Impacto da mudança no uso da terra nos estoques de carbono, dinâmica da matéria orgânica e agregação do solo sob sistemas integrados e pastagens no semiárido de Sergipe, Brasil.

Abstract

In Brazil, the semi-arid region is one of the most climatically challenged areas, experiencing irregular and low rainfall, with long periods of drought, high temperatures, and intense solar radiation, and is characterized by a unique biome known as Caatinga, which native vegetation is recognized as a unique regional vegetation; however, it is also linked to broader classifications as one of the tropical dry deciduous forests. and has undergone significant degradation due to deforestation for agriculture, livestock, and the use of firewood. In this context, nature-based solutions (NbS) that prioritize soil health are crucial due to the susceptibility of the semi-arid region to degradation. This study aimed to evaluate the impact of converting native vegetation (dense Caatinga) into two grasslands and two integrated livestock-forestry systems on soil organic carbon (SOC) stocks, soil organic matter (SOM) pools (particulate organic matter (POM) and mineral-associated organic matter (MAOM)), and soil physical quality through Water-stable Aggregate (WSA) classes and aggregation indices. The study was conducted at the Semi-arid Experimental Station of the Brazilian Agricultural Research Corporation (EMBRAPA), located in the municipality of Nossa Senhora da Glória, Sergipe, Brazil. Soil samples were collected at 0-10, 10-20, 20-30, 30-50, 50-70 and 70-100 cm layers in 5 different land uses: native vegetation (NV), integrated livestock-forestry system under no-tillage with gliricidia (Gliricidia sepium) + Urochloa (Urochloa decumbens) (ILFug), an integrated livestock-forestry system under conventional tillage with gliricidia + forage cactus (Opuntia cochenillifera) (ILFcg), improved pasture (ImpP), and degraded pasture (DegP). The ILFug system showed the highest stocks of MAOM, at all soil depths, and that led to increases in the SOC stocks, thus placing this system with the greatest SOC stocks. The ILFug system also showed the greatest aggregate stability index (ASI) in almost all soil layers. The exception was the 0-10 and 50-70 cm layers, where the NV had the highest values of 89.1% and 90.4%, respectively. The NV-DegP conversion represented a decline in soil quality, showing the most significant reductions in the POM fraction of SOM. Almost all parameters studied were significantly correlated with SOC, demonstrating that SOM is a primary agent in binding soil particles together, influencing the variation in WSA and aggregation indices. The ImpP and DegP exhibited similar SOC stocks; however, the ImpP showed a higher ASI and increased amount of macroaggregates (> 2.00 mm), highlighting the adverse impacts of degradation processes in soil structure. By promoting practices that enhance SOC stocks, C sequestration, reduce greenhouse gas emissions, and improve ecosystem resilience, NbS provides a sustainable approach to mitigating the impacts of climate change, while supporting local communities in the Brazilian semi-arid region. Keywords: Caatinga; nature-based solutions; soil quality; climate change; no-tillage.