Seletividade de herbicidas na cultura da soja em função de diferentes umidades do solo

Abstract

Climate change is increasingly affecting the quality and quantity of the world's agricultural production. In the state of Rio Grande do Sul, the search for alternatives that maximize productivity and contribute to the economic sustainability of the wetland ecosystem emerges as a justification for the use of the soybean crop in these areas, since it is one of the main commodities of Brazilian agribusiness. Chemical weed control constitutes the most widely adopted management method, however, little is known as the soybean crop responds to the use of herbicides in different soil moisture. Thus, this study aimed to evaluate physiological and biochemical responses in soy after applying herbicides recommended plants for growing in three soil moisture levels. The experiment was arranged in a randomized design in a factorial arrangement (7x3) with four replications. It was used to cultivate soy BMX Power RR, grown in pots (8L), keeping three plants per pot which, in stage V3 were subjected to three soil moisture: field capacity, Dry soil (50% below capacity field) and saturated soil (50% above the field capacity), followed by herbicide treatment: Glyphosate, Sulfentrazone, S-metolachlor, Glyphosate + Sulfentrazone, Glyphosate + S-metolachlor, Glyphosate + Sulfentrazone + S-metolachlor, beyond without herbicide treatment. At seven, 14 and 28 days after application (DAA) were evaluated chlorophyll content, flavonoids, nitrogen balance and gas exchange in the third trefoil fully developed. This time collected is still, leaf material for evaluation of osmotic potential, proline content, hydrogen peroxide, lipid peroxidation and activity of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX). For pigments and nitrogen balance index was little variation between treatments, since gas exchange were more affected in dry soil plants, especially at 14 and 28 DAA, with marked effect by the presence of herbicides. At seven DAA the herbicide Glyphosate in dry soil resulted in greater activation of antioxidant enzymes SOD and CAT, as well as increased production of hydrogen peroxide and is probably linked to increased oxidative stress caused by this herbicide. However, after 28 days from the application, increased synthesis of proline in this treatment, which leads to osmotic adjustments and consequent lower enzymatic activity. In saturated soil and field capacity responses triggered by Glyphosate herbicides, Sulfentrazone, S-metolachlor does not follow a pattern, but, in general, lead to lower stress compared to dry soil. The results of this study show that although the variation in soil moisture, changes the soybean crop metabolism, the application of herbicides in dry soil conditions or saturated accentuates this effect and may result in damage to the crop.