EFFECTS OF INTERMITTENT ACIDIC IRRIGATIONS ON SOYBEAN YIELDS AND FROGEYE LEAFSPOT

Acidic irrigations, adjusted to pH 2, were slightly injurious to leave s of Glycine max (L.) Merr., yet concentrations of most chemical eleme nts in leaf tissue, seed yield, seed size (100 seed weight), and plant weight of two southern cultivars ('Hampton-266A' and 'Kirby') were un affected by six or seven irrigations in the Georgia piedmont. Sulfur l evels in leaf tissue receiving acidic irrigations increased above thos e levels in plants receiving only ambient rain, but not above those ir rigated with well-water containing 10 ppm sulfate at pH 6.8-6.9. There was a suppression of lesions induced by Cercospora sojina K. Hara in acid-irrigated 'Kirby' soybean, but development of powdery mildew on ' Hampton-266A' soybean was not affected. Hydrogen ion concentrations of current ambient rains in the region probably have little effect on yi elds. If intermittent ambient precipitation with dramatically lower pH should occur, then frogeye leaf spot on soybean could be less severe.