Browsing by Author "Dougherty, Mark"

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    Evaluation of Two Irrigation Scheduling Methods and Nitrogen Rates on Corn Production in Alabama
    Da Cunha Leme Filho, Jose Franco; Ortiz, Brenda V.; Balkcom, Kipling S.; Damianidis, Damianos; Knappenberger, Thorsten J.; Dougherty, Mark (Hindawi, 2020-09-15)
    Regulations on nutrient application amounts and environmental impacts of fertilizers are promoting advances in agricultural management strategies to optimize irrigation application and N fertilization in corn. Previous studies have found a relationship between irrigation application, available water in the soil, and N fertilizer uptake. The objective of this study was to evaluate interactions between two irrigation scheduling methods and four N rate applications (0-control, 202, 269, and 336 kg ha−1) on grain yield, aboveground biomass, plant N concentration, N uptake, and nitrogen use efficiency in corn. The study was conducted at the Tennessee Valley Research and Extension Center (TVREC) during two growing seasons (2014 and 2015). The irrigation scheduling methods consisted of (i) the pan evaporation method, which is based on managing the crop’s estimated evapotranspiration (ET) using pan evaporation values and the crop’s consumptive water use and (ii) the sensor-based irrigation scheduling method based on soil matric potential values recorded by soil moisture tension sensors installed in the field. Irrigation amounts from both irrigation scheduling methods indicated that less water was applied with the sensor-based method. The different amounts of irrigation applied associated with the two irrigation scheduling methods did not impact grain yield, aboveground biomass, and NUE. In general, NUEs values decreased with increased N rates, which means that additional N fertilizer added to the soil was not converted into grain yield or/and adsorbed by plants; therefore, more N remained in the soil, increasing the risk for environmental problems.
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    Final Report: Quantifying NPS Pollutant Discharges from an Urbanizing Headwater Basin
    Dougherty, Mark; Dymond, Randel L.; Godrej, Adil N.; Grizzard, Thomas J.; Randolph, John; Zipper, Carl E. (Virginia Water Resources Research Center, 2003-09-26)
    This research evaluates nonpoint source (NPS) sediment and nutrient fluxes from four headwater basins in the Piedmont physiographic province of the Chesapeake Bay drainage for up to 24 years. The basins are part of the 1530 km2 Occoquan River watershed in northern Virginia. Three of the basins, ranging in size from 67 to 400 km2, are predominantly forest and/or mixed agriculture. The fourth basin, the 127 km2 Cub Run watershed, is rapidly urbanizing with approximately 50 percent of current land area classed as urban. Descriptions of the four Occoquan headwater basins, averaged over the study period, are presented below for reference throughout the document.
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    Nitrogen values of liquid dairy manure and dry broiler litter as affected by preservation treatment
    Dougherty, Mark (Virginia Tech, 1995-02-05)
    Five liquid dairy manures and five dry broiler litters were tested in the laboratory to determine the effects of four preservation techniques on the forms and concentrations of nitrogen. 300 ml samples of fresh manure from five Virginia dairy and five poultry farms were analyzed for total Kjeldahl, ammonium, and nitrate/nitrite nitrogen within 24 hours of farm sampling, and at the end of seven days. Samples of the fresh manure were analyzed immediately as a control. The four preservation techniques were storage of the samples: at ambient temperature (26°C), by freezing (-22°C), by refrigeration (4°C), and by acidification with sulfuric acid (H₂SO₄) to pH < 2 plus refrigeration (4°C). Concentrations of nitrogen fractions were tabulated on a dry-weight basis and statistically analyzed using a randomized block design, with subsampling of each treatment × farm combination. Organic and inorganic nitrogen concentrations from the preserved manures were compared to the corresponding fresh concentrations of nitrogen in each manure control. Ambient storage, freezing, and refrigeration did not significantly affect (α=.05) the 7-day nitrogen concentrations of the ten manures. Acidification reduced most N concentrations due to the aggressive physical action of the acid, which accelerated both mineralization of organic N and volatilization of ammonia. Ambient storage was recommended as the most practical preservative technique because, of the three successful preservation methods, ambient storage provided the simplest procedure for 7-day preservation of nitrogen in liquid dairy manures and dry broiler litters.
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    Quantifying Long-Term Hydrologic and NPS Pollutant Response in an Urbanizing Watershed
    Dougherty, Mark (Virginia Tech, 2004-06-03)
    Long-term hydrologic and nonpoint source (NPS) pollutant response is quantified for four headwater basins of the Occoquan River in northern Virginia using 24 years of observed rainfall, basin discharge, water chemistry, and derived land use/land cover (LULC) data. Long-term summaries document that several hydrologic and NPS pollutant delivery characteristics in the urbanizing Cub Run basin are significantly different from adjacent non-urban basins. Higher annual NPS fluxes of total suspended solids (TSS), phosphorus (P), and nitrogen (N) in Cub Run are identified with periods of increased soil disturbance from urban land development and significantly increased storm volumes resulting from higher mean impervious cover. Long-term summaries of nutrient flux are consistent with literature documenting increased ratios of particulate to soluble nutrients with increased discharge. Storm fluxes of NPS particulate P, soluble P, particulate N, and soluble N make up 92, 67, 89, and 50 percent, respectively, of total NPS nutrient fluxes from all headwater basins, with between 88 and 98 percent of mean annual TSS fluxes delivered by storm flow. Higher sediment and nutrient fluxes observed in Cub Run basin during the summer and fall growing season after 1983 demonstrate the impact of replacing vegetated cover with urban impervious surface (IS). Annual regression models indicate that mean IS above 10 percent and precipitation are significantly associated with total basin discharge (r2=0.65). The positive association of annual storm soluble phosphorus flux with cumulative mean IS suggests the need for continued evaluation of urban NPS soluble phosphorus strategies. Urban soil disturbance is indicated by measuring the annual change in mean IS (delta IS). Regression models show that urban soil disturbance is a significant source of TSS flux in all seasons. Long-term total soluble phosphorus and nitrogen fluxes are significantly and positively associated with precipitation, delta IS, and agricultural land use (r2=0.50 and 0.58, respectively). The significant impact of urbanization on hydrologic and NPS pollutant flux, especially during the growing season, is a major finding of this study.