extracted by both methods were highly correlated, recovering equivalent amounts of B and K. For other nutrients, nitric acid method extracted a greater amount than MAPA method. Therefore, this paper represents a first approach to the use of a method based on nitric acid for the recovery of total nutrient contents (P, K, Ca Mg, S, B, Cu, Mn, and Zn) in mineral fertilizers of varying solubility. Graphical abstractThe nutrients extraction from mineral fertilizers using nitric acid is more advantageous than MAPA-methods, because it produces a single extract for multi-elements analysis without heating. Therefore, it reduces the analysis costs, the execution time, the reagents consumption and the chemical waste generation

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.

Field trials with labeled fertilizers can be used to provide information on fertilizer efficiency, residual value, and nutrient fate. We assessed the uptake from elemental S (ES) and sulfate S (SO₄-S) in S-fortified monoammonium phosphate fertilizers by various crops at three sites in Argentina, Brazil, and Canada. The S sources were labeled with ³⁴S, and the ³⁴S abundance in the plant tissue was analyzed at an early stage and at maturity over two consecutive years. At the sites in Argentina and Canada, the recovery of ES in the crop was smaller than that of SO₄-S in the first year, while the opposite was true in the second year. At the Brazilian site, the recovery of ES was similar to that of SO₄-S in the first year, but higher in the second year. In the Argentina and Canada sites, the cumulative recovery of SO₄-S was >65% and that of ES was 20−25%. In the Brazilian site, the cumulative recovery of SO₄-S was 9% and that of ES 16%. The higher recovery of ES than of SO₄-S in the Brazilian site was attributed to leaching of added SO₄-S and relatively fast oxidation of ES due to the warm climate. These results suggest that ES may be more suitable than SO₄-S as a fertilizer S source in warm humid climates, while inclusion of SO₄-S in the fertilizer is recommended in colder climates as slow oxidation limits the initial availability of ES.

A possible way to improve phosphate rock (PR) agronomic performance is through the addition of elemental sulfur (S⁰). We used ³²P isotope dilution method to assess the P taken up by crops treated with PR. Two experiments, one with common bean and other with upland rice, were carried out, to evaluate the effect of S⁰ on the agronomic performance of two contrasting PR, applied in different methods. Gafsa (GPR) and Patos de Minas (PPR) were used as the high and low reactivity PR, respectively. The experiments were arranged in completely randomized design on factorial structure 2 × 2 × 2 + 2; which means 2 PR (GPR and PPR) versus 2 S⁰ condition (with or without-S⁰) versus 2 application methods (band and broadcast) plus 2 additional treatments (control and triple superphosphate). In band application the S⁰ increased the amount of P uptake by plants from fertilizer of GPR from 2.57 to 9.86 mg pot⁻¹ for common bean and of 2.26 to 7.05 mg pot⁻¹ to rice. Regardless the management adopted, less than 2% of P applied as PPR has been taken up by crops. The addition of S⁰ as a strategy to increase the agronomic performance of PR is PR characteristics dependent and fertilizers placement.

Core Ideas: A dual‐release boron (B) fertilizer can reduce the risks of seedling toxicity and leaching. Muriate of potash (MOP) was co‐compacted with slow‐ and fast‐release B sources. MOP+B resulted in a more uniform B spatial distribution compared to traditional bulk‐blends. Incorporation of colemanite in the formulation slowed the release of B from the MOP+B fertilizers. This novel B fertilizer may improve the synchrony between nutrient availability and crop demand. Boron (B) supply to crops is a challenging fertilization practice, due to its high mobility in soil, its narrow window between deficiency and toxicity and the necessity to evenly apply this micronutrient to the soil. We aimed to increase B fertilizer efficacy through the use of slow‐ and fast‐release borate compounds in a macronutrient carrier fertilizer. Borax, ulexite, and colemanite (alone or combined) were compacted with muriate of potash (MOP) to produce B‐enriched fertilizers varying in proportion of water‐soluble B. One such fertilizer was assessed for spatial B distribution compared with a bulk blend equivalent in a soil tray, while others were assessed for nutrient release in a soil column, and canola ( Brassica napus L.) growth in a leached and non‐leached pot trial. The compacted MOP+B fertilizer improved B distribution in soil compared to a simulated bulk blend. The release of B was fastest for borax (>93% released within 2.5 pore volumes [PV]) and slowest for colemanite (<20% released after 20 PV). The combination of slow‐ and fast‐release B sources resulted in initial fast‐release of B followed by a constant slower B release. In leached soil, the higher B losses (up to 80% of applied B) resulted in lower canola B uptake with increasing borax and decreasing colemanite in the formulation. In non‐leached soils, there was no difference in B uptake among fertilizer treatments. The use of dual release B sources in MOP+B fertilizer formulations effectively addresses the risk of B loss, and better matches crop B demands during growth.