Glifosato na capacidade sortiva de fósforo em solos típicos de Mato Grosso

Abstract

Glyphosate is currently the most used herbicide in crops and phosphorus (P) is the nutrient added in greater quantity via fertilizers. In soil, glyphosate acquires a negative charge and is able to bind to soil particles in a similar way to phosphate. The extent of this competitive adsorption is not well understood and depends on the type of soil and mineral involved in the sorption, with this arise concerns about the possibility of one affecting the sorption of the other, mainly due to the high amounts annually added of these elements on agricultural soils, concomitantly. The objective was to evaluate the interaction between glyphosate and phosphate ion in different soils, considering the influence of their different attributes. The study was carried out in the North and Middle-North regions of Mato Grosso, an important frontier for agricultural expansion. Different soils from the main soil classes in the region were sampled at two depths. The chemical and physical attributes of the soil were evaluated and the samples were submitted to sorption tests in a completely randomized design (DIC) using a triple factorial arrangement with five doses of glyphosate, six soils and two depths. The sorption isotherms were constructed by the Langmuir model and their sorption parameters, the Maximum P Adsorption Capacity (MPAC) and the Langmuir constant (KL), were used for statistical tests. The isotherms built by the linearized Langmuir single region model adapted to the typical soils of the region. The MACP by soils in the region is considered low for tropical soils and is mainly related to clay content, organic matter and the percentage of aluminum saturation. Glyphosate interferes with P sorption in most typical soils of Mato Grosso, reduced MACP in some soils by up to 10.5% and can reduce KL by up to 60% or increse it by up to 28%, which depends on the soil type of clay content, organic matter content and pH.