Doctoral Dissertations

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Acidity of certain Virginia soils as related to their mineralogy and chemistry
Dewan, Hari Chand (Virginia Polytechnic Institute, 1965)
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.
Alteration of dioctahedral micas in soils
Cook, M. G. (Virginia Polytechnic Institute, 1961)
Artificial and natural weathering studies were conducted on four dioctahedral micas found in soil parent material of the Virginia Piedmont. Emphasis was given to the relationship between loss of K (also Na in certain cases), increase in CEC, and expansion characteristics. Boiling treatments with several different solutions were used to promote artificial weathering. In terms of the three parameters of primary interest, the results were of three general types, depending upon the nature of the boiling medium. Boiling solutions of HCl and HOAc removed K and Na, but produced only slight expansion and a negligible increase in CEC. The acid solutions, being at low pH, liberated from the mineral large amounts of Al, which likely underwent hydrolysis later to form hydroxy-Al polymeric groups. These groups can occupy exchange sites, but they remain nonexchangeable. Boiling aalt solutions of NaCl and MgCl₂ removed K and Na in large amounts, produced considerable, but only a slight increase in CEC resulted. The explanation for the small increase in CEC was believed to be due also to blocking of exchange sites by nonexchangeable hydroxy-Al groups, because salts tend to accelerate the hydrolysis reaction. A boiling Na-citrate solution removed K effectively, produced marked expansion, and caused a large increase in CEC. Citrate complexes Al, which probably accounted for the high CEC. When a sample was treated with hot HCl prior to Na-citrate boiling, the loss of K and increase in CEC was stoichiometric. The equivalence was attributed to the removal of amorphous material by HCl and complexing of Al by Na-citrate. Vermiculite and kaolinite were the natural weathering products of the dioctahedral micas studies. There was a striking similarity between the artificially-produced vermiculite and that occurring under natural conditions. The product formed under both circumstances expanded to approximate 14 A. when glycerol-solvated and contracted to 10 A. upon K-saturation and heating. Although the artificial weathering media were not representative of natural weathering conditions, the basic mechanism of mica alteration apparently was similar. The soil micas altered easily in the laboratory compared to an Ontario muscovite. Thus, it was concluded that soil micas are quite different from the specimen-type micas. They may possess a lower charge or lack the structural control of specimen muscovites. The difference in ease of weathers between dioctahedral and trioctahedral micas likely is attributable to the difference in chemical composition, especially in the octahedral layer. Dioctahedral micas appear to be more strongly bonded than trioctahedral micas as a result of the higher-charged Al⁺⁺⁺ ion in the octahedral layer. This stronger bonding would tend to restrict initial alteration. Subsequent alteration also would be hindered because, as weathering proceeds, greater hydrolysis of Al in dioctahedral micas would result in more fixation of positively-charged hydroxy-Al polymers in the interlayer position. This fixed Al inhibits expansion of dioctahedral micas. In trioctahedral micas, which contain Fe and/or Mg, this type of fixation does not occur during acidic weathering. A significant finding was the occurrence of paragonite, the Na analogue of muscovite, in intimate association with muscovite. A relatively constant Na/K molar ratio of approximately one was maintained in both the parent rocks and soils. This indicated that equal molar quantities of paragonite and muscovite were present and that weathering of the two micas was similar. Paragonite is believed to be more widespread occurrence than previous work has indicated. Its influence on soil genesis, morphology, and classification may be significant.
An approach to studying soil-landscape relationships in Virginia
Stolt, 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 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.
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.
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.
