An evaluation of summer cover crops for use in vegetable production systems in North Carolina

Summer cover crops can produce biomass, contribute nitrogen to cropping sys tems, increase soil organic matter, and suppress weeds. Through fixation of atmospheric N, and uptake of soil residual N, they also contribute to the N requirement of subsequent vegetable crops. Six legumes {cowpea (Vigna ung aiculata L.), sesbania (Sesbania exaltata L,), soybean (Glycine mar L), hai ry indigo (Indigofera hirsutum L), velvetbean [Mucuna deeringiana (Bort.) M err.], and lablab (Lablab purpureus L.)}; two nonlegume broadleaved species [buckwheat (Fagopyrum esculentum Moench) and sesame (Sesamum indicum L)]; and five grasses {sorghum-sudangrass [Sorghum bicolor (L) Moench x S. sudan ense (P) Stapf.], sudangrass [S. sudanense (P) Stapf.], Japanese millet [Ec hinocloa frumentacea (Roxb.) Link], pearl millet [Pennisetum glaucum (L). R . Br.], and German foxtail millet [Setaria italica (L.) Beauv.)]}, were pla nted in raised beds alone or in mixtures in 1995 at Plymouth, and in 1996 a t Goldsboro, N.C. Biomass production for the legumes ranged from 1420 (velv etbean) to 4807 kg.h(-1) (sesbania). Low velvetbean biomass was attributed to poor germination in this study. Nitrogen in the aboveground biomass for the legumes ranged from 32 (velvetbean) to 97 kg.ha(-1) (sesbania). All of the legumes except velvetbean were competitive with weeds. kablab did not s uppress weeds as well as did cover crops producing higher biomass. Abovegro und biomass for grasses: varied from 3918 (Japanese millet) to 8792 kg.ha(- 1) (sorghum-sudangrass). While N for the grasses ranged from 39 (Japanese m illet) to 88 kg.ha(-1) (sorghum-sudangrass), the C : N ratios were very hig h. Additional N would be needed for fall-planted vegetable crops to overcom e. immobilization of N. All of the grass cover crops reduced weeds as relat ive to the weedy control plot. Species that performed well together as a mi xture at both sites included Japanese millet/soybean and sorghum-sudangrass /cowpea.