Effect of four acid soils on root growth of white clover seedlings using asoil-on-agar procedure

White clover (Trifolium repens L.) is widely distributed in the Appalachian region, except on highly acid soils. We used a procedure where a thin laye r of soil is placed on top of solidified water agar to characterize effects of acid soil on seedling root growth. Our objectives were to evaluate the soil-on-agar technique by using four soils (non-limed and limed) with diver se chemical characteristics and to relate root emergence to the chemical pr operties of the soils. We used three white clover cultivars, 'Grasslands Hu ia,;Grasslands Tahora' and 'Sacramento'. Daily counts of root emergence fro m soil into agar were made for 12 d. Liming hastened white clover root emer gence in three of the four soils. Days to 40% emergence were closely relate d (P < 0.01) to soil pH((H2O)) and to species of soil solution Al that are associated with Al toxicity in dicotyledonous plants. The r(2) values for t he regression of days to 40% root emergence on pH((H2O)), Al3+, Al(OH)(2+) and (Al3+ + Al(OH)(2+) + Al(OH)(2)(+)) were 0.95, 0.96, 0.94 and 0.96, resp ectively. Apparently, the primary factor responsible for delayed root emerg ence in the soil-on-agar procedure was Al toxicity. Because of the close re lationship between foot emergence and activity of toxic species of soil sol ution Al, we propose that the soil-on-agar technique should be useful for c haracterizing the response of many small-seeded species to Al.