Inoculação da soja com Bradyrhizobium no sulco de semeadura alternativamente à inoculação de sementes

Biological N fixation in soybean is indispensable in Brazil, sparing the use of mineral N and reducing crop production costs. The objective of this study was to compare in-furrow inoculation of soybean with Bradyrhizobium to the traditional practice of seed inoculation, in an experiment performed in a soil with low organic matter content and without soybean-nodulating rhizobia. A field experiment was carried out in the Cerrado of Roraima in 2006 and repeated in 2007, with the treatments: (1) control (no inoculation and no mineral nitrogen application), (2) application of 200 kg ha-1 N as urea, (3) in-furrow inoculation, and, (4) seed- inoculation. The two inoculation methods were evaluated in seeds treated or not with fungicides (carboxin + thiram and carbendazim + thiram). Soybean performance in the treatment with in-furrow inoculation resulted in nitrogen fixation contribution similar to seed inoculation, with no differences in plant dry matter weight, grain yield, and N accumulated in shoots and grains. On the other hand, when the seeds were treated with fungicides, especially carbendazim + thiram, there was a decrease in nodulation, shoot development, and grain yield in the seed inoculation treatment, while no effects were observed in the in-furrow treatment. Consequently, was demonstrated that in-furrow inoculation is useful alternative for soybean inoculation when the seeds are fungicide-treated.