Slow-release copper efficacy study on wheat: a sustainable solution for efficient crop micronutrient delivery

This study evaluated a novel slow-release copper fertiliser (soileos Cu) as a sustainable alternative to conventional copper sources for improving wheat yield and nutrient use efficiency. Traditional Cu fertilisers are often limited by rapid leaching and low efficiency, especially on sandy soils with low organic matter, contributing to environmental pollution. They also exhibit low plant-use efficiency due to strong adsorption and immobilisation in soils rich in organic matter and clay minerals, thereby reducing copper availability in the soil solution and contributing to environmental pollution. A multi-scale approach was employed, including laboratory incubation, greenhouse experiments, and multi-site field trials. Copper release was quantified in water over 30 days. Greenhouse experiments compared soileos Cu with copper sulfate (CuSO₄) across multiple application rates, assessing grain yield, biomass, spike count, chlorophyll index (SPAD), and tissue and grain nutrient concentrations. Field trials were conducted at four sites in Canada and the United States with contrasting soil Cu availability. Soileos Cu exhibited controlled, non-linear Cu release with substantially reduced leaching compared to CuSO₄. In greenhouse conditions, soileos Cu achieved maximum grain yield, biomass, and spike number at 25–26% lower Cu application rates than CuSO₄, indicating higher nutrient use efficiency. Field trials confirmed that yield responses were strongly dependent on baseline soil Cu levels, with the greatest yield increase (up to 13.3%) observed at a Cu-deficient site. Overall, soileos Cu provides an effective and environmentally responsible strategy for improving Cu nutrition and wheat productivity, particularly under Cu-limiting conditions.