Hairy vetch (Vicia villosa Roth) fixes N for corn (Zea mays L.) production, and cereal rye (Secale cereale L.) accumulates soil N to reduce potential N losses. The objective of this research was to identify optimum seeding rates of vetch‐rye cover crop mixtures at Coastal Plain and Piedmont locations in Maryland. Mixtures evaluated were 14, 21, and 28 kg vetch ha−1, and 47 or 94 kg rye ha−1 in complete factorial combination. Pure vetch, rye, and no cover crop were used as controls. Cover crops were killed in early April (early kill) and early May (late kill), followed by no‐till corn without fertilizer N. Corn grain yields were significantly higher following late‐killed covers. Coastal Plain grain yields ranged from 3.1 to 7.0 Mg ha−1 and Piedmont yields ranged from 5.2 to 10.7 Mg ha−1. Within each kill date, corn yield was highest following vetch, lowest following rye, and intermediate following all six mixtures. Cover crop yield increased by 160% in the Piedmont and 83% at the Coastal Plain location when kill was delayed. Except for pure rye, N content was 1.6 to 2 times greater by the late kill date. Total N content was equal for all vetch‐rye mixtures at each date and within location, ranging from 74 to 109 kg ha−1 for early kill, and from 136 to 219 kg ha−1 for late kill. Carbon‐to‐nitrogen ratios (C/N) were 25:1 for all mixture combinations at the Piedmont location and for mixtures with low rye component at the Coastal Plain location. The best seeding rate mixture for corn production was 21 kg vetch ha−1 and 47 kg rye ha−1. The vetch‐rye mixture can scavenge potentially leachable N, while maintaining corn yields by adding fixed N to the cropping system.

Spring kill date affects cover crop N content and N availability to subsequent no‐till corn (Zea mays L.). This 2‐yr study was conducted in 1990 and 1991 at Coastal Plain and Piedmont locations in Maryland to evaluate three cover crop kill dates, three corn planting dates, and four corn fertilizer N (FN) rates following hairy vetch (Vicia villosa Roth), cereal rye (Secale cereale L.) and a vetch‐rye mixture. No‐cover checks were included for each corn planting date. Fertilizer N rates were 0 to 202 kg ha−1 in the Piedmont and 0 to 270 kg ha−1 for the Coastal Plain. The vetch‐rye mixture contained as much or more N than vetch, and more N than rye within each kill date. Cover crop biomass and N content increased for each delay in kill. In a 50‐d period from late March until early May, vetch and the vetch‐rye mixture accumulated about 2 kg N ha−1 d−1, with total topgrowth N accumulation from 144 to 203 kg ha−1 over two locations and two years. Greatest rye N accumulation was 51 kg ha−1. Corn N content ranged from 37 to 293 kg ha−1, and was significantly affected by FN rate. Within FN rate, N content was greater following vetch or vetch‐rye than following rye or no cover, particularly at low FN rates. Corn N content was greater if cover kill and corn planting were delayed until late April or mid‐May. This was attributed to greater cover crop N production and mulching effects, and the timing of summer rainfall. Corn FN requirements were greatest following rye or no cover, intermediate following vetch‐rye, and least following vetch. This demonstrates that cover crop species and kill date can be managed to conserve N with rye, supply N for the next crop with vetch, or provide both N conservation and N supply with a vetch‐rye mixture.

