Browsing by Author "Martens, David C."

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    Adsorption of sulfate and phosphate at the mineral-water interface: isotherm, stoichiometry, and models
    He, Liming (Virginia Tech, 1995-10-15)
    Processes occurring at mineral-water interfaces play critical roles for regulating the composition of surface and groundwater, for soil development, and for the availability of plant nutrients. Sulfate adsorption at three pH levels was conducted on y-AI203 and kaolinite. The adsorption isotherms were described well by the simple Langmuir, two-site Langmuir, Freundlich, and Temkin equations. The capacity of SO42-adsorption for y-AI203 was five times greater than for kaolinite, indicating the difference in reactive site density between y-Ab03 and kaolinite. Mathematical analyses for the adsorption isothenns demonstrated that S042- may not be adsorbed on the d-plane, i.e., in the diffuse layer, whereas both outer- and inner-sphere complexation mechanisms predicted S042- adsorption equally well.
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    Agricultural use of sewage sludge : a literature review
    Kelley, 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.
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    Alfalfa growth on acid soil as influenced by Al, Ca, pH and Mo
    Rechcigl, John E. (Virginia Polytechnic Institute and State University, 1986)
    Soil acidity is a major cause of low yields of alfalfa (Medicago sativa L.) in the southeastern United States. Two field experiments were conducted on an Ernest silt loam soil (fine—loamy, mixed, mesic Aquic Fragiudult) to determine what conditions are necessary for optimal alfalfa growth in an acid soil environment. In the first experiment alfalfa was no—till planted to evaluate the influence of surface applied dolomitic limestone at 0 and 6.7 Mg/ha either 8 or 20 months before planting and at planting on alfalfa performance under acidic conditions. Yield increases, greater than two fold, resulted from surface application of limestone regardless of time of application. In the second field experiment treatments included surface and incorporated dolomitic limestone at either 6.5 or 13.0 Mg/ha, gypsum at 13.0 Mg/ha, foliar Mo at 560 g/ha and N as a split. Yields increased in response to surface and incorporated lime, Ca, Mo and N application, possibly as a result of Al activities in soil solution being as low as 0 and 0.05 uM in the surface and 1 m depth samples, respectively, for the surface limed soils. Low activity of Al in soil solution may explain why subsurface acidity was not toxic to alfalfa grown on these soils. This study showed that surface limestone at half the recommended rate is adequate for the growth of alfalfa under acidic conditions. The implanted soil mass technique was used to evaluate the influence of subsurface amendments (Ca, N, Ca and N, KOH and Ca(OH)2) on alfalfa root growth and N fixation on soils that received either 0 or 6.7 Mg/ha surface applied limestone. Of the various subsurface amendments the Ca(OH)2 treatment produced the most root growth and N fixation. This study showed that both the reduction in acidity and the availability of Ca are necessary for optimal N fixation and root growth. In vitro studies conducted in growth pouches showed that pH 4.5 nutrient solution was not ·detrimental to alfalfa growth unless A1 was present. Addition of 3.0 mM Ca to a nutrient solution containing 0.08 mM Al alleviated toxic effects of Al on alfalfa growth. No-till alfalfa can thus be grown on acid soils with surface lime by providing Ca and reducing acidity.
