An integral component of a conservation-tillage system in corn (Zea mays L.) and cotton (Gossypium hirsutum L.) is the use of a winter cover crop. A field experiment was initiated in 2002 to evaluate winter weed dynamics following various winter cover crops in both continuous cotton and a corn and cotton rotation. Winter cover crops included black oats (Avena strigosa Schreb.); two crimson clover entries (Trifolium incarnatum L.); two cultivars of forage rape (Brassica napus L. var. napus), spring and winter; oil radish (Raphanus sativus var. oleiformis Pers.); three cultivars of turnip ( Brassica rapa L. subsp. rapa); white lupin ( Lupinus albus L.); and a mixture of black oat and lupin. Two-year conservation-tillage rotational sequences included conventionally tilled continuous corn and cotton winter fallow systems as controls. The 10 conservation-tillage, winter cover-crop systems investigated were three continuous cotton systems that alternated a winter legume (lupin or clover), six cotton-corn systems, where lupin preceded cotton and radish, rape, or turnip preceded corn, and a cotton-corn system that had a lupin-black oat mixture as a winter cover crop every year. Use of lupin or 'AU Robin' clover resulted in weed biomass reduction of up to 80% and 54%, respectively, in weed biomass compared to the fallow system. The highest yielding corn-cotton conservation tillage rotation with a winter cover yielded 200 lbs/acre more that the continuous cotton winter fallow system. Continuous conventional corn with winter fallow yielded 30 bu/acre less than the highest yielding 2-yr, conservation tillage winter crop system.
