No abstract

The volatilization, photolysis, microbial degradation, and field persistence of imazethapyr were studied using formulated and14C-labeled imazethapyr. Volatilization losses from soil were less than 2%. Photodecomposition losses of up to 8% occurred from soil and up to 52% from a glass slide with no soil. Significantly greater photodecomposition occurred with chain-labeled than ring-labeled14C-imazethapyr. The amount of14CO2evolution from soil treated with either ring- or chain-labeled14C-imazethapyr was not significantly different. The total14CO2evolved from the soils ranged from 2.4 to 3.6% of the total14C-imazethapyr applied to the soil. However, degradation of imazethapyr from the same soils, as determined by high-pressure liquid chromatography, indicated that 62 to 82% of the applied14C-imazethapyr had been degraded. The degradation rate increased as soil moisture was increased from −100 to −33 kPa. Imazethapyr was more persistent in soil with the higher clay and organic matter content.

This research was aimed at understanding how far and how fast glyphosate-resistant (GR) Palmer amaranth will spread in cotton and the consequences associated with allowing a single plant to escape control. Specifically, research was conducted to determine the collective impact of seed dispersal agents on the in-field expansion of GR Palmer amaranth, and any resulting yield reductions in an enhanced GR cotton system where glyphosate was solely used for weed control. Introduction of 20,000 GR Palmer amaranth seed into a 1-m2circle in February 2008 was used to represent survival through maturity of a single GR female Palmer amaranth escape from the 2007 growing season. The experiment was conducted in four different cotton fields (0.53 to 0.77 ha in size) with no history of Palmer amaranth infestation. In the subsequent year, Palmer amaranth was located as far as 114 m downslope, creating a separate patch. It is believed that rainwater dispersed the seeds from the original area of introduction. In less than 2 yr after introduction, GR Palmer amaranth expanded to the boundaries of all fields, infesting over 20% of the total field area. Spatial regression estimates indicated that no yield penalty was associated with Palmer amaranth density the first year after introduction, which is not surprising since only 0.56% of the field area was infested with GR Palmer amaranth in 2008. Lint yield reductions as high as 17 kg ha−1were observed 2 yr after the introduction (in 2009). Three years after the introduction (2010), Palmer amaranth infested 95 to 100% of the area in all fields, resulting in complete crop loss since it was impossible to harvest the crop. These results indicate that resistance management options such as a “zero-tolerance threshold” should be used in managing or mitigating the spread of GR Palmer amaranth. This research demonstrates the need for proactive resistance management.

No abstract

More than 1 billion broiler chickens (Gallus gallus domesticus) are produced annually in Arkansas, with nearly 900 Gg of waste (i.e., litter) generated. Poultry litter is typically land applied as a means of disposal to nearby pastures as an organic fertilizer. Aside from essential plant nutrients, poultry litter also contains heavy metals, yet little is known about the potential of these metals to leach from soils with a history of litter application. The objective of this study was to continuously monitor the seasonal and annual effect of poultry litter application rate on soil leachate concentrations and leaching losses of metals (As, Cd, Se, Cr, Mn, Fe, Ni, Cu, and Zn) and dissolved organic carbon (DOC) from tall fescue (Festuca arundinacea Shreb.) pasture using automated equilibrium‐tension lysimeters over a 2‐yr period. Average annual drainage was 447, 235, and 592 mm in Year 1 (May 2003 through April 2004) and 833, 589, and 827 mm in Year 2 (May 2004 through April 2005) for control, low‐ (5.6 Mg ha−1), and high‐litter (11.2 Mg ha−1) treatments, respectively. Drainage was similar among treatments during all time periods except for Winter (November through January) Year 1. Flow‐weighted mean concentrations of Mn during Spring Year 1 (February through April 2004) and Ni and Cu for the whole year differed among litter treatments, but there were no consistent trends. In Spring Year 2 (February through April 2005), flow‐weighted mean concentrations of Cr and Fe differed among litter treatment, but there were no consistent trends. Metal leaching losses did not differ among litter treatment during Year 1. In Year 2, leaching losses of Zn, Fe, and As differed among litter treatments during Summer, Fall, and Winter, respectively, but there were no consistent trends. Results indicate that poultry litter application rate did not affect metal leaching within two the first 2 yr of altered management; thus simply reducing application rates in areas with a history of litter application may not ensure a short‐term reduction of potential further surface and groundwater impairment.