VTechWorks Repository :: Browsing by Author "Wolf, Dale D."

Browsing by Author "Wolf, Dale D."

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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.
Assessment of air pollution impacts on vegetation in South Africa
Botha, Amanda Theophila (Virginia Polytechnic Institute and State University, 1989)
Field surveys and biomonitoring network experiments were conducted in selected areas in South Africa to assess possible air pollution damage to vegetation. During field surveys, atmospheric fluoride was identified as an important pollutant that damaged vegetation in residential areas north of Cape Town. Gaseous air pollutants, including acid deposition and acidic mist, probably play a major role in the development of characteristic air pollution injury symptoms observed on pine trees in the Eastern Transvaal area. The impact of urban air pollution in the Cape Town area was evaluated by exposing bio-indicator plants in a network of eight biomonitoring network stations from June 1985 to May 1988. Sensitive Freesia and Gladiolus cultivars were used to biomonitor atmospheric fluoride, while a green bean cultivar was used as a biomonitor of atmospheric sulphur dioxide and ozone. At one location, bio-indicator plants were simultaneously exposed in a biomonitoring network station (plant cages), open-top chambers (filtered and unfiltered), as well as in open plots. The responses of plants grown under these different conditions were compared. During both the winter and summer seasons, ambient fluoride concentrations were estimated to be particularly high at the Loumar biomonitoring station (eastern side of Cape Town), as compared to that at the other biomonitoring stations. Elevated levels of atmospheric fluoride, as well as sulphur dioxide, appeared to prevail in the vicinity of industries located in the northern suburbs of Cape Town (Bothasig, Table View and Edgemead). Interveinal bleaching, which is characteristic of sulphur dioxide injury, was regularly observed on bean plants exposed at the Bothasig biomonitoring station and was usually determined to be significantly worse at this location than at the other biomonitoring stations. These results were confirmed by the evaluation of foliar sulphur content Ambient pollutant concentrations appeared to be effectively reduced inside filtered open-top chambers, as exemplified by higher biomass production and lower foliar fluoride and sulphur levels in the relevant bio-indicator species, compared to that of plants grown in the open plots. The methodology used during this research provided baseline data of the impact of air pollution on vegetation in South Africa which, in the absence of networks of sophisticated state of the art equipment, can be applied to aid in air pollution control strategies.
Canopy light environment influences apple leaf physiology and fruit quality
Campbell, Richard J. (Virginia Tech, 1991-04-11)
Several experiments were conducted to determine: the influence of canopy position, girdling, and defoliation on nectar production; whether instantaneous light measurements yield reliable estimates of cumulative seasonal light levels within the canopy; and the effect of the canopy light environment on spur leaf physiology and fruit quality. Defoliation of nongirdled flowering spurs had no effect on nectar production or composition, while defoliation of girdled spurs induced nectar sugar concentration by 24%. Canopy position had no influence on nectar production or composition. At full bloom there were differences in photosynthetic potential of spur leaves from different canopy positions. Exterior leaves had a greater maximum photosynthetic rate and an unique photosynthetic light response curve compared to the intermediate and interior leaves. Differences among positions persisted throughout the season. Stomatal conductance, specific leaf weight, dark respiration, and light levels were greater for the exterior leaves throughout the season. Instantaneous light measurements made on a single uniformly overcast day after the canopy was fully-developed (average of four times during the day) provided reliable estimates (predictive R2 > 0.90, n = 30) of total cumulative seasonal photosynthetic photon density (PPD). There was a I-to-l relationship between instantaneous and cumulative PPD after canopy development was complete providing both measures were expressed as a percentage. The relationships were equal over multiple dates for two consecutive years. Cloudless conditions provided poor estimates (predictive R2 = 0.49 to 0.80, n = 30). Light environment and harvest date influenced fruit quality characteristics within the canopy. Fruit red color, intensity of red color, and soluble solids concentration were all positively related to light level, with the highest R 2 on the early harvest dates. Fruit weight, firmness, length/ diameter ratio, starch index, and seed number were not consistently influenced by the light environment. The number of hours above an average photosynthetic photon flux density threshold of 250 I-£mol. m-2• sec'! explained slightly more of the variation in fruit quality characteristics than any other expressions of light.
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.
Controlled Grazing of Virginia's Pastures
White, Harlan E.; Wolf, Dale D. (Virginia Cooperative Extension, 2009)
A primary goal of livestock producers should be to utilize grazed forage for as many months of the year as possible while minimizing the need for stored feed.
