SEQUENTIAL COLD AND HOT-WATER EXTRACT OF BORON FROM SOILS AND REEXTRACTION 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 seque ntially after adsorption, over a range of pH values, onto bentonite, k aolinite, precipitated iron, and aluminum (Al) hydrous oxides have bee n examined, in an attempt to understand why hot water especially is su ccessful 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 bento nite, by extraction with cold water compared with that extracted by ho t water, Was related to pH, but this was not the case for kaolinite. C omparison of the results for the minerals and soil systems indicates t hat mineral composition and pH in combination probably regulate the re lative extraction power of cold and hot water for soil B. It may be as sumed, therefore, that hot water better reflects the capability of pla nt roots to access B from different adsorption sites than cold water d oes.