Canopy, microenvironment, and nitrogen effects on summer recovery of tall fescue
Stringer, William C. (Virginia Tech, 1977-07-05)
Stand losses in temperate grasses after summer defoliation of tall canopies inspired an investigation of microenvironmental and plant responses in tall fescue. Microenvironment and regrowth of tall fescue in response to mowing managements and nitrogen rates in spring that created different canopy structures was studied. In early spring, 50 and 160 kg/ha of N were applied. Mowing managements were: clipping at 4 or 8 cm biweekly, monthly, and in late June. In late June all 6 treatments were mowed to prescribed stubble heights with a seventh unmowed check. Canopy light regimes, leaf area index, and regrowth of tillers were monitored along with soil, fair, and shoot temperatures in stubbles after the June harvest. Mowing more frequently in spring decreased canopy yields of the June harvest, but increased leaf area (LAI) of stubbles as compared to spring-accumulated canopies. High nitrogen decreased specific leaf weights (SLW) in stubble leaves and increased LAI except in spring-accumulated canopies. Increased LAI decreased light penetration and canopy temperatures. Temperatures were highest in harvested spring-accumulated stubbles with a shift of 4-10 C between unharvested and harvested stands while radiation penetration into the stubble increased from 5 to 75% of total. Some large stand losses occurred in lodged portions of harvested Spring-accumulated plots. Generally, regrowth yields were not affected by prior clipping managements. Concentration of TNC was uniformly high with all treatments.
Characterization of delayed flowering in soybean in Virginia
Abeysiriwardena, D. S. de Z. (Virginia Tech, 1990-12-13)
Delayed flowering has the potential to overcome the problem of restricted vegetative growth, prior to flowering, that is often associated with double-cropped soybeans [Grycine max (L.) Merr.]. Objectives were to study delayed flowering in soybeans as influenced by date of planting, to estimate the lengths of the component vegetative periods in soybeans under short-day conditions, and to study the mode of inheritance of delayed flowering in soybeans. Date of planting experiments conducted in the field at two Virginia locations using 27 cultivars and breeding lines showed that genotypic differences exist for delayed flowering, especially between delayed and normal flowering isolines. Lengths of the juvenile and inductive periods were estimated for some selected early and late flowering genotypes. F85-84l7 had a longer juvenile period, and F85-1226 had both longer juvenile and inductive periods than their respective early flowering isolines and cultivar Essex. cultivar. The method of moving plants from inductive short-days to long-days, which has been used to estimate the length of inductive period, was adapted to estimate the length of the juvenile period as well. Delayed flowering in soybeans appeared to be controlled by two loci, each with two alleles, and delayed flowering appeared to be recessive. Anyone of the genes in the homozygous recessive state delayed flowering. F85-1226 may be segregating for both genes while F85-84l7 appeared to contain only one.
Chemisorption of ammoniacal nitrogen by clays
Du Plessis, Marius Charles François (Virginia Polytechnic Institute, 1962)
A desorption technique was employed to evaluate chemisorption of ammonia by clays under moist conditions. In equilibria involving ammonia, all factors favoring volatilization losses of gaseous ammonia would undoubtedly exert an influence on the ultimate equilibria which are reached. Investigation of the relationship between pH and ammonia equilibria in soils revealed that an increase in the concentration of ammonium ions, applied as ammonium sulfate, stimulated ammonia losses from fine-textured soils at pH's ranging from 4.5 to 7.1. Ammonia volatilization was directly related to the initial pH of the soil and increased with an increase in pH. It was postulated that ammonia may be volatilized, even from acid soils, due to the equilibrium NH₄⁺ + OH⁻ ⇌ NH₃ + H₂O. By using initial concentrations of ammonium ions from ammonium sulfate applied, initial pH of an aqueous suspension of the soil and a value K_b = 1.80 x 10⁻⁵, values of ammonia losses were predicted. The linear relationship found between predicted and measured amounts of ammonia losses from