Conversion of Sericea Lespedeza-dominant Vegetation to Quality Forages for Livestock Use
Wolf, Dale D.; Fike, John H.; Zipper, Carl E. (Virginia Cooperative Extension, 2010-09-01)
The purpose of this publication is to describe recommended strategies for converting the sericea-dominant vegetation typically found on older surface-mined benches to more favorable forages that can be more effectively utilized by livestock.
Conversion of Sericea Lespedeza-Dominant Vegetation to Quality Forages for Livestock Use
Wolf, Dale D.; Fike, John H.; Zipper, Carl E. (Virginia Cooperative Extension, 2018-03-15)
Discusses sericea lespedeza as a reclamation species for strip mines. Also discusses a two-year program for suppression of this species and the introduction of an improved pasture species mix.
Environmental influence on postemergence chemical control of crabgrass (Digitaria spp.) in turf
Chism, William John (Virginia Tech, 1990-05-16)
The influence of environment on efficacy of postemergence herbicides was quantified. A three-fold approach included: first, use of field test sites to select an herbicide sensitive to environmental conditions; second, quantify herbicide responses to temperature, moisture, and morphological conditions; and third, conduct laboratory research to determine if differential uptake, translocation, or metabolism would account for these responses to the environment. Section one of the research was designed to determine if field research can be used to detect herbicides sensitive to environmental influences. Herbicides compared were: imazaquin, BAS 514 and tridiphane to fenoxaprop-ethyl (the cool-season herbicide standard) for postemergence control of large crabgrass (Digitaria sanguinalis) in Kentucky bluegrass (Poa pratensis) and bermudagrass (Cynodon dactylon) turf. BAS 514 was significantly influenced by variable environment. Section two of the research studied control of southern crabgrass (Digitaria ciliaris) by BAS 514 as influenced by morphological and physiological factors. BAS 514 efficacy was influenced by crabgrass growth stage, air temperature, and irrigation level. Flowering crabgrass plants were the most tolerant, while preemergence and true-leaf stages were the most sensitive. Plants held at soil moisture levels near saturation and 25° C were the most sensitive to BAS 514. BAS 514 was not effective against plants grown at low moisture levels and 15° or 35° C. Section three of the research compared the uptake, distribution, and metabolism of ¹⁴C BAS 514 in southern crabgrass and Kentucky bluegrass plants, a sensitive and non-sensitive species. Foliar applied BAS 514 was rapidly absorbed by both species. Uptake and partitioning was similar in both species from 0.5 to 32 h, but different at 128 h, with bluegrass more uniformly distributing the herbicide. Metabolism of BAS 514 was low with only 3% metabolism in both species. Uptake, distribution, and metabolism apparently are not involved in differential sensitivity to BAS 514. Field research can be used to select an herbicide sensitive to environmental influences. Temperature and soil moisture influenced the herbicidal activity of BAS 514. Uptake, translocation and metabolism did not appear to influence selectivity of this herbicide.
Establishing and Managing Caucasian Bluestem
Wolf, Dale D.; White, Richard S.; Tinsley, Spencer Eugene, 1944- (Virginia Cooperative Extension, 2009)
Grazing warm-season forage grasses such as Caucasian bluestem shows promise for filling the production gap in June through September.
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.