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    Availability and distribution of copper in soils following eight annual applications of CuSO₄ or Cu-enriched swine manure
    Payne, Grover Garry (Virginia Polytechnic Institute and State University, 1986)
    Three field studies were established in 1978 and continued through 1985 in order to determine the effects of long-term Cu applications, as either CuSO₄ or Cu-enriched swine manure, at high application rates on corn (Zea mays L.) production. The studies were conducted on Bertie fine sandy loam (Aquic Hapludult), Guernsey silt loam (Aquic Hapludalf), and Starr clay loam (Fluventic Dystrochrept)-Dyke clay (Typic Rhodudult) soils in the Coastal Plain, Ridge and Valley, and Piedmont physiographic regions of Virginia, respectively. A laboratory incubation study was also conducted using the same soils to determine the effects of soil pH on the changes in forms of soil Cu present over a 256-day period following addition of CuSO₄ or Cu-enriched swine manure. Application of 336 kg Cu ha⁻¹ , as CuSO₄ , or up to 264 kg Cu, as Cu-enriched swine manure, from 1978 through 1985 had no adverse affects on corn grain yields or on Cu concentrations in corn ear leaves or grain. Copper concentrations in ear leaf tissue were increased only slightly (≤ 2.1 mg kg⁻¹) by the eight annual Cu additions with no increase in Cu content of grain being observed. Copper concentrations in both ear leaves and grain remained within normal levels. DTPA extractable Cu was linearly related to the cumulative amount of Cu applied to the three soils (r = 0.93 to 0.98, α= 0.01). Extractable soil Cu showed no relationship with Cu levels in grain or leaf tissue. Analysis of subsoil samples indicated little downward movement of the applied Cu due to leaching. Fractionation of the Cu in the three soils indicated increases in all fractions resulting from Cu treatments. Results of the laboratory incubation study showed that the distribution of applied Cu among soi 1 fractions was dependent on soil pH, length of time following Cu additions, and to some degree on the source of applied Cu. Levels of Ex-Cu and HOAc-Cu decreased with time and increasing pH. No consistent differences in Pyro-Cu were observed due to pH or length of incubation. Concentrations of Ox-Cu parallelled the levels of Fe and Mn in the soils and generally increased with time. Soils at low pH tended to contain less Ox-Cu than soils at higher pH levels.
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    Availability and distribution of heavy metals from sewage sludge in the plant-soil continuum
    Rappaport, 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.
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    Availability and distribution of heavy metals, nitrogen, and phosphorus from sewage sludge in the plant-soil-water continuum
    Rappaport, 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.
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    Availability and distribution of nitrogen and phosphorus from sewage sludge in the plant-soil-water continuum
    Scott, James D. (Virginia Tech, 1987-05-05)
    Research was conducted in 1984 and 1985 to determine N and P availabilities for barley (Hordeum vulgare L.) and com ( Zea mays L.) grown on four sludge-amended soils. Tests were conducted on the Acredale silt loam (Typic Ochraquall), Bojac loamy sand (Typic Hapludult), Davidson clay loam (Rhodic Paleudult), and Groseclose silt loam (Typic Hapludult) soils. An aerobically·digested sewage sludge from a sewage treatment plant with major industrial irrputs was applied at rates of 0, 42, and 84 dry Mg ha' 1 on the poorly-drained Acredale soil. Rates of 0, 42, 84, 126, 168, and 210 dry Mg ha'1 were applied on the well-drained Bojac, Davidson, and Groseclose soils. The 210 dry Mg haâ 1 sludge rate supplied 3300 and 6600 kg of N and P haâ 1, respectively. A 14-day anaerobic N incubation study indicated that mirreralization varied from approximately nine to four percent of sludge N from the 42 to 210 Mg haâ 1 application rates, respectively. Sludge application increased N uptake (rz = 0.98** to 0.99**) by the 1984 com grown on the three well-drained soils. Nitrogen balance data indicated that quantities of unrecovered N ranged from six to 21 percent where sludge was applied.
