Métodos de inoculação de Azospirillum brasilense e sua influência na promoção de crescimento do milho

Abstract

The use of plant growth promoting bacteria in maize stands out as an alternative to increase productivity, reduce the use of chemicals and preserve the environment. However, more efficient methods for the use of inoculant are sought, especially in the stage of management by the producer, seeking to preserve the microorganism’s viability. The objective of this study was to evaluate the influence of inoculation methods with Azospirillum brasilense in the metabolism and the plant growth promotion in maize hybrid Formula VT®. In greenhouse, using as experimental unit polyethylene pots with 25 liter capacity, filled with Oxisol, were cultivated maize plants in function of different inoculation methods with the strains Abv5 and Abv% from the plant growth promoting bacteria A. brasilense. The inoculation methods consisted in the absence of inoculation (control), seed inoculation (during the seeding moment), foliar inoculation (in the phenological stage V4) and seed inoculation associated to foliar inoculation (during the seeding moment and in the phenological stage V4, respectively). The plant’s chlorophyll relative content was fortnightly evaluated. In the phenological stages V8, VT and R6 was measured the readings of the CO2 liquid assimilation rate in function of different flux densities of photosynthetically active photons. From these data it was determined the CO2 compensation point, the quantum yield and the maximum CO2 liquid assimilation. Still in the phenological stages V8, VT and R6, it was measured the number of leaves, aerial height, basal stem diameter, root volume, dry mass of leaves, stem+leaf sheath, roots and total dry mass, foliar area and foliar contents of nitrogen, phosphorus and potassium. Finally, in the phenological stage R6 it was evaluated the ear diameter, ear length, number of rows, number of kernels per row, dry mass of the reproductive structure, 100 grain mass, total grain mass and the grain content of nitrogen, phosphorus and potassium. Plants with inoculation via seed and seed inoculation associated to foliar inoculation stood out as to basal stem diameter, leaves dry mass, root volume and the contents of nitrogen, phosphorus and potassium. Still, the inoculated plants showed a differentiated capacity of transport of electrons and efficiency of CO2 liquid assimilation rate in relation to the control in all evaluated stages. The inoculation method via foliar influenced in the adaptative demand of the plants, reducing their development speed in the initial stage. The inoculation methods influenced in physiological, morphometric and nutritional parameters of the development of maize, however, they did not had any influence in the final yield. The plant development related to the growth promotion was positively influenced by the inoculation, varying according to the utilized method.