Distinguishing Boron Desorption from Mineral Dissolution in Arid‐Zone Soils

Abstract

Boron release from six arid-zone soil samples from the San Joaquin Valley of California was investigated as a function of reaction time, solution pH, and suspension density. A multiple batch extraction experiment was performed for 362 d to distinguish B desorption from B released from mineral dissolution. Amounts of B released decreased rapidly and reached a low constant value after about 6 mo of reaction time. Slopes ofthe B release curves for the last eight extractions approached zero (constant release rate), indicating that this B release was from mineral dissolution. We also did a shorter term experiment that contained added Mg and silicate in solution. These experiments were conducted to evaluate the contribution of B release from dissolution of B-containing Mg silicate minerals. We determined that most ofthe B released from the soils can be attributed to release fiom Sorption sites radier than resulting from dissolution of B-containing Mg silicates. Various B soil tests were evaluated for their ability to measure native extractable adsorbed B. The diediylenetriaminepentaacetic acid (DTPA)-sorbitol extract was the best measure of available ad.sorbed B but still only extracted 48% ofthe amount of B released in the long-term experiment. The greatest amount of B was extracted at the lowest suspension density for DTPA-sorbitol (92%) and phosphate buflPer pH 6.6 (95%). These extractants are recommended for quantifying native extractable adsorbed B, which must be considered in application oí chemical speciation transport models to describe B movement in soils. Incorporation of our results will allow improved predictions of soil solution B concentrations under diverse agricultural and environmental conditions. B oron is an essential micronutrient element for plants; however, the range between deficient and toxic concentrations is smaller for B than for any other plant nutrient element. Boron deficiency often occurs in coarse-textured soils in humid regions and can be triggered by liming of acid soils due to increased adsorption at higher pH (Reisenauer et al., 1973). Boron toxicity results from high levels of B in soils, additions of B via irrigation waters, and lack of adequate drainage (Nable et al., 1997).Compared with other phytonutrient elements, the soil chemistry of B is simple. Boric acid is a very weak, monobasic Lewis acid that accepts a hydroxyl ion to form the borate anión, B(OH)4~. Boron does not undergo volatilization or oxidation-reduction reactions in soils. Boron-containing minerals can be either minerals derived from igneous or metamorphic rocks, precipitates from evaporating brines, or altered or in situ formed clay minerals. Primary minerals containing B, like tourmaline, dissolve very slowly, while hydrated B minerals, like borax and ulexite, that form under extreme evaporative conditions and are very soluble, dissolve rapidly. These B solid phases do not control the concentration of B in most soil solutions (Coldberg, 1993). Boron may also be released into soil solution from B in tetrahedral s...

Evaluation of boron concentration in water samples of Al-Diwaniya Governorate (in Iraq) using ICP/OES Techniques

“…The concentration of boron in the earth's crust has been estimated to be <10 ppm, but concentrations as high as 100 ppm can be found in boron-rich areas [2]. It does not appear on the earth in elemental form but is found in combined state as borax, boric acid, tourmaline, colemanite, kernite, ulexite and borates [3][4][5][6].Boron deficiency is much more common in crops that are grown in soil that have higher amount of free Carbonates, low organic matter, and high pH [7]. Boric acid, borates and per borates can introduced to environment as these have been used in mild antiseptics, cosmetics, pharmaceuticals [8].…”

A New Soil Test for Quantitative Measurement of Available and Adsorbed Boron

“…Because of this variability, amounts of B released using 1 or 100 g soil L −1 extractant were not statistically significantly different at the 95% level of confidence. A previous investigation (Goldberg and Suarez, 2011) had shown the greatest amount of B release at the lowest suspension density (6.7 g L −1 ) for DTPA-sorbitol extraction of the Tranquillity soil.…”