Aluminum Toxicity and Calcium Deficiency in Acid Subsoil Horizons of Two Coastal Plains Soil Series

Inadequate root proliferation in acid subsoil horizons of the Coastal Plain of the southeastern United States limits yields of many crops. The recognized root‐limiting chemical factors in these soils are Al toxicity and Ca deficiency, but it is not known if these properties can be predicted from soil series descriptions. In an effort to delineate Al toxicity and Ca deficiency by horizon and by soil series, six representative profiles from each of two major soil series of Alabama's Coastal Plain were sampled by horizon to a depth of 1 m. Three profiles from each of two major soil series were obtained from cultivated fields; the other three were obtained from adjacent woodlands. Horizon samples were subdivided and treated with one of the following: (i) check, or no treatment, (ii) CaSO 4 , (iii) MgO, and (iv) Ca(OH) 2 . Growth rate of cotton ( Gossypium hirsutum L.) taproots into each treated soil material was measured, and visual symptoms of Al toxicity and Ca deficiency on roots were noted. Six of seven Bt horizons in the Orangeburg series were Al toxic; four of 12 in the Dothan series were Al toxic. None of the five BE horizons were Al toxic. Seven Dothan horizons and four Orangeburg horizons were Ca deficient. No Ca‐deficient horizon occurred in cultivated fields and no Al‐toxic horizon occurred in woodlands. Aluminum toxicity occurred in some Bt horizons (but not all) of cultivated fields when soil‐solution Al was only 0.4µ M , but not in BE horizons of woodlands where solution Al ranged up to 11.5µ M by the 8‐hydroxyquinoline method. Neither was Al saturation a satisfactory predictor of Al toxicity. Nondeficient Ca levels (both soil solution and exchangeable) were lower in cultivated fields than in woodlands. There was no apparent difference between soil series relative to Ca deficiency and Al toxicity, making it seem unlikely that soil classification will be helpful in predicting Ca deficiency and Al toxicity in subsoil horizons.