Physiologically Balanced Culture Solutions with Stable Hydrogen-Ion Concentration

Abstract

To solutions adjusted to pH values of 4.3, 5.1, and 6.0 by suitable proportions of H3PO4, KH2PO4, and K2HPO4, varying proportions of KNO3, (NH4)2SO4, NH4NO3, Ca(NO3)2, and NH4NO3 were added to give a wide range of NO3: NH4 ionic ratios. With a suitable value of this ratio a physiologically balanced solution was obtained in which the pH tended to remain constant. This results from balancing the conc. of NO3 (the absorption of which removes H-ions from solution) against that of NH4 (the absorption of which removes OH-ions). For very accurate control of pH the NO3:NH4 ratio may need to be changed progressively as the plants increase in age.