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    Biodegradability of atrazine, cyanazine, and dicamba in wetland soils
    Gu, Ji-Dong; Berry, Duane F.; Taraban, Ronald H.; Martens, David C.; Walker, H. Lynn; Edmonds, William J. (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1992-02)
    Small amounts of applied pesticide chemicals eventually can end up in nontarget areas such as wetlands, sediments, and groundwater where anaerobic conditions often predominate. Runoff and leaching are major means by which pesticides move away from application sites. Pesticides also can find their way into nontarget areas as a result of inappropriate disposal and accidental spills. We evaluated the biodegradability of atrazine, cyanazine, and dicamba in wetland soils under nitratereducing and methanogenic conditions. Wetland soil samples were collected from three different sites in the Chesapeake Bay watershed region. These sites represented both tidal (Lawnes and Levy soils) and nontidal (Myatt soil) wetlands. Tidal wetlands are water-saturated throughout the year, whereas nontidal wetlands are saturated only during certain times of the year. Herbicide fate studies were conducted in wetland soil microcosms consisting of serum bottles filled with soil slurry and containing either atrazine, cyanazine, or dicamba. Atrazine was extremely stable in wetland soil microcosms regardless of incubation temperature, redox status (nitrate-reducing versus methanogenic conditions), or soil type. Neither temperature nor redox status affected cyanazine stability in Myatt wetland soil microcosms. We observed a significant decrease in cyanazine concentration in Lawnes wetland microcosms incubated under methanogenic and nitratereducing conditions. Losses were more pronounced at 25° than at 15°C. Results from enrichment culture studies suggest that cyanazine was cometabolized (i.e., cyanazine could not be used as a carbon and energy source by the microorganisms) in Lawnes soil microcosms. Dicamba was readily biodegraded in the wetland soils tested, although total mineralization was not achieved.
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    Biodegradability of dicamba and 2,4-D in riparian wetland soils
    Lopez, Alfredo R. (Virginia Tech, 1995-06-05)
    A general review of soils in Virginia counties bordering the Chesapeake Bay reveals that coastal plain soils, especially those most agriculturally productive, are dominantly sandy texture in the subsurface horizon, and have shallow water tables. Considering the high amounts of pesticides used in the coastal plain region and the porous nature of sandy texture soils, there is a great potential for pesticide leaching and subsequent contamination of surface and groundwater sources. This is of great concern because of the potential detrimental effects these agrochemicals represent on aquatic and animal life in the Chesapeake Bay, the largest and most productive estuary in the United States.
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    Biodegradation of pesticide and indolic compounds under methanogenic conditions
    Gu, Ji-Dong (Virginia Tech, 1991-10-15)
    Degradability of atrazine, cyanazine, and dicamba under methanogenic conditions was evaluated using serum bottle microcosms containing wetland soil inocula obtained from three different sites. Pesticides were monitored by high-performance liquid chromatography (HPLC) and the production of methane was measured with a gas chromatograph (GC). Dicamba was the most susceptible to degradation in the microcosms, followed by cyanazine. Atrazine was not degraded in the wetland soils. A dicamba-degrading methanogenic consortium was enriched from one of the initial wetland soil microcosms (Lawnes). Dicamba degradation was further examined using this consortium. Net methane production suggested that the aromatic ring was not degraded. Rates of dicamba degradation were enhanced with addition of 0.2 % yeast extract. Dicamba degradation was accomplished within 4 days compared to 22 days without yeast extract addition. The inability of the consortium to degrade the benzenoid ring was confirmed when no ¹⁴CO₂ was produced upon addition of [U-¹⁴C]dicamba to the cultures. Analysis of culture filtrate by HPLC revealed the presence of a possible metabolite that was aromatic in character.
