Rice and natural seeds are important foods for waterfowl in rice growing regions such as the Gulf Coast Prairies of Louisiana and Texas. We conducted a study from August-November 2010 and collected 2,250 soil cores in 50 farmed and 50 idle rice fields in the Louisiana Chenier Plain (CP) and Texas Mid-Coast (TMC) to estimate biomass of waste rice and natural seeds. Estimates are necessary to assess carrying capacity for waterfowl in this region by the Gulf Coast Joint Venture. Waste rice abundance was greatest in CP farmed fields that produced a second crop of rice (i.e., ratoon) and were not harvested in November (1,014.0 kg/ha; CV = 8.3%). Natural seed abundance was greatest in TMC fall disked idle rice fields in October (957.4 kg/ha; CV = 17.2%). Variation in rice and natural seed abundance in farmed and idled rice fields ranged from CV = 0.3%-97.9% in the CP and TMC, perhaps attributable to the variety of farming practices encountered. We did not observe a significant decline in waste rice and natural seed abundance in harvested rice fields from August-November as was reported for the Mississippi Alluvial Valley (MAV). We estimated an additional 6,000 soil cores would need to be collected and analyzed to achieve our goal for precision (i.e., CV â?¤ 15%); hence, we recommend continuation of this study.