Fall harvest management of alfalfa
Edmisten, Keith Lynn (Virginia Polytechnic Institute and State University, 1987)
Alfalfa (Medicago sativa L.) harvest schedules are often interrupted by rainfall, unfavorable environmental conditions for growth, and unfavorable weather for hay curing. Interruptions in alfalfa harvest schedules can delay the final harvest until dates considered critical to winter survival. Harvests made between 20 September and 30 October are considered detrimental to the persistence of alfalfa stands in geographical areas such as western Virginia. The objectives of this study were to determine if a critical period for fall harvest management actually exists in Virginia, if length of the growth period prior to fall harvest (GPPFH) influences plant persistence and succeeding spring yields, and if photosynthesis offsets respiration and allows more flexible fall harvest management than is currently recommended. Final alfalfa harvests were made 10, 20, or 30 September or 10, 20, or 30 October for 2 years in two identical experiments. Alfalfa was managed to achieve 30, 40, 50, or 60 days of growth prior to each fall harvest date. Total nonstructural carbohydrates (TNC) in tap roots and population of surviving plants were determined in December and March. Succeeding spring yields were measured in May. Zero, 45, and 60 percent shade were imposed following four fall harvest dates in a supplemental study to investigate the influence of photosynthesis on TNC levels and plant persistence. In the supplemental study, CO₂ exchange and TNC were measured at 2 week intervals in the fall following four fall harvest dates. Harvests made during the fall period previously considered as critical did not cause over-wintering plant losses. Length of growth period prior to fall harvests was more important than date of fall harvest in making management decisions for fall harvest. Although spring yield generally increased with length of GPPFH, the spring growth appeared healthy; so one might expect a few days of delay prior to the first spring harvest to eliminate any detrimental influence of short length of GPPFH. Succeeding spring yields and TNC levels were generally high for the 50-day GPPFH, and fall harvest yield offset any reductions in spring yield observed in this study. In addition, fall harvests made with a 50-day GPPFH maintained quality and leafiness as opposed to a 60-day GPPFH. Fall regrowth and plant maintenance were not dependent on root TNC accumulation. Photosynthesis offset TNC losses for regrowth and maintenance during the fall. High photosynthetic rates as compared to respiration occurred because temperatures were within the optimum range for photosynthesis of alfalfa during 68% of the daylight hours from September through November. There was no critical period for fall harvest management with the environmental conditions experienced during this study. A 50 or 60-day GPPFH prior to fall harvest was adequate for plant persistence and high succeeding spring yields.
Field evaluation of the northern bobwhite habitat suitability index model with implications for the conservation reserve program
Tonkovich, Michael J. (Virginia Tech, 1995-07-01)
A field evaluation of a modified version of the northern bobwhite (Colinus virginianus) Habitat Suitability Index (HSI) model was conducted using habitat and relative abundance data from 121 sites distributed throughout Halifax County, Virginia, 1986-1991. Model output and the index of relative abundance were only poorly correlated (r_s = 0.09, P = 0.31, n = 121). The model identified winter food as the limiting factor at 115 of the 121 sites. However, the Composition Suitability Index for the equivalent percent of the station providing winter food in optimum condition and the performance measure were not correlated (r_s = 0.09, P = 0.33, n = 121). Population performance at 49 of the 115 sites exceeded levels indicated by the model. Attempts to improve the fit of the model focused initially on the winter food component of the model. Attempts to improve the fit of the model by considering alternative food sources, the role of habitat interspersion, the individual variable Suitability Index curves, and a reassessment of the contribution of crop fields to the estimate of available winter food were unsuccessful. Quail appeared to be nest/brood habitat rather food limited. The index of quail abundance and the estimate of available nest/brood habitat were correlated positively (r_s = 0.55, P< 0.001, n = 121). Winter habitat use within the covey home range was evaluated January through April of 1990 and 1991 by comparing micro-habitat conditions at used and unused sites within the home range. Two different statistical treatments (regression and signed-rank) were used to determine if preferential habitat use was occurring. Whereas the signed rank test yielded significant (P = 0.04) results for only 1 of 7 micro-habitat parameters, results from the regression analyses were all significant (P < 0.05), indicating disproportional use of habitat characteristics. The potential effect of the Conservation Reserve Program (CRP) on northern bobwhite populations was evaluated by comparing nest/brood habitat conditions in crop and 4 CRP field types including CP1, CP3 < 8 yr, CP3 > 8 yr, and CP3 fields receiving some level of commercial thinning. Short-term effects are likely to be positive. Both CP1 and CP3 field types should provide more suitable nest/brood habitat conditions than crop fields. Long-term effects of the CRP on northern bobwhite are likely to be negative. Conservation Reserve fields with pines (CP3) > 8 yrs old provided virtually no nest/brood habitat. Commercial thinning did not appear to have a positive impact on habitat conditions.
Flue-cured tobacco: alternative management systems
Clarke, C. Taylor Jr. (Virginia Tech, 1996-05-05)
The United States share of the exported flue-cured tobacco market has decreased over the last decade as other countries have increased production of improved quality tobacco. Such tobacco is available at a substantially lower price than U. S. tobacco and thus desirable for the manufacture of less expensive discount cigarettes. Although world consumption of American style cigarettes is increasing, demand is not sufficient to maintain current production levels of premium quality U. S. flue-cured tobacco. Production systems that increase yields of suitable quality tobacco for discount cigarette manufacture without increasing production costs would allow tobacco to be offered competitively on the world market while maintaining current income. A study of ten management systems was conducted evaluating the influence of plant spacing, topping height, and harvest method on yield and quality of flue-cured tobacco. Leaf populations of 538,000/ha harvested once-over resulted in a 6.5%, 11.0%, 6.0%, and 13.5% increase in yield, value, price, and grade index, respectively, compared to the standard treatment. An expert panel showed no preference among systems and judged all systems acceptable in quality. A study conducted as a randomized complete block in a split plot arrangement evaluated the influence of row spacing and plant spacing on the yield and quality of flue-cured tobacco harvested once-over. Yield, value, and grade index increased while price per kg was unchanged as plant population increased. Flue-cured tobacco harvested in a single harvest produced cured leaf of acceptable quality; however, increased leaf populations are required to maintain acceptable yields.
