Inoculation in the soybean crop is a practice widely adopted all over the world. Despite of this fact, so far researchers have not come to a agreement regarding the amount of peat inoculant to be used under the no-tillage cultivation system. While in Paraná State the recommended amount is of 500g of inoculant for 50kg of seeds, in Rio Grande do Sul and Santa Catarina States this recommendation is of 200g, what brings into evidence the need to intensify research in this particular area. This study was carried out in the 1994/95 cropping season, in an area cultivated under the no-tillage system for five years, in Cruz Alta, Rio Grande do Sul State, Brazil, aiming at evaluating the effect of the peat inoculant dose on soybean under no-tillage. The treatments used were: check without inoculation, inoculant dosis of 250, 500, 750 and 1000g for 50kg of seeds and a treatment with 200kg of N/ha, applied in parcels, without inoculation. There was no difference between the check plots without inoculation and inoculant dosis for number and weight of nodules, dry matter of the plant shoots, dry matter of the roots, plant height and N content in the leaf. The treatment with mineral nitrogen showed a smaller number and weight of nodules and higher production of dry matter of the plant shoots, but this last parameter did not differ from the treatments: check without inoculation, 250 and 500g of inoculant. With mineral N application, plant height was significantly higher than the check and the inoculant dosis treatments. There was no positive effect of the inoculant on grain yield. These results led us to conclude that there is no need to use inoculant in areas after five years under the no-tillage cultivation system.
nitrogen biological fixation; inoculation; Glycine max; Bradyrhizobium japonicum
