Methods of inoculation of plant growth-promoting rhizobacteria in specialty maize genotypes under organic agriculture system

Organic agriculture systems have the nutrients supplied by plant or animal by-products, bioinoculants, and compost-based products as earthworm composts and green manures. However, the quantitative and qualitative parameters of soil amendments depend on their sources, and soil amendments are generally not sufficient to supply the nutritional requirements of maize crops. Moreover, specialty maize requires high levels of N. Thus, the aim of this study was to investigate specialty maize varieties supplied with two microbial inoculants applied in two inoculation methods. These factorial treatments were compared with their checks (varieties without inoculation), and the interaction among these factors was also investigated. The trials were carried out during the growing season in 2017–2018 in the State University of Maringá. The popcorn trial followed the randomized complete block design where the factorial 3 × 2 × 2 + 3 had five replications. The trial with white grits maize followed the same experimental design but the factorial scheme was 2 × 2 × 2 + 2 with three replications. Both trials had maize varieties and two species of microbial inoculants (Azospirillum brasilense and Methylobacterium sp.) applied in two inoculation methods, in the seeds and the foliar spray at V4 stage of plant development. The response traits were grain yield and the components of crop production. In both trials, we verified that the majority of the interactions among the factors was non-significant (p > 0.05), indicating the independence of these factors. Furthermore, the microbial inoculants had no beneficial effects on the traits. The possibility of a higher crop yield did not confirm the application of the inoculant in the stage V4. The organic compost may be the key point in mitigating the treatments with microbial inoculants due to the availability of N in the first stages of plant development. The traits also suggest the necessity of more trials about the influence of microbial inoculants on specialty maize production.