Cover Crop Effects on Corn Yield Response to Nitrogen on an Irrigated Sandy Soil

Nonlegume winter cover crops are extensively grown to control wind erosion in the Central Sands region of Wisconsin. Subsequent corn (Zea mays L.) yield benefits following winter cover crops can occur on these coarse-textured soils even though cover crop biomass and residual N recovery are minimal due to the limited time period for cover crop growth. A 3-yr study was conducted to determine cover crop species and management effects on subsequent corn grain yield responses to N fertilizer. Cover crops were planted in late summer following sweet corn harvest and included oat (Avena sativa L.), winter triticale (xTriticosecale), winter rye (Secale cereale L.) with and without the top growth removed, and fallow. Cover crop treatments were plowed in the spring, and corn was grown with six N fertilizer rates (0 to 280 kg ha-1). In 2 of 3 yr, economic optimum N rates (EONR) for corn were lower (32 ± 8 kg N ha-1), and corn grain yields at the EONR were higher (1.4 ± 0.3 Mg ha-1) where cover crops were grown compared with fallow. These results were similar following all cover crops, including winter-killed oat and rye with top growth removed, indicating that beneficial cover crop effects were primarily the result of a rotation effect rather than direct N contributions from the cover crop. The yield enhancement provided by cover crops probably offers the greatest practical benefit to growers since lowering N rates on these soils may increase the risk of N deficiency in years with high leaching potential.