Herbicides on nodulation and N2-fixation in cowpea

An experiment was carried out under greenhouse conditions in order to evaluate the effects of soil applications of different herbicides on nodulation and nitrogen fixation in cowpea [Vigna unguiculata (L.) Walp]. Treatments included a control (without herbicide) and application of the herbicides at the recommended rates and at the double of these rates (triflurarin 1.8 and 3.6 L.ha(-1); EPTC 5.0 and 10.0 L.ha(-1); pendimethalin 2.0 and 4.0 L.ha(-1); metribuzin 1.1 and 2.2 L.ha(-1); linuron 2.4 and 4.8 L.ha(-1); imazaquim 1.0 and 2.0 L.ha(-1)). All treatments were inoculated with Bradyrhizobium, strain NBF 09. Growth of cowpea was evaluated at 20, 40, 60, and 80 days after planting. The data suggested that cowpea nodulation was affected by trifluralin (1.8 L.ha(-1)) linuron (2.4 L.ha(-1)), and imazaquim (1.0 L.ha(-1)), but the effects occurred only at the earlier stages of cowpea growth. Total nitrogenase activity was reduced in the soil treated with herbicides. Metribuzin and linuron showed a large degree of fetotoxicity to the crop, inhibiting its vegetative growth. Notwithstanding these effects observed on nodulation and nitrogen fixation, the herbicides seem not to have affected nitrogen uptake.