No nodules were found in a peanut herbicide trial held at Ribeirão Preto, State of São Paulo, Brazil, during the growing season 1984/85. Since spontaneous nodulation is commom in this region, a hypotheses was raised that herbicides could have an inhibitory effect on nodulation. To test the effect of herbicides on nodulation and nitrogenase activity an experiment was carried out on two consecutive years, using a factorial design with two factors: a) five herbicides (alachior, linuron, oxadiazon, pendimethalin and trifluralin) applied in usual dosages and a control without herbicide and b) with and without Bradyrhizobium inoculation. Samples were collected at 28, 42, 63, 84 and 105 days after planting. The results showed that nodulation was abundant in all treatments. Nitrogenase activity in the non inoculated treatments persisted for a longer period than in the inoculated ones. Although some herbicides reduced nodulation and nitrogen fixation, peanut grain production was not affected.
peanuts; nodulation; nitrogenase activity; herbicides