WINTER COVER CROPS AS A BEST MANAGEMENT PRACTICE FOR REDUCING NITROGEN LEACHING

The role of rye as a winter cover crop to reduce nitrate leaching was investigated over a three-year period on a loamy sand soil. A cover cr op was planted after corn in the early fall and killed in late March o r early April the following spring. No-tillage and conventional tillag e systems were compared on large plots with irrigated corn. A replicat ed randomized block design experiment was conducted on small plots to evaluate a rye cover crop under no-tillage and conventional tillage an d with commercial fertilizer, poultry manure and composted poultry man ure as nitrogen fertilizer sources. Nitrogen uptake by the cover crop along with nitrate concentrations in groundwater and the soil profile (0-150 cm) were measured on the large plots. Soil nitrate concentratio ns and nitrogen uptake by the cover crop were measured on the small pl ots. There was no significant difference in nitrate concentrations in the groundwater or soil profile with and without a cover crop in eithe r no-tillage or conventional tillage. Annual amounts of nitrate-N leac hed to the water-table varied from 136.0 to 190.1 kg/ha in 1989 and fr om 82.4 to 116.2 kg/ha in 1991. Nitrate leaching rates were somewhat l ower with a cover crop in 1989, but not in 1990. There was no statisti cally significant difference in corn grain yields between the cover cr op and non-cover crop treatments. The planting date and adequate rainf all are very important in maximizing nitrogen uptake in the fall with a rye cover crop. On the Delmarva Peninsula, the cover crop should pro bably be planted by October 1 to maximize nitrogen uptake rates in the fall. On loamy sand soils, rye winter cover crops cannot be counted o n as a best management practice for reducing nitrate leaching in the M id-Atlantic states. (C) 1998 Elsevier Science B.V. All rights reserved .