Evaluation of boron chelates in extracting soil boron

Abstbact

The hot water extractable boron (HWB) soil‐test procedure does not lend itself to rapid routine analysis. This study was conducted to evaluate boron (B) chelates in extracting soil B in comparison to the HWB soil‐test procedure. The following B chelates were examined as soil B extractants: mannitol, salicylic acid, 2‐hydroxyisobutyric acid, and sorbitol. Soil B chelate extractants were prepared in a buffered solution that contained IN ammonium acetate and 0.1M triethanolamine. For each respective chelate, chelate concentrations were evaluated at 0.05, 0.2, and 0.5M at a soil:extract ratio of 1:4, extract pH of 7.3, and a shake time of 15 minutes for extracting soil B. For only the sorbitol B extractant (0.2M), various soihextract ratios (1:2, 1:4, 1:6, and 1:10), extract pH (5.0, 7.3, and 8.8), and shake times (15, 30, 60, and 120 min) were examined. All soil B determinations were by ICP. Maximum amounts of B were extracted at a chelate concentration of 0.2M for all four chelates evaluated. Maximum amounts of B were extracted at pH 5.0, 1:6 soiL:extract ratio and a shake time of 120 min. Based on laboratory efficiency and instrument detection limits, a chelate concentration of 0.2M, 1:4 soil extract ratio, pH 7.3, with a shake time of 15 minutes was selected for standard operating procedures. Soil extractants were ranked in terms of amount of soil B extracted as follows: HWB>mannitol=sorbitol>salicylic acid>2‐hydroxyisobutyric acid. Quadratic regression equations explained 84 to 88% of the HWB variability when mannitol, salicylic acid, or sorbitol were used as the independent variable. Stepwise regression equations were developed that explained 90 to 92% of the HWB variability when soil pH in addition to chelate extractable B was entered into the equation. Based on chelate expense and ability to extract soil B, sorbitol would be suggested as a replacement for the HWB soil test procedure in determining available soil B.