Grass-legume bicultures as winter annual cover crops may combine the N
scavenging ability of grasses and the biological N-2 fixation capacit
y of Legumes to improve N management in crop production systems of the
southeastern USA. A 3-yr field experiment was conducted on a Norfolk
loamy sand (fine-loamy, kaolinitic, thermic: Typic Kandiudults). The f
ocus of this research was to examine the differences among legume mono
cultures and grass-legume bicultures with regard to early spring dry m
atter (DM) and N accumulation, and related effects on soil inorganic N
levels and subsequent corn (Zea mays L.) yield. Austrian winter pea [
Pisum sativum E. subsp. sativum var. arvense (L.) Poir.], crimson clov
er (Trifolium incarnatum L.), common vetch (Vicia sativa L.), and hair
y vetch (Vicia villosa Roth) were grown in monoculture and in bicultur
es with rye (Secale cereale L.), oat (Avena sativa L.), and wheat (Tri
ticum aestivum L.). Aboveground plant material was harvested in early
March, late March, and mid-April. Biomass was separated into component
species and analyzed for total N and C concentrations. Averaged over
3 yr, legume component DM accumulation in monoculture and biculture ra
nged from 0.87 to 2.53 Mg ha(-1), with a ranking of Austrian winter pe
a > hairy vetch > common vetch > crimson clover. For the same period,
the grass component DM accumulation ranged from 1.31 to 2.28 Mg ha(-1)
, in the order rye = oat > wheat. Three year mean N accumulation value
s for the legume component followed the same relative ranking and rang
ed from 24 to 93 kg N ha(-1). Grass factor N content ranged from 18 to
39 kg N ha(-1) in the order rye > oat > wheat. For all bicultures, th
e average C:N ratio over the 3-yr experiment was <30, suggesting that
net N mineralization would occur from the decomposing cover crop resid
ues. Profile soil inorganic N (0 to 90 cm) was greater in legume monoc
ulture than in grass-legume biculture: treatments, indicating the abil
ity of grasses to capture sail N. Corn yield was affected by the treat
ments in 1 of 3 yr, with greater yields following a Legume monoculture
than a grass-legume biculture. Collectively, these results suggest th
at grass-legume bicultures as winter annual cover crops have the poten
tial to utilize residual soil NO2 and thereby minimize leaching while
adding fixed N to cropping systems in the southeastern USA.