acid as well as neutral soils, was interpreted as evidence of the existence of the proposed volatilization mechanism in soils. In attempting to evaluate the characteristics of ammonia retention by homo-ionic bentonites and kaolinites under moist conditions, it was found that base-saturated clays did not chemisorb ammonia in a fashion which could be described by Langmuir's adsorption isotherms. The S-shaped curves did not necessarily reflect polymolecular sorption. In strong contrast, chemisorption of ammonia by Al-saturated clays, followed Langmuir's equation almost perfectly. Evaluation of the inverse values of the differential slopes of two straight line segments obtained in the desorption isotherms corresponded closely to values obtained for the permanent charge (CEC) and the total charge (total CEC) developed at a specific pH higher than 6 respectively. It was shown that if sufficient ammonia is applied, exchangeable Al⁺⁺⁺ of Al-compounds may be precipitated as Al(OH)₃. An attempt to evaluate pseudo-equilibrium constants for aluminum-clay ammonia equilibria by using Langmuir's adsorption equation, was unsatisfactory. Chemical kinetic studies indicated that ammonia volatilization reactions could be described by a fast reaction and a slow reaction. The slow reaction represented chemisorption of ammonia on the permanent charge exchange sites. Extrapolation of the slow reaction to zero time yielded values corresponding closely to the CEC permanent charge. Investigation of the effects of CO₂, the NH₄⁺ concentration is increased, resulting in more effective replacement of basic cations for "permanent charge" exchange spots. The lower pH and higher effective NH₄⁺ concentration resulted in higher retention of NH₄⁺ in Na⁺- and K⁺-clays. The most striking retention of NH₄⁺ was obtained in Mg- and particularly in Ca-bentonites. It is believed that the Ca and Mg ions, exchanged by NH₄⁺ ions, are effectively removed from the soil solution as a result of the precipitation of these compounds which are sufficiently insoluble to ensure conservation of ammonia as chemisorbed ammonium ions.
A comparison of determinate and indeterminate soybean lines for double cropping in Virginia
Pyle, Marjorie Elizabeth (Virginia Polytechnic Institute and State University, 1982)
Forty lines, 20 determinate and 20 indeterminate, from four soybean (Glycine max L. Merrill) crosses were evaluated under full-season and double cropping conditions to compare the performance of the two plant types under both cropping systems. The parents and selected lines were in the range of Maturity Groups IV and V. In 1980, the lines were planted 1 July in a replicated test at Warsaw, VA while in 1981 these lines were planted in three replicated tests on 11 June and 8 July at Warsaw and on 12 June at Orange, VA. Both June plantings were considered full-season. Standard cultivars in 1980 included 'Essex', 'Williams', and 'Crawford'. 'Bay' and 'Will' were added in 1981. Yields were similar in 1980 for both plant types with the determinates yielding 10.1 q/ha and the indeterminates yielding 9.9 q/ha. In 1981, the yields were similar for both types at Orange with the determinates and indeterminates yielding 26.4 and 26.5 respectively. The types were significantly different in the 11 June planting at Warsaw, with yields of 28. 6 and 28. 0 q/ha for the determinate and indeterminate lines, respectively. The opposite was observed for the 8 July planting in which the indeterminates yielded 21.2 q/ha and the determinates yielded 20.8 q/ha. A comparison of the two determinate and indeterminate lines with the highest yields in both 1981 Warsaw plantings showed that indeterminates were more adaptable to double cropping, though high yielding lines of both types were present. The high yielding indeterminates of the 8 July planting had a tendency to be taller and more erect than the determinates, an attribute desirable for double cropping. Lines that were highest yielding in the 11 June planting were ranked lower in the 8 July planting and vice versa. Spearman' s rank correlation for yield in the two Warsaw plantings had a coefficient of 0. 23, indicating a high degree of specific adaptation to the two environments. Selection of better adapted lines for double cropping appears feasible. The indeterminate trait appears to make some contributions to this adaptation.
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.
