Long-term impact of conventional management on soil carbon and nitrogen stocks in the semi-arid region of Brazil: A meta-analysis

The conversion of native vegetation to agricultural systems has impacted soil carbon and nitrogen stocks in tropical regions, with their maintenance, increase and losss depending on several factors, such as climate, cultivation time, management, depth and classe of soil. Our aim, therefore, was to evaluate the impact of con-verting areas under Caatinga vegetation to conventional agricultural systems (cropland and pasture) on stocks of carbon (soil organic carbon -SOC; labile carbon -CL and non-labile carbon -CnL) and nitrogen by means of a meta-analysis. In the present research, seven studies were used, with a total of 76 paired comparisons on 14 farms distributed over seven municipalities in three states in the semi-arid region of Brazil were identified from the literature. A dataset of 44 paired comparisons was formed: 14 from areas of native Caatinga vegetation (references), 25 with annual crops, and five under pasture, which came from. The effect of converting Caatinga to conventional systems in the semi-arid region was markedly negative, generating average losses of 10.78%, 9.51%, 23.53% and 15.36% for SOC, nitrogen, CL and CnL, respectively. The loss of nitrogen and carbon stocks (SOC, CL and CnL) decreases with soil depth. The most sensitive soil classes to a change in land use in the semi-arid region of Brazil were the Alfisols, Aridisols and Ultisols, while the Inceptisols showed gains in SOC and CnL.