Technical Abstract: There much interest in carbon (C) sequestration (C accounting) in cropping systems due the potential for agriculture to participate in ‘Cap and Trade’ opportunities, or purely as a matter of understanding soil quality. In this report we have constructed carbon budgets for two temperate grass species, perennial ryegrass (Lolium perenne L.) and Italian ryegrass (L. multiflorum Lam.). Data were collected from western Oregon grown grass seed crops. The range of soil C for these two grass seed crops was approximately 28,000 to 37,000 kg C/ha and soil organic matter ranged from 4.43 to 5.69%. We hypothesized that most temperate grass seed systems grown in western Oregon that are not limited by water or nutrients will have similar C budgets. It has been reported that soil C in grass seed cropping systems, over the long-term, can be affected by crop rotation, tillage, and residue management but usually the effects are minor. Soils of grass seed production systems in western Oregon have high organic C levels, greater than those frequently observed in conventional annual cropping systems that often involve annual soil disturbance for crop establishment. Future reports will construct more precise C budgets with more subcomponents (e.g., longer- vs. shorter-term sequestered C), but these data establish a baseline that will be useful for evaluating C cycling in grass seed production systems.