Studies in the Nutrition of Apple Rootstocks

Plants of the apple rootstock M.VII were grown for a single season by spraying their roots continuously with nutrient solutions: (a) complete, (b) low iron, (c) low magnesium, and (d) low iron and low magnesium. Detailed records were taken throughout the season of fresh weight, shoot length, diameter, and leaf area, while the fresh and dry weights of component parts were determined on harvested samples. The leaves of the iron-deficient plants were chlorotic and had a lower dry weight and higher water content per unit area than those of the control plants. Growth and net assimilation rate were both reduced but the distribution of assimilates was similar to that in the controls. Total growth was also markedly reduced by the low-magnesium treatment, but the leaf symptoms were different and the plants were morphologically distinct from the control plants. Very little chlorosis occurred, but necrosis and severe defoliation, progressing up the shoot, reduced the leaf area ratio and probably largely accounted for the low net assimilation rate and relative growth rate. The diameter of the shoot was affected much more than its length and the shoot/root ratio was greatly increased. Plants deficient in both iron and magnesium showed less defoliation than when magnesium alone was low. More dry matter accumulated in the old stem and less in the new shoot than would have occurred with a simple combination of the single deficiencies.