We estimate soil carbon sequestration in two ways, direct measurement of soil C stocks through time and calculating inputs and outputs of C to the system, i.e. net ecosystem production (NEP). In one project, we have demonstrated a loss of about 200 g C m2/y over a 3-y period using the direct measurement method. The most alarming part of this finding is that grasslands are generally considered carbon sinks, but none of the 5 grassland communities we established were accumulating carbon during this period, irrespective of disturbance and nutrient management. In experiments where we are estimating NEP by measuring NPP and soil respiration, both Wisconsin pasture and California annual grassland were losing carbon at equivalent rates during the same 3-y period.