Adsorption, leaching, and dissipation of pyroxasulfone and two chloroacetamide herbicides

2012 Summer.Includes bibliographical references.Pyroxasulfone is a new pyrazole herbicide that controls weeds by inhibiting very long chain fatty acid synthesis. This mechanism of action places pyroxasulfone in the Weed Science Society of America (WSSA) group 15 or Herbicide Resistant Action Committee (HRAC) group K3 herbicides that include s-metolachlor and dimethenamid-p. Dimethenamid-p and s-metolachlor are referred to in literature as acetamide, acetanilide, chloroacetamide, or chloroacetanilide herbicides. In this thesis, these two herbicides are referred to as chloroacetamide herbicides based on the HRAC classification. The soil interactions of pyroxasulfone were evaluated and compared to s-metolachlor and dimethenamid-p to better understand how pyroxasulfone will behave under various field conditions Pyroxasulfone was compared with these two standard herbicides because of their similar mechanisms of action, use patterns, potential for use in similar cropping systems, and similar weed control spectrums. Sorption coefficients were determined for 25 different soils to evaluate relative differences in binding among pyroxasulfone, dimethenamid-p, and s-metolachlor. Across all soil types, the relative order of binding was pyroxasulfone=dimethenamid-p < s-metolachlor. Pyroxasulfone and dimethenamid-p were not statistically different in terms of their binding; however, s-metolachlor binding was statistically greater than both dimethenamid-p and pyroxasulfone. For all three herbicide, organic matter was the only soil property which was highly and significantly correlated to herbicide adsorption; all other soil properties correlated with herbicide adsorption could be explained by the correlation of OM and those soil properties. Based on the water solubility of these three herbicides, we expected the order of binding to be dimethenamid-p < s-metolachlor < pyroxasulfone. This study displayed the unique characteristics of pyroxasulfone in that it has the lowest water solubility of the three herbicides, yet sorption coefficient values indicate that pyroxasulfone is only loosely adsorbed by soil. Reduced soil binding along with a higher unit of activity makes pyroxasulfone a potent herbicide that provides comparable weed control when applied as low as one-eighth of typical application rates for other chloroacetamide herbicides. Field studies were conducted in 2009 and 2010 at two contrasting field sites to evaluate the dissipation and movement of pyroxasulfone and s-metolachlor in the top 30 cm of the soil profile. The site at the horticultural farm (HORT) has a Nunn clay loam soil (Argiustoll), whereas the site at the Limited Irrigation Farm (LIRF) has an Olney fine sandy loam soil (Haplargid). Dissipation half-lives (DT50) were the shortest at the Hort farm site with the heavier textured clay loam soil and increased moisture content. The LIRF site with lighter textured sandy loam soil and decreased moisture resulted in extended DT50 values and more variation between replicates for both herbicides. Across both years and field sites, pyroxasulfone DT50s were approximately twice as long as for s-metolachlor. The extended half-life of pyroxasulfone suggests that it would provide longer weed control compared to s-metolachlor. Herbicide movement in the top 30 cm of the soil profile was greater at the LIRF site which suggests that movement was influenced by soil type to a greater extent than irrigation amount, since the LIRF site received much less total irrigation yet had the most movement downward in the profile. In general, pyroxasulfone moved downward in the profile to a greater extent than s-metolachlor. Observed herbicide movement confirmed sorption coefficient data that shows that pyroxasulfone is bound less to the soil compared to metolachlor and, hence, is more available in the soil solution where the herbicide movement is influenced by mass flow. Extended observed half-lives, reduced soil binding, and increased unit activity indicate that pyroxasulfone is a potent inhibitor of very long chain fatty acid (VLCFA) biosynthesis that can provide comparable weed control for longer periods of time at reduced use rates when compared to commonly used chloroacetamide herbicides

Code Generation = A* + BURS

A system called BURS that is based on term rewrite systems and a search algorithm A* are combined to produce a code generator that generates optimal code. The theory underlying BURS is re-developed, formalised and explained in this work. The search algorithm uses a cost heuristic that is derived from the termrewrite system to direct the search. The advantage of using a search algorithm is that we need to compute only those costs that may be part of an optimal rewrite sequence

Efeitos competitivos da mistura de stands de trigo e biotipos de kochia (Kochia scoparia) resistentes e susceptíveis aos herbicidas inibidores da acetolactase sintase