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    Boron chemistry in selected Virginia soils and hydroxy aluminum and iron systems
    Jin, Ji-yun (Virginia Polytechnic Institute and State University, 1985)
    Greenhouse and laboratory experiments were conducted to investigate the distribution of native B, the availability of native and applied B in 14 Virginia soils and the specific reactions of B in soil and hydroxy Al and Fe systems. Total B in the 14 soils ranged from 21.5 to 96.3 mg kg⁻¹. Only a small portion of the total B was in soil solution, non-specifically and specifically adsorbed forms and Mn minerals. These fractions of B are readily available to plants. A large part of the total B was associated with non-crystalline and crystalline Al and Fe minerals and soil silicates. These forms of B contribute little to B absorption by plants. Hot water soluble B, NH₄-acetate extractable B, mannitol exchangeable B and Mehlich III extractable B from the soils closely correlated with the concentrations in corn plants from native B in the greenhouse experiment. A yield response of corn plants to B application did not occur on the soils. Both tissue B concentration from applied B and maximum B adsorption by the soils closely correlated with soil clay, hydroxylamine hydrochloride extractable Mn and NH₄—oxalate (pH 3.25) extractable Al and Fe (under UV light). These data indicated that soil clay and Al-, Fe- and Mn-oxides and hydroxides have high affinities to adsorb B in plant unavailable forms. Boron adsorption on both gibbsite and goethite was pH and temperature dependent. At pH 6.5, boric acid was major species in the system and B was absorbed by the negatively charged surface of gibbsite and the positively charged surface of goethite. At pH 10, borate was primarily species in the system and B was adsorbed on negatively charged surfaces of both minerals. Boron adsorption was greater at pH 10 than at pH 6.5. An increase in temperature increased B adsorption on both minerals at both pH levels. This indicated that the B adsorption was an exothermic process. Boron adsorption on gibbsite and goethite shifted the ZPC of the minerals downward. This verified that specific B adsorption occurred on the surfaces. Aluminum substitution in goethite increased the affinity of the surface for B adsorption.
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    Copper adsorption/desorption characteristics on copper amended soils
    Reed, Stewart T. (Virginia Tech, 1993)
    Laboratory tests were conducted to determine Cu availability of three Virginia soils amended with Cu as either Cu-rich pig manure or CuSO₄ with the same Cu content as that in manure. The study also assessed the capability of Mehlich-3 to estimate deficient and toxic Cu levels in soil. Application of Cu as manure or CuSO₄ did not affect grain yield or grain Cu concentration in corn grown at each site. Young corn plant height was reduced by CuSO₄ application on the Bertie sandy loam, an indication of greater toxicity from inorganic than organic Cu. Very little exchangeable or solution Cu was present in any of the three soils. The vast majority of Cu was distributed between the organic and soil oxide fractions. The ratio of soil oxide to organic matter determines the relative distribution of Cu among these fractions. Most organically bound Cu was held by specific adsorption mechanisms and Mehlich-3 strongly extracts this fraction. Mehlich-3 extraction patterns were indicative of Cu binding strength in the different soils. Since Mehlich-3 strongly extracts specifically bound Cu and only poorly removes oxide Cu, this test may underestimate Cu availability on sandy soils with low organic matter content. However, Mehlich-3 provides an acceptable test for soil Cu. Soil sorption characteristics were studied for Cu, Pb, and Zn added, both alone and simultaneously. Copper sorption energy was higher than both Pb or Zn, however, sorption capacity followed the order Pb > Zn > Cu. High Pb and Zn sorption was in part due to precipitation reactions especially at high initial solution concentrations. Zinc was bound to soil mostly by weak electrostatic forces. Copper and Pb were bound at specific sorption sites and by complex multi-site bonding mechanisms possibly involving organic substances. These specific and multi-site mechanisms account for metal ions removed from solution at low concentration. Even at low metal concentration, Cu and Pb sorption results in concurrent release of H⁺ and Ca²⁺ at a greater than one to one charge basis. Soils adjusted to various pH levels were equilibrated with Cu solution and then extracted with a series of dilute acid extractions to determine Cu adsorption and fixation capacities. Copper adsorption and more importantly Cu fixation increased with an increase in soil pH. Soil with a high organic matter content as a result of manure applications adsorbed and fixed more Cu at all pH levels than the control and CuSO₄ soil. The presence of organic matter may have a greater effect on metal sorption characteristics than maintenance of pH ≥ 6.5. Heavy metal sorption was accompanied by concurrent release of H⁺ and Ca²⁺ which represents exchangeable and specifically bound cation nutrients. Soils which receive heavy metal applications from sewage sludge or animal manure would have a short-term increase in plant available nutrients at the expense of long-term reserve capacity. Soil tests for cation nutrient availability on soils receiving heavy metal applications should be adopted to account for these responses.
