Effects of nematicides on population of pratylenchus penetrans and growth of flue‐cured tobacco

Abstract

Field studies were conducted on loamy sand at Tamscu farm, Delhi, Ontario, to compare the spring ridge application of Telone C17 at 73 and 101L/ha, Vorlex at 28 and 84L/ha, Vorlex CP at 50L/ha, and spring rotovated application of oxamyl at 2.24kg/ha respectively for the control of Pratylenchus penetrans (Cobb) Filip. and Stek., and for effects on the yield and quality of fluecured tobacco. Experiments were conducted on May 9 in an area that had been summer fallowed in previous year. Nematode densities of P. penetrans per kilogram of soil were lower than other treatments and controls with Telone C17 at 73 L/ha treated plots on May 24; with Vorlex at 28 L on June 7; Vorlex at 84 L on May 24 and on June 7; Vorlex CP on June 7, and with oxamyl on Sept. 6. The nematode population counts per gram dry weight of root were lower with Telone C17 at 73 L/ha on June 7, July 5, and at 101 L/ha on July 5; with Vorlex at 28 L/ha on June 7, July 5, and Sept. 6; with Vorlex at 84 L/ha on June 7, June 21, July 5 and Sept. 6, and with Vorlex CP at 50 L/ha on June 7, July 5 and Sept. 6 in the ridged soil. The population was lower with oxamyl on June 21, July 5, and Sept. 6 in the rotovated soils. There was no difference in the agronomic data on yield, indices of grade, crop and maturity, while tobacco plant height and dry weight in the ridged fanning were greater with treatments of Vorlex at 84 L and Vorlex CP at 50 L/ha. The ridged farming had greater yield of tobacco than rotovated farming. Vorlex was the most effective of all nematicides used in the experiment.     

Pattern-oriented modeling of bird foraging and pest control in coffee farms

We develop a model of how land use and habitat diversity affect migratory bird populations and their ability to suppress an insect pest on Jamaican coffee farms. Bird foraging—choosing which habitat patch and prey to use as prey abundance changes over space and time—is the key process driving this system. Following the “pattern-oriented” modeling strategy, we identified nine observed patterns that characterize the real system's dynamics. The model was designed so that these patterns could potentially emerge from it. The resulting model is individual-based, has fine spatial and temporal resolutions, represents very simply the supply of the pest insect and other arthropod food in six habitat types, and includes foraging habitat selection as the only adaptive behavior of birds. Although there is an extensive heritage of bird foraging theory in ecology, most of it addresses only the individual level and is too simple for our context. We used pattern-oriented modeling to develop and test foraging theory for this across-scale problem: rules for individual bird foraging that cause the model to reproduce a variety of patterns observed at the system level. Four alternative foraging theories were contrasted by how well they caused the model to reproduce the nine characteristic patterns. Four of these patterns were clearly reproduced with the “null” theory that birds select habitat randomly. A version of classical theory in which birds stay in a patch until food is depleted to some threshold caused the model to reproduce five patterns; this theory caused lower, not higher, use of habitat experiencing an outbreak of prey insects. Assuming that birds select the nearby patch providing highest intake rate caused the model to reproduce all but one pattern, whereas assuming birds select the highest-intake patch over a large radius produced an unrealistic distribution of movement distances. The pattern reproduced under none of the theories, a negative relation between bird density and distance to trees, appears to result from a process not in the model: birds return to trees at night to roost. We conclude that a foraging model for small insectivorous birds in diverse habitat should assume birds can sense higher food supply but over short, not long, distances.     

Linking richness, community variability, and invasion resistance with patch size

The influence of community dynamics on the success or failure of an invasion is of considerable interest. What has not been explored is the influence of patch size on the outcomes of invasions for communities with the same species pool. Here we use an empirically validated spatial model of a marine epibenthic community to examine the effects of patch size on community variability, species richness, invasion, and the relationships between these variables. We found that the qualitative form of the relationship between community variability and species richness is determined by the size of the model patch. In small patches, variability decreases with species richness, but beyond a critical patch size, variability increases with increasing richness. This occurs because in large patches large, long-lived colonies attain sufficient size to minimize mortality and dominate the community, leading to decreased species richness and community variability. This mechanism cannot operate on smaller patches where the size of colonies is limited by the patch size and mortality is high irrespective of species identity. Further, invasion resistance is strongly correlated with community variability. Thus, the relationship between species richness and invasion resistance is also determined by patch size. These patterns are generated largely by an inverse relationship between colony size and mortality, and they depend on the spatial nature and patch size of the community. Our results suggest that a continuum of possible relationships can exist between species richness, community variability, invasion resistance, and area. These relationships are emergent behaviors generated by the individual properties of the particular component species of a community.     

