Slow and Fast-Release Boron Sources in Macronutrient Fertilizers.

Boron (B) deficiency limits crop yields in agricultural areas worldwide, mainly in high rainfall regions due to leaching losses. This micronutrient is usually applied in NPK blends. However it has been shown ineffective due to non-uniform distribution, which is an important issue as B is the plant nutrient with the narrowest window between deficiency and toxicity. To address these issues we produced slow- and fast-release borate fertilizers using a macronutrient formulation as carrier. Borax, ulexite and colemanite (alone or combined) were compacted with muriate of potash (MOP) to produce a wide range of water soluble B. The fertilizers were tested for the nutrient release over time and their effect on canola growth. Fertilizer granules were placed into a soil column before deionized water was introduced at a constant flow rate using a peristaltic pump. The leachate solutions containing dissolved nutrients from the fertilizer were collected at regular intervals and the B concentration determined. The release was fastest for borax and slowest for colemanite. A combination of slow- and fast-release B sources resulted in initial fast-release followed by a constant and slower B release over time. The pot trial was carried out with canola (12 weeks growth) with or without leaching of soil prior to planting, using MOP+0.5% B fertilizer with varying ratios of borax or colemanite. In the leached soils, the leaching losses were higher and the B uptake by canola was lower as there was more borax and less colemanite in the fertilizer. In the non-leached soils, there was no difference in B uptake between fertilizer treatments. The use of dual release B sources in MOP+B formulations seems to be an effective strategy to address the risk of B losses in high rainfall environments, while better matching the crop demands during the entire season.