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    Corn response to long-term application of CuSO₄, ZnSO₄ and Cu-enriched pig manure
    Gettier, Stacy W. (Virginia Polytechnic Institute and State University, 1986)
    Three studies, two field and one laboratory, were performed to evaluate Cu or Cu and Zn from either sulfate sources or Cu-enriched pig manure. The studies were designed to investigate the effects of Cu and Zn in soils and corn (Zea mays L.). The first field study consisted of continuing a longterm field experiment which was established in 1967 to evaluate corn response and changes in a Davidson clay loam soil to yearly additions of Cu and Zn sulfates. In 1983, the 17 annual additions of Cu and Zn resulted in cumulative totals of 280 kg Cu and 560 kg Zn ha⁻¹. These Cu and Zn additions, either alone or together, did not cause any grain or stalk yield decreases. The DTPA extractant effectively separated all soil treatment levels for both Cu and Zn. Copper concentrations in the blades and grain were not related to soil additions of Cu or Zn. However, Zn concentrations in blades and grain were directly related to each other, r=0.87**, to soil Zn treatment levels and to DTPA extractable Zn. The second field experiment was designed to evaluate the effects of soil application of Cu-enriched pig manure and CuSO₄ on corn. The five treatments in each of three field locations consisted of a control, low and high Cu-enriched pig manure levels, and Cu, as CuSO₄, equivalent to Cu amounts in the manure. The soils varied in texture from clay loam to fine sandy loam, and ranged in CEC from 5 to 12.3 cmol(+) kg⁻¹. Copper-enriched pig manure, containing 1285 mg Cu kg⁻¹, was produced by pigs fed diets supplemented with 242 mg Cu kg⁻¹. After six years, 198 mg Cu kg⁻¹ had been applied by the high treatments. The DTPA extractable Cu was not related to leaf nor grain Cu levels but was linearly related, r=O.95**, to applied Cu. No nutrient deficiencies or toxicities were observed. The third study was a laboratory incubation of added Cu. The 15 soils ranged from 54 to 489 mg kg⁻¹ in clay and from 5.4 to 7.4 in pH. Extractable Cu had simple correlations with five soil properties, clay, surface area, hydrous Al, hydrous Fe, and hydrous Mn. Three treatments, a control and 22 kg ha⁻¹ Cu as CuSO₄, and as Cu-enriched pig manure (equivalent to 975 mt wet manure ha⁻¹), were applied to the soils at 33 k Pa moisture. Copper was extracted in the following order for the control and CuSO₄, treatments: AlCl₃ in O.5M HC1 > EDTA > DTPA. A different order of Cu extraction occurred for the Cu-enriched pig manure treatment such that EDTA > DTPA > AlCl₃ in 0.5M HC1. Extractable Cu decreased with time regardless of Cu source.
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    Cotton Yield as Related to Selected Physical and Chemical Properties of Soils of the Coastal Plain of Virginia and North Carolina
    Adcock, Clyde Wesley (Virginia Tech, 1998-08-28)
    Cotton (Gossipium hiristum, L) is a warm season perennial with indeterminant growth habit. In 1995, 42,500 and 300,000 hectares were grown in Virginia and North Carolina, respectively. Soil physical and chemical properties may limit cotton yields. The objective of this study was to; 1) determine influences of soil physical and chemical properties on yield, 2) validate existing preharvest yield estimators, and 3) determine the effect of subsoiling and/or subsurface liming on cotton development and root growth. Two hundred sites were sampled across the Coastal Plain of Virginia and North Carolina to a depth of 92 cm representing 5 major soil series. Soil samples were analyzed for selected physical and chemical properties from each horizon. Boll and plant counts were obtained while harvesting a 3-meter length of row at each site to determine yield for the 1996 and 1997 growing season. Cotton was grown in the greenhouse on 30 cm diameter cores of a soil with low subsoil pH and a hard pan to determine the effects of subsoiling and/or subsurface liming. Ninety days after planting, the cotton plants were harvested and the above ground biomass and rootmass were analyzed. Physical and chemical properties explained 52% of yield variability in 1996 and 27% in 1997. Physical and chemical properties that were significant to yield were surface bulk density, available water holding capacity, depth of the water table and Bt horizon, Mg, K, Ca, and Al content. Soil analysis for nutrient status at depths up to 45 cm were better indicators of cotton yield. Subsoiling with or without subsurface liming increased rooting depth over the untreated check. The subsurface liming reached first flower 11 days prior to the other treatments. The additional period for flowering and boll set in Virginia and North Carolina could increase potential yield.
