Abstract
This study performed with soybean (Glycine max L.), one of the most important crops for human and animal nutrition, demonstrates that changes in the leaf surface structure can increase the adhesion of applied droplets, even on superhydrophobic leaves, to reduce undesirable soil contamination by roll-off of agrochemical formulations from the plant surfaces. The wettability and morphology of soybean (Glycine max L.) leaf surfaces before and after treatment with six different surfactants (Agnique® SBO10 and five variations of nonionic surfactants) have been investigated. The leaf surface structures show a hierarchical organization, built up by convex epidermal cells (microstructure) and superimposed epicuticular platelet-shaped wax crystals (micro- to nanostructure). Chemical analysis of the epicuticular wax showed that 1-triacontanol (C30H61OH) is the main wax component of the soybean leaf surfaces. A water contact angle (CA) of 162.4° (σ = 3.6°) and tilting angle (TA) of 20.9° (σ = 10.0°) were found. Adherence of pure water droplets on the superhydrophobic leaves is supported by the hydrophilic hairs on the leaves. Agnique® SBO10 and the nonionic surfactant XP ED 75 increased the droplet adhesion and caused an increase of the TA from 20.9° to 85° and 90°, respectively. Scanning electron microscopy showed that surfactants with a hydrophilic–lipophilic balance value below 10 caused a size reduction of the epicuticular wax structures and a change from Cassie–Baxter wetting to an intermediate wetting regime with an increase of droplet adhesion.
Highlights
The cuticle, as the outermost layer of higher plant surfaces, represents the interface between plants and their environment and accomplishes essential functions to ensure the maintenance of a terrestrial plant life, such as the reduction of water loss [1], control of gas exchange [2,3], protection from harmful UV radiation [4] and aiding mechanical stability [5]
This study performed with soybean (Glycine max L.), one of the most important crops for human and animal nutrition, demonstrates that changes in the leaf surface structure can increase the adhesion of applied droplets, even on superhydrophobic leaves, to reduce undesirable soil contamination by roll-off of agrochemical formulations from the plant surfaces
The micromorphology of leaf surfaces was investigated by scanning electron microscopy (SEM) and 3D light microscopy
Summary
The cuticle, as the outermost layer of higher plant surfaces, represents the interface between plants and their environment and accomplishes essential functions to ensure the maintenance of a terrestrial plant life, such as the reduction of water loss [1], control of gas exchange [2,3], protection from harmful UV radiation [4] and aiding mechanical stability [5]. The leaf surfaces are composed of epidermis cells covered by a cuticle, which is a continuous extracellular membrane on primary plant tissues (shoots, leaves, fruits) of higher plants [10,11]. It is built up by a network of the cross-linked ester-like biopolymer, cutin, with integrated (intracuticular) and superimposed (epicuticular) waxes [12,13]. The hydrophobic characteristic of epicuticular waxes and their three-dimensional micro- to nanometer-scaled structures play a crucial role in surface wettability
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