IntroductionAgronomists have frequently noted that different strains of common crop plants often show marked developmental contrasts when grown under uniform nutritive conditions, a tendency often termed differential feeding capacity. Such physiological differences are frequently great enough to necessitate profound modifications in tillage and fertilizer practice whenever contrasted strains of a single species are cultivated.An experiment was undertaken to isolate sharply contrasted strains of inbred corn selected on a performance basis under controlled nutritional conditions, and next to determine which inorganic elements were ineffectually utilized.The application of nutrients on a rational basis not only requires that the absorbing power of individual species for particular elements be known but that the optimum time for making these elements available to the roots of the growing plant should be considered. There is much discussion in the literature of plant nutrition (12,22,29) with regard to this time element,