Inoculant reduces productivity losses in corn intercropped with brachiaria

Research conducted by Embrapa Agropecuária Oeste (MS) proved that the use of an inoculant based on the bacteria Azospirillum brasilense in corn intercropped with brachiaria contributes to reducing grain productivity losses caused by forage competition. The research results open new horizons for the consortium of the two cultures.

In addition to good agronomic performance, the microorganism, when in association with grasses, such as corn, promotes root growth, due to the action of phytohormones, enabling nitrogen fixation in plants. The technology favors the reduction of the use of nitrogen fertilizers and more sustainable agriculture. The work was published in the magazine Brazilian Agricultural Research (PAB).

Agricultural engineer and analyst at Embrapa Gessí Ceccon highlights the importance of the research. He explains that, in the case of corn crops intercropped with brachiaria, there is generally a deficiency of nitrogen, one of the main elements responsible for grain production. The high demand for this chemical element by plants and its low availability in Brazilian soils make nitrogen fertilization an indispensable practice.

“Inorganic fertilizers end up being the traditional and standard way of adding this nutrient to the soil”, says Ceccon. Inoculation technology supported by a biological input, such as Azospirillum brasilense, associated with a biological insecticide, reduces environmental impacts. “This is a sustainable and viable alternative in times of scarcity and high prices for chemical fertilizers”, he reinforces.

The agronomist also points out that, from the second year of the consortium, the brachiaria begins to leave cover, that is, organic matter, in the soil, which contributes to greater growth of corn roots. “Inoculating corn with Azospirillum does not completely replace chemical fertilizer, which contains other elements, in addition to nitrogen, such as potassium, phosphorus, calcium and magnesium. But it reduces costs related to the amount of fertilizers demanded by crops, providing gains for the producer.”      

About the research

Ceccon says that the objective of the research was to evaluate the agronomic performance of corn intercropped with the forage Urochloa ruziziensis (new scientific nomenclature for Brachiaria ruziziensis), in succession to soybeans inoculated with the nitrogen-fixing bacteria Bradyrhizobium japonicum and Azospirillum, as well as inoculation and the re-inoculation of corn with A. brasilense, in sandy soil.

In corn crops, where the seeds were inoculated, the positive effect of A. brasilense was observed, which was greater when the plant was intercropped with brachiaria. “In the scientific literature it is observed that this bacteria benefits crops when all conditions are met, however in this study we found that this biological inoculant was effective even under restrictive conditions. In our case, still in sandy soil conditions, with lower fertility, and competitiveness with brachiaria”, he states.

The results revealed that the bacteria Azospirillum brasilense contributes to the growth of corn roots, providing increased productivity. “Thus, despite cultivation in sandy soil and competitive farming, the results proved that inoculation and re-inoculation with this bacteria reduce corn productivity losses caused by competition from brachiaria, especially in sandy soil”, celebrates Ceccon.

Biological Nitrogen Fixation (BNF)

The Azospirillum brasilense is one of several microorganisms beneficial to plants, which can colonize their roots and stimulate their growth. Bacteria of the genus Azospirillum gained worldwide prominence from the 1970s onwards, with the discovery, by Embrapa researcher Johanna Döbereiner (1924-2000), of their ability to biologically fix nitrogen when in association with grasses.

In practice, these bacteria are able to capture nitrogen from the atmosphere and transform it so that it can be assimilated by plants, reducing chemical nitrogen fertilization. This natural process that occurs in associations of plants with diazotrophic bacteria is called Biological Nitrogen Fixation (BNF).

In addition to the economic gains, since the fertilizer market in Brazil is dependent on imports, the FBN results related to improvements in soil quality are significant, such as protection against erosion, greater fertility, moisture retention and reduction of weeds. .

Another point that deserves to be highlighted refers to the increase in the depth of the corn roots, as this width allows the plant, in periods of prolonged drought, to seek water in the deeper layers of the soil, contributing to the sustainability of the crop.

Competitiveness of the consortium system

The forage's competition with corn was the main motivation for the research. Thus, the quantity of forage plants inserted into the system was greater than indicated, with the aim of stimulating this competition. “In a conventional crop, adequate and adjusted planting between the brachiaria and corn populations is essential”, highlights Gessí Ceccon.

He explains that this adjustment can be made when planting the crop, but also throughout its development, when necessary. “It is possible to use herbicide to suppress brachiaria, which is the same one used to control weeds.”      

Competition initially occurs for water and then for other nutrients, especially nitrogen. This nutrient is present in the atmosphere and is converted into forms that can be used by plants. The reaction is catalyzed by the enzyme nitrogenase, found in all fixing bacteria.

Quantified productivity reduction

Gessí explains that research is carried out in experimental crops to identify the productive potential of each hybrid, in search of results that make it possible to quantify the reduction in productivity of a crop.

“It works like this: experiments are carried out with the cultivation of single corn, without brachiaria, in which the productivity of this crop is evaluated in isolation. In another area, cultivation is carried out in an intercropped manner. This difference is then calculated to arrive at a quantification of productivity losses. As a parameter, the number of grains per ear of corn harvested can be evaluated, as well as checking the weight of the ears harvested. We will then have the results of quantifying the reduction in productivity”.