Foliar Application of Nickel and Copper On Pecan Performance

The mobilization and conversion of reserve nitrogen (N) is critical for pecans [Carya illinoinensis (Wang.) K. Koch] during early spring when trees begin growing actively.  Conversion of N reserves to translocatable forms (amides, amino acids, ureides) is adversely affected by a nickel (Ni) shortage. Nickel is required for urease (EC 3.5.1.5, urea amidohydrolase) activation and appears to function in additional enzymes affecting N metabolism. The orchard used for study received an unusually high amount of N annually from nitrate contaminated irrigation water.  High N induces copper (Cu) deficiency by inhibiting transport in plants. Copper, Ni and Ni + Cu were applied as a foliar spray application at the parachute stage of leaf development (19 April), followed by two additional applications at two weeks intervals. Nickel and Ni + Cu increased the weight per nut. Kernel percent and quality were not affected by treatment.  Kernel necrosis, a malady characterized by necrotic tissue at the basal end of the kernel, was not affected by treatment. Pecan kernels contain about 70% oil that is compartmentalized in oil bodies.  Leakage of these bodies into intercellular spaces, termed opalescence, affects appearance and reduces shelf-life. Treatments increased opalescence compared to the control, perhaps the result of increased oil content. The Ni + Cu treatment reduced yield and yield efficiency; whereas, other treatments were similar to the control. Trunk growth and area per leaf were increased by Ni application, but specific leaf weight was unaffected.  Leaf P, K, Ca, Mg, Fe, and Mn were not affected by treatment, but Cu and Zn concentration of foliage and nuts were affected. Results indicate that foliar Ni application was beneficial, but Cu was not, in this particular orchard situation. Zinc sulfate was applied as a standard management practice to the control and was combined with Ni, Cu, and Ni + Cu treatments.  Results indicate the possibility that combining Zn, Ni and Cu in the foliar application may reduce yield via either an excess salt-effect or by competitive inhibition of the timely physiological availability of a key nutrient.