INFLUENCE OF SUBSOIL ACIDITY ON ROOT DEVELOPMENT AND CROP GROWTH IN SOILS OF ALBERTA AND NORTHEASTERN BRITISH COLUMBIA

Abstract

Experiments were conducted in the field and greenhouse with soils of Alberta and northeastern British Columbia to determine the influence of subsoil acidity on acid-sensitive crops. Experiments involved liming of only the topsoil, liming of both topsoil and subsoil, and measuring the aboveground crop yield and the yield of roots in the topsoil and subsoil. In both field and greenhouse, subsoil acidity reduced the yields of top growth and subsoil root pernetration for both barley and alfalfa. The reductions in yield of top growth and roots in the subsoils were correlated closely with the amount of Al (extractable in 0.02 M CaCl2) in the unlimed subsoil. Lowering the soil temperature did not reduce root growth more in acid soils than in limed soil. There were five field experiments, and in the three of these which had subsoils high in extractable Al, the limed subsoils had less moisture at the time of harvest than the unlimed subsoils. The damage to crops caused by subsoil acidity was eliminated by deep liming or in one case by large applications of P to the subsoil or topsoil. These methods of correcting subsoil acidity would not be economically feasible on a field scale. A preliminary field survey was conducted to delineate agricultural areas where subsoil acidity (based on soil pH and extractable Al content) is a significant problem. The largest areas were found in northwestern Alberta and northeastern British Columbia. Key words: Aluminum toxicity, subsoil acidity, liming, temperature, phosphorus, barley