Browsing by Author "Simpson, Thomas W."
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- Agricultural use of sewage sludge : a literature reviewKelley, W. D.; Martens, David C.; Reneau, Raymond B.; Simpson, Thomas W. (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1984-12)Stricter regulations on discharge of sewage into waters, higher costs of alternate disposal procedures, and higher prices of chemical fertilizers have increased interest in the use of sewage sludge in crop production. This review addresses the benefits and risks of agricultural use of sewage sludge. Topics evaluated in this study are the biological, chemical, and physical aspects of sewage sludge relating to trace elements, pathogens, nitrogen, and phosphorus and also the economic aspects of land application of sewage sludge. For each topic, additional research needs are identified.
- An approach to studying soil-landscape relationships in VirginiaStolt, Mark H. (Virginia Tech, 1990)Various methods and techniques were used to examine soil-landscape relationships for residual and colluvial soils of Virginia. Soil micromorphology indicated that although some BC and C horizons in the field appeared structureless, evidence of pedogenic process was observed. These were designated as either BCt, BC, or CB horizons depending on the amount of oriented clay and the rates of change with depth of clay, DCB extractable Fe, and sand contents. Soil variability was examined for the overall study, as well as within toposequences, pedons, and individual horizons. Most of the overall variability was attributed to differences between study sites or between horizons, with minimal amounts due to landscape position. Substantial lateral variability occurred within horizons indicating a strong need for subsampling within horizons of the same pedon. Lithologic discontinuities were found to be difficult to recognize without obvious field evidence. Reconstruction analysis was used to examine soil and saprolite formation. Summit and backslope soils were found to be essentially the same in both morphology and degree of profile development. Sand weathering and clay eluviation/illuviation were the major soil forming processes occurring within these soils. Footslope soils were less developed than associated summit and backslope soils, with both depositional and pedologic processes contributing to soil formation and development. Thickness of saprolite was found to decrease. from the summit to the footslope. Thicker saprolite at the summit was apparently related to the greater stability of the summit position compared to the backslope and footslopes. A bucket auger was modified to obtain undisturbed samples of deep saprolite for reconstruction analysis. Saprolite reconstruction indicated that between 20 and 36 % of the mass of the partially weathered rock, which is the precursor to saprolite, is lost during saprolite formation. Most of these losses were either Al or Si. Initial soil formation was shown to occur at a faster rate than saprolite formation, but after substantial profile development, soil formation is reduced to a rate below that of saprolite formation, and saprolite accumulates below the solum. Reconstruction analysis was found to be a valuable tool in studying soil-landscape relationships.
- Availability and distribution of heavy metals from sewage sludge in the plant-soil continuumRappaport, Bruce D. (Virginia Polytechnic Institute and State University, 1986)An investigation was conducted using in situ lysimeters (1.5 m x 2.3 m) to determine Cd, Cu, Ni, and Zn availabilities for barley (Hordeum vulgare L.) and corn (Zea mays L.) grown on four sludge-amended soils. These lysimeters were constructed in Acredale silt loam (Typic Ochraqualf), Bojac loamy sand (Typic Hapludult), Davidson clay loam (Rhodie Paleudult), and Groseclose silt loam (Typic Hapludult) soils. An aerobically digested sewage sludge from a sewage system with major industrial inputs was applied at rates of 0, 42, and 84 dry Mg ha-t to the lysimeters in the poorly-drained Acredale soil. Rates of 0, 42, 84, 126, 168, and 210 dry Mg ha-1 were applied to the lysimeters in the well-drained Bojac, Davidson, and Groseclose soils. Tissue metal concentrations were determined in 1984 and 1985 for a three crop rotation, which consisted of corn, barley, and corn on the Acredale soil. Increases in sludge-borne Ni and Zn led to increases in Ni and Zn concentrations in corn earleaf, corn grain, and barley silage. Copper concentration was increased in barley silage but not in corn grain and stover. On this poorly-drained soil, metal movement did not occur below the Ap horizon even when Cu was applied in excess of USEPA guidelines. Although there were increases in metal levels, all four metals were within the range considered normal for corn and barley growth. Soil, corn, and barley plants were sampled in 1984 and 1985 to determine Cd, Cr, Cu, Ni, and Zn availabilities for crops grown on the sludge-amended Bojac, Davidson, and Groseclose soils. Levels of DTPA-extractable Cd, Cu, Ni, and Zn in the Ap horizon of these soils increased linearly with sludge rate. Corn grain and stover yields were not decreased on the Bojac, Davidson, and Groseclose soils when 4.5, 5105, 760, 43.0, 135, and 620 kg ha-1 of Cd, Cr, Cu, Ni, Pb, and Zn were added as a sludge-amendment. Copper and Zn applied in excess of 480 and 60 kg ha- 1 of USEPA guidelines, respectively on the Bojac, Davidson, and Groseclose soils were not phytotoxic to corn plants in 1984. Corn and barley tissue sampled for three consecutive seasons had Cr concentrations <2.8 mg kg-1.
