MORPHOLOGICAL, PRODUCTIVE, AND CHEMICAL TRAITS OF XARAÉS GRASS: NITROGEN TOPDRESSING VERSUS INOCULATION WITH DIAZOTROPHIC BACTERIA

Nitrogen topdressing is essential for forage production, but the high cost of fertilizers stimulates the search for new technologies, such as the use of diazotrophic bacteria, which can fix the atmospheric nitrogen. To evaluate the potential of this technology in providing the amount of nitrogen requested by xaraes grass as topdressing, plants were fertilized at planting with an N rate of 100 kg ha-1, inoculated with strains of diazotrophic bacteria and Azospirillum brasilense, and compared with plants that received 100 kg ha-1 of N at planting and as topdressing during two periods of shoot growth (58 days in the first period and 26 days in the second period) in 20-dm³ pots. The data were subjected to analysis of variance and means compared by the Scott-Knott test at 5% significance. The leaf area of xaraes grass inoculated with strain UN42 was similar to that of plants that received nitrogen topdressing. However, grass biomass production was higher when nitrogen topdressing was applied. Plant inoculation with Azospirillum brasilense and strains UN16, UN17, UN21, UN33, UN49, and UN78 increased crude protein contents of xaraes grass when compared to nitrogen fertilization at planting without inoculation. However, grass inoculation with diazotrophic bacteria does not replace nitrogen topdressing completely.Keywords: Azospirillum brasilense, biological nitrogen fixation, root system, sustainable production, Urochloa brizantha