Phytotoxic doses of boron in contrasting soils depend on soil water content

Jelle Mertens, Liesbeth Van Laer, Peter Salaets, Erik Smolders

Research outputpeer-review


Boron (B) affects plant growth in soil at B doses (mg added B kg-1 soil) that appear in the range of natural background B concentrations. A study was set up to determine B bioavailability by testing B toxicity to plant as affected by soil properties and ageing after soil dosing. Nineteen soils (pH 4.4-7.8) and 3 synthetic soils (sand-peat mixtures) were amended with 7 doses of H3BO3. Barley root elongation was determined immediately after B amendment and after 1 and 5 months ageing. Soil solution B concentrations increased linearly with added B concentrations with almost no detectable adsorption. In contrast, the ratio of aqua regia soluble B/soil solution B in unamended soils (no B added) was 10-25 times higher than in B amended soils at similar aqua regia soluble B concentrations illustrating a much lower B availability in unamended soils. Soil solution B concentrations did not decrease by ageing. The toxic B doses or soil B concentrations that decreased barley root growth by 10% (EC10 values) varied about tenfold (respectively 3-27 mg added B kg-1 and 5-52 mg B kg-1) among soils. Corresponding thresholds in soil solution varied less than fourfold (16-59 mg B l-1). Soil ageing for 5 months did not significantly change EC10 and EC50 values, expressed either as total soil B or as soil solution B, unless in 1 soil. Variability in EC10 and EC50 values was explained by various soil properties (soil moisture content, background B, %clay, cation exchange capacity), but covariance of these properties with the soil moisture content suggest that B dilution is the critical factor explaining B toxicity. It is concluded that effects of B amendments do not decrease by ageing and that soil solution B or B doses corrected for soil moisture content may be used as an index for B toxicity across different soils.

Original languageEnglish
Pages (from-to)73-82
Number of pages10
JournalPlant and Soil
Issue number1-2
StatePublished - May 2011


Acknowledgements The authors thank the IMA REACH Borates Consortium for financing this project. J. Mertens received a grant as a postdoctoral researcher from the Research Foundation-Flanders (FWO-Vlaanderen). The authors thank Dr. Sabine Goldberg for providing the U soils. The data in this publication may not be used for REACH registration without approval of the IMA REACH Borates Consortium (Roger Doome, Rue des Deux Eglises 26, B-1000, Brussels).

FundersFunder number
FWO - Fonds Wetenschappelijk Onderzoek Vlaanderen
FWO - Fonds Wetenschappelijk Onderzoek Vlaanderen

    ASJC Scopus subject areas

    • Soil Science
    • Plant Science

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