Studies in the Nutrition of Apple Rootstocks

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Abstract
One-year rooted shoots of apple M. VII rootstock were grown for a single season by spraying their roots continuously with nutrient solutions containing (0)), a mild deficiency (Mg(1)), normal foliage and growth (Mg(2)), and a high level of Mg (Mg(3)). The effect of Mg nutrition on the leaves can explain most of the observed effects on vegetative growth. Depression of growth of Mg(1)) plants was not detected until late in the season although necrosis, typical of Mg deficiency, occurred on the lower leaves by mid-July. This loss of photosynthetic area of leaf was to a large extent compensated for by increased efficiency of the remaining green leaves; as the deficiency symptoms progressed, the loss of leaf, and therefore of carbohydrate production, predominated and total growth was affected. The form of the plant was little altered. Symptoms were apparent on leaves of severely deficient Mg(0) plants by late June, and reductions in growth and modifications in form by August. The poor root systems and thin shoots are largely attributed to loss of leaf rather than to the low Mg concentration in these organs. No symptoms of toxicity developed on the Mg(3) plants although by the end of the season the total dry weights were less than those of the Mg(2) controls, and the plants also produced thicker shoots. Plant dry weight, and more especially Mg uptake, increased from Mg(0) to Mg(2) but above this level the gradient of Mg uptake in relation to supply was less steep. The excess Mg taken up at the Mg(j) level led to the relatively lower weights of these plants. Much of the excess Mg accumulated in the leaves, especially in the older ones. Mg moved from, or accumulated in, the lower leaves of the shoot according to the level of Mg supplied to the plants. Thus the shoot apex tended towards normality both in the concentration of Mg and in its growth. In general, growth of the plant, and of individual component parts, governed the uptake of elements other than Mg, although more K, Ca, and Mn and less Fe per unit of plant dry weight accumulated at the lower levels of Mg than at the higher levels.

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