Corn root growth and distribution as influenced by soil physical properties
Logsdon, Sally D. (Virginia Polytechnic Institute and State University, 1985)
Mechanisms of root growth under variable field conditions were investigated by observing corn ( Zea mays L.) root growth and distribution in the field and by observing the influence of soil physical stresses on corn seedling root growth in controlled environments. The field soil was Groseclose silt loam (clayey, mixed, mesic Typic Hapludult). Groseclose A horizon material was used for the growth chamber experiments where corn was grown in a range of aggregate sizes, bulk densities, low and high soil moisture levels, and temperatures. Rooting patterns in the field were altered by drought. Root length density decreased in the dry surface soil and proliferated in the moist subsurface soil. Distribution of roots length densities was skewed. A few samples contained many roots and many samples contained few roots because roots were restricted to interpedal voids. In the growth chamber experiments, roots were not able to penetrate large aggregates and were restricted to interaggregate zones. This tortuous path of root growth led to transitory impedances as roots were deflected around aggregates. Corn roots were able to push small aggregates out of their path. An equation was developed to describe this impedance as a function of aggregate size, root diameter, and deflection angle. Mechanical impedance, oxygen stress, lower temperatures, and moisture stress reduced seedling root elongation to some extent, but the influence of reduced temperature was the most dramatic. At 6 days corn root length at 21°C was 20% of that at 25°C while root length at 17°C was only 5% of that at 25°C. Mechanical impedance and reduced temperatures also increased root diameter. In wet soil, oxygen stress was the most immediate factor affecting root growth, but after 4 days root elongation was stimulated suggesting other unknown factors. Two semi-empirical models were developed. One was based on the exponential growth rate of the root system and the other based on the linear growth rate of each root member. These models accounted for the reduction in root growth rate due to the soil physical stresses.
Diallel analysis of rind puncture and grain yield and their interactions with plant densities for twelve elite inbred lines of maize, Zea mays L
Perry, Christopher O. (Virginia Polytechnic Institute and State University, 1983)
To better understand the genetics of stalk quality in elite Corn Belt germplasm, combining ability estimates for stalk quality as measured by rind puncture were obtained for twelve inbred lines of maize representing elite Corn Belt germplasm. Secondly, an attempt was made to assess the practical utility of the rind penetrometer as a tool to measure stalk quality in an applied maize breeding program. The twelve inbred lines of maize were crossed in a diallel manner to produce the 66 F₁ single cross hybrids. Hybrids were hand planted in single-row plots with three replications at Holland, Virginia on 10 April and 15 and 16 April, 1981 and 1982, respectively. Plots were comprised of four split-plots corresponding to planting densities of 39,536, 49,420, 59,304 and 69,188 plants per hectare. Rind puncture data were collected from five competitive plants in each density for each hybrid at midsi lk and two to three weeks later. Data were also collected on percent erect plants, stalk pinch values, and grain yield. Analyses of variance were performed on the means for each hybrid-density combination for all traits. Model I, Method 4 of Griffing (1956) was followed to obtain estimates of GCA and SCA effects. Highly significant differences were detected among hybrids and densities for rind puncture and grain yield in both years. Significant differences were also detected among hybrids for percent erect plants and stalk pinch value, although no significant difference among densities was evident. No significant difference was detected between dates of measurement for rind puncture. nents were highly significant for all GCA and SCA compotraits. Hybrid by density interaction was significant for grain yield and percent erect plants but not for rind puncture or stalk pinch. Hybrid by date interaction for rind puncture was highly significant in 1982 only. Considerable additive genetic variation associated with GCA was detected for rind strength as measured by rind puncture in elite Corn Belt germplasm. The rind penetrometer appears to be a useful tool to aid the breeder in identifying genotypes with superior rind strength, which in turn is a component of total stalk strength.
