Effect of a soil fulvic acid on stem elongation in peas

Summary Previously observed marked stimulating effects on root initiation produced by a naturally occurring fulvic acid, prompted a further study of the growth reactions of plants exposed for short durations to high concentrations of this acid. Fulvic acid concentrations up to 4000 ppm were found to inhibit stem elongation in dark grown Alaska pea stems in the presence and absence of added IAA by 46% and 33% respectively. Concentrations higher than 4000 ppm produced toxic reactions which increased sharply at pH 4.0 and lower and at pH 7.0 and higher. The fulvic acid appeared to block the uptake of GA₃ in Laxton's Progress No 9 peas when the two substances were applied simultaneously to the leaves, but when these substances were applied separately the fulvic acid had no effect on GA₃-stimulated growth. Contribution No.114 of the Food Research Institute; No.291 Soil Research Institute, Canada Department of Agriculture, Ottawa, Ontario.