Produtividade e eficiência do uso de nitrogênio na cultura do milho inoculado com Azospirillum brasiliense e adubado com molibdênio

Abstract

Nitrogen (N) is one of the most important nutrients required by the maize crop and the most burdensome on agricultural production since in most arable soils this element is not available at the levels necessary to achieve high yields. An alternative is the use of biological products (bacteria of the genus Azospirillum) and the micronutrient molybdenum (Mo), which is also important, as this micronutrient directly interferes with N metabolism. The objective of this work was to investigate the effect of inoculation with A. brasilense associated with the application of Mo and N on the productive development and on the N use efficiency and N photosynthetic efficiency in maize plants grown in soil from the humid tropic region of Maranhão. Three field experiments were carried out in the municipality of São Luís (2° 30' S, 44° 18' W, 24 meters above sea level), State of Maranhão, Brazil. The experimental design was in randomized blocks with four replications and eight treatments. When the treatment effect was significant, seven orthogonal contrasts were analyzed. The treatments were a dose of N 140 kg ha-1, a dose of Mo 90 g ha-1 and methods of inoculation of A. brasilense (seed and leaf). The dependent variables analysed were: leaf chlorophyll index, plant height, stem diameter, height of insertion of the first ear, weight of 100 seeds, grain yield, harvest index, shoot dry matter and nitrogen use efficiency. We also evaluated physiological characteristics at the beginning of the flowering stage (approximately 20 days after top dressing) and milky grain (approximately 40 days after top dressing). The characteristics were: photosynthetic CO2 assimilation, stomatal conductance and intercellular concentration of CO2. leaf chlorophyll index and photosynthetic N use efficiency. Inoculation with A. brasilense, nitrogen and Mo proved to be potentially usable as the results showed that the combination (A. brasilense, Mo and N) increased 5.1% of the nitrogen use efficiency and 12.68% of the photosynthetic nitrogen use efficiency. However, there was no increase in grain yield. On the other hand, Mo and N combined increased grain yield by 17.8% when compared to corn plants inoculated only with A. brasilense. Given these results, it is necessary to propose further research with the role of better elucidating the role of Mo in the link with growth-promoting bacteria and its effects on the rhizosphere and on grain yield