Biological nitrogen fixation and urea-N recovery in 'Coastcross-1' pasture treated with Azospirillum brasilense

Abstract

The objective of this work was to quantify the inoculation effect of Azospirillum brasilense (Ab-V5 and Ab-V6 strains) on the forage yield, biological nitrogen fixation (BNF), and urea-15N recovery of the forage grass 'Coastcross-1'. The experiment was carried out in a 2 (with or without inoculation) × 2 (without N fertilizer and with 100 kg ha-1 N per year as urea) × 7 (cuts) factorial arrangement. The natural 15N abundance method was used to determine BNF; to determine urea-N recovery, 15N-labeled urea was applied in microplots. Forage yield was higher in grasses subjected to inoculation, with 7.4 Mg ha-1 dry matter per year, for the treatment without N fertilizer, and 8.0 Mg ha-1 dry matter per year for the treatment with 100 kg ha-1 N per year, respectively, which shows an additive effect of inoculation and N fertilization. The contribution of BNF was 23.0 and 53.8 kg ha-1 per year for the unfertilized treatment, both in uninoculated and inoculated plants, respectively. Urea-15N recovery was 13.7 and 16.5 kg ha-1 per year for uninoculated and inoculated treatments, respectively, corresponding to 13.7 and 16.5% of the urea-N applied. Inoculation with A. brasilense increases forage yield and the contribution of BNF to grass nutrition with N, as well as urea-N recovery by the forage grass.

Response of jiggs grass to inoculation with plant growth-promoting microrganisms

“…Inoculation of plants with distinct microrganisms as a mixed inoculum is a potential synergistic tool, given that different growth-promoting mechanisms are combined. Azospirillum is far known for biological nitrogen fixation and production of phytohormones that promote proliferation of roots (BASHAN; DE-BASHAN, 2010;FUKAMI et al, 2018). Bacillus and Pseudomonas action of mode relies on the ability for form biofilms, which improve water retention in the rizosphere and act against pathogens through antibiotic production (RAAIJMAKERS et al, 2010;ALTAF, 2017;TORRES et al, 2020).…”

“…When reinoculation was performed, values as high as 33 kg were achieved, what represents a 56% increment compared to absence of inoculation. In a following experiment, A. brasilense improved dry matter from 3.9 to 7.4 Mg ha -1 (AGUIRRE et al, 2020). Nitrogen accumulation increased from 81.8 to 156.6 kg ha -1 .…”

“…Other Cynodon cultivars comprise jiggs (Cynodon dactylon cv. Jiggs), one the most recently groups introduced in Brazil (ATHAYDE et al, 2013). Preliminary data suggest that jiggs is preferred by animals over other cultivars such as Tifton 85, Tifton 68 and Russel due to its higher quantity of leaves, what makes plants more palatable (RANDÜZ, 2005).…”

Co-inoculation with Azospirillum brasilense promotes growth in forage legumes

“…With increasingly demanding consumers, there is the necessity of new alternatives to reduce and optimize the use of nitrogen fertilizers (Aguirre et al, 2020). These alternatives can promote improvements in soil characteristics and increases production.…”

“…Inoculation with Azospirillum may represent a key component for degraded pasture recovery programs, providing a higher accumulation of nitrogen in the biomass, in addition to helping with carbon sequestration (Hungria et al, 2016). Aguirre et al (2020) highlight the use of the associative bacterium Azospirillum brasilense, which, in addition to its ability to fix nitrogen, also produces phytohormones responsible for root growth, increasing the density, length, and volume of roots (Moreira et al, 2010). Considering that, in Brazil, there are about 175 million hectares of pasture (Lapig, 2017), the impact of any increase in the efficiency of N is considered significant, both in terms of production and recovery of these areas (Aguirre et al, 2020).…”