A diallel study of flowering and of ear components of yield in Corn Belt maize and their interactions with population density
McClane, John Michael (Virginia Polytechnic Institute and State University, 1985)
A diallel study of American Corn Belt maize (Zea mays L.) was conducted at Holland, Virginia in 1981 and 1982. All possible crosses of twelve inbred parents (A619, A632, B73, H60, H93, H96, Mo17, Oh7B, Pa91, Val7, Va.79:419, Va85) were planted in three replications with population density treatments of 39,536, 49,420, 59,304, and 69,188 pl/ha in strips across hybrid treatments. Analyses of variance and combining ability analyses were performed on traits measuring the timing of anthesis (pollen shed) and silk emergence, on ear components of yield, and on components of kernel size. Density effects were highly significant for all traits, except for that of pollen shed duration, in the analyses combined over years. Hybrid-by-year interactions were highly significant for all traits. Correlations between GCA effects of grain yield and GCA effects of silking delay (anthesis-to-silking interval), kernels per row on the ear, ear kernel number, and kernel depth[(ear diameter - cob diameter)/2] were -0.79, 0.64, 0.66, and 0.80 in 1981, and 0.24, 0.81, 0.71, and 0.26 in 1982, respectively. Moisture stress sufficient to cause wilting occurred before and during silking in 1981. Apparently, short silking delay was associated with high moisture stress tolerance for grain yield in 1981 and was associated with long ear shoot length in 1982. Deep kernel depth apparently was associated with drought stress tolerance for yield as well. The heritabilities of ear traits were higher the earlier they became established in the sequence of development. Heritabilities of silking delay and most ear components of yield were increased by increasing planting density. However, the correlations among flowering and ear traits largely were unaffected by density, perhaps because densities were not high enough to make barrenness a substantial factor in grain yield. The most important traits related to yield were silking delay, kernels per row, kernel depth, and kernel row number. GCA to SCA variance component ratios were increased by combining data over years and by the more optimum season for yield.
The effect of distance between artificial drainage facilities and disposal trenches on the movement of biological and chemical pollutants from septic tank effluent
Stewart, Larry Wayne (Virginia Polytechnic Institute and State University, 1982)
A field study was conducted at a residence in Chesapeake, Virginia to determine the effect of setback distances from a drainage ditch on the disposal of septic tank effluent. The study was done from September 1979 to August 1981. The soil used is the Tomotley series belonging to the fine-loamy, mixed, thermic family of Typic Ochraquults. Four prototype trenches were installed at 1.5, 3, 6 and 21 m from the edge of a drainage ditch which was 1.5 m deep. The trenches were pressure dosed equally with 2.4 to 4 cm per day. Replicated nests of sampling wells at depths 90, 150 and 300 cm were placed with distance from the trenches. Continuous stage recorders were positioned 4.5, 29.1 and 60 m from the ditch to monitor water table behavior. Groundwater analysis included fecal coliforms, the NH₄, NO₃, NO₂, Na, Ca, Mg, Cl and PO₄ ions, pH and EC. Ammonium concentrations in the soil beneath the trenches indicated nonuniform effluent infiltration yet more uniform than with conventional gravity flow distribution. High sodium absorption ratios of the septic tank effluent ranging from 18 to 45 did not significantly reduce infiltration rates as no ponding of effluent in the trenches was observed. The existing land surface was sloped greater than the water table gradient resulting in decreasing unsaturated depths with closeness to the ditch. The mean distances between the trench bottom and the water table were 64 cm at 3 m, 80.1 at 6 m and 90.4 cm at 21 m. The accumulation of fecal coliforms, NH₄, P, Cl and total salts (EC) in the groundwaters at 120 to 150 cm depth was inversely proportional to the mean distances from the trench bottoms to the water table. The lack of denitrification occurring underneath the trench with the most extensive unsaturated zone suggests NO₃ may accumulate under disposal systems that have mean unsaturated depths of ≥ 90 cm. Effluent movement was mainly lateral and in the upper zone of the water table with limited vertical movement below the water table surface. An equation applying D-F theory to infinitely deep soil was developed to describe flow for the given drainage system and for the inclusion of standard size drain fields. The current practical setback distance of 21 m is considered counterproductive for effluent treatment for some situations.