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    Denitrification in onsite wastewater treatment and disposal systems
    Degen, Marcia B.; Reneau, Raymond B.; Hagedorn, Charles III; Martens, David C. (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1991-11)
    The effects of effluent type, effluent loading rate, dosing interval, and temperature on denitrification in onsite wastewater treatment and disposal systems (OSWTDSs) were evaluated in this study. The variables were soil horizon, effluent type, effluent loading rate, dosing interval, and temperature. Surface and subsurface soil cores were collected from a Groseclose silt loam soil (clayey, mixed, mesic Typic Hapludult) and subjected to the following treatments: aerobic and anaerobic effluent, loading rates of 0.5, 1.0, and 1.5 times the Virginia Department of Health (VDH)-recommended levels, 24-hour and 48-hour dosing rates, and summer and winter temperatures. The effects of the treatments on denitrification were evaluated based on analyses of leachate from the cores, soil chemical analyses, and microcosm studies to estimate actual denitrification activity. From the study, a model was developed that predicted the mean nitrous oxide (N20) production for each combination of the experimental treatments. The results of the study and the model indicate that denitrification can be enhanced in OSWTDSs by the application of anaerobic effluent at the VDH-recommended effluent loading rate to surface soil horizons using a 48-hour dosing interval. A field study was conducted on a Lowell silt loam soil (fine, mixed, mesic Typic Hapludalf). Denitrification was measured at this site using acetylene blocking, and the results compared to those predicted by the denitrification model developed from the laboratory data. The field measurements of denitrification based on N20 concentration in the soil atmosphere were almost three orders of magnitude higher than that predicted by the model.
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    Development of field-specific spring N rate recommendations for winter wheat
    Scharf, Peter C. (Virginia Tech, 1993)
    Optimum spring N fertilizer rates for winter wheat in Virginia vary widely from field to field, but traditionally spring N is applied at a uniform rate to all fields. A recently-developed tissue test procedure provides a field-specific evaluation of crop N status and predicts optimum N rate for the second spring N application in a split spring application management system. However, this procedure is based on a small number of researcher-planted experiments utilizing a single cultivar; it fails to provide field-specific rate recommendations for the first spring N application; and it is not accessible to farmers who are unwilling to split their spring N applications. Our objectives were: to evaluate the reliability of the tissue test procedure in a large number of farmer fields; to develop a method for making field-specific N rate recommendations for the first spring application in a split-application management system; and to develop a method for making field-specific N rate recommendations in a single-application management system. Forty-five spring N rate experiments were established in farmer fields over a five-year period. A range of N fertilizer rates was applied in early spring (Zadoks growth stage 25) and again in mid-spring (Zadoks growth stage 30) in all possible combinations. Yield data were used to calculate economic optimum N rates at growth stage (GS) 25 and GS 30 with split-application management, and at GS 25 with single-application management. These optima were regressed against a variety of predictor variables measured in the same fields. The reliability of the previously-developed tissue test procedure for making GS 30 N rate recommendations was confirmed. Tiller density was the best predictor of optimum GS 25 N rate with split-application management, while soil nitrate to 90 cm was the best predictor of optimum GS 25 N rate with single-application management. These three relationships fit together to form a flexible and powerful system for making spring N rate recommendations for winter wheat. This system increased estimated profit and apparent fertilizer efficiency in these experiments.
