Banca de DEFESA: WESLEY DOS SANTOS SOUZA

Carbon and nitrogen dynamics in soil under Marandu grass pasture (Urochloa brizantha cv. Marandu) in monoculture and mixed with forage legume.

Arachis pintoi, Desmodium ovalifolium, carbon sequestration, SOC.

Due to the current scenario of climate change that has been causing global warming, there is a need to adopt strategies to mitigate greenhouse gas (GHG) emissions. Among the various areas of action to mitigate greenhouse gases emissions, the agriculture is responsible for a large part of emissions in Brazil. There is a need to implement systems with potential for soil carbon sequestration. Therefore, this study aimed to: 1- Assess whether the use of a system with pasture mixed with forage legumes will be efficient in the carbon sequestration as a monoculture system fertilized with nitrogen. 2- To study the impact on the carbon and nitrogen accumulation in the soil after the system implantation in the same year, evaluating pastures with and without fertilized with nitrogen or mixed with forage legumes in two regions under different edaphoclimatic conditions. To achieve these objectives, three experiments were performed, where 1- systems with productive pasture of Urochloa brizantha cv. Marandu with mixed pasture of forage peanut (Arachis pintoi)-Marandu grass 8 after pasture of elephant grass (Pennisetum purpureum) fertilized with N, 2- study installed in two areas located in regions with different edaphoclimatic experimental conditions, where they were solved systems with Marandu grass pasture with and without nitrogen fertilization and intercropped with forage leguminous, in addition to also evaluating older existing systems and the area of native vegetation in the surroundings. In all systems, soil samples were collected for analysis of soil density, carbon, and nitrogen concentration and ¹³C isotopic abundance. As results found with these studies, for the implementation of systems that favor carbon sequestration in the soil, systems with pastures intercropped with forage legumes (Arachis pintoi and Desmodium ovalifolium) are recommended, as they accumulate carbon at similar or even higher rates than yeast-fertilized monoculture pasture systems. Systems with well-managed pastures, in monoculture or intercropping, had high rates of carbon sequestration in the initial years after implementation and reduce with advancing years of improvement until reaching a balance. This interferes with the use of the short-term sequestration rate to project the GHG mitigation potential of long-term systems. The improved system for carbon credit purposes and GHG mitigation projects, aimed at storing and sequestering carbon in the soil, respond differently when updated in rules with edaphoclimatic conditions and/or history of management prior to different implementation.