Co-Inoculation with Azospirillum brasilense and Bradyrhizobium sp. Enhances Nitrogen Uptake and Yield in Field-Grown Cowpea and Did Not Change N-Fertilizer Recovery

Abstract

This study was designed to investigate the effects of Azospirillum brasilense and Bradyrhizobium sp. co-inoculation coupled with N application on soil N levels and N in plants (total N, nitrate N-NO3− and ammonium N-NH4+), photosynthetic pigments, cowpea plant biomass and grain yield. An isotopic technique was employed to evaluate 15N fertilizer recovery and derivation. Field trials involved two inoculations—(i) single Bradyrhizobium sp. and (ii) Bradyrhizobium sp. + A. brasilense co-inoculation—and four N fertilizer rates (0, 20, 40 and 80 kg ha−1). The co-inoculation of Bradyrhizobium sp. + A. brasilense increased cowpea N uptake (an increase from 10 to 14%) and grain yield (an average increase of 8%) compared to the standard inoculation with Bradyrhizobium sp. specifically derived from soil and other sources without affecting 15N fertilizer recovery. There is no need for the supplementation of N via mineral fertilizers when A. brasilense co-inoculation is performed in a cowpea crop. However, even in the case of an NPK basal fertilization, applied N rates should remain below 20 kg N ha−1 when co-inoculation with Bradyrhizobium sp. and A. brasilense is performed.

Effect of Azospirillum brasilense Addition and Organic Matter on Irrigation Efficiency, NPK Availability and Wheat Yield (Triticum aestivum L.)

“…While the effect of irrigation periods was not significant in the percentage of available potassium in the soil. These results agreed with [38].…”

Contribution of Biofertilizers to Pulse Crops: From Single-Strain Inoculants to New Technologies Based on Microbiomes Strategies

“…Valdez-Nunez et al [ 193 ] isolated bacterial strains from healthy cowpea root nodules capable of solubilizing tricalcium phosphate, producing siderophores, and with antagonistic activity against Fusarium oxysporum . Regarding this, the co-inoculation of efficient Bradyrhizobium strains [ 194 ], with Azospirillum brasilense [ 194 , 195 , 196 , 197 ], AMF [ 78 , 150 ], Trichoderma [ 198 , 199 ] and P-solubilizing fungi [ 200 ] may help cowpea plants absorb more nutrients from soil and increase grain yield.…”

“…For several plant species, including the common bean, Soldan et al [ 223 ] propose that the rhizosphere microbiome may have been affected in modern cultivars compared to their wild ancestors. The effects of the characteristics of domesticated plants resulting from direct and indirect selection on the assembly of the host microbiome can lead to species loss, species gain, or species replacement, with the endophyte microbiota varying more among plant organs than among bean varieties [ 196 , 224 ]. Perez-Jaramillo et al [ 225 ] showed that wild common bean relatives were enriched in bacterial taxa of the phylum Bacteroidetes , relative to modern relatives that were enriched in Actinobacteria .…”