Feasibility study of using brine for carbon dioxide capture and storage from fixed sources

A laboratory-scale reactor was developed to evaluate the capture of carbon dioxide (CO2) from a gas into a liquid as an approach to control greenhouse gases emitted from fixed sources. CO2 at 5-50% concentrations was passed through a gas-exchange membrane and transferred into liquid media--tap water or simulated brine. When using water, capture efficiencies exceeded 50% and could be enhanced by adding base (e.g., sodium hydroxide) or the combination of base and carbonic anhydrase, a catalyst that speeds the conversion of CO2 to carbonic acid. The transferred CO2 formed ions, such as bicarbonate or carbonate, depending on the amount of base present. Adding precipitating cations, like Ca++, produced insoluble carbonate salts. Simulated brine proved nearly as efficient as water in absorbing CO2, with less than a 6% reduction in CO2 transferred. The CO2 either dissolved into the brine or formed a mixture of gas and ions. If the chemistry was favorable, carbonate precipitate spontaneously formed. Energy expenditure of pumping brine up and down from subterranean depths was modeled. We conclude that using brine in a gas-exchange membrane system for capturing CO2 from a gas stream to liquid is technically feasible and can be accomplished at a reasonable expenditure of energy.     

TMDL Balance: A Model for Coastal Water Pollutant Loadings

Bacterial contamination accounts for more than 60% of the impairments included on the 2008 Texas 303(d) List. Many of these bacterial impairments are along the Texas Gulf Coast because coastal waters often are regulated for oyster harvesting, which have strict water quality standards. Under the Clean Water Act, each one of these impaired waterbodies requires a total maximum daily load (TMDL) study to be performed. A recent, statewide study recommended the development and application of simple modeling approaches to address the majority of Texas's bacteria TMDLs, including “… simple load duration curve, GIS [geographic information systems], and/or mass balance models.” We developed the TMDL Balance model in response to this recommendation. TMDL Balance is a steady state, mass balance, GIS‐based model for simulating pollutant loads and concentrations in coastal systems. The model uses plug‐flow reactor and continuously‐stirred tank reactor equations to route spatially distributed point and nonpoint source loads through a watershed via overland flow, non‐tidal flow, and tidal flow, decaying the loads via first‐order kinetics. In this paper, we explain the development of the watershed loading portion of the TMDL Balance model, demonstrating the methodology through a case study: computing bacterial loads in the Copano Bay watershed of southeast Texas. The application highlights an example of distributing bacterial sources spatially based on land use data.     

Denitrification in the shallow ground water of a tile-drained, agricultural watershed

Nonpoint-source pollution of surface water by N is considered a major cause of hypoxia. Because Corn Belt watersheds have been identified as major sources of N in the Mississippi River basin, the fate and transport of N from midwestern agricultural watersheds have received considerable interest. The fate and transport of N in the shallow ground water of these watersheds still needs additional research. Our purpose was to estimate denitrification in the shallow ground water of a tile-drained, Corn Belt watershed with fine-grained soils. Over a 3-yr period, N was monitored in the surface and ground water of an agricultural watershed in central Illinois. A significant amount of N was transported past the tile drains and into shallow ground water. The ground water nitrate was isotopically heavier than tile drain nitrate, which can be explained by denitrification in the subsurface. Denitrifying bacteria were found at depths to 10 m throughout the watershed. Laboratory and push-pull tests showed that a significant fraction of nitrate could be denitrified rapidly. We estimated that the N denitrified in shallow ground water was equivalent to 0.3 to 6.4% of the applied N or 9 to 27% of N exported via surface water. These estimates varied by water year and peaked in a year of normal precipitation after 2 yr of below average precipitation. Three years of monitoring data indicate that shallow ground water in watersheds with fine-grained soils may be a significant N sink compared with N exported via surface water.     