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    Development of Nitrogen rate Recommendations for No-till Dryland Grain Sorghum in Virginia
    Khosla, Rajiv (Virginia Tech, 1998-10-26)
    Little research has been done in the humid mid-Atlantic region to develop full-season N fertilizer recommendations for dryland no-tillage grain sorghum (Sorghum bicolor L. Moench) production. The objectives of this study were: (i) to determine the optimum rate of band-placed starter N fertilizer needed in combination with side-dress N applications to achieve economic grain yields, (ii) to investigate if pre-plant broadcast N applications are as efficient as band-placed plus side-dress N applications, (iii) to evaluate the response of grain sorghum yield to partitioned side-dress N applications, and (iv) to study the influence of residual soil profile mineral-N (nitrate and ammonium) on sorghum response to applied N fertilization. Multi-location field studies were conducted over three years. A range of N treatments of various starter-band and side-dress N rates were applied. The experimental data indicate that an optimum rate of N fertilization depends on residual soil mineral-N. Little or zero starter-band-N in conjunction with side-dress-N applications of 130 kg of N ha-1 for soils testing high in mineral-N ( 50 kg N ha-1 in the top 0.3m of surface soil) at planting, and a starter-band-N supplement of 40 kg N ha-1 in conjunction with 130 kg N ha-1 side-dress N for soils testing low in mineral-N at planting, optimized the grain sorghum yields in these experiments. Broadcast N applications were observed to be as efficient as band placed N applications when followed by rainfall soon after application. Grain sorghum yields did respond to the partitioned side-dress N applications. However, partitioning of side-dress N application again depends on the residual mineral-N level present in the soil. In order to consider residual soil mineral-N in making N fertilizer recommendations "Associated Nitrogen Fertilizer Equivalency" (ANFE) values were calculated. ANFE is the amount of applied N that has potential to produce the same yield as that produced by the residual soil mineral-N. The N fertilizer recommendations based on ANFE values were quite close for two out of four sites as compared to the N rates at which the maximum yields were obtained in this study.
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    Distribution and physical parameters of solid waste disposal sites in Southwestern Virginia and the nature of leachate emissions
    Black, Elwood David (Virginia Tech, 1975-03-04)
    A total of 62 solid waste disposal sites were documented and evaluated in the 18 county study area of southwestern Virginia. The solid waste disposal operations encompassed a combined area in excess of 458.7 ha. An estimated 32 workers and 40 pieces of heavy equipment were utilized for the disposal of the waste at the various dumps, landfills, and sanitary landfills. The largest number of disposal sites were operated as dumps (62%), while only 14% of the sites qualified as sanitary landfills. The dump type of operation was characterized by: erosion, odor, leachate, minimum compaction, burning, lack of final or daily cover, and limited soil, financing, cover material, personnel, equipment, and planning. Generally, the waste was deposited at a remote or obscure site and left unattended. The landfill form of waste disposal, which occurred in 17% of the sites, required the construction of a trench for the disposal of the waste material which was later covered. The landfill form of waste disposal was characterized by shallow soils, limited cover material, steep slopes, and/or underground springs. The sanitary landfills were located in areas of deep soils, with moderate slopes, and showed an absence of interacting water. These sites demonstrated proper management of the resources and limited alteration of the surrounding area.
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    The distribution of anaerobic bacteria along a soil drainage catena
    Dolan, Rodney Martin (Virginia Tech, 1977-03-05)
    Strict anaerobic culture techniques were used to enumerate the anaerobic bacteria present in three soil sites located along a drainage catena near Blacksburg, Virginia. An anaerobic cooked meat plus 0.5% glucose medium cultured the largest number of anaerobes from the poorly drained soil. The population of obligate anaerobes ranged from 10⁶/ g dry weight soil on the poorly drained soil (% moisture = 112.06) to 10⁵/g dry weight soil on the intermediate soil (% moisture = 34.51) to 10⁴/g dry weight soil on the well drained soil (% moisture 20.81). The population of organisms able to grow anaerobically (facultative plus obligate) ranged from 10⁶/g dry weight soil on the poorly drained site to 10⁵/g dry weight soil on the well drained site. This same population on the poorly drained site was relatively constant over a nine month period with the exception of a sharp rise in early spring. The clostridia constituted at least one third of the obligately anaerobic bacteria present on the poorly drained soil. A sizeable percentage of the obligate anaerobic isolates on this site were either clostridia which formed spores unable to germinate in the medium employed, clostridia which were very pleomorphic in cell shape and gram reaction, or nonsporeforming obligate anaerobes. These results indicate that strict anaerobes and possibly nonsporeforming strict anaerobes exist in soils of different drainage character even though facultative organisms appear to be more successful competitors on the more well drained sites.
