The influence of four cover crops (hairy vetch, rye, biculture of vetch and rye, and winter weeds)and three N fertilization rates (0, 60 to 65, and 120 to 130 kg N ha^-1) was examined on plant C input from cover crops, cotton, and sorghum and soi organic C (SOC) in tilled and non-tilled soils in central GA. As plant C input varied by treatments and years, total input from 2000 to 2002 increased in cover crops compared to weeds and ranged from 6.8 to 22.8 Mg ha^-1. The SOC at 0- to 10-cm fluctuated with C input from Oct. 1999 to Nov. 2002 and was greater in cover crops than in weeds in no-tilled soil. In contrast, SOC at 10- to 30-cm in no-tilled soil and at 0- to 60-cm in chisel-tilled soil declined gradually and was greater in biculture than in weeds. As a result, the biculture sequestered 267 compared with 33, -133, and -967 kg C ha^-1 yr^-1 at 0- to 30-cm in rye, vetch, and weeds, respectively, in no-tilled soil. In strip-tilled and chisel-tilled soils, SOC lost from 233 to 1233 kg C ha^-1 yr^-1. The SOC at 0- to 10- and 10- to 30-cm also increased in cover crops with 120 to 130 kg N ha^-1 (9.1 to 11.8 and 14.0 to 17.1 kg C ha^-1) than in weeds with 0 kg N ha^-1 (8.0 to 10.6 and 12.4 to 14.0 kg C ha^-1), regardless of tillage. In the subhumid region, cover crops and N fertilization can increase plant input C and C storage in tilled and non-tilled soils compared with no cover crop and N fertilization. Because of greater residue C, hairy vetch/rye biculture was more effective in sequestering C in no-tilled soil or reducing its decline in tilled soil than monocultures or weeds.