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.

Abstract

Young, budded Valencia orange trees were grown for several years in outdoor sand cultures with three levels each of nitrogen, potassium, and magnesium in factorial combinations. Total growth and fruitful-ness were greatly dependent on the nitrogen level but relatively independent of the two base elements over a very wide range of supply. These responses and those pertaining to fruit quality were recently described in detail (18). The nutritional status of the trees was evaluated by yearly collections of leaf samples. At the termination of the experiment in January, 1951, samples of leaves, fibrous roots, and woody structures were taken. The present report describes some of the results of mineral analyses made on these tissues. About 5,000 individual determinations of elements were made on over 900 samples. Only mean values are presented in the tables, for illustrative purposes. They represent the main trends and relations found. MIATERIALS AND METHODS Details of culture method have been described elsewhere (18). The trees were grown under differential treatment for slightly over three and one half Nears and satisfactory growth and fruiting resulted where the combinations of nutrients were favorable. The levels of K and Mg were changed somewhat during the second year to alleviate excessive Mg deficiency. During most of the culture period the following concentrations, in ppm, of the three elements were used: N 30, 80 and 200; K 8, 32 and 180; and Mg 12, 24 and 72. These are referred to hereafter as low, intermediate, and high. The N was supplied as 80 % nitrate and 20 % ammoniacal. The other essential elements were supplied in constant amounts as previously described (18). The first leaf samples were taken in September, 1947, about 3.5 months after the start of the experiment. Subsequent leaf samples were taken on dates given in table I. All leaf samples were detergent-washed (19) except the final collections, which were quite bulky, since they contained all the leaves from the 1-tree plots. The fibrous root samples were not washe(d because of the possibility of altering their base composition through exchange reactions but they were carefull3l rinsed in water and most adhering sandl particles were removed by jarring the dried samples before grinding. The fact that the sand me-(lium was continuously acidic (pH 4.5 to 5.0) is thought to have prevented most compounds from accumulating on the root surfaces as precipitates. Iron determinations for the root tissues, however, are probably meaningless since the roots penetrated the asphalt paint and were partially in contact with the 1 Received October 28, 1953. iron containers. Woody samples (including bark) of trunk, limbs, and large roots were also taken.