Abstract
The concentration of fluorine (F) in New Zealand pastoral soils is increasing as a consequence of Phosphorus (P) fertiliser application, and there is concern over the long-term impact of this F on animal and soil microbiological health. Ongoing soil F monitoring to underpin comprehensive soil F management practices requires an accurate and simple test to quantify both the total and bioavailable concentration of F in soil. In this study, soils were collected from various locations across New Zealand, representing different soil orders and land uses. The total soil F concentration was measured using an ion specific electrode following extraction with four different concentrations of NaOH (4 mol L−1, 8 mol L−1, 12 mol L−1 and 16 mol L−1), or fusion with NaOH (the conventional method used to analyse total soil F). We concluded that NaOH extraction gave an acceptable level of accuracy for organic matter and volcanic parent material derived soils. Agreement was, however, less strong for recent and pallic soils. The extraction method was subsequently validated through repeat analysis of three further soils (n = 270).To define a method for quantification of the bioavailable concentration of F in soil, samples were extracted with water, 1 mol L−1 HCl, 0.01 mol L−1 CaCl2, 0.01 mol L−1 KCl, and 1 mol L−1 NH4Cl. The correlation between 0.01 mol L−1 CaCl2, 0.01 mol L−1 KCl, and water extracted F concentrations were significant (p < 0.05), and extracted the same soil F fractions. Results were normalised to the water-extractable concentration to compare recovery as a function of soil order. The recovery percentage of 0.01 mol L−1 CaCl2 was high compared with water for soils which have high Al and Fe contents. We propose that 0.01 mol L−1 CaCl2 extraction should be adopted as a standard method to assess the bioavailable F concentration of New Zealand pastoral soils.
Published Version
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