REDROOT PIGWEED COMPETITION IN SOYBEANS AND SIMULATION OF REDROOT PIGWEED GROWTH (CROP ROW WIDTH, WEED DENSITY, INTERFERENCE)
Abstract
Field trials were conducted to determine the influence of soybean (Glycine max (L.) Merr.) row width and redroot pigweed (Amaranthus retroflexus L.) density on patterns of biomass production for both crop and weed, to evaluate the influence of these factors on soybean seed yield, and to establish the structural relationship occurring within the canopy between both species. Soybean populations of either row widths were subject to little variation in density. A slight density advantage coupled to optimal placement of soybean plants caused more biomass to be produced by soybean in narrow rows under both weed-free and weedy conditions. Within each row width, both low and high densities of pigweed reduced soybean biomass to comparable extent. Narrow-row planting was beneficial to soybean seed yields, especially under conditions of greater moisture availability. Redroot pigweed populations experienced mortality and emergence during the early part of the growth season, but the low to high density ratio (1:2) was conserved throughout. Mixed stands of pigweed produced less biomass than pure stands. Pigweed biomass production was even more suppressed in narrow-row treatments. Pigweed was most competitive in wide-row treatments where it produced up to 50% of the total biomass. Soybean produced two to three times more leaf area than pigweed. Soybean leaf area distribution in the canopy showed a pyramidal profile with less leaf area produced in the higher strata. When pigweed was grown in mixed stands with soybean, pigweed leaf area was concentrated in higher strata, reducing light availability to soybean leaves in strata below. Pigweed growth data from pure stands were used to validate a physiological growth model, AMSIM (AMaranthus SIMulation). Simulated results were compared to actual field data from 1984 and 1985. AMSIM provided accurate predictions of biomass and leaf area index accumulations, and of plant height. Sensitivity analysis conducted for a wide range of environmental conditions indicated that simulated pigweed growth agreed with known growth characteristics of pigweed.
Degree
Ph.D.
Subject Area
Botany
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