Autumn residual fertilizer nitrogen (FN) can be easily leached into groundwater in humid climates. Winter cover crops were evaluated for their ability to assimilate residual corn FN and thereby reduce N losses. Labelled FN (15N depleted) was applied to corn in Maryland in 1986 and 1987 at rates of 0, 168, and 336 kg FN ha− on a Mattapex silt loam (fine‐loamy, mixed, typic Hapludult). Cover crop treatments following corn harvest were hairy vetch (Vicia villosa Roth), crimson clover (Trifolium incarnatum L.), cereal rye (Secale cereale L.), or annual ryegrass (Lolium multiflorum Lam.), and a weed/fallow control of chickweed (Stellaria media L.). The covers were harvested three times the following spring and dry matter yields (DM), %N, and atom % 15N were determined to assess FN uptake. Fall labelled N in the soil (to 80 cm) averaged 17 and 114 kg FN ha−1 over both years for the 168 and 336 kg FN ha−1 rates, respectively. However, the quantity of total residual mineral N (soil N plus FN) after the 168 kg ha−1 rate was 87 kg N ha−1, which was comparable to the quantity of labelled N at the high fertilizer rate. The average cover crop FN uptake (kg FN ha−1) in mid‐April after the 336 kg N ha−1 treatment was 48 for cereal rye, 29 for annual ryegrass, 9 for hairy vetch, 8 for crimson clover, and 6 kg FN ha−1 for the native weed cover (LSD P = 0.05 of 7 kg FN ha−1). Corresponding percent recoveries of the fall N in the aboveground DM were 45% for cereal rye, 27% for annual ryegrass, 9 for hairy vetch, 8% for crimson clover, and 8% for native weed cover. These results show that grass cover crops conserved the most FN. Cereal rye recovered more FN through mid‐April because of its growth in cool weather, although annual ryegrass was equally effective if grown to mid‐May. Renewed efforts should be made to utilize grass cover crops to conserve N in humid climates.

No‐tillage systems utilizing winter cover crops can reduce erosion and leaching losses. Fall‐seeded legumes can also supply significant amounts of N to subsequent corn (Zea mays L.) crops. The suitability of 14 fall‐seeded legumes, three small grains and four legume/grass mixtures was evaluated for winter covers from 1982 through 1985 on Matapeake silt loam (fine‐loamy, mixed, mesic, Typic Hapludult) and Mattapex silt loam(fine‐silty, mixed mesic, Aqualfic Normuldult) Coastal Plain soils as well as Delanco silt loam and Chester silt loam (fine‐loamy, mixed, mesic, Aquic Hapludult) Piedmont soils. Hairy vetch (Vicia villosa Roth), crimson clover (Trifolium incarnatum L.) and Austrian winter peas [Pisum sativum (L.) Poir.] were the most promising cover crops. Fall growth and early soil coverage was highest with crimson and lowest with vetch which had higher winter survival and spring growth. Peas and, to a lesser extent, crimson clover stands were damaged in some years by Sclerotinia trifoliorum Eriks. In some years top growth of vetch contained up to 350 kg N/ha. While N concentration varied among species, total N production was determined more by dry matter yield. Legume cover crops had a greater influence on corn grain yields on the heavier textured soils and longer growing season of the Coastal Plain. In 1985, N contribution to the subsequent corn crop was reduced when small grains were seeded with annual legumes. Results from these studies show that winter annual legumes can reduce N costs while providing better soil protection during winter months.

Winter cover crops can supply N to the next crop, reduce erosion and N leaching, and conserve or deplete soil moisture. To identify optimum corn fertilizer nitrogen (FN) rates following cover crops, we evaluated hairy vetch (Vf: Jlicia villosa Roth), Austrian winter pea [PE: Pisum sativum L. subsp. sativum var. arvense (L.) Poir.], crimson clover (CR: Trifolium incartUllum L.), and wheat (WH: Triticum aes· ti~·um L.) winter cover crops in the U.S. Coastal Plain and Piedmont for no-tillage corn (Zea mays L.) at four FN rates (topdressed NH 4 N0 3 ) onr 4 yr. Parameters evaluated included cover crop yield and N content, corn N uptake, and corn grain yield. On the Coastal Plain, Vf, PE, CR, and WH topgrowth averaged 205, 180, 170, and 40 kg N ha-•, respectively, and ~40% less for the Piedmont. With no FN, grain yields were generally greater after legumes than after no cover crop, and lowest after WH, with the best yields after legumes with 90 to 135 kg FN ha-•. Synergistic responses occurred when FN was ap· plied after legumes. Non·N-Iimited grain yield increases averaged 2 Mg ha-• (Coastal Plain) and 0.5 Mg ha-• (Piedmont), and were not directly related to cover crop N. With no cover crop, FN needed for maximum yield averaged 80 kg ha -• (Piedmont) and 135 kg ha -• (Coastal Plain). After WH, FN needs increased 15 to 30 kg ha-•, but decreased 10 to 75 kg ha-• after legumes. Hairy vetch provided the most consistent increases, with average grain yield of 10.6 Mg ha-1 (Coastal Plain) and 8.2 Mg ha-1 (Piedmont), and an economic opti· mum FN rate of 127 (Coastal Plain) and 66 kg ha-• (Piedmont).