Abstract
ABSTRACT: Studies show that soil organic carbon (SOC) decreases between 3 % and 9 % in degraded grasslands in tropical regions, mainly due to the absence of techniques to enhance carbon contribution to soils. This study assessed SOC stock change factors for grassland management, specific to the semi-arid region of Brazil. These factors may contribute to a better understanding of SOC dynamics and could be used to improve inventories on GHG emissions. In addition, they could be used for updating default factors used by the Intergovernmental Panel on Climate Change. This study considers both soil sampling and a literature review, and comprises 27 paired comparisons, where the dataset was analyzed using a mixed linear model. For the grassland in the Brazilian semi-arid region, the SOC stock is reduced by between 12 % and 27 % due to inadequate management, overgrazing, and edaphoclimatic conditions of the Brazilian semiarid. However, this depends on aspects, such as land use and soil layer, which represents substantially more severe losses than in other regions of the country. We also found that losses occur during the first five years after conversion of native vegetation. The results also indicated a trend for SOC stocks to recover over time, reaching 4 % after 30 years of use as grassland, probably related to the long period without soil tillage and the role of gramineas root system.
Highlights
The Brazilian cattle herd comprises roughly 172 million of animals and occupies an area of approximately 150 million hectares of grassland (IBGE, 2017)
We found that losses occur during the first five years after conversion of native vegetation
In 0-30 cm layer and for 20 years of use, the management factor was 0.75 ± 0.11, which means a reduction of 25 % in soil organic carbon (SOC) stock
Summary
The Brazilian cattle herd comprises roughly 172 million of animals and occupies an area of approximately 150 million hectares of grassland (IBGE, 2017). Overall, about 20 % of these grasslands show some degree of degradation (Santana et al, 2019), and the main causes are related to inadequate management, especially the burning of native vegetation, low biomass production, and overgrazing, which exceeds the soil recovery capacity (FAO, 2017). In addition to management issues, high temperatures and evapotranspiration, low and irregular rainfall in the region limit plant biomass production, which, among other factors, hinders stocks of soil organic carbon (SOC) in the semi-arid region (Oliveira et al, 2015). Maia et al (2009) found 9 % reduction in degraded grasslands and 19 % increase in improved grasslands in the Amazon and Cerrado regions of Brazil These authors cite overgrazing and inadequate pasture management as the main factors for SOC losses
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