ROBUST PURPLE FOXTAIL COMPETITION IN SOYBEANS AND SIMULATION OF FOXTAIL DENSITIES
Abstract
Field experiments were conducted to evaluate the influence of soybean row spacing, robust purple foxtail density, and duration of competition on the growth and yield of both the crop and weed. Soybean row spacings were 25 and 76 cm and weed densities were 0, 60, and 120 plants/m('2). Foxtail was removed at 0 (weed-free), 21, 35 or 49, and 56 or 70 days after emergence (dae), depending on the year. The effect of 30 to 220 plants/m('2) densities on the growth foxtail was evaluated to develop a density factor for the foxtail growth model SETSIM (SETaria SIMulation). Weed-free soybeans grown in 25-cm rows produced 10 to 20% greater seed yield than soybeans in 76-cm rows. Soybean yield among the two row spacings was equivalent in years with a moisture deficit. Foxtail competition reduced soybean seed yield an average of 18% more in 76-cm rows. When foxtail was removed by 21 dae, soybean yield was not reduced. Soybeans planted in 25-cm rows produced 95% shade two weeks earlier than soybeans in 76-cm rows, as a result, greater biomass and leaf area were produced by foxtail in the wide-row spacing. Foxtail grown in monocultures produced greater biomass and leaf area as density increased. Growth of foxtail converged into two general groupings for dry weight and leaf area production; 30 to 60 and 90 to 220 plants/m('2). Total nonstructural carbohydrate in stems and leaves did not vary with changing density, and obtained a maximal value at anthesis. Foxtail growth data from the monocultures were used to recalibrate and validate the SETSIM model. SETSIM accurately predicted biomass accumulation and leaf area index when compared to actual field data, but plant height was underestimated in densities below 90 plants/m('2). Sensitivity analysis of SETSIM was conducted to determine how the model responds to wide ranges in temperature and solar radiation. The greatest increases in biomass and crop growth rate were obtained at combinations of intermediate to high temperature and high solar radiation regimes. The simulated results agreed well with results for actual foxtail responses to temperature and irradiance reported in the literature. (Abstract shortened with permission of author.)
Degree
Ph.D.
Subject Area
Agronomy
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