Abstract

It is difficult to compare the effectiveness of different zinc formulations because of low uptake percentages, high variability of zinc content in the plant before application and generally low mobility. We have developed a method that is consistent and effective, and demonstrates dramatic differences among formulations. It involves peach (Prunus persica 'Nemaguard') seedlings grown in washed sand and fertilized with 10% Hoagland solution minus zinc. Once the seedlings are about 30 to 40 cm in height, they begin to show typical zinc deficiency symptoms of narrow, pointed, chlorotic leaves at the shoot tip. Plants are then sprayed with different zinc formulations and fertilizer strength is increased to 40% Hoagland solution to help promote vigorous growth and stimulate lateral shoots. Generally after 20 to 30 days there are distinct differences among treatments. The biggest effect tends to be on lateral shoot growth in both length and especially leaf area. There is also an increase in individual leaf area on the primary shoot and in zinc concentration of the new growth. The degree of increase demonstrates the relative effectiveness of the material. Using this method, we conducted four separate experiments testing a total of 12 different zinc formulations. By completion of the fourth experiment we came to the conclusion that effectiveness of zinc formulations was related to solubility and size of the accompanying anion. Our hypothesis is: the more soluble the material and the smaller the accompanying anion (lower molecular weight), the more effective the formulation.