Grain Sorghum Field Emergence and Seed Vigor Tests
Detoni, Cezar Ernesto (Virginia Tech, 1997-06-30)
Poor emergence of sorghum [(Sorghum bicolor (L) Moench] affects the stand and potential yields. The major objective of this research was to find correlations among field emergence data and laboratory seed vigor tests. Thirty-two and 30 hybrids of sorghum were planted at three Virginia locations in 1995 and 1996, respectively. Field emergence was subsequently compared with results from laboratory tests that included: 1) standard germination; 2) osmotic-stress using polyethylene glycol 8000 (mw); 3) heat-shock using 2 hr at 50°C stress; 4) electrical conductivity of steep water of germinating seeds; and 5) seed mass. Field emergence of grain sorghum differed among hybrids, years and locations. Mean emergence across years and locations was 67.5%, whereas mean germination in the laboratory was 87.8%. There were interaction between hybrid and location and between hybrid and year. Germination under optimal conditions (standard germination test) and with osmotic or heat-shock stress differed among hybrids. Regression analyses showed a weak correlation between laboratory germination (with or without stress) and field emergence in both years. The fresh weight of seedlings whether from standard germination or stress tests also differed among hybrids in both years, and the associations with field emergence were weakly correlated in 1996. Hybrids showed significant differences in radicle length when grown under laboratory stress in both years following standard germination. There was a weak correlation with field emergence and radicle length following heat-shock treatment in 1996. The measurement of electrical conductivity in the seed steep water showed significant differences among hybrids. A weak correlation with field emergence was seen in 1996. Conductivity values per gram of seed and per cm² of seed area revealed differences among hybrids. The correlation of these parameters with field emergence was higher than conductivity per seed. Seed mass varied among hybrids in both years , but was no correlation between seed mass and emergence. Of the laboratory parameters examined, germination proved to be the most consistent predictor of variations in field emergence of sorghum hybrids.
Influence of Acremonium coenophialum on Festuca arundinacea growth, chemical composition, digestibility and tall fescue toxicosis
Buttrey, Sherri A. (Virginia Polytechnic Institute and State University, 1989)
Infection of tall fescue (Festuca arundinacea Schreb.) with the endophyte fungus (Acremonium coenophialum, Morgan-Jones and Gam) has been associated with toxicity symptoms observed in cattle. The overall objective was to investigate the influence of endophyte infection on growth and chemical composition of tall fescue and the toxicity of endophyte-infected (EI) tall fescue to cattle. In a greenhouse study with pairs of genetically identical EI and non-infected (NI) ‘Kenhy’ tall fescue clones, concentration of N, Ca, Mg, Al, B, Mn and Zn was higher and K and S was lower in NI, compared to EI tall fescue. Insect resistance was higher in EI, compared to NI. Yield and chemical composition of high and low EI tall fescue were measured at four growth stages (stockpiled, prebloom, bloom and regrowth after harvest at bloom), two sites (Glade Spring and Blackstone) and three rates of N fertilization (0, 40 and 80 kg/ha) in a field study. Tall fescue grown at Glade Spring was higher in N, Mg, Al, Cu, Fe and Mn, compared to Blackstone. Nitrogen fertilization increased N, Mg, Ca, B, Cu, Na, Zn and decreased NDF, ADF, cellulose, P and S concentration in tall fescue. Neutral detergent fiber, ADF, cellulose, lignin, Fe and Na were higher in low, compared to high EI tall fescue. Concentrations of Cu, Na and Zn in stockpiled and Ca, Cu, Na and Zn in bloom-cut tall fescue hay were below dietary requirements for 227-kg steers. A disc meter was also evaluated for use in predicting yield of tall fescue. The meter is useful for non-destructive estimation of yield. Three feeding studies were conducted with steers (6/treatment/year). Diets were orchardgrass/alfalfa hay, spring-cut EI tall fescue hay, spring-cut EI tall fescue silage and fall-cut EI tall fescue silage. Serum prolactin and cholesterol were depressed in steers fed fescue hay and silages, compared to steers fed orchardgrass/alfalfa hay. Differences in mineral composition of hay and silage were reflected in serum minerals in steers. Ergopeptine alkaloids in EI tall fescue may have contributed to the depression of serum prolactin. The spring-cut silage contained the highest concentration of ergopeptine alkaloids, compared to other diets. Steers fed the spring-cut tall fescue silage had the lowest basal and thyrotropin-releasing hormone stimulated prolactin compared to steers fed the other diets.