- Availability and distribution of heavy metals, nitrogen, and phosphorus from sewage sludge in the plant-soil-water continuumRappaport, Bruce D.; Scott, James D.; Martens, David C.; Reneau, Raymond B.; Simpson, Thomas W. (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1987)Research was conducted during 1984 and 1985 to determine Cd, Cu, N, Ni, P, and Zn availabilities to barley (Hordeum vulgare L.) and corn (lea mays L.) grown on four sludge-amended soils. Field studies were conducted on Acredale silt loam (Typic Ochraqualf), Bojac loamy sand (Typic Hapludult), Davidson clay loam (Rhodie Paleudult), and Groseclose silt loam (Typic Hapludult). An aerobically digested sewage sludge, which was dewatered for approximately 2 years on sandbeds, was obtained from a sewage treatment plant with major industrial inputs. In the spring of 1984, this sludge was applied at rates of 0, 42, and 84 dry Mg ha- 1 to the poorly drained Acredale soil and at rates of 0, 42, 84, 126, 168, and 210 dry Mg ha - 1 to the well-drained Bojac, Davidson, and Groseclose soils. The 210 dry Mg ha-1 sludge rate supplied 4.5 kg Cd, 750 kg Cu, 3350 kg N, 43 kg Ni, 6900 kg P, and 600 kg Zn ha - 1. A 14-day anaerobic N incubation study indicated that mineralization of sludge organic N varied from 9.2% at the 42 Mg ha - 1 sludge rate to 4.2% at the 210 Mg ha - 1 rate. Th is relatively low percentage of N mineralized from the sludge may reflect the inhibitory effects of the high sludge metal levels on N transformations and the changes in sludge composition during long-term dewatering on sandbeds. Sludge application increased crop yields, except where the amounts of N mineralized from the sludge was inadequate to supply the N requirement of the crop. Crop yields were not decreased by either metal phytotoxicity or P deficiency on the four sludge-amended soils. On the three well-drained soils, Cu and Zn phytotoxicity did not occur where these metals were applied in excess of US EPA guidelines of 280 kg Cu and 560 kg Zn ha- 1. Although there were increases in Cd, Cu, Ni, and Zn in plants grown on the sludge-amended soils, the metal concentrations were within the ranges of those reported for nonsludged soils. Levels of DTPA-extractable metals in the Ap horizon of the soils provided a good indication of the amounts of metals in the soils from sludge application. Relatively low correlations occurred between DTPA-extractable Cd, Cu, Ni, and Zn and the respective metal concentrations in plant tissue. These low correlations were attributed to the small increases in metal concentrations in tissue from metals supplied by sludge application. The DTPA-extractable Cd, Cu, Ni, and Zn concentrations in soils sampled from various depths indicated no downward movement of these metals in the sludge-amended soils, except for virtually negligible downward movement of Cu in the Groseclose soil. Dilute double-acid extractable P in these samples indicated a small amount of P movement in only the sludge-amended Bojac and Davidson soils. The limited N mineralization of the sludge under study substantially reduced the potential for NQ3- contamination of groundwater.
- Characterization and composition of selected Cecil map units in the Virginia PiedmontThomas, Pamela J.; Baker, James C.; Simpson, Thomas W. (Virginia Agricultural Experiment Station, 1993-08)A study in Appomattox, Pittsylvania, and Lunenburg counties in the southern Piedmont of Virginia assessed composition and variability of a map unit named for a taxon of Typic Kanhapludults. Twelve delineations of Cecil sandy loam, 2 to 7 percent slopes, three to eight sites within each delineation, and three profiles within each site were randomly located in a two-level nested sampling scheme. Soil physical, chemical, and morphological data were collected from the Ap, Bt, and C horizons of each profile. In Appomattox County, 38 percent of the 81 profiles met the criteria for the Cecil soil series. An additional 33 percent of the profiles were taxonomically similar to Cecil. The remaining 29 percent were taxonomically dissimilar inclusions. In Pittsylvania County, 48 percent of the 75 profiles were Cecil series. An additional 47 percent of the profiles were taxonomically similar to Cecil. The remaining 5 percent were taxonomically dissimilar inclusions. In Lunenburg County, 42 percent of the 45 profiles were the Cecil series; the remaining 58 percent of the profiles were taxonomically similar to Cecil. Thus, the map unit in all three counties would be named Cecil and the map unit description in Appomattox and Pittsylvania counties would include dissimilar soils according to National Cooperative Soil Survey criteria. Taxonomic variability was reflected in the variability of taxonomically important soil properties. Percent base saturation decreased with depth in the profile. Maximum clay content occurred in the Bt horizon and ranged from 25 to 75 percent. The solum exhibited large variation in thickness. Subsoil properties important to classification (percent base saturation in the chemical control section, clay percentage in the particle-size control section, and solum thickness) exhibited considerable variation within delineations, but the variability was consistent from delineation to delineation. Intrusions of mafic material into the felsic crystalline system, from which Cecil and similar soils form, probably accounts for most of the variability in soil properties. Low plant available water, low bases, and high P-fixing capacity are major management concerns of the Cecil and similar soils. Understanding the interrelationship between map unit composition, variability, and soil properties is essential in increasing the productivity of these major landscape units.
