Soil zinc fertilization in one-year-old potted 'Wichita' pecan trees in alkaline soil

This study was conducted to evaluate the effect of soil application of various Zn sources on potted pecan trees. One-year-old 'Wichita' pecan trees were planted in 40 L containers on February 28, 2008. Treatments included an untreated control, soil-applied Zn sulfate, Zn EDTA, Zn Avail (dicarboxylic acid polymer resin), manure, manure plus Zn sulfate, and foliar applied Zn sulfate. The manure application rate was 11.4 ton·ha^-1, and the Zn application rate was 74 kg Zn·ha^-1 for each material. The foliar sprayed solution was ZnSO₄ (0.24% w/v) plus urea ammonium nitrate (0.25% v/v). Soil treatments were applied once on April 4. Foliar sprays were applied every three weeks from April 4 to August 15. The experimental design used was a Latin Square with seven replications, with each tree comprising one plot. Data collected included plant growth, chlorophyll index, and leaf mineral composition. Sorption studies were conducted to determine the effect of Zn source (Zn sulfate, Zn EDTA, and Zn Avail) and organic matter on soil Zn adsorption. Plant growth was not affected significantly by treatments; however, total leaflet growth was higher in the Zn EDTA treatment with 30.6 g per plant versus 20.2 g per plant in the untreated control. Trees treated with Zn EDTA had the highest leaf Zn concentration (240 μg·g^-1). Foliar sprayed trees had foliar Zn levels about half that of trees treated with Zn EDTA. Soil adsorption isotherms showed that of the three fertilizers evaluated Zn sulfate was adsorbed most strongly by the soil (1.5 mg Zn·g^-1 of soil). Soil adsorption from Zn EDTA solutions was insignificant. Zinc EDTA can increase soil Zn availability to pecans growing in alkaline, calcareous soils.