Greenhouse experiments were conducted to compare the competitive ability of sulfonylurea resistant and susceptible kochia (Kochia scoparia L. Schard) compared to wheat. The results of several replacement series experiments indicate that wheat was the dominant competitor, and an average of one wheat plant reduced resistant kochia yield per plant equal to the effect of 4.8 resistant kochia or 5.4 susceptible kochia plants. Intraspeciflc competition was more important than interspecific competition for wheat, whereas the reverse was true for the resistant and susceptible kochia. The results of the niche differentiation index (NDI) indicate that wheat and either resistant or susceptible kochia are only partly limited by the same resources. The resistant and susceptible kochia, however, are limited by the same resources.Experimentos foram instalados em condições de casa-de-vegetação com o objetivo de comparar a capacidade competitiva de biotipos resistentes e suscetíveis aos herbicidas inibidores da enzima acetolactase synthase da planta daninha kochia (Kochia scoparia L. Schard) comparada com trigo. Os resultados de diversos experimentos, utilizando a metodologia chamada de substitutiva, indicaram que o trigo foi o competidor dominante, e em média uma planta de trigo reduziu o crescimento da planta de kochia resistente igual ao efeito de 4,8 plantas de kochia resistente ou 5,4 plantas de kochia suscetível. A competição chamada de intraespecífíca foi mais importante que a competição interespecífica para o trigo, porém o inverso foi verdadeiro para os biotípos resistentes e susceptíveis de kochia. Os resultados do índice de diferenciação ecológica indicaram que trigo e qualquer um dos dois biotípos de kochia estudados foram limitados apenas parcialmente pelos mesmos recursos de crescimento. No entanto, o crescimento dos biotípos resistentes e susceptíveis de kochia foram limitados pelos mesmos fatores de crescimento

Putting a cap on causality violations in CDT

The formalism of causal dynamical triangulations (CDT) provides us with a non-perturbatively defined model of quantum gravity, where the sum over histories includes only causal space-time histories. Path integrals of CDT and their continuum limits have been studied in two, three and four dimensions. Here we investigate a generalization of the two-dimensional CDT model, where the causality constraint is partially lifted by introducing weighted branching points, and demonstrate that the system can be solved analytically in the genus-zero sector.Comment: 17 pages, 4 figure

On the inverse problem of blade design for centrifugal pumps and fans

The inverse problem of blade design for centrifugal pumps and fans has been studied. The solution to this problem provides the geometry of rotor blades that realize specified performance characteristics, together with the corresponding flow field. Here a three-dimensional solution method is described in which the so-called meridional geometry is fixed and the distribution of the azimuthal angle at the three-dimensional blade surface is determined for blades of infinitesimal thickness. The developed formulation is based on potential-flow theory. Besides the blade impermeability condition at the pressure and suction side of the blades, an additional boundary condition at the blade surface is required in order to fix the unknown blade geometry. For this purpose the mean-swirl distribution is employed. The iterative numerical method is based on a three-dimensional finite element method approach in which the flow equations are solved on the domain determined by the latest estimate of the blade geometry, with the mean-swirl distribution boundary condition at the blade surface being enforced. The blade impermeability boundary condition is then used to find an improved estimate of the blade geometry. The robustness of the method is increased by specific techniques, such as spanwise-coupled solution of the discretized impermeability condition and the use of underrelaxation in adjusting the estimates of the blade geometry. Various examples are shown that demonstrate the effectiveness and robustness of the method in finding a solution for the blade geometry of different types of centrifugal pumps and fans. The influence of the employed mean-swirl distribution on the performance characteristics is also investigated

Factors Influencing and Steps Leading to the Adoption of Best Management Practices by Louisiana Dairy Farmers

A logistic regression procedure was used to assess the impact of socioeconomic attributes on the best management practices (BMPs) adoption decision by Louisiana dairy farmers relative to cost-share and fixed incentive payments. Analysis of the steps in the BMP adoption decision process indicated visits between producers and the U.S. Department of Agriculture–Natural Resource Conservation Service significantly increase likelihood of BMP adoption. Producer willingness-to-pay results indicate that marginal increases in dairy BMP adoption and associated improvement in environmental quality require increased technical and financial assistance.best management practices, bootstrap, cost-share, manure, steps in BMP adoption, Agribusiness, Agricultural and Food Policy, Farm Management, Food Consumption/Nutrition/Food Safety, Q16, Q25, Q53,

Willingness to Participate in Dairy Programs to Reduce Manure Related Problems in Louisiana's Major Dairy Production Region

Logistic and tobit models were used to understand the factors affecting dairy program participation and stated bid values by respondents. Results indicated that past participation is the key variable in regression. Bootstrap result confirms that most of the estimated parameters fall within the range of bootstrap confidence interval.Livestock Production/Industries,

Influence of Cost Share and EQIP Incentive Payments on Adoptions of Best Management Practices by Louisiana Dairy Farmers

Adoption of best management practices (BMPs) minimizes the negative externalities created by the manure by-product of milk production. Logistic regression procedure was used to understand the impact of socioeconomic attributes of Louisiana dairy farmers on BMP adoption decision relative to the cost share and incentive payment.Farm Management,

Getting to know you: Accuracy and error in judgments of character

Character judgments play an important role in our everyday lives. However, decades of empirical research on trait attribution suggest that the cognitive processes that generate these judgments are prone to a number of biases and cognitive distortions. This gives rise to a skeptical worry about the epistemic foundations of everyday characterological beliefs that has deeply disturbing and alienating consequences. In this paper, I argue that this skeptical worry is misplaced: under the appropriate informational conditions, our everyday character-trait judgments are in fact quite trustworthy. I then propose a mindreading-based model of the socio-cognitive processes underlying trait attribution that explains both why these judgments are initially unreliable, and how they eventually become more accurate