Most field experiments are conducted over two or more locations or years, yet statistical references do not contain sufficient detail for complete analysis. The purpose of this paper is to provide a reference for analysis of combined experiments. Tables include sources of variation, degrees of freedom, and F‐ratios for one factor and split‐plot experiments combined over locations and/or years. The F‐ratios are given for fixed, mixed, and random models.

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.

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).

Spring cover crop kill date effects on N and water availability to subsequent no‐till corn (Zea mays L.) have not been studied. This 2‐yr study was conducted in 1990 and 1991 at Coastal Plain and Piedmont locations in Maryland to evaluate soil moisture and corn responses to three cover crop kill dates, three corn planting dates, and four fertilizer N (FN) rates following cover crops of hairy vetch (Vicia villosa Roth), cereal rye (Secale cereale L.), and vetch‐rye mixture. No‐cover checks were included for each corn planting date. Corn yield ranged from 0.8 to 13.3 Mg ha−1 in 1990, and from 3.9 to 12.6 Mg ha−1 in 1991. Corn grain yield without FN was greatest following vetch or vetch‐rye mixture. Late April or early May kill dates consistently resulted in greater corn yield than earlier kill dates, probably due to differences in N availability and moisture conservation. Cover crops killed late did not deplete surface soil moisture. The economic FN rate reflected N contributions and moisture conservation by each cover crop. At the Coastal Plain location, economic FN rates were 30 to 76 kg ha−1 for corn following vetch, 65 to 193 kg ha−1 following vetch‐rye mixture, 161 to 247 kg ha−1 following rye, and 201 kg ha−1 following no cover crop. Similar rankings were observed for the Piedmont location, but maximum yield was lower following rye, and lower FN rates were required to attain that yield. Summer soil water conservation by cover crop residues was more important than spring moisture depletion by growing cover crops in determining final corn yield.

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