Leaf Surface Electrostatics: Behavior of Detached Leaves of Beans, Maize, and Other Plants Under Natural Conditions

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Abstract
To determine if leaves become charged under natural conditions, the electrical fields associated with leaf surfaces of beans (P. vulgaris) and maize (Z. mays) were measured over periods ranging 1-5 days during both fine and unsettled weather. Electrical fields were measured with an electrostatic sensor (field mill) positioned 10 mm above adaxial leaf surfaces. Surfaces of leaves became charged, with average field intensities < 500 V cm-1. The highest field intensity measured was 1600 V cm-1. The size of electrostatic fields apparently related directly to changes of humidity and was also influenced by intensity of solar radiation. As relative humidity decreased, field intensities increased; conversely, as humidity increased, leaf surface charges were dissipated. Highest field intensities were recorded on warm, sunny, and dry days, and wind apparently had no effect. At night, when the humidity was high, leaves remained uncharged. During cloudy periods with rain, field intensities were small or nonexistent. Polarity of leaves was consistently positive on sunny, dry days, but on several cloudy days with intermittent rain, leaves were of mixed polarity and predominantly negative on one occasion. A direct comparison of electrical field intensities of beans and maize leaves over several 3- to 5-day periods revealed essentially identical behavior. Detached leaves of 8 other plant species were also electrically charged under sunny, warm and dry conditions. Field intensities for the 8 spp. ranged 100-400 V cm-1, all with positive polarity. [The 8 spp. were apple (Malus sylvestris Mill.), rose (Rosa sp. cv. Camelot), grape (Vitis vinifera L. cv. Seneca), table beet (Beta vulgaris L.), English laurel (Laurus nobilis Linn.), thornless loganberry (Rubus sp.), cherry (Prunus avium L. cv. Royal Anne) and rhododendron (Rhododendron sp.)].