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A three-year study determined the effect of winter cover crops on weeds and vegetable crops in a vegetable production system. Winter rye and hairy vetch were interseeded in the fall of 1990, 1991 and 1992 at 112 and 34-kg ha-1, respectively. The cover crops were killed by ether applying glyphosate at 1.1 kg a.i ha-1 [reduced tillage(RT)] or mowing and disking the cover crop (Disked). The conventional tillage (CT) was bare ground with a preplant incorporated application of 0.84 kg a.i ha-1 of trifluralin. During the three years, the greatest snap bean yields were in the CT; total yields of cabbage and tomato varied between the years; and were not affected by management systems. Weed control was similar in the RT and CT treatments during the three years. Disked cover crop treatments tended to have greater weed numbers than either RT or CT treatments.
The effect of cover-crop management on growth and yield of `Bravo' cabbage (Brassica oleracea var. Capitata L.), `Market Pride' tomato (Lycopersicon esculentum Mill.), and `Mustang' snap bean (Phaseolus vulgaris L.) was determined. Each fall, `Wheeler' winter rye (Secale cereale L.) and `Oregon Crown' hairy vetch (Vicia villosa Roth) were interseeded. The following spring, the cover crops were killed by either applying glyphosate and mowing (CC-G) or mowing and disking (CC-D). Trifluralin was preplant incorporated into bare ground as a conventional tillage (CT) treatment. In 1992 and 1993, a chicken (Gallus gallus L.) based fertilizer was applied to half the subplots. The greatest snap bean and cabbage yields were in CT. The system with the greatest tomato yields varied. In 1991, the greatest tomato yields were in the CT treatment, while in 1992 yields were greatest in the CT and CC-D treatments, and in 1993 the greatest yields were in CT and CC-G. Cabbage yields were greater in the fertilized than the unfertilized treatments. In 1992, infestations of diamondback moth, imported cabbageworm, and cabbage looper were greater in CT than in the CC-G treatment. Three years of the CC-G treatment increased soil organic matter from 3.07% to 3.48% and increased soil pH from 6.30 to 6.51, while neither changed in the CT. Chemical names used: N-(phosphonomethyl) glycine (glyphosate); 2,6-dinitro-N,N-dipro`pyl-4-(trifluoromethyl) benzenamine (trifluralin).
Field experiments were conducted in 1992 and 1993 to determine the effect of N fertility, cropping system, redroot pigweed (Amaranthus retroflexus L.) density, and harvesting frequency on collard (Brassica oleracea var. acephala D.C) and cowpea [Vigna unguiculata (L.) Walp.] growth. The N fertilization regimes were 0, 80, 160, and 240 kg·ha-1, applied as urea in a split application. Four weeks after crop planting, redroot pigweed was seeded at 0, 300, and 1200 seeds/m2. Between weeks 6 and 12, collard leaves were harvested at 1- to 3-week intervals. Year, N fertility, and cropping system interacted to determine collard leaf number and mass. For example, in 1992, with N at 160 kg·ha-1, collards intercropped had more total leaf mass than those monocropped. Pigweed density had no effect on collard yields, which were greatest from the 3-week harvest frequency. Cropping system and pigweed density interacted to determine cowpea vine length, shoot dry mass, and branching. The high density of pigweed caused a 56% reduction of cowpea dry mass in 1992.