Seed inoculation need and post-emergence herbicide effects, in the presence of endemic rhizobia population, were studied on plant growth, nodulation, symbiotic nitrogen fixation and grain yield of peanut (Arachis hypogaea L. cv Tatu) in a dark red latosol of Ribeirão Preto, SP, Brazil. The experiment was a split-plot design with the main plots arranged in a randomized complete block design with four replications. The effect of seed inoculation with recommended strains was studied in the main plots. Within each plot the effect of the herbicides was studied: fomesafen (250 g/ha), lactofen (192 g/ha), fluazifop-p-butyl (187 g/ha), haloxifop-methyl (240 g/ha) and fomesafen (250 g/ha) + fluazifop-p-butyl (187 g/ha) mixture applied in post-emergence. There was no herbicide effect on root dry weight. The shoot dry weight was higher when fomesafen, and mainly lactofen, were applied. Nodulation was affected only at 28 DAT, and nodule dry weight and nodules number were adversely affected by fluazifop-p-butyl. Inoculation treatment affected nitrogenase activity, which was higher with inoculated seed treatment. Symbiotic nitrogen fixation decreased four hours after herbicide treatment, fluazifop-p-butyl and haloxifop-methyl having been the most depressive. Seed inoculation did not affect grain yield indicating there is no need of this treatment when there is endemic rhizobia population. Peanut grain yield was affected by herbicides. The highest grain yield was observed with fomesafen + fluazifop-p-butyl mixture and with fomesafen and lactofen.
Arahis hypogaea L.; peanuts; seed inoculation; nodulation; herbicide