Effect of Differential Nitrogen, Potassium, and Magnesium Supply to Young Valencia Orange Trees in Sand Culture on Mineral Composition Especially of Leaves and Fibrous Roots.

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Abstract
Comparisons of the concentrations of 12 mineral elements in leaves and fibrous roots showed differences in every case. N, P, K, Ca, Mg, and Na concentrations tend to be parallel in the two tissues, but the roots usually contained lower levels than the leaves. Analytical values for Mn, Fe, Cu, Zn, B, and Al indicated wide differences between the two plant parts. The metal elements showed several-fold concentration in roots while B tended to accumulate in leaves. Numerous interactions occurred between the N level and either the K or Mg levels of supply on the concentrations of various elements in both roots and leaves. This indicates the desirability of studying N in factorial experiments as its effects on tissue composition may vary appreciably with different supplies of other elements. Very few interactions were found between K and Mg, however, indicating that these elements could be studied in nutritional experiments as single variables. Reciprocation among base elements was evident in all parts of the tree. Leaves tended to show a constant total base equivalence of about 200 meq per 100 g dry wt., as long as Ca did not exceed about 170 meq., regardless of large differences in nutrient composition of the culture solution and large differences in growth of the trees. Other tree parts also showed constant equivalent totals in trees of similar size. Greater growth of the tree, associated with increased N supply, tended to dilute the base elements in tissues other than leaves.