The response of oat, foxtail millet, proso millet, and sunflower to atrazine and clomazone applied the previous fall was investigated two years in field studies near Akron, CO and Sidney, NE. Foxtail millet biomass, and proso millet and sunflower grain yields were not reduced when these crops were seeded into soil that had been treated the previous fall with atrazine and/or clomazone at rates of 0.6 or 1.1 kg ai/ha. Forage yield of oat was reduced 11 to 18% by some treatments, but this effect was not consistent over years or sites. Treatments containing 1.1 kg/ha of atrazine provided 1 to 5 wk of residual weed control in foxtail millet, proso millet, and sunflower. The study indicated that producers have flexibility in crop selection when using atrazine and clomazone in reduced- and no-till production systems.

Dry pea improves corn yield and tolerance to weed interference compared with soybean, spring wheat, or canola as preceding crops. To understand this synergy between dry pea and corn, growth and nutrient concentration of corn were examined following dry pea or soybean in sequence. Each corn plot was split into weed-free and weed-infested subplots, with foxtail millet established at one density to provide uniform weed interference. Compared with soybean, dry pea improved corn grain yield 10% in weed-free conditions and corn tolerance to weed interference more than twofold. Dry pea synergy to corn in weed-free conditions was not related to differences in corn development, height, or nutrient status of corn seedlings. When foxtail millet was present, dry pea increased corn height and rate of development late in the growing season compared with soybean. Improved corn tolerance to weed interference was not related to seedling emergence or growth of foxtail millet, as these parameters did not vary with preceding crop. Other biological factors must be involved in dry pea synergy to corn.

Crop diversity may improve tolerance to weed interference and reduce the need for herbicides. This experiment measured weed interference in corn as affected by the preceding crop in two studies. The first study, based on interference of the resident weed community, compared dry pea, soybean, canola, and spring wheat for effect on corn tolerance to weeds. Prominent weeds were green and yellow foxtail. The second study examined corn tolerance to a uniform infestation of foxtail millet as affected by dry pea, soybean, spring wheat, and corn as preceding crops. Each plot was split into weed-free and weed-infested subplots in both studies. Corn was most tolerant to weed interference following dry pea; compared with soybean, dry pea improved corn tolerance more than twofold. Corn also yielded the highest in weed-free conditions following dry pea; compared across 4 yr, corn yielded 7 to 23% more following dry pea than following either soybean or spring wheat. Crop diversity has helped producers reduce herbicide inputs in the Great Plains and may provide an additional benefit of reducing weed impact on crop yield.