Sample Washing Procedures Influence Mineral Element Concentrations in Zinc‐Sprayed Apple Leaves

Abstract

Widespread use of postbloom zinc (Zn) nutritional sprays in tree fruit and nut orchards can lead to substantial surface contamination of apple leaf samples by Zn spray residue, which complicates diagnosis of tree Zn status and Zn nutritional requirements. Detergent washing alone substantially reduced the Zn, iron (Fe), and aluminum (Al) concentrations of Zn‐sprayed Golden Delicious apple (Malus domestica Borkh.) leaves compared to unwashed leaves. Adding a 0.1M HCl washing step further reduced leaf Zn concentration, but had no additional effect of leaf Fe and Al concentrations. There was evidence for nitrogen (N) and sodium (Na) contamination of the leaf samples, possibly from chemical components of the detergent washing solution. The results indicate that the detergent washing is critical for eliminating Fe or Al contamination introduced by dust or soil adhering to leaves collected from trees grown in dusty environments or impacted by soil splash. Adding the acid wash should improve the estimate of the physiologically meaningful Zn concentration in Zn‐sprayed leaf tissue; however, the resulting leaf Zn concentrations may still be biased by a small and possibly variable amount of Zn spray residue.

Keywords:

• Malus domestica
• apple
• tree fruit
• mineral nutrition
• foliar spray
• micronutrient
• zinc
• sample preparation

Acknowledgments

This research was conducted under Project WNP0747, College of Agricultural, Human, and Natural Resource Sciences, Washington State Univ., Pullman. Funding support was provided by the College and by the Washington Tree Fruit Research Commission. I thank Jennifer Moore, and Casimir Lorentz for their technical support.