Soybean plants (Glycine max [L.] Merr. cv Ransom) were grown for 21 days on 4 sources of N (1.0 mM NO-3, 0.67 mM NO-3 plus 0.33 mM NH+4, 0.33 mM NO-3 plus 0.67 mM NH+4, and 1.0 mM NH+4) in hydroponic culture with the acidity of the nutrient solution controlled at pH 6.0, 5.5, 5.0, and 4.5. Dry matter and total N accumulation. © 1990, Taylor & Francis Group, LLC. All rights reserved.