COMPARISON OF EXCHANGEABLE AL, EXTRACTABLE AL, AND AL IN SOIL FRACTIONS

Exchangeable Al values determined by 1 M KCl and 1 M NH4Cl, extractable Al values determined by 1 M NH4OAc, pH 4.8, 0.01 M CaCl2, 0.5 M CuCl2, 0.33 M LaCl3, and 0.005 M NTA, were compared with each other and to the activity of Al3+ in soil solution as well as Al in soil fractions. Aluminum in fractions was measured to determine the forms solubilized by the extractants. The fractions extracted were exchangeable [M Mg(NO3)2], organic bound, Mn oxide, amorphous Fe and Al oxide, and crystalline Fe and Al oxide. Aluminum in the crystalline Fe/Al oxide fraction correlated well with that extracted by CuCl2, LaCl3, NTA, and NH4OAc, pH 4.8, leading to the possible conclusion that these extractants solubilize Al from plant-unavailable fractions. -from Author