Influence of nitrogen rate, harvest frequency, lower leaf management, and chemical topping on mammoth cultivars of flue-cured tobacco
Long, Robert Sherman (Virginia Tech, 1989-05-15)
Mammoth cultivars of tobacco do not flower under normal production conditions. A field management system must be devised for these cultivars to optimize agronomic traits and chemical constituents of the cured leaf. Field experiments were conducted at the Southern Piedmont Agricultural Experiment Station near Blackstone, Virginia in 1987 and 1988 to determine the influence of nitrogen rate, harvest frequency, and time and number of basal leaf removal on several agronomic and chemical properties of a mammoth cultivar of flue-cured tobacco. The feasibility of chemically topping two mammoth cultivars was also investigated. Increasing nitrogen rates increased values per hectere by $176 and total alkaloids by 0.5% in 1987. Increasing the number of harvest increased percentage lugs (X) and reducing sugars for stalk position B in 1988 but decreased reducing sugars for stalk positions A and C in 1988. Delaying leaf removal increased yield and values per hectare by 141 kg ha⁻¹ and $84, respectively, and decreased lug production in 1987 and 1988. Total alkaloids decreased by 0.7% with delayed leaf removal in 1987. Delayed leaf removal increased reducing sugars at stalk position A by 2% in 1988. Removing fewer basal leaves increased yields by 115 kg ha⁻¹, values per hectare, and percentage smoking leaf (H) for both years. Alkaloids for stalk position B increased with fewer basal leaves removed in 1988. Decreased basal leaf removal decreased plant height by 9 cm, percentage leaf (B), and reducing sugars in stalk positions A, B, and D in 1988. Delaying basal leaf removal and decreasing harvest frequency increased the percentage of cutters (C). Percentage smoking leaf increased with nitrogen rate and removal of fewer basal leaves. Chemical topping created taller plants with more leaves, narrower tip leaves, lower total alkaloids, and equal or higher reducing sugars relative to hand topping. Tip leaves from chemically topped plants were 6 to 8 cm shorter than hand-topped plants in 1987. Maleic hydrazide treatments resulted in 429 to 700 kg ha⁻¹ lower yields and lower values than hand topping and 6 more suckers than all other treatments. The fatty alcohol / maleic hydrazide treatment produced 380 kg ha⁻¹ higher yields and grade indices lower than the hand-topped control in 1987. Above normal nitrogen rate, 3 or 5 time harvest, removal of 4 to 6 leaves at topping or via senescence, and chemical topping with Prime+ or fatty alcohol / maleic hydrazide tank mix provided the best field management system for mammoth cultivars under the conditions of this study.
Moisture stress conditioning, potassium nutrition, and tolerance of Salvia splendens 'Bonfire' to moisture stress
Eakes, Donald Joseph (Virginia Polytechnic Institute and State University, 1989)
The objective of this study was to determine the leaf water relations, gas exchange, and growth of the bedding plant salvia Salvia splendens 'Bonfire‘ as influenced by moisture stress conditioning (MSC - exposing plants to 4 sublethal dry-down cycles) and potassium (K) nutrition. Plants were fertilized with one of six K rates: 25, 75, 150, 300, 450, and 600 ppm as KCl in experiment one. Seven weeks after seeding plants were subjected to MSC. MSC and increasing K rate resulted in osmotic adjustment and increased cellular turgor potentials. Foliar K content increased as osmotic potentials decreased due to treatment. Although there was no interaction, MSC and high K rates both reduced transpiration (E), leaf conductance (g₁), and daily gravimetric water loss during well watered conditions. Greatest shoot dry weight occurred for plants grown with 300 ppm K and no-MSC. Gas exchange of salvia as influenced by MSC during the onset of moisture stress was determined in experiment two. On day one following final irrigation, MSC plants had lower mid-day E, g₁, hourly gravimetric water loss per unit leaf area, and net photosynthesis (Pn) compared to controls, despite no differences in leaf water potential (ψ₁). Percentage of stomatal inhibition of Pn (SI) was greater for MSC plants than controls with no differences in mesophyllic resistance to CO₂ (r_m). On day two, MSC plants had greater Pn, E, g₁, and hourly gravimetric water loss per unit leaf area, while SI and r_m were lower than controls. MSC plants maintained positive Pn rates and turgor to lower ψ₁ than control plants. Water use efficiency (WUE) estimates for MSC plants were greater than for controls. Salvia plants were fertilized with 75, 300, or 600 ppm K to determine the influence of K rate on gas exchange during the onset of moisture stress in a third experiment. On day one following final irrigation, plants grown with K rates of 300 and 600 ppm had lower E, g₁, hourly gravimetric water loss per unit leaf area, and Pn compared to 75 ppm K plants. On day two, 600 ppm K plants had greater Pn, E, and g₁ as the experiment was terminated compared to plants grown with 75 ppm K, although ψ₁ was similar. Potassium rate had little affect on WUE.
