REDUCTIONS IN EXCHANGEABLE MAGNESIUM WITH LIMING OF ACID OHIO SOILS

Reductions in exchangeable Mg with liming have frequently been reported in acid soils. It has been suggested that such reductions are due to an interaction between exchangeable Mg and soil Al; however, the form(s) of Al responsible for the interaction has not been adequately defined. Consequently, the objectives of this study were to fractionate the Al occurring in a series of acid Ohio soils and to determine if a relationship between Al and Mg could be defined in order to predict those soils where reductions in exchangeable Mg with liming may pose a potential problem for plant nutrition. Laboratory treatments were applied to seven soil materials in a 4 multiplied by 2 factorial, with four lime (no lime, pH 5, pH 6, pH7) and two Mg levels (0 and 25% of the cation exchange capacity, CEC). The reduction in exchangeable Mg was positively correlated with several soil Al fractions including exchangeable, organically chelated, and poorly crystallized inorganic species; however, exchangeable Al produced the best correlation supporting the hypothesis that Mg 'fixation' is due to the occlusion or coprecipitation of Mg with Al upon liming.