Two rice varieties, M-206 and Clearfield XL745 (CXL745) were chosen to represent the two widely-planted rice types grown in CA(M-206) and the Southern US (CXL745).M-206 is a widely planted medium grain japonica rice currently grown on approximately 50% of CA rice area (CA Cooperative Rice Research Foundation,2014).CXL745 is a non-transgenic, herbicide resistant hybrid rice variety widely planted in most Southern states (the most widely planted rice variety in the USA) (RiceTec, 2015).US rice production systems are direct seeded; CA rice is primarily water-seeded(i.e.—pre-soaked seed is applied to flooded fields via airplane),whereas Southern US rice is primarily drill-seeded. Although data was not collect on site-specific management, management was assumed to follow recommended best practices at each site . Like wise, we assume both varieties are planted at recommended rates;350 seeds m−2for M-206 (Hill, 2013) and 50 seeds m−2 for CXL745(Runsick and Wilson, 2009).