Combination of Azospirillum and Bradyrhizobium on Inoculant Formulation Improve Nitrogen Biological Fixation in Soybean

Mateus Manara Picoli,Cesar Yoshio Muraoka,João Vitor Gomes Pasquetto,Alessandro Lucca Braccini,Karina Maria Lima Milani,Ivana Marino Bárbaro Torneli,Fernanda Bruna Bento Marin,Tiago Tezotto,Edson Luiz Souchie,Stella Consorte Cato,Edson Lazarini

doi:10.5539/jas.v14n4p145

Abstract

Co-inoculation in soybean with Azospirillum brasilense and Bradyrhizobium spp. is a consolidated practice to ensure nitrogen supply and maximize productivity and sustainability. This study aimed to evaluate the agronomic efficiency of the co-inoculation in soybean, via seed or in-furrow, of doses of the mixed inoculant containing Bradyrhizobium spp. and A. brasilense in the same formulation. The experiments were conducted under field conditions in four different edaphoclimatic regions to compare seven treatments: Control without nitrogen (N) and inoculant (T1), 200 kg ha-1 of mineral N fertilizer (T2), 100 mL of standard liquid inoculant of Bradyrhizobium spp. (T3) in 50 kg-1 seeds, 100 mL (T4) or 200 mL (T5) of the mixed liquid inoculant in 50 kg-1 seeds, 200 mL (T6) or 300 mL (T7) ha-1 of the mixed inoculant applied in-furrow. Nodulation characteristics (number and mass of nodules) and carbon and N metabolism (dry mass, N content, and N accumulation in the aerial part) were evaluated at the phenological stage R2 (full flowering&mdash;there is an open flower at one of the two uppermost nodes). At maturity (R8&mdash;full maturity&mdash;95% of the pods have reached their full mature color), yield, the mass of 1,000 grains, N content in the grains, and grain N export were measured. The data were submitted to analysis of variance using the F test and comparison of means was performed using the Duncan test (5%). Under field conditions, the mixed inoculant at doses of 200 mL 50 kg-1 seed or 300 mL ha-1 applied in-furrow were equivalent or superior to the standard inoculant for the total number of nodules, N content in the grains, grain N export, productivity, and mass of 1,000 grains. The use of the mixed inoculant containing Bradyrhizobium spp. and A. brasilense in the same formulation meets the demand of grain N export and resulted in increases of 28%, 18% and 7.4% in soybean productivity compared with control without nitrogen, mineral N fertilizer and standard liquid inoculant of Bradyrhizobium spp. respectively.

Highlights

Plants can obtain N through the decomposition of organic matter, non-biological fixation, N fertilization, and biological N fixation (BNF); the last two are the ones that most contribute to N supply (Hungria et al, 2001; 2007)
The reaction is catalyzed by the enzyme nitrogenase, found in all N-fixing bacteria
The process occurs in typical structures formed in the roots, the nodules (Hungria et al, 2013)

Summary

Introduction

Nitrogen (N) is one of the essential chemical elements for plant development and is required in larger quantities by crops. Plants can obtain N through the decomposition of organic matter, non-biological fixation, N fertilization, and biological N fixation (BNF); the last two are the ones that most contribute to N supply (Hungria et al, 2001; 2007). BNF is the process by which N present in the atmosphere (N2) is converted into forms that plants can utilize. The reaction is catalyzed by the enzyme nitrogenase, found in all N-fixing bacteria. The symbiosis between N-fixing bacteria (belonging to several genera and species of bacteria, collectively known as rhizobia) and jas.ccsenet.org. Vol 14, No 4; 2022 legumes such as soybean [Glycine max (L.) Merrill] is the most important. The process occurs in typical structures formed in the roots, the nodules (Hungria et al, 2013)

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