Alfalfameal, sucrose, and peat moss were added in large amounts to very acid soil to find their effects on yields of barley and alfalfa grown in the greenhouse. Alfalfameal was found to be the most effective. Its action was attributed primarily to complexing of exchangeable Al and, in consequence, decreasing toxic quantities of Al in the soil. The Al-organic matter complexes formed by the nonincubated alfalfameal were mostly soluble in water, but those formed by the incubated (4 weeks) alfalfameal were insoluble in water. In both cases, complexing was caused mainly by the water-soluble component of the original, i.e., nonincubated alfalfameal. Release of NH3from the decomposing alfalfa meal was not considered a major cause of decrease in exchangeable Al, since most of that decrease had taken place before there was an increase in exchangeable NH4.