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

Priscila Flôres Aguirre,Sandro José Giacomini,Vinicius Felipe Bratz,Clair Jorge Olivo,Maurício Pase Quatrin,Gilmar Luiz Schaefer

doi:10.1590/s1678-3921.pab2020.v55.01242

Priscila Flôres Aguirre, Sandro José Giacomini + Show 4 more

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https://doi.org/10.1590/s1678-3921.pab2020.v55.01242

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Abstract

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.

Highlights

Grasses of the genus Cynodon show advantages for its use as a source of fiber for dairy cattle in Brazil, since they are perennial, and show a rapid establishment and high-forage production (Ziech et al, 2016)
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'
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

Summary

Introduction

Grasses of the genus Cynodon show advantages for its use as a source of fiber for dairy cattle in Brazil, since they are perennial, and show a rapid establishment and high-forage production (Ziech et al, 2016). Much of the applied N is lost by leaching, volatilization of ammonia, and denitrification, with detrimental effects to the environment (Hungria el al., 2016). In this context and faced with a consumer market that is increasingly demanding for food produced in a more sustainable way, alternatives are required to reduce and use better N fertilizers. In addition to its capacity to fix N2, this bacteria produces phytohormones that are responsible for the greater development of the grass root system, increasing the density and length of root hairs, and number and volume of lateral roots (Moreira et al, 2010). The inoculation of this bacteria may increase the nutrient uptake capacity, with a consequent higher recovery of the fertilization applied to pastures. Considering the large extent of pasture land in Brazil, totaling more than 175 million ha (Lapig, 2017), the impact of any increase in N-use efficiency could be very significant

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