WINTER COVER CROPS AND NITROGEN MANAGEMENT IN SWEET CORN AND BROCCOLIROTATIONS

Cover crops hold potential to improve soil quality, to recover residua l fertilizer N in the soil after a summer crop that otherwise might le ach to the groundwater, and to be a source of N for subsequently plant ed vegetable crops, The objective of this 5-year study was to determin e the N uptake by winter cover crops and its effect on summer vegetabl e productivity. Winter cover crops [red clover (Trifolium pratense L.) , cereal rye (Secale cereale L. var. Wheeler), a cereal rye/Austrian w inter pea (Pisum sativum L.) mix, or a winter fallow control] were in a rotation with alternate years of sweet corn (Zea mays L. cv. Jubilee ) and broccoli (Brassica oleracea L. Botrytis Group cv. Gem). The subp lots were N rate (zero, intermediate, and as recommended for vegetable crop). Summer relay plantings of red clover or cereal rye were also u sed to gain early establishment of the cover crop, Cereal rye cover cr ops recovered residual fertilizer N at an average of 40 kg.ha(-1) foll owing the recommended N rates, but after 5 years of cropping, there wa s no evidence that the N conserved by the cereal rye cover crop would permit a reduction in inorganic N inputs to maintain yields. Intermedi ate rates of N applied to summer crops in combination with winter cove r crops containing legumes produced vegetable yields similar to those with recommended rates of N in combination with winter fallow or cerea l rye cover crops. There was a consistent trend (P < 0.12) for cereal rye cover crops to cause a small decrease in broccoli yields as compar ed to winter fallow.