The aim of the present work is to analyze the effect of different foliar products of nickel (Ni) on the nutrient concentration, chlorophyll content, and enzymatic activity of urease as the possible bioindicator of the levels of Ni in the leaves of pecan [Carya illinoinensis (Wangenh.) K. Koch]. The experiment consisted of the foliar application of Ni to pecan cv. Western Schley, using two commercial products: Nickel Plus®T 1 and Speedfol™ PecanoT 2 , and a control T 0 received no Ni treatment. The following variables were evaluated: the total chlorophyll concentration, the concentration of macro-and micronutrients including Ni, and the activity of urease. The results demonstrated that the pecan trees treated with Ni increased in the concentration of this element and that the product Nickel Plus® T 1 increased by 41.24% with respect to control. The foliar application of Ni led to significant differences in the foliar concentrations of N, P, K, Ca, Mg, Fe, Mn, Cu, Zn, and Ni. Chlorophyll showed a significant reaction to the foliar application of Ni. The enzymatic activity of urease proved to be positively related to the foliar level of Ni, and thus could be considered a good physiological bioindicator of the nutritional state of foliar Ni in the leaflets of the pecan tree.

Zinc deficiency limits pecan nut production. The objective of this study was to evaluate changes in nutrient concentration and oxidative metabolism in pecan leaflets in response to the application at different doses of zinc. The foliar concentration of nutrients, leaflet area, total chlorophyll, dry weight (leaflets and root), superoxide dismutase (SOD), hydrogen peroxide, catalase (CAT), guaiacol peroxidase (GP) and antioxidant capacity were evaluated. Statistical analysis indicates that the application of 200 µmol Zn²⁺ affected the foliar concentration of N-total (24.50 ± 2.51 g/kg), P (10.34 ± 2.53 g/kg), Fe²⁺ (153.33 ± 6.27 mg/kg) and Zn²⁺ (42.00 ± 2.84 mg/kg), showing a greater area of the leaflet, total chlorophyll content and dry weight (leaflets and root). Plants treated with 50 µmol Zn²⁺ showed a higher level of SOD activity (1.38 ± 0.016 units/min/g), GP (5.56 ± 0.229 nmol glutathione/min/g), and the production of hydrogen peroxide, without exceeding the control. On the other hand, Zn treatments caused a significant decrease in CAT activity. Zn is an essential micronutrient for the growth and development of pecan, which promotes the accumulation of other nutrients. Therefore, its absence affects the generation of oxidative stress with the subsequent activation of the antioxidant defense enzyme system.