Selected Calcium Salt Formulations: Interactions between Spray Deposit Characteristics and Ca Penetration with Consequences for Rain-Induced Wash-Off

ABSTRACT

The effect of two ethoxylated rapeseed oils (RSO) as surfactants for foliar-applied calcium chloride CaCl₂ and calcium acetate Ca(CH₃COO)₂ on deposit characteristics, penetration, and calcium (Ca) residues after rainfall was investigated in columnar apple trees (CAT, Malus domestica Borkh.) and apple seedlings. Irrespective of salt and apple variety, both surfactants enhanced droplet spreading and led to a greater area covered by calcium within the droplet residues. The addition of the rather lipophilic surfactant RSO 5 and the rather hydrophilic RSO 60 increased penetration of Ca from both salts through isolated apple leaf cuticular membranes. Our data demonstrate that penetration is better reflected by area covered with calcium than by droplet spreading area. Considering the point of deliquescence (POD) from the salts and results of cuticular Ca penetration, we postulate that in case of CaCl₂ reduction of wash-off was due to enhanced penetration, whereas for Ca(CH₃COO)₂ wash-off was decreased due to distinct enhancement of rainfastness.

Keywords:

• foliar fertilization
• cuticular penetration
• droplet spread
• residue area
• SEM-EDX
• Malus domestica

ACKNOWLEDGMENTS

This project is funded by the German Research Foundation (DFG) and is part of the Research Training Group 722 “Use of Information Technologies for Precision Crop Protection”. We thank Cognis GmbH, Duesseldorf, Germany, for providing RSO surfactants, Dr. Lutz Damerow for conceptual design of the rain simulator, Dr. Andreas Ulbrich for fruitful discussion in the run-up of the experiments, and Libeth Schwager and Knut Wichterich for their technical assistance.

Notes

^a Means in the column for each salt and each evaluated parameter with no letters in common are significantly different (Duncan, P ≤ 0.05).

^a Means in the column for each salt and each evaluated parameter with no letters in common are significantly different (Duncan, P ≤ 0.05).