Erosion control with vegetation in highway corridors
Wright, David (Virginia Polytechnic Institute and State University, 1977)
Grading operations in highway corridors disturb the natural vegetation and land contours, thereby causing erosion and pollution. Minimizing erosion is predicated on the principle of maximizing water infiltration to reduce massive runoff of water. This depends on grading and soil preparation methods, augmented temporarily by mulches, but perfected by developing a vegetative cover quickly. The speed of developing a vegetative cover and shifts in plant biota to persistent covers depend on grading and subsoil preparation, soil amendments, mulches, and specially designed seed mix:tures for seeding at various seasons. The management of these factors, through plant succession, results in persistent vegetative covers of legumes like crownvetch (Coronilla varia L.) or sericea (Lespedeza cuneata G. Don.), requiring little or no mowing or fertilizer maintenance. In difficult environments or in adverse seeding seasons, multi-step seeding and fertilization is usually required. Erosion from slopes with sparse grassy vegetative covers in highway corridors can be minimized or eliminated by overseeding with persistent legumes and the application of needed soil amendments. Topsoiling is not needed nor recommended on properly graded subsoil materials with adequate lime and fertilization, especially when the final botanical component is a persistent legume. Soil moisture was higher and temperatures lower for rough graded subsoil as compared to roughened topsoil, providing a more favorable microenvironment for plant growth with subsoils. Stands and vegetative covers were similar, although weed growth on topsoil materials was more severe than on subsoils. Roughened topsoil or subsoil surfaces sharply enhanced growth and vegetative cover as compared to the smooth topsoil or glazed subsoil. This was attributed to better infiltration and higher soil moisture, allied with improved bulk density and porosity. Twelve species of grasses and legumes were grouped into three categories according to total emergence. Perennial (Lolium perenne L.) and annual (L. multiflorum Lam.) ryegrasses, German millet (Setaria italica L.), redtop (Agrostis alba L.), and Abruzzi rye (Secale cereale L.) had the highest rate and total seedling emergence with maximum emergence obtained by day 6 under favorable moisture conditions. Crownvetch at 21 C, creeping red fescue (Festuca rubra L.), Kentucky bluegrass (Poa pratenses L.), Kentucky 31 fescue (Festuca arundinacea Schreb.), and weeping lovegrass (Eragrostis curvula Schrad. Nees.) at both temperatures. had intermediate rates and total emergence with maximum emergence obtained by day 8. Crownvetch at 28 C and sericea and common bermudagrass (Cynodon dactylon L.) at both temperatures had the slowest rates and least emergence, obtaining maximum emergence between days 10 and 13.
Estimating daily green leaf area index for corn in Virginia
Ebodaghe, Denis Abumere (Virginia Polytechnic Institute and State University, 1986)
A model to predict the daily green leaf area index (GLAI) for corn has been developed for Indiana conditions. Using daily maximum and minimum temperatures the GLAI was predicted for the vegetative stage, reproductive and grain filling stage, and the leaf senescing stage of corn. Predictions of GLAI for corn can be made on a daily basis from the day corn is planted until it is harvested for grain. The GLAI model was tested under Virginia conditions using green leaf area measurements collected from corn plants grown on Davidson silty clay loam, Davidson silty clay, and Mayodan sandy loam soils in the Piedmont region of the State. Maximum and minimum temperature data were also collected at the three sites. Measurements were made for two growing seasons using corn hybrid Pioneer 3369A, three plant population densities and two irrigation schedules. Short duration temperature data were also collected to compare with the daily maximum and minimum temperature data for the Mayodan site. Also a combination of soil temperature at 10 cm depth and air temperatures were used for the temperature functions accumulated from date of planting at the Mayodan site. Results of this study show that the predicted and measured GLAI values compare favorably under irrigated conditions on the Davidson soil. The results were not as favorable on the irrigated corn on the Mayodan soil. When the corn is subjected to severe moisture stress on either soil, GLAI cannot be predicted with this model. Short duration temperature data resulted in a better prediction of GLAI on the Mayodan soil. When applying nitrogen fertilizer to the corn through the irrigation system through the grain filling stage, the measured GLAI values compared favorably with the predicted GLAI values. However, the application of nitrogen and sulfur fertilizer together resulted in GLAI being maintained above that predicted for a longer period of time during the grain filling stage before its decline.
