Summary

Twentieth century zinc research has discovered that a lack of zinc is expressed in plants as rosettes, low vigor, poor leaf development, and eventual death progressing from the terminal branches. Zinc is unavailable in alkaline soils because of formation of insoluble ZnCO₃ and in acid soil where zinc is in competition with nickel. Foliar application has proven difficult because of cuticular barriers as leaves become mature. Frequent zinc foliar applications are more successful than occasional treatments. Traditional ZnSO₄ foliar treatments have proven inadequate compared to a nitrate-based zinc spray. The new formula is NZN consisting of Zn(NO₃)₂⁺NH4NO₃⁺urea. Nitrogen is superior to sulfur for many reasons in enhancing zinc absorption. Nitrogen is an integral part of all amino acids, whereas sulfur is found in only a few. Sulfur accumulates on the surface of treated crops and can cause spray burn in many. Nitrates are hydrophilic and sulfates are hydrophobic which influence their ability to enter cuticles of treated crops in arid environments.

The increase from 200,000 to 12 million pounds of pecan production in the 30 year span from 1967 to 1997 of the zinc research in the Trans Pecos area of Texas is more than a coincidence (USDA Agricultural Statistics, Texas Department of Agriculture, 1997). This comparison is more justified than in other areas because lack of zinc was the limiting factor in that area. The zinc nutrition problem that confronted the industry in 1965 has been solved. Obviously, the efforts of a number of hard-working pecan growers and horticulturists were instrumental in securing this massive production increase.

There has been a long, unsuccessful struggle to develop a rootstock that will facilitate zinc root absorption. A small percentage of pecan seedlings will absorb and transport zinc. Zinc-regulated transporter proteins have been found in some pecan seedlings that promise to revolutionize the pecan industry and other species. This development is the future to which we can all look, for all of our zinc-deficient species. The preceding horticulturist and agronomists cited in this sections have discovered the problem. Now the next generation, using advanced technology like zinc-regulated transporter proteins, will eliminate the expense of foliar sprays and soil treatments.