Co-inoculation with Rhizobium, Azospirillum, and microalgae increases common bean yield and profitability

Widely used as inoculants in agriculture, nitrogen-fixing bacteria can be associated with other plant growth-promoting microorganisms (PGPMs) to increase crop grain yield. This study aimed to evaluate whether co-inoculation with Rhizobium tropici and Azospirillum brasilense associated with microalgae or cyanobacteria enhances common bean (Phaseolus vulgaris) grain yield and its economic gains in contrasting sandy and clayey soils. Water-soluble protein content and indole-3-acetic acid (IAA) production of two cyanobacteria (Anabaena cylindrica and Calotrix brevissima) and six Chlorophyta microalgae (Nannochloropsis oculata, Haematococcus pluvialis, Muriellopsis sphaerica, Chlorella protothecoides, Chlorella vulgaris, and Botryococcus braunii) were determined. Anabaena cylindrica and C. brevissima had the highest IAA production, 336.7 ± 44.7 and 94.1 ± 11.8 µg IAA mg⁻¹ of protein, respectively. Two field experiments were carried out to evaluate the triple inoculation of these Chlorophyta microalgae and cyanobacteria associated with R. tropici plus A. brasilense on the agronomic efficiency and profitability of common bean. Co-inoculation of C. vulgaris plus R. tropici and A. brasilense in common bean had grain yield of 1277.5 kg ha⁻¹ in clayey soil and 2960.3 kg ha⁻¹ in sandy soil, increasing by 219.7 and 656.0 kg ha⁻¹, respectively, in relation to double inoculation of R. tropici + A. brasilense. In the sandy soil, common bean with triple co-inoculation had the highest profit ($956 ha⁻¹), which was 25.6% higher than the N fertilized plants. Co-inoculation with PGPMs generated the highest economic gains, and in addition, it is an eco-friendly agronomic practice for sustainable food production.