Meta-analysis of maize responses to Azospirillum brasilense inoculation in Brazil: Benefits and lessons to improve inoculation efficiency

Abstract

The inoculation of maize with the plant-growth-promoting bacteria (PGPB) Azospirillum brasilense Ab-V5 and Ab-V6 strains has impressively increased in Brazil in the last decade. In the present study, we conducted a meta-analysis with 60 studies published between 2010 and 2021, comprising 103 field trials in 54 locations in Brazil, aiming to assess the benefits and factors that affect the efficiency of A. brasilense inoculation of maize. Results showed that bacteria inoculation increased 12.1% of root mass, 4.3% N leaf concentration, 5.4% grain yield, and 3.6% of N in grains. The analysis of cultivars, edaphoclimatic conditions, and others detected positive effects of inoculation on maize under all the study conditions and yield ranges. However, inoculation benefits were higher at yields ≤3000 kg/ha (+21%) than between 3000 and 12,000 kg/ha (+1.5% to +6.2%), and yield responses tend towards greater increases at lower N rates (≤ 50 kg/ha, +8%) that at higher ones (> 200 kg/ha, +3.8%). Seed inoculation was more efficient than inoculation via leaf spray, especially by applying solid (peat) inoculants (+9.5%) than liquid formulations (+5.5%). Leaf-spray inoculation showed positive effect on grain yield (+3.1%) only when performed at the initial vegetative growth stages (V2–V3). A. brasilense inoculation represents an important biotechnology tool to increase yields and nutritional value of maize crops under most agronomic and environmental tropical and subtropical conditions.