Predicted impact and evaluation of North Carolina's phosphorus indexing tool

Increased concern about potential losses of phosphorus (P) from agricultural fields receiving animal waste has resulted in the implementation of new state and federal regulations related to nutrient management. In response to strengthened nutrient management standards that require consideration of P, North Carolina has developed a site-specific P indexing system called the Phosphorus Loss Assessment Tool (PLAT) to predict relative amounts of potential P loss from agricultural fields. The purpose of this study was to apply the PLAT index on farms throughout North Carolina in an attempt to predict the percentage and types of farms that will be forced to change management practices due to implementation of new regulations. Sites from all 100 counties were sampled, with the number of samples taken from each county depending on the proportion of the state's agricultural land that occurs in that county. Results showed that approximately 8% of producers in the state will be required to apply animal waste or inorganic fertilizer on a P rather than nitrogen basis, with the percentage increasing for farmers who apply animal waste (approximately 27%). The PLAT index predicted the greatest amounts of P loss from sites in the Coastal Plain region of North Carolina and from sites receiving poultry waste. Loss of dissolved P through surface runoff tended to be greater than other loss pathways and presents an area of concern as no best management practices (BMPs) currently exist for the reduction of in-field dissolved P. The PLAT index predicted the areas in the state that are known to be disproportionately vulnerable to P loss due to histories of high P applications, high densities of animal units, or soil type and landscapes that are most susceptible to P loss.     

Empirical relationship between use, area, and ambient air concentration of methyl bromide

Methyl bromide (MeBr) is one of the most widely used soil fumigants. Human exposure to MeBr above threshold values can cause serious health problems. The exposure assessment of MeBr depends on estimation or measurement of its air concentrations. This study proposed a methodology for systematically exploring the empirical relationship between MeBr use intensity and ambient air concentrations. Monitored air concentrations were regressed to MeBr use over various spatiotemporal scales that step-wise increased around the monitoring site and monitoring period. The results showed that the goodness-of-fit varied with the spatiotemporal scale of MeBr use. The best fit was Y = 0.46 + 0.00120X (R2 = 0.95, n = 11), where Y was the 8-wk average ambient air concentration (microg/m3), and X was the weekly average use (kg/wk) over an area of 11.3 x 11.3 km (7 x 7 mi). The model was calibrated with air-monitoring data and use data of 2000, and verified with the same type data of 2001. The model estimated subchronic air concentration with reasonable accuracy.     

Ground‐Water Response to Forest Harvest: Implications for Hillslope Stability1

Abstract: Timber harvest may contribute to increased landsliding frequency through increased soil saturation or loss of soil strength as roots decay. This study assessed the effects of forest harvest on hillslope hydrology and linked hydrologic change before and after harvest with a simple model of hillslope stability. Observations of peak water table heights in 56 ground‐water monitoring wells showed that soil saturation levels on hillslopes differed significantly with harvest intensity at one of the two study locations following 25%, 75%, and 100% harvest. Before the forest was cut 100%, the average rainfall needed for 50% saturation of the soil was 54 mm, but after clearcutting soils reached an equivalent saturation with 61% less rainfall (21 mm). Hillslope stability model results indicate that shallow soils at both study locations, with slopes generally < 30° (58%), were not steep enough to be affected significantly by observed increases in saturation. The stability model indicates that with 100% harvest, there is a 7% reduction in the factor of safety for slope gradients of 35° (70%) with soil depths of 1.25 m. Forest managers may be aided by an understanding that variable hydrologic effects may result from similar forest harvests having different landscape position, land contributing area, and soil depths.     

Evaluating the “Catch‐Can” Test for Measuring Lawn Sprinkler Application Rates1

Abstract: The effectiveness of measuring lawn sprinkler application rates using the catch‐can test was evaluated. A survey of sources recommending the catch‐can test for measuring application rates show that catch‐can test procedures differ in the collector type, collector placement, number of collectors, and test duration. Analyses of catch‐can tests were performed to address these procedural differences, with emphasis on the type and number of collectors required to provide a reasonable level of confidence in test results. The accuracy of the catch‐can test generally improves as the number of randomly placed collectors increases. In order to achieve an accuracy of ±25% for 90 out of 100 catch‐can tests, the number of randomly placed collectors required ranged from 6 to over 50 for hand‐move systems, while for in‐ground systems, the number of randomly placed collectors required ranged from 2 to 8, depending on the pressure and percent overlap of the water distribution pattern. As long as a reasonable number of collectors were used when performing a catch‐can test, no consistent differences were observed in catch‐can test results due to type of collectors when using tuna fish cans, soup cans, or coffee mugs.