The use of grass‐legume bicultures grown as winter annual cover crops may provide farmers with additional cover crop management options regarding the availability of cover crop residue N. A 2‐yr field experiment was conducted to determine dry matter (DM) accumulation, chemical composition, and N release from grass and legume cover crops grown in monoculture (rye, crimson clover, and hairy vetch) and biculture (rye‐crimson clover and rye‐hairy vetch). Air‐dried plant material was placed on the soil surface in 1‐mm mesh nylon bags for 1, 2, 3, 4, 6, 8, and 16 wk. Following retrieval, mesh bag contents were analyzed for total N, C, cellulose, hemicellulose, and lignin concentrations. The 2‐yr mean cover crop DM production was in the order of rye‐hairy vetch > hairy vetch > rye‐crimson clover > rye > crimson clover. The greatest cover crop N content (2‐yr mean) occurred with hairy vetch monoculture (154 kg N ha−1), compared with a low of 41 kg N ha−1 for the rye monoculture. When grown in biculture with rye, hairy vetch accumulated more DM and biomass N compared with crimson clover, both as a proportion of the biculture and as DM yield. In general, the order of N release rates (rapid to slow) was hairy vetch > crimson clover = rye‐hairy vetch > rye‐crimson clover = rye. Estimates of N (kg ha−1) released from cover crop residue after 8 wk of field decomposition, averaged over 2 yr, were 24 for rye, 60 for crimson clover, 132 for hairy vetch, 48 for rye‐crimson clover, and 108 for rye‐hairy vetch. Results of this study demonstrate only slight reductions in N release from grass‐legume bicultures compared with legume monocultures.

Efficient utilization of N contained in cover crop residues by the subsequent summer crop requires an understanding of temporal patterns of N release as related to specific management strategies. The objective of this research was to determine, under field conditions, changes in plant composition and subsequent patterns of N release resulting from two desiccation dates approximately 2 wk apart (early and late) for rye (Secale cereale L.), crimson clover (Trifolium incarnatum L.), and hairy vetch (Vicia villosa Roth) cover crops. Averaged over 2 yr the late desiccation treatment resulted in increases in cover crop dry matter of 39, 41, and 61% for rye, crimson clover, and hairy vetch, respectively. Corresponding increases in total N content of the respective cover crops were 14, 23, and 41%. Significant differences in cellulose, hemicellulose, and lignin contents were found among cover crop residues between desiccation times. Nitrogen release from decomposing cover crop residues was monitored using nylon mesh (53 µm) bags. In general, the order of N release was hairy vetch > crimson clover > rye. Cover crops desiccated early decomposed faster, however, the relative magnitude of these N release patterns differed sharply between years. The percentage of initial residue N remaining after 16 wk for the early desiccation date in 1984 was 53, 14, and 13% for rye, crimson clover, and hairy vetch, respectively, compared with corresponding values of 59, 42, and 35% in 1985, which was characterized by a relatively dry growing season. Estimates of N released from each cover crop indicated that the potentially larger available N pool resulting from a delay in desiccation was offset by the slower rate of N release, especially for rye and crimson clover.

Cover crop management in no‐tillage systems prior to planting the principal crop can be an important tool in maximizing the beneficial effects of the cover crop on the principal crop. A field experiment was conducted in 1984 and 1985 to examine timing effects of cover crop desiccation relative to corn planting [early desiccation/early plant (EE), early desiccation/late plant (EL), and late desiccation/ late plant (LL)] and fertilizer N (0, 100, and 200 kg ha−1) on corn growth and yield. These management schemes were evaluated for fallow, rye (Secale cereale L.), crimson clover (Trifolium incarnatum L.), and hairy vetch (Vicia villosa Roth.) cover crop systems. Corn dry matter production and N uptake, monitored in all 0 kg N ha−1 treatments, were significantly affected by cover crop management and varied according to stage of development and climatic conditions. Cover crop type had a pronounced effect on corn growth, with corn dry matter production in a rye cover crop lower than in legume cover crops. Grain yield response to applied N was greatest in a rye cover crop system. In contrast, a grain yield response up to the first increment of fertilizer N (100 kg ha−1) in legume cover crop systems was observed only in 1984. Corn recovery of legume N was estimated at 40 to 45 kg N ha−1 (2‐yr avg.), representing approximately 36 and 30% of the total N content of crimson clover and hairy vetch, respectively. These data indicate that winter annual legume cover crops are capable of providing a substantial portion of the N required by corn. Additionally, cover crop management should insure that corn planting is not delayed to allow for additional legume growth and N production.

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Grass‐legume bicultures as winter annual cover crops may combine the N scavenging ability of grasses and the biological N2 fixation capacity 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 focus of this research was to examine the differences among legume monocultures and grass‐legume bicultures with regard to early spring dry matter (DM) and N accumulation, and related effects on soil inorganic N levels and subsequent corn (Zea mays L.) yield. Austrian winter pea [Pisum sativum L. subsp, sativum var. arvense (L.) Poir.], crimson clover (Trifolium incarnatum L.), commonve tch (Vicla saava L.), and hairy vetch (Vicla villosa Roth) were grown in monoculture and in bicultures with rye (Secale cereale L.), oat (Arena satira L.), and wheat (Triacum 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 ranged from 0.87 to 2.53 Mg ha−1, with a ranking of Austrian winter pea < hairy vetch < commonv etch < 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 values for the legume component followed the same relative ranking and ranged 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, the average C:N ratio over the 3‐yr experiment was >30, suggesting that net N mineralization would occur from the decomposing cover crop residues. Profile soil inorganic N (0 to 90 cm) was greater in legume monoculture than in grass‐legume biculture treatments, indicating the ability of grasses to capture soil N. Corn yield was affected by the treatments in 1 of 3 yr, with greater yields following a legume monoculture than a grass‐legume biculture. Collectively, these results suggest that grass‐legume bicultures as winter annual cover crops have the potential to utilize residual soil NO3 and thereby minimize leaching while adding fixed N to cropping systems in the southeastern USA.