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Biculture legume–cereal cover cropping may enhance above‐ and belowground biomass yields and C and N contents. The increase in C and N supply to the soil has the potential to improve soil quality and crop productivity compared with monoculture cover crop species. We examined above‐ and belowground (0‐ to 120‐cm soil depth) biomass yields and C and N contents of a legume [hairy vetch ( Vicia villosa Roth)], nonlegume [rye ( Secale cereale L.)], and biculture of legume and nonlegume (vetch and rye) cover crops planted without tillage in the fall of 1999 to 2001 in central Georgia. After cover crop kill in the spring, cotton ( Gossypium hitsutum L.) and sorghum [ Sorghum bicolor (L.) Moench)] were planted using three tillage practices (no‐till, strip till, and chisel till) with three N fertilization rates (0, 60 to 65, and 120 to 130 kg N ha −1 ). The field experiment was arranged in a split‐split plot treatment with three replications on a Dothan sandy loam (fine‐loamy, kaolinitic, thermic, Plinthic Kandiudults). Aboveground biomass yield of rye decreased from 6.1 to 2.3 Mg ha −1 from 2000 to 2002, but yield of hairy vetch varied (2.4 to 5.2 Mg ha −1 ). In contrast, biomass yield of vetch and rye biculture (5.6 to 8.2 Mg ha −1 ) was greater than that of rye and vetch planted alone in all years. Compared with winter weeds in no cover crop treatment, C content in rye (1729 to 2670 kg ha −1 ) was greater due to higher biomass yield, but N content in vetch (76 to 165 kg ha −1 ) was greater due to higher N concentration, except in 2002. As a result, C (2260 to 3512 kg ha −1 ) and N (84 to 310 kg ha −1 ) contents in biculture were greater than those from monocultures in all years. Similarly, belowground biomass yield and C and N contents were greater in biculture than in monocultures. In 2001, aboveground biomass yield and C and N contents in cover crops were also greater in strip till with biculture than in other treatments, except in chisel till with vetch and biculture, but belowground biomass yield and N content were greater in chisel till with biculture than in no‐till, strip till, and chisel till with weeds. Cotton lint yield was lower with biculture than with rye, but sorghum grain yield and cotton and sorghum biomass (stems + leaves) yields and N uptake were greater with biculture than with rye. Because of higher biomass yield and C and N contents, biculture of hairy vetch and rye cover crops may increase N supply, summer crop yields, and N uptake compared with rye and may increase potentials to improve soil organic matter and reduce N leaching compared with vetch.