CARBOFURAN EFFECTS ON ESTABLISHMENT OF LEGUMES IN RELATION TO PLANT GROWTH, NITROGEN FIXATION, AND SOIL NEMATODES

Abstract

Field experiments were conducted to determine the effects of carbofuran on the establishment and subsequent yields of sod-seeded legumes. The effects of carbofuran on plant growth, nodulation and nitrogen fixation of birdsfoot trefoil (Lotus corniculatus L.) in non-sterilized and sterilized soil were evaluated in growth cabinet experiments. In the field experiments carbofuran, applied immediately after seeding, had a positive effect on plant stand and seedling dry matter production of birdsfoot trefoil and alfalfa (Medicago sativa L. ssp. falcata L.) in the weeks following seeding. In the first production years of these field trials, there was a trend for the total and legume yields to be higher in the carbofuran plots than where carbofuran was not used. In either growth cabinet experiment, however, shoot growth was not affected by carbofuran but a reduction in the number of plants in the non-sterilized and carbofuran pots occurred. A toxic effect of carbofuran on seedlings may have been involved. No correlation between soil nematode numbers and plant stand or dry matter production was found in either field or growth cabinet experiments. In the growth cabinet experiments, carbofuran did not affect the number of nodules but improved nitrogen fixation in sterilized pots of exp. B. Carbofuran increased the dry weight of individual nodules in the sterilized pots of exp. A but a decrease was observed in exp. B. These effects of carbofuran on the dry weight of individual nodules and specific nodule activity were also observed in the nematode-free environment created by sterilization. In view of these responses in sterile soil, it was suggested that the effect of carbofuran was not as a nematicide but rather a positive physiological effect on the plant component of the plant-rhizobium system.Key words: Carbofuran, establishment, legumes, nitrogen fixation, nematodes