Academic literature on the topic 'Slow-release; boron; fertilizers'

Boron (B) deficiency and/or toxicity have caused significant impacts on agricultural crop production worldwide. The most commonly used sources of fertilizer B are water soluble, and are therefore susceptible to leaching in high rainfall environments. This may result in insufficient supply of B for plant growth later in the crop growth cycle (e.g. flowering), when B supply is most needed. Moreover, these highly soluble sources pose an increased risk of B toxicity to seedlings just after planting. One possible way to reduce nutrient losses and avoid seedling toxicity is by using slow-release fertilizer. Slow-release fertilizers provide an effective means to overcome the low use-efficiency and problems associated with highly soluble fertilizers in soils prone to nutrient leaching. This study has identified boron phosphate (BPO₄) compounds as potential raw materials for incorporation into macronutrient fertilizers to produce compound fertilizers containing slow-release B. The BPO₄ compounds were found to differ significantly from most commercially available B sources in terms of their physical and chemical characteristics. Boron phosphate compounds synthesized at 500 and 800 °C had low water solubility, with solubility decreasing with decreasing pH, slow kinetics of B release and B concentrations released initially from this B source by water were below the toxicity level for most crops. Products synthesized at these two temperatures were free flowing and were readily incorporated into granular mono-ammonium phosphate (MAP) granules. The solubility of other slow-release B sources, namely ulexite and colemanite, were enhanced when co-granulated with MAP due to the low pH and high P concentrations in this macronutrient fertilizer – they therefore lost their slow release characteristics when co-granulated with MAP. This limitation did not apply to BPO₄ compounds where low pH and high P concentrations did not affect, or even slowed, B release. A rapid method to screen fertilizers for possible adverse effects of high B concentrations on germinating seedlings was developed, by assessing canola (Brassica napus L.) germination in Petri dishes using image analysis. The MAP fertilizers co-granulated with ulexite, borax and colemanite had an adverse effect on emerging canola seedlings even at a low total B concentration in the product (0.5% B). On the other hand, no toxicity symptoms were observed with the application of MAP co-granulated with BPO₄ even at higher B concentrations in the fertilizer (2.0% B). Concentrations of hot-water soluble B measured around the granule application site were in agreement with the toxicity results, with concentrations in the toxic range close to the granule for the most soluble B sources. In plant uptake experiments examining the recovery of B by plants from the various slow-release formulations by two crops of canola, the application of co-granulated soluble B sources led to toxicity in the first crop and deficiency in the second crop. The canola shoot dry weight was increased in treatments using co-granulated BPO₄ products compared with the unfertilized control for both crops. This result suggested that a single application of a macronutrient fertilizer containing co-granulated BPO₄ would be an effective slow-release B fertilizer for several cropping cycles. In summary, co-granulated BPO₄ products have potential as sources of slow-release B for incorporation into macronutrient fertilizers designed for high rainfall environments. This research work could have important implications for future B fertilizer development.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2015