NITROGENOUS METABOLISM OF PYRUS MALUS L.: IV. THE EFFECT OF SODIUM NITRATE APPLICATIONS ON THE TOTAL NITROGEN AND ITS PARTITION PRODUCTS IN THE LEAVES, NEW AND ONE YEAR BRANCH GROWTH THROUGHOUT A YEAR'S CYCLE

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Abstract
These studies are an extension of the partition investigations on 2 Stayman Winesap trees of the same age, growing on sod in a homogeneous soil. One of these trees was treated in 2 applications with 20 lbs. of NaNO3 and the other left untreated. In general, the present findings confirm the conclusions drawn in the previous studies and in addition indicate that the total N content of the 1-yr. (1923) branch-growth of the fertilized tree from the period of full bloom to the end of Sept. increased 10%, but the total N of the 1-yr. branch-growth of the unfertilized tree decreased 35% during this period. This lower plane of N metabolism of the untreated tree as compared with the treated tree is also indicated by the total N results of the leaves, new (1924) branch-growth, and older branch-growth. The period of most rapid absorption of the NO3 ion is characterized by a large increase in the total water-soluble and non-protein N, concomitant with which is an increase in the amino, amide, basic, and "rest" N fractions of the fertilized as compared with the unfertilized tree in the leaves, 1-yr. (1923), and new (1924) branch-growth. From the course of the curves for total water-soluble N, non-protein N, or amino N of the fertilized as compared with the unfertilized tree it can be deduced that the 1st application of NaN03 on April 20 took 3 weeks to reach the 1-yr. branches. The same curves show that the absorption and translocation of the NOs ions of the 2nd application on June 6 are much more rapid, taking about 1 week only to get to the more metabolically active parts of the tree. The total water-soluble N and non-protein fraction is much higher in the more metabolically active parts of the treated tree as compared with the untreated tree throughout the whole cycle. These differences correspond to the relative vigor of the trees and must be associated with differences in enzymatic activity. The fact that the amino acid N parallels the total water-soluble curve throughout the whole cycle suggests a simplification of the N distribution problem in practical horticulture. N is stored in the fall as "amide" N and "rest" N compounds, and, as indicated by the % present during this period, is much higher in the fertilized than in the unfertilized tree. The "rest" N compounds form an important connecting link in the synthesis and degradation of proteins and there is a need for an investigation into the nature of these "unclassified" compounds whose role in metabolism seems so important.