Research result shows that inoculant reduces productivity loss in corn intercropped with Brachiaria

The use of inoculants contributed to reduce productivity loss in corn caused by competition with the forage

Research conducted by Embrapa Western Agriculture proved that Azospirillum brasilense bacteria-based inoculant in corn intercropped with Brachiaria grass contributes to the reduction of grain productivity caused by competition with the forage. The research results open up new horizons to the intercropping.

In addition to a good agronomic performance, this microorganism, when associated with grasses such as corn, promotes root growth, due to the action of phytohormones, which enables nitrogen fixation in plants. This technology favors the reduction of the use of nitrogen fertilizer and a more sustainable agriculture. The study was published in the journal Pesquisa Agropecuária Brasileira (PAB).

Agricultural engineer Gessí Ceccon, analyst at Embrapa, highlights the importance of the research. He explains that in corn and Brachiaria intercrops there is usually nitrogen deficiency, which is one of the main elements that is 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', Ceccon says. The inoculation technology supported by a biological input such as Azospirillum brasilense, in association with a biological insecticide lowers environmental impacts. "This is a sustainable and viable alternative in times when chemical fertilizers are limited and expensive", he stresses.

The agricultural engineer also points out that, from the second intercropping year, the Brachiaria grass starts leaving mulch, that is, organic matter, in the soil, which contributes to higher growth of corn roots. "The inoculation of corn with Azospirillum does not fully replace chemical fertilization, which contains other elements such as potassium, phosphorus, calcium and magnesium. But it reduces costs related to the amount of fertilizer demanded by crops, which provides benefits for the farmer″      

About the research

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

The A. brasilense bacteria had a positive effect on the corn crops, in which the seeds were inoculated, and it was even more effective when the plant was intercropped with Brachiaria grass. "In the scientific literature, it is observed that these bacteria benefit crops when all conditions are met, but in this study we found that this biological inoculant had an effect even under restrictive conditions. In our case, even under conditions of sandy soil, lower fertility and competitiveness with Brachiaria", he says.

The results showed that the Azospirillum brasilense bacteria contributes to the growth of corn roots, which increases productivity. "Thus, despite cultivation in sandy soil and in competitive crops, the results showed that inoculation and reinoculation with these bacteria reduce corn productivity loss caused by competition with Brachiaria, especially in a sandy soil", Ceccon celebrates.

Biological Nitrogen Fixation (BNF) Azospirillum brasilense is one of many microorganisms that are beneficial to plants, as they are able to colonize roots and stimulate plant growth. Bacteria of the Azospirillum genus have gained prominence worldwide in the 1970s due to their capacity for biological nitrogen fixation when in association with grasses, discovered by researcher Johanna Döbereiner (1924-2000), from Embrapa. In practice, these bacteria can modify the nitrogen that is taken up from the atmosphere by the plants so that it is assimilated by their roots, which allows chemical nitrogen fertilization to be reduced. This natural process that occurs in associations of plants and diazotrophic bacteria is called Biological Nitrogen Fixation (BNF). In addition to economic gains – since the Brazilian fertilizers market depends on imports –, BNF's results are significant related to improvements in soil quality, such as protection against erosion, better fertility, moisture retention and weed reduction. Another point to be highlighted is an increase in the depth of corn roots, since it allows the plants, in long drought periods, to seek water in the deeper layers of the soil, which contributes to the crop's sustainability.

Competitiveness of intercropping The competition of the forage with corn was the main motivation for the study. Thus, the amount of forage plants inserted in the system was bigger than the one recommended, in order to stimulate this competition. "In conventional crops, adequate and adjusted sowing between brachiaria and corn populations is essential", Gessí Ceccon highlights.   He also explains that this adjustment can be made while sowing the crop, but also throughout its development when necessary. "It is possible to use herbicides for the suppression of the Brachiaria, which is the same used for weed control."      Competition happens initially 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 the plants. The reaction is catalyzed by the nitrogenase enzyme, which is found in all fixing bacteria.

Quantified productivity reduction Gessí explains that, in experimental crops, research is carried out to identify the potential of production of each hybrid, in search of results that make it possible to quantify the productivity reduction of a crop. "It works like this: experiments are carried out with corn alone, without Brachiaria, in which the crop's productivity is evaluated in isolation. In another area, the cultivation is intercropped. This difference is then calculated in order to quantify productivity loss. As a parameter, we assess the number of grains per harvested ears of corn, as well as the weight of the harvested ears. We will then have the results of the quantification of productivity reduction″.