Biculture Legume–Cereal Cover Crops for Enhanced Biomass Yield and Carbon and Nitrogen

leach into groundwater after crop harvest in the fall, and depending on the species, can sequester atmospheric C Biculture legume–cereal cover cropping may enhance aboveand and/or N, thereby reducing the amount of N fertilizer 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 required for summer crops (Hargrove, 1986; Meisinger and crop productivity compared with monoculture cover crop species. et al., 1991; Kuo et al., 1997a, 1997b). Other benefits of We examined aboveand belowground (0to 120-cm soil depth) cover crops include increased soil aggregation and water biomass yields and C and N contents of a legume [hairy vetch (Vicia infiltration capacity (McVay et al., 1989; Drury et al., villosa Roth)], nonlegume [rye (Secale cereale L.)], and biculture of 1991; Roberson et al., 1991), improved water-holding legume and nonlegume (vetch and rye) cover crops planted without capacity (Smith et al., 1987), reduced soil erosion (Frye tillage in the fall of 1999 to 2001 in central Georgia. After cover et al., 1985; Langdale et al., 1991), and increased root crop kill in the spring, cotton (Gossypium hitsutum L.) and sorghum growth of summer crops (Sainju et al., 2001) compared [Sorghum bicolor (L.) Moench)] were planted using three tillage with no cover crop. Cover cropping can provide opporpractices (no-till, strip till, and chisel till) with three N fertilization tunities to conserve soil organic C and N concentrations 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 in regions, such as in southeast USA, where organic on a Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic matter concentration is lower than in the northern areas Kandiudults). Aboveground biomass yield of rye decreased from 6.1 and where mild winter allows cover crop growth (Harto 2.3 Mg ha 1 from 2000 to 2002, but yield of hairy vetch varied (2.4 grove, 1986; Doran, 1987; Doran and Smith, 1987). to 5.2 Mg ha 1). In contrast, biomass yield of vetch and rye biculture Legume cover crops can supply N to succeeding crops (5.6 to 8.2 Mg ha 1) was greater than that of rye and vetch planted and increase crop yields compared with nonlegume or alone in all years. Compared with winter weeds in no cover crop no cover crops (Hargrove, 1986; Clark et al., 1994, Kuo treatment, C content in rye (1729 to 2670 kg ha 1) was greater due et al., 1997b). In contrast, nonlegume cover crops are to higher biomass yield, but N content in vetch (76 to 165 kg ha 1) effective in increasing soil organic matter by supplying was greater due to higher N concentration, except in 2002. As a result, C through increased biomass production (Kuo et al., 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. 1997a, 1997b; Sainju et al., 2000) compared with legume Similarly, belowground biomass yield and C and N contents were or no cover crops. Nonlegume cover crops also reduce greater in biculture than in monocultures. In 2001, aboveground bioNO3–N leaching from the soil profile better than legume mass yield and C and N contents in cover crops were also greater in or no cover crops do (Meisinger et al., 1991; McCracken strip till with biculture than in other treatments, except in chisel till et al., 1994). A mixture of legume and nonlegume cover with vetch and biculture, but belowground biomass yield and N concrops would be ideal to supply both C and N inputs in tent were greater in chisel till with biculture than in no-till, strip till, adequate amounts that help to improve soil quality and and chisel till with weeds. Cotton lint yield was lower with biculture reduce N leaching compared with legumes and increase than with rye, but sorghum grain yield and cotton and sorghum biocrop productivity compared with nonlegumes. mass (stems leaves) yields and N uptake were greater with biculture The N content or C/N ratio of cover crops is a princithan with rye. Because of higher biomass yield and C and N contents, biculture of hairy vetch and rye cover crops may increase N supply, pal determinant factor for soil N availability, regardless summer crop yields, and N uptake compared with rye and may increase of placement of their residues in the soil (Hargrove, potentials to improve soil organic matter and reduce N leaching com1986; Smith et al., 1987; Ranells and Wagger, 1996). As pared with vetch. N content of plant residue is increased or C/N ratio decreased, initial soil N mineralization potential and N mineralization rate increased (Frankenberger and AbW cover cropping compared with bare fallow delmagid, 1985; Kuo and Sainju, 1998), and the crosscan maintain or increase organic C and N concenover time for net N mineralization decreased (Kuo and trations in the soil by providing additional crop residue Sainju, 1998). Therefore, one of the management opthat increases C and N inputs to the soil (Hargrove, tions to increase N content or reduce C/N ratio of non1986; Kuo et al., 1997a, 1997b; Sainju et al., 2000). Winlegume cover crops is to mix legumes and nonlegumes ter cover crops use soil residual N that may otherwise as bicultural treatments because nonlegume cover crops, such as rye, typically have low N content or high C/N U.M. Sainju, USDA-ARS-NPARL, 1500 North Central Ave., Sidney, ratio and thus have little effect on soil N availability MT 59270; and W.F. Whitehead and B.P. Singh, Agric. Res. Stn., Fort and crop yields (Clark et al., 1994; Ranells and Wagger, Valley State Univ., Fort Valley, GA 31030. Received 12 Nov. 2004. 1996; Kuo and Jellum, 2002). Research has shown that *Corresponding author ([email protected]). including hairy vetch or crimson clover (Trifolium incarPublished in Agron. J. 97:1403–1412 (2005). natum L.) with rye in biculture increased N content or Soil and Crop Management decreased C/N ratio of rye, thereby reducing the potendoi:10.2134/agronj2004.0274 tial for N immobilization from rye residue (Sullivan © American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA et al., 1991; Ranells and Wagger, 1996; Vaughan and 1403 Published online September 19, 2005