The influence of topdressing nitrogen on Azospirillum spp. inoculation in maize crops through meta-analysis

The Azospirillum is considered one of the most studied plant growth promoter genus. These bacteria are capable of promoting plant growth through several factors. However, the effect of Azospirillum spp. associated to nitrogen fertilization on maize grain yield has brought about controversial results. Thus, the objective of this study was to verify the influence of topdressing nitrogen on the effect of Azospirillum spp. inoculation on maize crops through meta-analysis. Data were collected from articles published in scientific journals, obtained from the Web of Science (R), Scopus (R) and Google Scholar (R) databases. The bibliographic review included only articles with direct comparisons between maize yield in the presence and absence of Azospirillum spp. under held conditions in Brazil. The meta-analysis of the random effects was carried out using all entries. Subgroup and meta-regression analysis were realized to verify the influence of nitrogen fertilization on the explanation of the possible heterogeneity among effect measures. Maize inoculation with Azospirillum spp. showed an average yield increase of 651.58 kg.ha(-1), considering all trials, and of 1034.28 kg.ha(-1) considering only the trials without topdressing nitrogen. There was no significant increase in grain yield when inoculation with bacteria from the Azospirillum genus was realized together with nitrogen fertilization, indicating that such technologies are non-additive.