Abstract
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.
Highlights
High grain yield levels of cereal crops, such as corn, can be achieved when large amounts of fertilizers are applied, especially nitrogen fertilizer
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 treatments that resulted in higher leaf N concentration in the 1st crop harvest was with N fertilizer application and without inoculation (US + N1 and US + N2) or with the application of A. brasilense in the sowing furrow (IF + N1 and IF + N2)
Summary
High grain yield levels of cereal crops, such as corn, can be achieved when large amounts of fertilizers are applied, especially nitrogen fertilizer. Optimization of the nitrogen use efficiency is fundamental to obtain high crop grain yield, reduce the production cost and reduce the environmental and economic damages related to the inadequate use or low efficiency of the fertilization. In this sense, the association of cereal crops with endophytic diazotrophic bacteria may represent one of the most promising alternatives to promote plant growth, soil management and environmental quality. Regardless of soil N availability, the absorption efficiency is the most important component of the N use efficiency (Vale et al, 2012), creating the possibility of using the bacterium Azospirillum brasilense. Martins et al (2017) used corn seeds inoculated with A. brasilense and reported a higher N recovery provided by mineral fertilization, which increased the grain yield of the crop. Ferreira et al (1987) and Pereira-Defilippi et al (2017) verified changes in the nitrate reductase (NR) activity, an enzyme directly related to the N metabolism of the plant
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