Browsing by Subject "herbicides"
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Item Extraction, Degradation, and Microbial Respiration Effects of Mesotrione in Selected Texas Soils(2014-08-08) Romero, Madahy BThe heavy use of pesticides in agriculture, have encouraged researchers to evaluate their behavior and potential environmental impacts of newer herbicides when applied alone or in combination with other herbicides. Mesotrione (2-[4-(methysulfonyl)-2-nitrobenzoyl]-1, 3-cyclohexanedione), a pre- and post-emergence herbicide is one of these newer herbicides used to control broadleaf weeds in corn. Assessing the soil behavior of newer herbicides is important to understand the potential impacts on key ecological processes. The primary objectives of this research were to: 1) determine the optimal conditions to extract mesotrione from four soils with varying physical and chemical characteristics using Accelerated Solvent Extraction (ASE); 2) study the effect of atrazine on mesotrione degradation in soil; and 3) determine if mesotrione, mesotrione + atrazine treatments, and application rates had an impact on soil microbial activity (respiration). In the first experiment, mesotrione recoveries were not significantly different between two tested solvents across the four soils. The 4:1, acetonitrile: 5% acetic acid solvent was selected as the extraction solvent for all subsequent tests. When the three static cycles (1, 2, and 3) were evaluated, mesotrione recoveries were not significantly different between the three static cycles across the four soils. The two static cycles was selected as optimal, resulting in higher recoveries for the four soils. The investigation of extraction temperatures (50?C, 100?C, and 150?C) resulted in no significant differences between temperatures of 50?C and 100?C, and the temperature of 50?C was selected since higher recoveries obtained with that temperature. In the second experiment, the results demonstrated that mesotrione + atrazine herbicide mixtures have the potential to decrease mesotrione degradation in soils. However, it remained unclear whether the reduced degradation was due to the combined impacts of the herbicides, varying soil characteristics, and/or the soil microbial populations present in each soil. The third experiment resulted in the mesotrione and mesotrione + atrazine treatments that inhibited microbial activity (respiration) only at certain incubation time periods and rates for some soils. Furthermore, the mesotrione treatment was found to also stimulate microbial respiration at the 10X rate in the Orelia soil. Although rates effects on microbial respiration occurred, a trend was not observed in this study.Item Intensive culture of loblolly pine (Pinus taeda L.) seedlings on poorly drained sites in the Western Gulf region of the United States(Texas A&M University, 2004-09-30) Rahman, Mohd ShafiqurA significant acreage of poorly drained sites occurs in the Western Gulf region of the United States. These sites experience standing water through much of the winter and spring, resulting in poor seedling survival. In addition, the sites occasionally experience a summer drought that affects tree growth. This study was designed to determine the effects of intensive forest management on seedling growth and physiology, and to enhance seedling performance under these harsh conditions. Fertilization, chemical vegetation control and mechanical site preparation were used in different combinations to test the effects of these intensive forest management tools on seedling above- and below-ground growth, survival, water status, gas exchange attributes, and nutrient concentrations in the foliage and soil solution. Ten sites were established in southern Arkansas in 1998 and 1999 to monitor loblolly pine (Pinus taeda L.) seedling performance in three consecutive growing seasons between 1998 and 2000. Fertilization, chemical vegetation control and mechanical site preparation increased above-ground growth. Growth increment from mechanical site preparation was comparable to that from fertilization. Survival was not affected by any treatment. Fertilization enhanced root growth, more so in the shallow soil layers. Subsoil bulk density greatly restricted root growth, resulting in decreased above-ground growth. Chemical vegetation control made more soil water available to the seedlings during drought, resulting in increased seedling water potential. The effect of chemical vegetation control on seedling water potential was absent in the early growing season when soil moisture was abundant. Seedlings on plots treated with bedding-plus-fertilizer or bedding alone experienced stomatal closure at times of severe water stress while those treated with chemical vegetation control were able to continue net carbon dioxide assimilation. Fertilization did not increase needle nutrient concentrations, but increased needle weight, thereby increasing total nutrient content. Fertilization increased base cation concentrations in the soil solution, but had no effect on nitrogen and phosphorus concentrations. Intensive forest management was found to be a viable tool for optimum loblolly pine seedling growth and survival on poorly drained sites in the Western Gulf region of the United States.