Michael J. McLaughlin

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.

Increasing zinc (Zn) concentrations in crops is important for alleviation of human Zn deficiency. Arbuscular mycorrhizal fungi (AMF) contribute to plant Zn uptake, but their contribution to Zn in the edible portion of crops has not yet been investigated. This study aimed to quantify the mycorrhizal pathway of Zn uptake into grain of wheat and barley under varying soil Zn availabilities. Bread wheat (Triticum aestivum) and barley (Hordeum vulgare) were grown in pots with a hyphal compartment containing 65Zn. Plants were inoculated with Rhizophagus irregularis and grown at three soil Zn concentrations. Radioactive Zn in grain and straw was measured and the contribution of AMF to Zn uptake was calculated. The mycorrhizal pathway of Zn uptake contributed up to 24.3% of total above-ground Zn in wheat, and up to 12.7% of that Zn in barley. The greatest contribution by the mycorrhizal pathway was observed in barley at the lowest Zn addition, and in wheat at the highest one. In addition, grain yield of bread wheat was increased by AMF. These results suggest that AMF have a substantial role in uptake of Zn into cereals, and the proportional contribution by the MPU is dependent on plant species, as well as available soil Zn.

The environmental problems and low efficiency associated with conventional fertilizers provides an impetus to develop advanced fertilizers with slower release and better performances. Here, we report of development of a new carrier platform based on graphene oxide (GO) sheets that can provide a high loading of plant micronutrients with controllable slow release. To prove this concept, two micronutrients, zinc (Zn) and copper (Cu), were used to load on GO sheets and hence formulate GO-based micronutrients fertilizer. The chemical composition and successful loading of both nutrients on GO sheets were confirmed by X-ray photoelectron spectroscopy, thermogravimetric analysis, and X-ray diffraction (XRD). The prepared Zn-graphene oxide (Zn–GO) and Cu-graphene oxide (Cu–GO) fertilizers showed a biphasic dissolution behavior compared to that of commercial zinc sulfate and copper sulfate fertilizer granules, displaying desirable fast and slow micronutrient release. A visualization method and chemical analysis were used to assess the release and diffusion of Cu and Zn in soil from GO-based fertilizers compared with commercial soluble fertilizers to demonstrate the advantages of GO carriers and show their capability to be used as a generic platform for macro- and micronutrients delivery. A pot trial demonstrated that Zn and Cu uptake by wheat was higher when using GO-based fertilizers compared to that when using standard zinc or copper salts. This is the first report on the agronomic performance of GO-based slow-release fertilizer.