LAUSR

Abstract Historically, the Amazon region has been undergoing significant land use changes due to the introduction of cattle ranching. However, over the few last years, soybean plantations have increased in importance, with consequences for soil organic carbon (SOC) stocks. We measured the SOC stock changes in a chronosequence of native forest, pasture and soybean sites established during different periods on a farm in Rondonia State (Brazilian Amazon). The native forest was converted to pasture and later to soybean. The pasture sites were 11, 15 and 26 years old, while the soybean sites were one (two sites) and 3 years old. SOC stocks (0 to 0.3 m) of the native forest and the six sites were measured for comparison. Overall SOC stocks (up to 0.3 m depth) did not change when forest was converted to pasture. While the overall SOC stock quickly decreased immediately after the pasture was converted to soybean. This information about the increase (pasture) or immediate decrease (pasture-soybean) of SOC stocks after conversion from forest to agricultural areas is important for future studies on soil C dynamics.