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Type: Thesis
Title: The development of new slow-release boron fertilizers.
Author: Abat, Margaret
Issue Date: 2015
School/Discipline: School of Agriculture, Food and Wine
Abstract: 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.
Advisor: McLaughlin, Michael John
Degryse, Fien
Baird, Roslyn
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2015
Keywords: slow-release; boron; fertilizers
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at:
Copyright material removed from digital thesis. See print copy in University of Adelaide Library for full text.
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