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Organic matter and sorption of herbicides in no-till soils of tropical and subtropical regions of Brazil


The no-till system is extensively adopted in Brazil because it is a conservative practice, capable to improve soil quality and reduce yield costs when compared to the conventional till. The different edaphoclimatic conditions and the adoption of different crops inter-harvests suggest distinctions in the soil organic matter (SOM) distribution and quality, mainly for no-till systems due to the reliance period of the straw. The interactions between SOM and pesticides were already studied, but only partially cleared once most of the studies consider the SOM as a homogeneous compartment neglecting the role of its different molecular components. Therefore, this research aims to evaluate the effects of the SOM composition and distribution on the sorption of herbicides applied to soybean and corn crops under no-till in different edaphoclimatic conditions: tropical (Midwest Region of Brazil) and subtropical (South Region of Brazil). The alachlor, bentazon, diclosulam and imazethapyr herbicides were selected due to their wide use for the selected crops, their different physical-chemical properties, and their availability in the radiolabelled forms (14C). Ten soil samples will be collected (five representative soils from Paraná and Mato Grosso States, respectively) to perform sorption studies in the whole soil and its different size fractions. The physical fractionation of the soils and the use of spectroscopic techniques (nuclear magnetic resonance, Fourier transform infrared spectroscopy and laser induced fluorescence) will be used to characterize SOM distribution and quality, which will allow correlating their attributes to herbicides sorption potential in soils. (AU)

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