- Effects of tillage and nitrogen fertilization on nitrogen losses from soils used for corn productionMenelik, G.; Reneau, Raymond B.; Martens, David C.; Simpson, Thomas W.; Hawkins, George W. (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1990-12)Research was conducted in soils of the Chesapeake Bay area to determine the effects of tillage practice and nitrogen (N) fertilizer application rates on N leaching from corn fields. Three well known computer models (NTRM, CERES-Maize, and VT-MAIZE) were tested to determine their ability to predict the distribution of N in (a) soil and crop, (b) the components of the N cycle, and (c) corn yields. To accomplish the above objectives, two field sites were selected on agronomically important soils for either a corn (Zea mays L.)-wheat (Triticum aestivum L.)-soybean (Glycine max [L.] Merr.) or a continuouscorn rotation. The corn-wheat-soybean rotation was located on a Suffolk sandy loam soil (coarse loamy, siliceous, thermic Typic Hapludult) in the immediate Chesapeake Bay drainage basin. The continuous-corn rotation was located on a Groseclose silt loam soil (clayey, mixed, mesic Typic Hapludult) typical of finer-textured soils located in the upper reaches of tributaries that drain into the Chesapeake Bay. Management practices evaluated included tillage system and rate, source, and time of N application. Specifically, we looked at conventional vs. no-till; inorganic N vs. sewage sludge; preplant vs. split application of N; and a variety of N application rates. The N treatments for corn were 0, 75, 150, and 225 kg N ha-1 applied preplant; 150 kg N ha-1 applied 4 weeks after emergence; and 150 kg of mineralizable N ha-1 from anaerobically digested and either lime- or polymer-conditioned sewage sludge. The N treatments for wheat were 20 kg N ha-1 applied in the fall and 30, 60, or 90 kg N ha-1 applied in the spring; 60 kg N ha-1 split application; and 80 kg of mineralizable N ha-1 applied in the fall from either lime- or polymer-conditioned sewage sludge. In the Groseclose soil, there was an increase in total yield and N uptake when sewage sludge was applied compared to the split and preplant application of inorganic N. There was no difference between polymer-or lime-conditioned sewage sludge application. Also, there were no differences between preplant and split application of N. Where no-till was used, there was an increase in both yield and N uptake compared with conventional till. In the Suffolk soil, tillage management did not influence yield or N uptake where time and source of N application were studied. This lack of response on the Suffolk soil is attributed to severe moisture deficits that were present during the growing season on this coarse-textured soil. Nitrogen losses from the soil profile were directly related to the quantity of N remaining in the upper 1 m of the soil profile after the crop was harvested. Larger quantities of N were lost from the Groseclose soil where conventional till was employed during the first year of the study. This was attributed to enhanced mineralization where no-till was converted to conventional till and to lower yields and lower N recovery with conventional till. Losses of N tended to be higher from the conventional till plots because of the larger quantities remaining at the end of the growing season. It should be noted that the years during which these xvii studies were conducted were extremely dry, and the in the Groseclose soil where no-till management was employed resulted in increased yield and increased N recovery. This study also emphasizes the need for better methods for making N recommendations for crop production. The model performances varied from year to year and from one tillage practice to another. Because they were written for average soil and climatic conditions, they did not make satisfactory predictions in many instances. Such models require adjustment to reflect the moisture stress conditions that often prevail in this region for corn production.
- Land application of sewage sludge for agricultural purposesSimpson, Thomas W.; Nagle, Steven M.; McCart, Gerald D. (Virginia Cooperative Extension Service, 1985)Provides information and guidelines on the proper use of sewage sludge on cropland.
