Sequential cold and hot water extract of boron from soils and re-extraction after adsorption by bentonite, kaolinite, iron, and aluminum hydrous oxides over a range of pH values

The relative amounts of boron re-extracted by cold and hot water sequentially after adsorption, over a range of pH values, onto bentonite, kaolinite, precipitated iron, and aluminum (Al) hydrous oxides have been examined, in an attempt to understand why hot water especially is successful as an extractant to indicate plant availability of boron (B). The relative ability of cold and hot water to extract boron was also tested on some Scottish soils. The recovery of boron adsorbed by bentonite, by extraction with cold water compared with that extracted by hot water, Was related to pH, but this was not the case for kaolinite. Comparison of the results for the minerals and soil systems indicates that mineral composition and pH in combination probably regulate the relative extraction power of cold and hot water for soil B. It may be assumed, therefore, that hot water better reflects the capability of plant roots to access B from different adsorption sites than cold water does.