Effect of pH on Boron Adsorption-Desorption Hysteresis of Soils

Abstract

Lime is regularly used to increase soil pH, which will increase boron (B) fixation in soils. The effects of raising pH on B adsorption and the reversibility of adsorbed B in acid soils are essential for soil B management. In this study, B adsorption and desorption in limited concentration as a function of pH were measured in five finetextured red soils. Immediately after adsorption of B, four consecutive desorption steps were carried out by successive dilution. The sorption results were described well by the Freundlich equation. Boron adsorption markedly increased as pH increased. This increase was more pronounced when Ca(OH) 2 , as opposed to NaOH, was used for pH adjustment. The presentation of desorption data was based on the traditional isotherm approach and on time-dependent isotherms. Apparent hysteresis was observed in that both derivational families of desorption isotherms deviated from the adsorption isotherm for the five soils at their original pH. Moreover, hysteresis coefficients, n des /n ads and L trad for the traditional approach, had a positive correlation with organic carbon content, but they had a negative correlation with free Fe 2 O 3 and free Al 2 O 3 content. As pH increased, the hysteresis diminished, and adsorbed B became more likely to be desorbed. This finding may be because B adsorption and raising pH increase the negative charge on the surface, which creates electrostatic repulsion and results in an increase in desorption as pH increases.

Role of Organic Matter on Boron Adsorption-Desorption Hysteresis of Soils

“…The Woburn (pH 6.7) and Zegveld (pH 4.7) soils, both having a pH below neutral, were hysteretic in the long-term experiment in contrast to the Hanford soil having a higher pH (7.4), which was not. Our long-term results are in agreement with those of Chen et al (2009), who found increasing hysteresis with decreasing soil pH. Hysteretic behavior can result from the experimental procedure itself.…”

“…Boron adsorption by the inorganic soil constituent clay minerals, kaolinite, illite, and montmorillonite, did not exhibit hysteresis (Hingston, 1964). Desorption hysteresis was found to be present at low solution pH and low B concentration and absent at higher solution pH and increasing B concentrations (Meyer and Bloom, 1997;Chen et al, 2009;Majidi et al, 2010). Clearly, the contribution of soil organic matter to the hysteresis of B adsorption-desorption requires further investigation.…”

Effect of pH on boron adsorption in some soils of Paraná, Brazil

“…However, Rosolem and Bíscaro (2007) found that even with the applying of relatively high rates of lime, the B adsorption by soil is only significant in the year that the liming was carried out, so that over time a greater amount of B remains in the soil solution under conditions of being readily absorbed by plants or even being lost by leaching. Similarly, Chen et al (2009) observed that soil re-acidification caused an increase in B desorption, increasing the element's content in solution. Indicating that B adsorption by soils submitted to liming is characterized by a rapid and reversible chemical reaction between the adsorbed and soluble B.…”

“…Rosolem and Bíscaro (2007) also found a higher adsorbed B value of 24.2 mg kg -1 at higher pH (5.6) compared to 9.5 mg kg -1 at lower pH (4.5). Various studies have reported that one of the most important factors affecting the adsorption of B in soils is pH (Saltali et al, 2005;Soares et al, 2008;Chen et al, 2009). Boron adsorption by soils increases in the pH range between 3.0 and 9.0, and decreases in the range of 10.0 to 11.5, giving a typical bell curve with an adsorption peak of about 9.0, very close to the boric acid pKa of 9.2 (Goldberg, 1997).…”

Liming Effects on Extractable Boron in Six Acidic Soils

“…These oxides might have adsorbed added B and lowered the recovery (particularly with L 1 ). Decreased availability of added B with liming below neutrality has been reported by some researchers (Fleming 1980;Chen, Ho, and Lee 2009), whereas others found no definite trends (Gupta and MacLeod 1977) or an increased availability (Mandai, Adhikari, and De 1993).…”