EFFECT OF TILLAGE AND CORN ON PIGWEED (AMARANTHUS SPP) SEEDLING EMERGENCE AND DENSITY

We studied the effect of no-till, chisel, and moldboard plow and the p resence or absence of corn on soil temperature, moisture and, subseque ntly, the emergence phenology and density of pigweed seedlings at 2 si tes from 1993 to 1995 inclusively. Tillage significantly affected the phenology of pigweed seedling emergence only during a June drought at one site in 1994. Soil temperature and moisture, measured at 2.5-cm de pths, also were unaffected by tillage. Weed phenology is usually earli er in no-till because more seeds are located closer to the surface (< 5 cm deep) in no-till, thereby reducing the delay in penetrating throu gh the soil, and because soil temperatures and moisture are nearer the germination and emergence optima. However, pigweed seedlings are alre ady physiologically restricted to germination depths of less than 2.5 cm regardless of tillage; therefore, this prior constraint eliminated any potential differences in emergence phenologies caused by tillage. The presence or absence of corn also did not affect soil temperatures, soil moisture, or pigweed seedling emergence phenologies. Pigweed see dling density was significantly higher in no-till; this may have been caused by increased numbers of seeds near the soil surface in no-till. The presence or absence of corn did not affect pigweed seedling densi ty; the lack of a significant effect: probably reflects high variances in density. Although necessary for most weed species, tillage may be a less important factor to consider in predicting pigweed population d ynamics and subsequent management recommendations.