Graduate Thesis Or Dissertation
 

The mobility and plant availability of boron in selected western Oregon soils

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/cz30pw772

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  • Several crops grown in the Willamette valley of western Oregon respond to applications of boron fertilizers. The acid, highly-leached soils of this area are naturally low in plant-available B. Application of B to the soil annually or at less frequent intervals is currently recommended, but the fate of applied B and the residual effect on plant growth has received little attention. In studying boron in these soils a more convenient and more accurate method for determining hot-water-soluble B based on the azomethine-H procedure was developed and adopted to replace the curcumin method. Substitution of 0.02 M CaC1₂ for distilled water for extraction of soil B resulted in clear, colorless solutions which permitted accurate colorimetric determination of B. A greenhouse experiment was established to investigate 1) the influence of soil properties on the mobility and plant-availability of B, 2) the magnitude of the loss of B from the surface soil by leaching, and 3) the residual effect of applied B on plant growth and the B supplying power of soils. Soil samples from sixteen locations representing five agriculturally important soil series were studied. The percentage of B from a 2.0 mg B /kg application recovered in 25 cm of leachate decreased as soil organic matter, clay, and free iron and aluminum oxide content increased. The results clearly indicated the importance of organic matter in reducing the mobility of B, and suggested that free Fe and Al oxides, and perhaps clay, may also be important. Soil acidity over a pH range of 5.4 to 7.5 did not influence the mobility of B. Dry matter yields for three cuttings of New Zealand white clover (Trifolium repens L.) were not significantly affected by B soil test level or B applied at planting. Plant tissue concentrations of B were high compared to field-grown forage legumes and, while these concentrations were affected by extractable soil B level or B application, the correlations between soil test level of B and plant content of B were low. A balance-sheet approach, where the amounts of leachate, plant, and extractable soil B were tabulated, indicated a B supplying power for the soils studied. All sixteen soils released B to leaching and cropping with minimal decreases in hot-water-soluble B content. When B was applied to the soils, only those higher in organic matter and/or free Fe and Al oxides tended to "fix" B in a form not recoverable by leaching, cropping and hot-water extraction. The capacity of the soils to maintain soluble B levels under cropping depended both on the individual soil and the amount of B present (i.e., check vs. B applied). The results are in agreement with a small body of literature suggesting the importance of intensity/capacity relationships in the availability of B to plants.
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