Evaluation of African trifolium species for growth and biological nitrogen fixation
Friedericks, James Bahadur (Virginia Polytechnic Institute and State University, 1989)
Throughout the African highlands forage legumes are relied on to add soil N, support increasing livestock populations, and reduce soil erosion. This research addresses a constraint designated by the International Livestock Center for Africa (ILCA) to identify African clover (Trifolium) germplasm and Rhizobium trifolii strain combinations with high productivity potential for the African highlands. A Vertisol and an Eutric Nitosol (Paleudalf), and seed from Trifolium decorum, T. quartinianum, T. rueppellianum, T. steudneri, and T. tembense were obtained from ILCA in Addis Ababa, Ethiopia. A commercial collection and R. trifolii strains isolated from the Ethiopian soils were evaluated for symbiotic effectiveness with these clovers. Effective combinations were evaluated for growth and biological nitrogen fixation (BNF) in a greenhouse on both soils with limited, adequate, and excessive soil moisture. Rhizobia were also evaluated for survival in desiccated soil (12.5 and 17.5 g H₂O g⁻¹ soil) and for competitive nodule forming ability. Effective strains were found among soil isolates but not in the commercial collection. Highest dry matter yields and total BNF accumulation were obtained from T. tembense on all soil and moisture treatments followed by T. decorum and T. quartinianum. Trifolium rueppellianum and T. steudneri had low yields and BNF capacities. Plants receiving adequate and excessive moisture had higher yields than moisture stressed plants. The highest levels of cumulative BNF were obtained on the nitosol soil with either adequate or limited moisture. The moisture limited vertisol supported the lowest BNF levels. Rhizobial strains survived desiccation only in the vertisol at 17.5 g H₂O g⁻¹ soil. All strains could compete with background rhizobia populations to nodulate host plants. Nodule occupancy rates of 20 to 30% were required for high yields. Trifolium tembense, T. decorum, and T. quartinianum are adapted to soils with adequate or excessive moisture, T. rueppellianum and T. steudneri are suited to moisture limited conditions or short growing seasons. Effective rhizobia inoculants and selected clovers have the potential for increasing forage productivity in highland areas.
Expanding the genetic variability of flatpea using tissue culture, mutagenesis, and intercrossing techniques
Coulombe, Bruce Armand (Virginia Polytechnic Institute and State University, 1988)
Flatpea (Lathyrgs sylvestris L.) is a potentially valuable forage legume but contains high levels of 2,4-diaminobutyric acid (DABA), a compound that can have adverse effects on some animals, including rats and poultry. To increase genetic variability in foliar DABA content and other traits of interest, three approaches were utilized: (1) regeneration of flatpea plants from tissue culture to produce potential somaclonal variants, (2) seed irradiation and screening of potentially mutated progeny, and (3) intercrossing among flatpea accessions. Low-frequency whole plant regeneration of flatpea was obtained from hypocotyl-derived callus cultures. Auxin concentrations above 5.0 µM resulted primarily in root formation without shoots. Conditions for optimum whole plant regeneration were as follows: callus was initiated on a modified Schenk-Hildebrandt low-ammonium medium containing 5.0 µM IAA (indole acetic acid) and 2.5 µM zeatin for callus initiation; after two subcultures, calli were transferred to a regeneration medium containing 0.1 µM IAA and 1.0 µM zeatin. Calli and regenerated root tissue contained 47 and 381 as much DABA as leaf tissue from 'Lathco' flatpea plants, respectively. Initial tests established that the effective range of gamma irradiation for seed treatment was between 10.0 and 17.5 kR. Within this range, reduction in percentage of both seedling height and plant survival was a linear function of dose. Individual M₂ plants that contained reduced levels of DABA were identified. No significant trend in DABA concentration with increasing gamma irradiation was apparent. Flatpea pollination methods were evaluated prior to utilization of intercrossing for inducing genetic variability. Appropriate flower stages for emasculation were determined by in vitro germination of pollen. Lines that produced high numbers of seeds per pollination were identified by crossing in all possible combinations among seven flatpea accessions. Cross-pollinations resulted in significantly higher seed set than selfing. Pollination using caged honeybees was the most efficient method of hybridization. Greater range and coefficient of variation in DABA concentration were observed for flatpea accessions than for intercrossed progeny produced by honeybee pollination.

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