Estoque, recuperação e esgotamento de carbono em classes de agregados do solo em Caatinga em regeneração e agricultura de subsistência

Abstract

The Caatinga is an exclusively Brazilian biome that presents high biodiversity and peculiarities in relation to climatic conditions of high temperatures and evapotranspiration, and low rainfall. As a result, it consists of a biome highly susceptible to environmental degradation. Soil management practices in many places associated with subsistence agriculture with low inputs of waste have caused the loss of soil carbon stocks and reduced physical quality. In this sense, this study aimed to evaluate the recovery and depletion of the soil carbon stock and the proportional distribution of the mass of large (2-8 mm) and small (0.25-2 mm) macroaggregates of the soil, and of microaggregates (0.053- 0.25 mm), as well as the potential for carbon accumulation in these classes of aggregates, in Caatinga under regeneration and subsistence bean cultivation compared to preserved Caatinga, in the Sertão do Alto Pajeú-PE. The samples were collected in three areas with different uses (an area of semi-shrub Caatinga preserved for 30 years, one of Caatinga in regeneration for 10 years and an area in bean cultivation with 30 years). The collections were carried out in the layers of 0.00-0.05, 0.05-0.10 and 0.10-0.20 m of a Luvissolo. In the soil samples, analyzes of physical and chemical characterization were carried out, and fractionated by means of wet sifting to obtain large macroaggregates, small macroaggregates and microaggregates. Carbon analyzes were performed on undisturbed samples and soil aggregates using the wet combustion method. The preserved Caatinga showed greater proportional mass of large macroaggregates at all depths with 84% at 0.00-0.05 m, 69% at 0.05-0.10 m and 66% at 0.10-0.20 m. Due to management, the mass of large macro aggregates decreased significantly in the area cultivated with beans with 63% large macro aggregates in 0.00-0.05 m, 62% in 0.05-0.10 m and 62% in 0.10-0, 20 m. The regenerating Caatinga also showed higher proportions of large macro-aggregates. Of the classes of aggregates, the large macroaggregates showed greater potential for carbon accumulation in the soil. The preserved Caatinga showed the highest stocks in this class of aggregates with 92% of carbon in the 0.00-0.05 m layer, 77% in 0.05-0.10 m and 70% in 0.10-0.20 m. For the regenerating Caatinga considering the 0.00-0.20 m layer, it was observed that the recovery rate of the stock in large macroaggregates was 79%. The area cultivated with beans, on the other hand, showed a loss of carbon stock in the class of large macroaggregates with reduction in all depths, with 63% of the stock in the 0.00-0.05 m layer, 67% in 0.05-0.10 m and 62% in 0.10-0.20 m. When considering the 0.00-0.20 m layer, there was a 64% depletion of the soil carbon stock in large macroaggregates under bean cultivation. Regarding total carbon, the regenerating Caatinga recovered 89% of the carbon stock in the 0.00-0.20 m layer and the cultivation of subsistence beans caused 54% of the soil carbon stock to be depleted in this layer. Thus, in the studied semi-arid climate environment, the large macroaggregates predominated in the constitution of the soil structure and presented a greater potential for carbon stock in this class. The adoption of a conventional system with monoculture caused a loss in the carbon stock of the soil, in contrast the natural regeneration of the Caatinga in a short period of time promoted the partial recovery of carbon from the soil.