WEEKLY ABSORPTION OF NITRATE BY YOUNG, BEARING ORANGE TREES GROWING OUT OF DOORS IN SOLUTION CULTURES

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Abstract
A record of the weekly absorption of nitrate by 2 young, bearing Valencia orange trees growing out of doors in complete nutrient solns. for a continuous period of > 3 yrs. has been made. The period of least absorption in each of the 3 yrs. was during Jan. and Feb. The period of max. absorption was that of late spring, summer, and early fall. These periods of varying absorption, as is to be expected, were related to soln. and air temps. The week-to-week absorption varied widely at times, however, even when temp. conditions were constant. The relation between the quantities of nitrate and of water absorbed was variable from week to week. During one period when the 2 trees used in these expts. were out of phase with one another in respect to root- and top-growth, it became apparent that nitrate absorption was more closely related to periods of active root-growth; but water absorption was more closely related to cycles of active top-growth or, more specifically, to the physiol. activities associated with root- and top-growth. Under the conditions of low nitrate conc. prevailing throughout the exptl. period, nitrate was absorbed relatively more rapidly than water, although the degree of selectivity varied widely from time to time. While periods of rapid nitrate absorption were usually associated with periods of active root-growth, substantial amts. of this constituent were taken in by roots which had become brownish colored and partially suberized. From Jan. to May in every yr. no new root-growth occurred, the spring blossom and leaf cycle having completely emerged before the first signs of new root growth became manifest. With reference to the seasonal N requirement of citrus, the data suggest that the major accumulation of N reserves requisite for vigorous spring growth, blossoming, and fruit setting probably occurs in the preceding fall and early winter. Vegetative growth is less active during this period but nitrate is absorbed in substantial quantities.

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