Quantification and spectroscopic characterization of dissolved organic matter in soils under pastures and integrated production systems

Abstract

Brazil is a country that presents a highly competitive agriculture, being the biggest commercial producer and exporter of beef in the world. On the other hand, studies show that the livestock sector is one of those responsible for increasing the concentration of greenhouse gases (GHG), especially through the emission of methane gas by ruminants, with implications for global climate change. Therefore, new actions are needed to mitigate the emission of these GHGs, and thus make livestock practice more sustainable. Strategies have been used, such as the use of Integrated Production Systems, with different variations including crop-livestock integration, livestock-forest integration and crop-livestock-forest integration, as well as the improved management and recovery of degraded pastures. Recent results indicate that integrated production systems and adequate pasture management have demonstrated the ability to sequester carbon, either by transforming CO2 through photosynthesis, by tree biomass, or by increasing the carbon content in the soil (which occurs through the increase of soil organic matter), contributing directly and indirectly to the mitigation of GHGs. Studies in this line are being developed in a broad Thematic Project, supported by FAPESP, entitled "Strategies Practices for Mitigating Greenhouse Gas Emissions in Grassland Systems of the Brazilian Southeastern" (Process FAPESP 2017 / 20084-5). Dissolved organic matter (DOM) is a complex mixture of thousands of organic compounds, being highly mobile and reactive in the soil. It acts in many biogeochemical processes, such as the carbon cycle, in addition to assisting in the translocation and immobilization of nutrients and retention of toxic metals for plants. In addition, studies have already shown that DOM is significantly affected by land use, management practices, as well as climatic factors. Thus, DOM is a crucial component in the soil carbon balance, and the study of its dynamics and stability is also of great importance for aspects of soil fertility. However, in soils of tropical areas, the DOM studies are still very limited. Thus, the objective of this project aims to advance the understanding of the mechanisms responsible for the dynamics and reactivity of DOM collected in soils under integrated production systems, the livestock-forest integration type and pastures under different managements, these areas of experiments being provided for in the thematic project supported by FAPESP. For this, the extraction and chemical and structural characterization of the DOM of these soils will be made. Different techniques will be used, such as Ultraviolet-visible spectroscopy, 2D Nuclear Magnetic Resonance, 2D Molecular Fluorescence and Excitation-Emission Matrix, and LIBS ("laser-induced breakdown spectroscopy"), as well as data treatment using chemometric tools. In addition, reference methods such as Elemental Analysis (CHN) and Inductive Coupled Plasma Optical Emission Spectrometry (ICP-OES) will be used for calibration and in a complementary techniques to spectroscopic analyzes. Therefore, the expectation is that the results of this study will provide important information for a better understanding of the composition, structural aspects and reactivity of DOM in tropical soils in areas with potential for carbon sequestration. (AU)