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    Effect of Poultry Litter-Yard Waste Compost Application on Phosphorus Availability in Diverse Soils
    Mankolo, Regine Ndole (Virginia Tech, 1997-10-08)
    Land application of poultry litter has been successfully practiced for centuries to maintain and improve soil fertility, although over application may promote loss of nutrients through runoff or leaching. To decrease the potential for adverse environmental impacts of N and P in groundwater, a new approach developed in this research was to use a composted mixture of poultry litter (PL) and yard waste (YW) as a soil amendment for corn (Zea mays L.) production. Objectives of this research were to evaluate effects of pre-compost C:N substrate ratios for poultry litter-yard waste compost (PYC) on the availability of soil P, to determine the P response of corn plants to inorganic P, PL and PYC application, and to study relationships between P availability and both inorganic P and PYC application. Langmuir isotherms were used in this research to select soils with relatively high P fixation capacities. Phosphorus sorption maximum for soils evaluated were as follows: 304 and 449 micrograms of P per gram for A horizon Coastal Plain soils (Series: Kempsville and Myatt, respectively); 487 micrograms of P per gram for an A horizon Ridge and Valley soil (Series: Frederick); 918 and 603 micrograms of P per gram for A horizon Piedmont soils (Series: Elioak and Vance, respectively); 1099 microgram of P per gram for mine tailings (Series: Emporia located in the Coastal Plain); and 1524 microgram of P per gram for A and upper mixed horizon soil (Series: Starr from Piedmont region). Based on intermediate to high P sorption maxima, soil from the Vance and Starr series and mine tailing from Emporia series were selected for greenhouse research to evaluate P availability of PYC . Treatments applied to the soil in the greenhouse and field studies consisted of various levels of P as Ca(H₂PO₄)₂.H₂O, PL and PYC from 15:1, 20:1, and 25:1 C:N ratio substrates. Each P source increased dry weight of corn plants grown in the greenhouse by alleviation of P deficiency. Phosphorus uptake from PYC and PL application was either equal to or higher than P uptake from an equal level of P application as Ca(H₂PO₄)₂.H₂O. Application of 87.2 kg of P per ha increased corn grain yields in a field experiment on Vance sandy loam from 6340 kg per ha on the control to a range of 10,170 to 11,350 kg ha for PYC digested from the three C:N ratio substrates. The yields on PYC treatments were attributed to a combination of factors including slow mineralization of P with less fixation during the growing season. The low P fixing capacity results from the blockage of H₂PO₄⁻ sorption by competition of negative charge from organic material and from the displacement of H₂PO₄⁻ in soil solution by OH⁻ from application of the alkaline composts. It would be desirable from the standpoint of more PL utilization to prepare composts from low substrate ratio substrates. Hence, in this research composts were prepared from 15:1, 20:1, and 25:1 C:N substrates, which consisted of PL and YW. The composting process was complete after only four months for the PYC from the 20:1 and 25:1 C:N ratio substrates. Yard waste compost without PL may require somewhere between two to three years for complete composting as opposed to four months with PL addition. The composting was incomplete in four months (presence of undigested leaves and NH₃) for the PYC from the 15:1 C:N ratio substrate. The latter compost resembled poultry manure rather than a high quality compost after the 4-month composting period.