Banca de DEFESA: RICARDO CESARIO DOS SANTOS

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : RICARDO CESARIO DOS SANTOS
DATE: 28/11/2022
TIME: 09:00
LOCAL: online
TITLE:

PLANT GROWTH PROMOTING MICROORGANISMS TO CONTROL N2O EMISSIONS FROM SOIL UNDER BRACHIÁRIA PASTURE

KEY WORDS:

Azospirillum; Brachiaria; N₂O; N₂.

PAGES: 65
BIG AREA: Ciências Agrárias
AREA: Agronomia
SUBÁREA: Fitotecnia
SPECIALTY: Fisiologia de Plantas Cultivadas
SUMMARY:

In Brazil, emissions of nitrous oxide (N₂O), a green-house-gas (GHG) with a high global warming potential, occur mainly due to the deposition of cattle excreta in the pasture soil. This process is also observed with the use of nitrogen fertilizers. For pastures, there is evidence that the forage Brachiaria humidicola naturally produces nitrification inhibitors that could affect the N₂O production, but so far little progress has been made as an effective control measure for N₂O emissions. In a different line of investigation, studies conducted in Brazil show that inoculation of plants with root growth-promoting bacteria can increase the uptake of N from the soil, resulting in greater efficiency in the use of nitrogen fertilizers. In addition, several of these bacteria in the nitrification/denitrification process, among the main ones, have N₂ as the end product of denitrification, which can be an advantage in reducing/eliminating N₂O emission from the soil. Thus, this thesis aimed to evaluate the potential for mitigating N₂O emissions by Brachiaria species, inoculated or not with associative diazotrophic bacteria that promote plant growth, in soil treated with bovine urine. The experiments were initially carried out in the laboratory, moving to a controlled condition in a greenhouse and ending with the field evaluation. Laboratory incubations tested bacteria grown in culture medium, which were treated with nitrate, followed by analysis of N₂O and N₂ using the technique of inhibiting the N₂O reduction step with acetylene. Subsequently, four strains were tested in soil without plant but with the addition of N. In a greenhouse, plants of B. humidicola and B. ruziziensis were grown in pots with soil containing bovine urine, and inoculated with bacteria, and production of N₂O was monitored. The study was extended to the field, but using B. brizantha treated with bovine urine and inoculated with Azospirillum brasilense. The results with 9 strains showed that five of them, all of A. brasilense (Sp 245, AbV5, AbV6, AZB12 and CD), were able to denitrify up to N2, while the others were not. When applied to non-sterile soil, four of these positive strains showed strong N₂O reduction. The Sp245 strain was not tested. In the greenhouse test with urine application, the use of the same strains reduced N₂O emissions, and the use of the WA3 strain, which did not show the ability to produce N₂ in vitro, did not change the emissions in relation to the treatment with only bovine urine. The dry mass of Brachiaria was increased, as well as the acquisition of N from the urine, when inoculated with AbV5, AbV6 and CD. In the following study, N₂O emissions were higher in soil with B. humidicola compared to B. ruziziensis, both with addition of urine to the soil. However, inoculation with AbV5+AbV6 strains reduced emissions by more than 50%. In both cases, inoculation significantly increased the dry matter and N accumulated by the plants. In the field trial, the inoculation of B. brizantha cv Marandu reduced N₂O emissions from bovine urine by 50%, with a gain in dry mass. Taken together, the results prove that inoculation with growth promoters increases the plant's ability to use N from bovine urine, reducing the impact on N₂O emissions, an effect that is also associated with the denitrifying capacity of some of the strains used.

COMMITTEE MEMBERS:
Presidente - ***.898.198-** - SEGUNDO SACRAMENTO URQUIAGA CABALLERO - EMBRAPA
Externa ao Programa - 1815763 - IRENE DA SILVA COELHO - UFRRJExterno ao Programa - 387256 - JORGE JACOB NETO - UFRRJExterno à Instituição - CARLOS VERGARA TORRES JÚNIOR - UFRRJ
Externo à Instituição - JERRI ÉDSON ZILLI - EMBRAPA