Use of biostimulants in soy

The use of biostimulants in the treatment of soybean seeds shows promising results in enhancing root growth and better N absorption, energy savings, increased plant resistance to biotic and abiotic stresses and a consequent positive effect on productivity.

The increase in population brings with it the need to produce more and more food. To meet this demand, more and more technologies have been sought that make it possible to increase the productivity of cultivated plants. Among the technologies used, the use of biostimulants in both seed treatment and foliar applications has shown to be promising.

Biostimulants can be made up, among others, of nutrients, hormones, algae extract, amino acids, humic and fulvic acids and vitamins that are offered to plants so that they only absorb them, shortening metabolic processes, culminating in energy savings that can be used to increase production. As a result, more and more work has been carried out seeking to understand and verify the action of these products on plants.

In this sense, a trial was conducted at the University Center of Patos de Minas (Unipam) in the 2014/15 harvest to evaluate the physiological influence of biostimulants in the treatment of soybean seeds (cultivar NS 7114 RR). The products tested were based on amino acids (13%), algae extract (3%), Cobalt (7,56 g/ L) and Molybdenum (75,6 g/ L) and the other was based on salicylic acid (15 %). Physiological parameters, chlorophyll content in the leaf, NO assimilation were evaluated.₃^- and grain productivity.

It was observed that the use of biostimulants in soybean seeds causes an increase in the assimilation of N in the form of nitrate in the initial phase. This characteristic is extremely relevant, as it is at this stage that seedlings essentially depend on N in the soil. Considering that biological fixation is established from V₃, the initial growth of plants depends on other sources of nitrogen, whether from the soil, the fertilizer applied or the reserve in the seed itself. On average, considering 40% protein content, for sowing with a population of 300.000 plants, using 60 kg/ ha seeds (11% water), 3,2 kg/ ha N are added via seed. Until biological fixation establishes (V₃), a soybean crop with the same population has already accumulated around 11,8 kg/ha N (Figure 1). Therefore, there is a deficit of 8,6 kg/ha N, which must be supplied via fertilizer or mineralization of organic matter. Therefore, it is important that this deficit is met, considering the efficiency of fertilizer use by the plant and, therefore, depends on the activity of the nitrate reductase enzyme. Furthermore, it is important to highlight that N added via fertilizer can serve as a stimulus for root development and enhance the formation of nodules.

The increase in N assimilation caused an increase in the chlorophyll content of the leaves. This means that they had a more intense green color. How are chlorophylls that absorb light energy and transform it into chemical energy for the assimilation of CO₂ in photosynthesis, this physiological parameter has a direct relationship with productivity. Salicylic acid (SA) used in foliar treatment acted as a resistance inducer in plants due to its action on different routes and synthesis of phytoalexins. Furthermore, SA acts on stability, chlorophylls and the activity of the nitrate reductase enzyme, parameters that were maximized by the application of this product as observed in the data. The enhancement of the physiological variables evaluated was one of the possible causes of the positive effect of biostimulants on productivity found in the trial, which ranged from 9,9% to 20,6% in relation to the control. It is important to highlight that in the field the increase is not as high as observed in this work because these are smaller experimental areas and in the field there are other variations that affect both maximizing and minimizing the effects. Based on work carried out in commercial areas in other harvests, it was clear that these increases range from 3% to 6%.

These effects are possibly related to the application of salicylic compounds that acted to induce plant resistance to biotic and abiotic stresses, enabling the reallocation of energy that would be spent to replace cellular structures that would have suffered damage. All of this combined with the effect of cobalt, molybdenum and amino acids, which possibly enhanced biological nitrogen fixation, resulted in a significant increase in productivity. The simplified physiological model is presented in Figure 2.

Ellen Mayara Alves Cabral, Evandro Binotto Fagan, Luís Henrique Soares, Marina Rodrigues dos Reis, Isabella Sabrina Pereira, Unipam; Jérssica Nogueira Soares, Esalq/Usp

 

Article published in issue 207 of Cultivar Grandes Culturas.