Plant growth-promoting bacteria associated with nitrogen fertilization at topdressing in popcorn agronomic performance

ABSTRACT The use of plant growth-promoting bacteria is a promising alternative with low environmental impact to increase the efficiency of use of chemical fertilizers, ensuring high yield with better cost-effective ratio. In maize crops, several studies have demonstrated an increased yield when Azospirillum-based inoculants are used. In the case of popcorn, there are no available studies related to use of inoculation and its response on yield parameters. Thus, the aim of this study was to evaluate the field performance of popcorn when inoculated with the commercial product Masterfix L (A. brasilense Ab-V5 and A. brasilense Ab-V6) and the non-commercial inoculant UEL (A. brasilense Ab-V5 + Rhizobium sp. 53GRM1) associated with nitrogen fertilization. The trials were conducted in Londrina and Maringá, Paraná State, Brazil, in a randomized block design with four replications, in a split plot design with the inoculation treatments located in the plots (uninoculated, Masterfix L, and UEL) and the different N rates located in the subplots where ammonium sulphate was applied in the topdressing at the V6 stage (0, 50, 100, and 150 kg∙ha–1). The variance analysis showed significant effects (p < 0.05) of inoculation (Londrina environment) and N rates (both environments) only for grain yield. There was no inoculation effect in the grain yield when inoculants were applied together with N-fertilization at topdressing. In the absence of N-fertilization at topdressing, the inoculants Masterfix L. and UEL promoted higher grain yield as compared to the uninoculated plants, with resulting increases of 13.21 and 26.61% in yield, respectively. RESUMO A utilização de bactérias promotoras de crescimento vegetal é uma alternativa promissora e de baixo impacto ambiental para aumentar a eficiência de uso de fertilizantes químicos, garantindo elevadas produtividades com melhor relação custo-benefício. Na cultura do milho, diversos trabalhos vêm demonstrando o aumento de rendimento de grãos quando inoculados com Azospirillum spp. No caso do milho pipoca, trabalhos relacionados ao uso da inoculação sobre a produtividade da cultura são inexistentes. Dessa forma, o objetivo do trabalho foi avaliar o efeito da inoculação do produto comercial Masterfix L. (A. brasilense Ab-V5 e A. brasilense Ab-V6) e da formulação experimental UEL (A. brasilense Ab-V5 e Rhizobium sp. 53GRM1), associada à adubação nitrogenada, sobre o desempenho agronômico de milho pipoca. Os experimentos foram conduzidos