BROMIDE CONTENT OF VEGETABLES (TOMATOES, LETTUCE) AFTER SOIL DISINFESTATION WITH METHYL BROMIDE

Due to its high effectivity against soil sickness, to its deep and good penetration, its spreading into the soil and to its short after-effect, methyl bromide or a mixture of methyl bromide and chloropicrine are generally used in Belgian greenhouses. Besides the effectiveness of these precultural means, at present very much attention is given to the residue of these products e.g. the bromide content in vegetable crops; from there an important problem can rise with the bromide residue in MB fumigated soils.

About 400 samples - taken at random - of tomatoes and lettuce were analysed; at the same time an inquiry had been set up looking for the dose and frequency of MB application, the number of intercroppings, the amount of water leached into the soil, the type of the soil and fertilization with other monovalent anions such as chlorides and nitrates.

Plants grown on untreated soils normally contain small quantities of bromide (in lettuce about 20 ppm, in tomatoes less than 10 ppm). The residue values are very high immediately after a soil disinfestation, in loamy soils without leaching the soil (in lettuce even more than 300 ppm, in tomatoes up to 100 ppm). Different methods such as increasing the number of intercroppings after disinfestation, and increasing the amount of water during leaching are very important factors to decrease the bromide residue. Possibilities to reduce the bromide content by nitrate or chloride fertilization seems to give a solution to growers who do not have the possibility to leach the soil or in cases were leaching the soil is undesirable from phytotechnical point of view.

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