- Municipal yard waste composting: process parameters, windrow gases, and leachate qualityChristian, Archer H. (Virginia Tech, 1995-08-14)A Municipal Yard Waste Composting Research and Demonstration Project was conducted to examine the process, quality of leachate, and viability of this technology for large-scale, low-technology application. Project research objectives were: 1) to characterize C/N, temperature, and moisture relationships of yard waste during composting and the elemental composition of the finished compost; 2) to investigate the oxygen (O₂), carbon dioxide (CO₂) and methane (CH₄) relationships in the composting yard waste; and 3) to quantify water quality parameters of the leachate from yard waste composting mixes. Mixes of 3 parts leaves/1 part grass, 2 parts woodchips/1 part grass, and leaves alone were composted in windrows. Process control was by a front-end loader/back-hoe according to a 60°C maximum temperature set-point, initially, and by temperature plateaus or moisture conditions following most active composting. Composting was more efficient with the presence of grass clippings. Some CH₄ was observed within windrows microsites, even under overall aerobic conditions. Occasional methane production not in excess of approximately 4x10⁻² mmol/l reflects inconsequential anaerobiosis. Leachate from individual windrows was minimal but contained high concentrations of total Kjehldahl nitrogen (TKN), total phosphorus, and biological oxygen demand. Soil degradation processes should ameliorate these. The leaf/grass mix generated the greatest quantities of carbon dioxide, strongly correlated oxygen and carbon dioxide concentrations, steepest temperature profile, and the highest concentrations of plant nutrients in material composted for between 8 and 24 weeks. Low-technology composting of yard wastes can be an effective, low-cost alternative to landfilling, with substantial societal and environmental benefits.
- Observation scale effects on fluid transport behavior of soilAlbrecht, Karen A. (Virginia Tech, 1985-01-15)Variabilities of hydraulic and solute transport properties of soil are examined at three scales: pore-scale, sample volume-scale, and field-scale. Undisturbed soil cores were taken at 19 subsites spaced logarithmically along a 150 m line transect in a Groseclose mapping unit near Blacksburg; Virginia. Three core sizes were taken at each subsite at the soil surface and 0.5 m depth. 'Small' cores were-40x54 mm; 'medium' cores were 60X100 mm; and 'large' cores were 100x150 mm. Macropore effects on solute transport were evaluated using monocontinuum and bicontinuum models. Bicontinuum-predicted solute breakthrough curves (BTC) closely agreed with observed BTC data with mean errors of reduced concentrations
- Soil-saprolite-landscape relationships in the Piedmont and Blue Ridge Highland regions of VirginiaStolt, Mark H.; Baker, James C.; Simpson, Thomas W. (Virginia Agricultural Experiment Station, 1994)Various methods and techniques were used to examine soil variability and soil-saprolite-landscape relationships in Virginia. Variability analysis indicates that for the overall study, most soil variability is attributable to differences between study sites or between horizons, with minimal amounts due to landscape position. Substantial lateral variability occurs within horizons, indicating a strong need for subsampling within horizons of the same pedon. Although some soil-saprolite transition horizons appear structureless in the field, soil micromorphology indicated evidence of pedogenic process within these horizons. Soil-saprolite transition horizons were designated as either BCt, BC, or CB, depending on the amount of oriented clay, and rates of change with depth of clay, DCB extractable Fe, and sand. Summit and backslope soils have essentially the same morphology and degree of profile development. Soil reconstruction indicates that sand weathering and clay eluviation/illuviation are the major soil-forming processes occurring within these soils. Footslope soils are less developed than are associated summit and backslope soils, with both depositional and pedologic processes contributing to soil formation and development. Saprolite thickness decreases from summit to footslope. Thicker saprolite at the summit is apparently related to the greater stability of the summit position compared to associated backslope and footslopes. Saprolite reconstruction indicates that between 20 and 36 % of the mass of the partially weathered rock, which is the precursor to saprolite, is lost during saprolite formation. Most of these losses are either Al or Si. Initial soil formation occurs at a faster rate than that of saprolite formation, but after substantial profile development, soil formation is reduced to a rate below that of saprolite formation, and saprolite accumulates below the solum.
- The Virginia Yard Waste Management ManualEvanylo, Gregory K.; Sherony, Caroline A.; May, Jim; Simpson, Thomas W.; Christian, Archer H. (Virginia Cooperative Extension, 2009-05-01)This manual is designed as a total management to guide public and private sector composters through the steps necessary to site, design, and operate a yard-waste management program. Information on the principles of composting are presented along with technologies that can assist the composter in making a consistently high quality product.
- The Virginia yardwaste management manualMay, Jim; Simpson, Thomas W. (Virginia Cooperative Extension Service, 1990)This manual is a hands-on guide to the steps necessary to site, design and operate a yard waste management program.