Residual do herbicida 2,4-D no solo e sua correlação com a produtividade e os parâmetros químicos e físicos do solo.

Abstract

Large amounts of herbicides are used in agriculture to control weeds that pose risks to crops, resulting in increased production cost of farms. Also, if not applied properly, its use can cause resistance of spontaneous plants and result in residues in the environment, in the soil, the water or in toxicity to the crops. The objective of this research was to evaluate the residue of the 2,4-D herbicide in soil and its correlation with yield, as well as physical and chemical properties of the soil. The experiment was conducted on a farm in the city of Nova Santa Rosa, in the state of Paraná in the years 2011 and 2012. The main crops grown in the area are corn and soybeans, in rotation. Soil samples were collected to determine their physical and chemical properties and for analysis of residual 2,4-D before implementation (RI) and after application (RF) of the 2,4-D herbicide. Initially, the glyphosate herbicide was applied in a single dose (2.5 L ha-1) and then the 2,4-D herbicide was applied at two doses (1,0 and 1,5 L ha-1) with boom sprayer and, after 5 days of application, soil samples were collected for analysis of RF. After extracting the 2,4-D from the soil, high performance liquid chromatography (HPLC) was carried out to detect the active ingredient. In order to map the spontaneous plants, before and after spraying the herbicide the method of systematic sampling was used. The soybean yield for both years were also analyzed, and finally, spatial correlation of the parameters evaluated was performed. The results of RI of 2,4-D in the soil in both years, demonstrating that this is a herbicide that can remain retained in the soil over time and, depending on the soil characteristics, the preparation of the area and climatic conditions, this time can be longer. In 2011, the maximum detection of the active ingredient was 609 μg kg-1 and in 2012 was 652 μg kg-1. The RI of 2,4-D in the soil showed negative spatial correlation for chemical attributes K, organic matter and pH and for physical density, macroporosity, microporosity, total porosity and soil moisture it showed positive spatial correlation with sand and the chemical attributes Cu, Mg, Mn, P and Zn in the first year assessed. In 2012 the spatial correlation was positive with clay. The spontaneous plants type horseweed (Conyza bonariensis), did not present spatial correlation among the parameters evaluated in 2011, however, showed a positive correlation with the micropores of the soil in 2012. As residual 2,4-D in the soil and many attributes analyzed presented spatial correlation, spatial correlation among the variables analyzed proved to be an important tool to understand the influence of a parameter over the other. Both doses satisfactorily controlled the incidence of spontaneous plants. The 2,4-D showed some points with detection and other with no detection of the active ingredient in the soil, a fact that demonstrates the importance of assessing the spatial correlation of soil properties (chemical and physical) with residual herbicide in the soil, determining the influence of one attribute over the other.