CRITICAL ZINC+2 ACTIVITIES FOR SOUR ORANGE SEEDLINGS DETERMINED USING A CHELATOR-BUFFERED NUTRIENT SOLUTION

Abstract

Chelator-buffered nutrient solutions were used to study the effect of different levels of Zn+2 activity on the growth of various tissues of sour orange seedlings. Zn+2 activities were calculated with a computerized chemical equilibrium model, GEOCHEM-PC, and were buffered by adding 74 and 44 uM of diethylenetriamine pentaacetate (DTPA) in excess of the sum of Fe, Mn, Zn, and Cu in Exp. 1 and 2, respectively. Root dry wt. was least sensitive to Zn deficiency followed by leaf number and white root growth, stem dry wt., leaf dry wt., shoot elongation and leaf area. The critical Zn+2 activities in the nutrient solutions for these growth parameters ranged from 10-10.4 to 10-10.05M. Increases in growth were observed from Zn applications even when visible Zn deficiency symptoms were absent. Seedlings with > 23 ppm Zn in their leaves did not respond to further additions of Zn to the nutrient solution. Zinc foliar sprays were less effective than Zn applications to the roots in alleviating severe Zn deficiency.