Abstract:Mixed crop?livestock long-term experiments (LTE) are critical to increase the understanding of sustainability in complex agroecosystems. One example is the ?Palo a Pique? LTE which has been running for 25 years in Uruguay (from 1995 to present), evaluating four pasture?crop rotations under livestock grazing with no-till technology in soils with severe limitations. The results demonstrate that cropping systems reduced soil organic carbon (SOC) compared with permanent pastures, and that perennial pastures rotating with crops were critical to mitigate SOC losses.