Purpose: Boron (B) is an essential micronutrient required throughout the growth cycle of plants so effectively supplying crops with B using fertilizers is challenging. The purpose of this study was to assess the agronomic effectiveness of mechanochemically synthesized zinc borate as a slow release B source and compare it to commonly used B sources after incorporation with different macronutrient carriers. Methods: Zinc borate synthesized using a green mechanochemical method as well as commercial B sources (borax, colemanite, and commercial zinc borate) were incorporated with various macronutrient fertilizers (monoammonium phosphate – MAP, muriate of potash – MOP and urea). The fertilizers were evaluated by a) assessing the solubility behaviour of these products; and b) comparing potential leaching losses, plant growth, and plant uptake through a greenhouse study. Results: The mechanochemically synthesized zinc borate, commercial zinc borate, and colemanite had similar dissolution rates when MAP was the carrier, but both zinc borates dissolved more B than colemanite when MOP and urea were the carriers. In the pot trial, high losses of B in leachates resulted in low B uptake by plants fertilized with soluble sodium tetraborate. All the slow-release B sources showed less B leaching and greater B uptake compared to the soluble B treatment, but more B was leached for the mechanochemically synthesized than for the commercial zinc borate. Conclusions: Our study indicates that mechanochemically synthesized zinc borate could be effective in matching plant demand for B and reducing leaching losses in high rainfall environments, particularly with urea as the carrier, while providing the benefit of lower waste stream production compared to commercial zinc borate sources.

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.

Subtropical mountain economic tree plantations are constrained by pronounced spatial heterogeneity in resource availability, yet the spatial scales at which soil properties, topography, and canopy structure regulate vegetation vigor remain poorly resolved. To address this gap, a spatially consistent multi-scale dataset combining 10 m high-density soil sampling, UAV-LiDAR, and multispectral remote sensing was used to quantify the scale-dependent drivers of the Leaf Chlorophyll Index (LCI) across 3–50 m within a Chinese hickory (Carya cathayensis Sarg.) plantation. The relative contributions of canopy, soil, and topography to LCI were decomposed across scales using an interpretable machine-learning framework (XGBoost–SHAP). At fine scales (3–10 m), vegetation vigor was primarily controlled by tree-level canopy structure, particularly tree height, reflecting localized resource acquisition. At intermediate scales (10–20 m), a distinct coupling window emerged, characterized by increased interaction complexity: LCI was predominantly driven by interactions between canopy structure and soil nutrient availability, whereas single-factor effects weakened. Notably, at 20 m this interaction pattern largely weakened and reverted to single-metric dominance. At broader scales (>30 m), complex interactions re-emerged, and dominant SHAP contributions shifted from nutrients and canopy structure toward topography and soil texture. These findings reconcile strong fine-scale drivers with weaker predictability at intermediate extents and demonstrate that soil–canopy relationships reorganize across spatial scales rather than remaining static. On the basis of these findings, a scale-hierarchical framework for precision forestry is proposed that aligns management interventions with the ecological scales at which dominant correlates operate across spatial supports.