Soil-applied zinc-EDTA: Growth and nutrient acquisition of non-bearing pecan grown on an alkaline and calcareous soil

Foliar zinc application is routine in southwestern US pecan orchards. Soil zinc application has not been part of pecan management in high pH, calcareous soils because of these soils' ability to adsorb soluble zinc. We are evaluating efficacy of fertigating chelated ZnEDTA in an Arizona pecan orchard with a silty clay loam soil having pH 8.1. 'Wichita' and 'Western Schley' pecan trees were planted in 2011. ZnEDTA was injected into the microsprinkler system throughout the 2011-2013 growing seasons. Three zinc rates (0, 2, or 4 kg ha^-1 Zn annually) were applied to plots arranged in a randomized complete block design with four replicates. Leaf samples were collected and analyzed for zinc levels each season and trees were visually evaluated for zinc deficiency. Trunk diameters were measured each dormant season. Soil samples were collected in 2013. Foliar zinc levels were elevated in both cultivars each year, indicating soil-applied zinc was taken up by the trees. The highest foliar zinc levels in fertigated trees were 29 and 25 mg kg^-1 in 'Western' and 'Wichita' trees, respectively. Corresponding untreated tree zinc concentrations were 7-8 mg kg^-1. Treated trees exhibited slight visible zinc deficiency symptoms, which were significantly less severe than that of untreated trees. In 2013, trunk diameter growth was 19-20% greater in ZnEDTA-treated 'Wichita' trees than in control trees. DTPAextractable zinc levels were elevated from <1 mg kg^-1 in untreated plots to 4-6 mg kg^-1 in soil 60 cm from the base of trees treated with 4 kg ha^-1 Zn.