Importance of soybean nutrition and impact on disease management

Plant nutrition is directly linked to natural defense against external agents, such as diseases. A well-nourished plant is naturally more tolerant or even resistant to pathogen attack, but how does this work? Plants defend themselves mainly in two ways: by fortifying external barriers, such as lignification of the cell wall, and even counterattacking through the production of substances that fight pathogens such as phytoalexins.

The first form is part of the plant's primary metabolism, therefore it is carried out during its natural development, and some of the most important nutrients for this are calcium, magnesium and boron. Calcium is a nutrient present in the middle lamella of the cell wall, magnesium is a cofactor in the production of enzymes necessary for the transfer of phosphates (energy) in the plant and boron is essential for cell elongation and, therefore, good cell formation. and the structures constituted by these. Without the limitation of macro and micronutrients, the plant naturally develops more resistant, remaining healthy for longer, just as humans do.

The counterattack as a defense mechanism is part of secondary metabolism. It happens when something activates this mechanism, such as the attack of diseases or the stimulation of the plant's natural defense routes, starting to produce natural substances to inhibit or delay the development of pathogens. The activation of this process represents energy expenditure, which can be compensated with the help of nutrition. In this case, it is essential to use nutrients such as copper, which is essential for the activation of enzymes, nitrogen fixation in legumes and mainly helps in the assimilation of energy by the plant, as it is part of photosynthesis. Nitrogen is also important, as it boosts plant development, providing greater growth and carbon assimilation capacity. Another nutrient is phosphorus, which is responsible for storing and subsequently transferring energy. Along with it is potassium, which helps in the transport and accumulation of carbohydrates, contributing to greater productivity. It is also important to remember that this activation of the plant's nutritional defense favors the regulation of energy processes, which would otherwise be unbalanced, causing losses due to the occurrence of diseases. Another benefit of this management technique is its contribution to the maintenance of plant structures, reducing losses of leaf area and aiding photoassimilation.

Furthermore, both a lack of nutrients and an excess can be harmful to the plants themselves or beneficial microorganisms in the rhizosphere, as well as favoring the development of diseases, making it important to provide nutrients in a balanced way, especially in the soil.

Plant nutrition also becomes essential along with the application of pesticides to plants, as just like the use of medicine in humans, they are beneficial, but can bring side effects, such as chlorosis and blockage, which can affect productivity. A widely known example is glyphosate, which, as it is a molecule with high affinity for free charges, temporarily makes some nutrients unavailable. This effect, for example, can be mitigated with the use of nutrients such as manganese, zinc and sulfur. The use of substances that increase the absorption and use of nutrients, such as amino acids, is also very interesting to alleviate stress, as it increases the efficiency of nutrient use and regulates the plant's metabolism, accelerating the release of this blockage.

In short, the producer must closely monitor the nutritional needs of his crop, providing supplies according to each phase of the crop. After all, a well-nourished plant is naturally more resistant to the most diverse stresses.

Vinicius Abe, Alltech Crop Science and State University of Maringá (UEM)

Cultivating Great Crops September 2020

With each new edition, Cultivar Grandes Culturas publishes a series of technical content produced by renowned researchers from all over Brazil, which address the main difficulties and challenges encountered in the field by rural producers. Through research focused on controlling the main pests and diseases in the cultivation of large crops, the Magazine helps farmers in the search for management solutions that increase their profitability. 

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