Application methods of Azospirillum brasilense in first- and second-crop corn

ABSTRACT This study investigated whether inoculation of Azospirillum brasilense in the seeds or sowing furrow could reduce the need for nitrogen fertilizer application in the corn grown in the first and second crop harvest. The experiments were conducted, in the municipality of Chapadão do Sul, MS, Brazil, in the first crop harvest (2014/2015) and in the second crop harvest (2016). The early maturity hybrids CD 384 HX and P3132H were used in the first and in the second harvest corn, respectively. In both experiments, the experimental design was the randomized blocks with eight treatments and three repetitions. At the silking (R1 stage), the leaf N concentration, relative chlorophyll index and nitrate reductase activity were measured, at the physiological maturity (R6 stage), the plant height, first ear insertion height, one hundred grain mass, grain yield and grain N concentration were measured. In the first crop harvest, the application of Azospirillum brasilense at the sowing furrow resulted in higher N concentration and relative chlorophyll index in corn leaves, while the inoculation of A. brasilense in the seeds provided higher N concentration in the grains. The nitrate reductase activity in corn leaves was lower when inoculation was performed. In the second crop harvest, the inoculation did not affected the N concentration in the leaves and in the grains, the relative chlorophyll index and the growth of corn plants. Inoculation in the sowing furrow associated with the application of 20 kg N ha-1 at sowing and 120 kg N ha-1 at topdressing resulted in lower nitrate reductase activity. RESUMO Objetivou-se verificar se a inoculação de Azospirillum brasilense via semente ou sulco de semeadura pode reduzir a necessidade de adubação nitrogenada no milho, em primeira e segunda safra. Os experimentos foram conduzidos, no município de Chapadão do Sul, MS, em primeira safra (2014/2015) e segunda safra (2016). Na primeira safra utilizou-se o híbrido CD 384 HX e na segunda safra, o híbrido triplo P3132H, ambos de ciclo precoce. Para os dois experimentos, o delineamento experimental foi em blocos ao acaso com oito tratamentos e três repetições. Foram mensurados, no estádio R1: o teor de N foliar, índice relativo de clorofila, atividade da redutase de nitrato, e na maturação fisiológica: a altura de plantas e de inserção de primeira espiga, massa de cem grãos, produtividade de grãos e teor de N nos grãos. Na primeira safra, a inoculação de Azospirillum brasilense na