Abstract
Abstract: 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 xaraés 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 xaraés 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 xaraés grass when compared to nitrogen fertilization at planting without inoculation. However, grass inoculation with diazotrophic bacteria does not replace nitrogen topdressing completely.
Highlights
Brazil has more than 170 million hectares of arable lands occupied by pastures, in which the genus Urochloa
Inoculation of xaraés grass with the diazotrophic bacteria strains UN02, UN21, UN28, UN31, UN33, UN35, UN40, UN42, UN51, and UN71 in the first growth period resulted in higher leaf width values than in plants inoculated with Azospirillum brasilense, but lower values when compared to those of plants that received nitrogen topdressing (Table 1)
The highest values of leaf length and leaf area were found when plants received nitrogen topdressing, but plant inoculation with strain UN42 resulted in values close to those observed in this treatment, in both growth periods of the xaraés grass shoots
Summary
Brazil has more than 170 million hectares of arable lands occupied by pastures, in which the genus Urochloa The low natural fertility of soils, associated with a low fertilizer application, is among the main factors that result in the pasture degradation process[3]. Fertilization is essential to maintain the productive capacity of pastures, especially nitrogen fertilization[4]. Nitrogen changes some morphological characteristics of pastures, such as leaf size and development and appearance of tillers[5]. This nutrient can improve nutritional traits of forage plants by increasing the crude protein content and decreasing the concentration of structural carbohydrates[6,7]
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