A new soil test for quantitative measurement of available and adsorbed boron

Authors: Goldberg, Sabine; Suarez, Donald

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2014
Publication Date: 4/8/2014
Citation: Goldberg, S.R., Suarez, D.L. 2014. A new soil test for quantitative measurement of available and adsorbed boron. Soil Science Society of America Journal. 78(2):480-485.

Interpretive Summary: Boron is a specifically adsorbing anion that can be detrimental to plants at elevated levels. Detrimental levels can occur because of high levels of boron in the soil solution or from additions of boron via the irrigation water. Release of native adsorbed B was quantified on six arid zone soils. Various extracting solutions containing sugar alcohols were evaluated for their ability to measure native adsorbed B. We evaluated the extraction performance at varying soil to solution ratios and reaction times. We selected sorbitol as the extractant and used a soil to solution ratio of 10 g/L and a reaction time of 24 hours. This soil test was able to provide quantitative recovery of added boron from a diverse group of soils from California, Iowa, and Oklahoma. Our results will benefit scientists who are developing models of boron movement in arid zone soils. The results can be used to improve predictions of boron behavior in soils and thus aid action and regulatory agencies in the management of soils and waters which contain elevated concentrations of boron.

Technical Abstract: Boron soil tests currently in use, do not extract all plant available B but are used by relating the extractable amount of B to plant B content. There is a need to accurately measure all plant available or adsorbed B because B can be toxic to plants at elevated concentrations and can cause marked yield decrements. Determination of the adsorbed B pool in the soil is also required for evaluation of the extent of leaching needed when B levels in soil solution are excessive, as well as for modeling studies regarding B transport in soils. Sugar alcohols form strong bonds between their cis-diol groups and B and are therefore, ideal for use as extractants for soil B. We evaluated the extraction performance of various sugar alcohols: sorbitol, mannitol, xylitol and varying soil to solution ratios (1 to 1000 g/L) and reaction times (1 to 48 hours). We selected sorbitol as the extractant, utilizing a soil to solution ratio of 10 g/L, and reaction time of 24 hours. This soil test was able to provide quantitative recovery of B added to a diverse set of seven soils from California, Iowa, and Oklahoma. Results from the new B soil test can be used to quantify adsorbed B and thus provide needed input to both chemical speciation-transport models such as UNSATCHEM to obtain accurate predictions of B transport and partitioning in soils, as well as allowing for improved management of waters and soils high in B.