The Botanical Review

, Volume 50, Issue 2, pp 171–223 | Cite as

The effect of externally applied electrostatic fields, microwave radiation and electric currents on plants and other organisms, with special reference to weed control

  • M. F. Diprose
  • F. A. Benson
  • A. J. Willis
Article

Abstract

A wide-ranging review is presented of the effects of various forms of externally applied electrical energy upon plants and other organisms. Although investigations involving both small and large amounts of energy directed at the targets are considered, a particular emphasis of this review is the feasibility of each type of electrical stimulation for weed control.

Electrostatic fields ranging from 100 V m−1 to 800 kV m−1 have been applied to plants under laboratory conditions and in field trials since the 1880’s. Some beneficial effects have been reported (e.g. increase in yield from both cereal and vegetable crops), but the results have been erratic and the electrical conditions leading to definite benefits on a large scale could not be confidently predicted from early studies. High electric fields are reported to damage plants if currents greater than 10−6 A are induced to flow through leaves causing corona discharges from the tips. The nature of the damage and the effects on metabolic processes are discussed. The results from experiments on the growth of plants in which the density and charge of air ions have been varied are also reviewed.

The effects of microwave radiation (mostly 2450 MHz) upon seeds, plants and other organisms in soil are discussed. These effects depend upon the power density of the radiation and the electrical properties of the targets. Factors such as size of seeds and plants, shape and moisture content are important, as are the properties of the soil irradiated (notably water content). Although microwaves can be effective in killing plants and also seeds that are buried several centimeters deep in soil, high power equipment is required and treatment times are long e.g. a 60 kW machine could take up to 92.6 hours per hectare. Other experiments reported show that microwave radiation can kill nematodes in the soil and that it is also very effective in killing fungi and bacteria. The potential of the various possible uses of microwave radiation in agriculture is also described.

Electric currents have been caused to flow through plants by the application of electrodes to the leaves. The effects range from nil, when 50–100 V and 1 or 2 μA are used, to very striking when voltages from 5 to 15 kV are applied causing currents of several amperes to flow and resulting in the rapid destruction of the target. Small electric currents passed through soil containing plants are reported to increase their growth. The effects of small current on the growth of individual leaves are reviewed. The use of high voltage tractor-borne equipment for weed control is also considered.

Sommaire

Une revue á larges thèmes présente les effets des diverses formes d’application externe d’énergie électrique sur les plantes et autres organismes. Bien que des recherches comportant á la fois de petites et grandes quantités d’énergie dirigées sur les cibles en question soient prises en considération, un des aspects particuliers de cette revue est la possibilité d’application de chaque type de stimulation électrique au contrôle des mauvaises herbes.

Depuis environ 1880, les plantes ont eté soumises, soit en laboratoire, soit lors d’essais sur le terrain, á des champs électrostatiques allant de 100 V m−1 á 800 kV m−1. Quelques effets bénéfiques ont été enregistrés, par exemple, l’accroissement de la production des récoltes de céréales et de légumes; mais les résultats étaient irréguliers et les conditions électriques conduisant á des profits bien déterminés á grande échelle ne pouvaient pas être prédites avec confiance des premières études. On s’est aperçu que de grands champs électriques pouvaient déteriorer les plantes si des courants supérieurs á 10−6 A étaient amenés á circuler dans les feuilles, entraînant des décharges de la couronne á partir des pointes. La nature des dégâts ainsi que les effets sur les procédés métaboliques sont ici étudiés, de même que les résultats des expériences sur la croissance des plantes pour lesquelles la densité et la charge des ions dans l’air ont été changés.

Les effets du rayonnement par micro-ondes (pour la plupart de 2450 MHz) sur les graines, les plantes et autres organismes du sol sont ici exposés. Ces effets dépendent de la densité électrique du rayonnement et des propriétés électriques des objectifs. Des facteurs tels que la taille des graines et des plantes, leur forme et leur teneur en humidité sont importants, comme le sont les propriétés d’un sol irradié (notamment sa teneur en eau). Bien que les micro-ondes puissent être efficaces pour tuer des plantes et aussi des graines enterrées á plusieurs centimètres de profondeur, un important appareillage électrique est nécessaire et les temps de traitement sont longs; par exemple une machine de 60 kW peut prendre jusqu’á 92,6 h ha−1. D’autres expériences démontrèrent que le rayonnement par micro-ondes pouvait tuer les nématodes dans la terre et qu’il était très efficace pour détruire les champignons et les bactéries du soussol. Le potentiel des diverses utilisations possibles de la radiation par micro-ondes en agriculture est également décrit.

Des courants électriques ont été amenés á circuler á travers des plantes par l’application d’électrodes sur les feuilles. Les effets, nuls quand 50 á 100 V et 1 á 2 μA sont utilisés, sont par contre frappants quand des voltages de 5 á 15 kV sont appliqués, entraînant la circulation de courants de plusieurs ampères et la destruction rapide des cibles. On remarque cependant que, de petits courants électriques envoyés dans un sol contenant des plantes, accélèrent leur croissance; les effets d’un faible courant sur la croissance des feuilles individuelles sont ici réexaminés. L’utilisation d’un appareillage á haut voltage mobile pour le contrôle des mauvaises herbes est aussi pris en considération.

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Copyright information

© The New York Botanical Garden 1984

Authors and Affiliations

  • M. F. Diprose
    • 1
  • F. A. Benson
    • 1
  • A. J. Willis
    • 2
  1. 1.Department of Electronic and Electrical EngineeringUniversity of SheffieldSheffieldUK
  2. 2.Department of BotanyUniversity of SheffieldUK

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