Weed competitiveness and soil health response to weed management practices

After more than 50 years of chemical weed control, weeds continue to be a problem in agriculture. Three separate field studies were conducted to determine the effect of weed management practices on weed competitiveness and soil health.;The first study was conducted at Ashland Bottoms near Manhattan, KS in 2001 and 2002 to quantify Palmer amaranth, velvetleaf, and giant foxtail response to preemergence herbicides. Cumulative weed emergence was not reduced or delayed by herbicide application except for Palmer amaranth by 20 days after planting with 78% reduction in emergence in 2001. Seedling mortality was highest when isoxaflutole was applied to all weed species. Weed height and biomass were reduced when isoxaflutole was applied.;In the second study, competitiveness and seed production of Palmer amaranth or velvetleaf that survived a preemergence herbicide were determined at Ashland Bottoms in 2001 and 2002 and Rossville, KS in 2002. At Rossville, six Palmer amaranth plants m−1 of row that escaped isoxaflutole or flumetsulam application caused 25% corn yield loss (YL) compared to 38% YL from six untreated plants. At Ashland Bottoms in 2002, six velvetleaf plants m−1 of row that escaped flumetsulam caused 6% corn YL while six untreated velvetleaf plants caused 50% YL. Except for velvetleaf at Ashland Bottoms in 2002, seed production m−2 was similar between escaped and untreated plants.;Response of soil microbial and nematode communities to glyphosate-resistant cropping systems were evaluated under conventional tillage and no-till practices at Ashland Bottoms and Hays, KS from 2001 to 2003. Herbicide treatments were conventional soybean (cloransulam + S-metolachlor + sulfentrazone) and corn (acetochlor + atrazine) herbicides, and glyphosate applied when weeds were 10 or 20 cm tall. Soil microbial biomass carbon, substrate-induced respiration, and BIOLOG substrate utilization were similar between conventional herbicide and glyphosate treatments. Total nematode densities were not altered by glyphosate-resistant cropping systems. However, herbivore nematode density was reduced in late glyphosate treatment at Hays in the fall of 2001. A separate growth chamber experiment showed no difference in nematode densities in response to different rates of glyphosate when compared to the control, indicating that glyphosate was not toxic to the nematodes.