Multiple stresses by insect and plant-competition on growth and productivity of Canada thistle
Ang, Ban-Na (Virginia Tech, 1992-08-04)
Canada thistle is an aggressive perennial weed throughout temperate areas for both the northern and southern hemisphere. As various single tactics have shown limited success in controlling this weed, I believe that a combination of different stress factors is necessary for effective sustainable control of Canada thistle. This study evaluates the competitive abilities of tall fescue grass and crownvetch in conjunction with a thistle feeding insect for Canada thistle control. The goal of the study was to determine what levels of the herbivore and plant competition are needed to suppress Canada thistle. Field studies were conducted to determine the effects of multiple stresses caused by defoliation and plant competition on growth and survival of Canada thistle (Cirsium arvense Scop.). Plant competition was from a cornbination of tall fescue (Festuca arundinaceae Schreb.) and crownvetch (Coronilla varia L). Artificial defoliation was used to determine the influence of level and frequency of defoliation in combination with plant competition on Canada thistle. The effects of various densities of a defoliator, Cassida rubiginosa (Coleop:Chrysonlelidae), in the presence and absence of plant competition were also determined. A three-season study determined the combined effects of C. rubiginosa and plant competitors at various densities on the growth and productivity of Canada thistle plantings of various ages.
Nitrification inhibition by metalaxyl as influenced by pH, temperature, and moisture content in three soils
Moore, J. Michael (Virginia Polytechnic Institute and State University, 1989)
Metalaxyl, [N—(2,6-Dimethylphenyl)-N-(Methoxyacetyl)-alanine methyl ester], is used extensively in tobacco (Nicotiana tabacum L.) production for prevention of black shank (Phytophthora parasitica Dast. var. nicotianae), blue mold (Peronospora tabacina Adam), and damping-off (Pythigm spp.). Metalaxyl is also patented as a nitrification inhibitor, although not marketed for that purpose. Proper maturity and ripening of flue-cured tobacco depends on an adequate supply of N through the time of removal of the inflorescence, with a declining supply of N from that point. Use of a chemical which might prolong the availability of N in tobacco could delay maturity and reduce the quality of the cured leaf. These studies were conducted to determine whether metalaxyl might inhibit nitrification under a broad range of soil physical and environmental conditions prevalent in the tobacco producing areas of Virginia. The influence of soil type, soil pH, soil temperature, and soil moisture on inhibition of nitrification by metalaxyl (1 mg kg⁻¹) were investigated in three soils used extensively for tobacco production. Soils used in the study were Cecil sandy loam (clayey, kaolinitic, thermic Typic Hapludult), Appomattox fine sandy loam (clayey, mixed, thermic Typic Kandhapludult), and Mattoponi sandy loam (clayey, mixed, thermic Typic Hapludult). Metalaxyl did not inhibit nitrification under any of the conditions studied. However, NO₂⁻ accumulation with metalaxyl was sometimes greater than the control, especially at high pH (7.0) in the Cecil and Appomattox soils, and at 10 and 20°C. Nitrite and NO₃⁻ accumulations from four rates of metalaxyl (1, 5, 25, and 125 mg kg⁻¹) were compared with those of an untreated control and a nitrapyrin standard over a seven week soil incubation period in further studies using the same soils and adjusted pH levels. Significant NO₂⁻ accumulation occurred during the first week after treatment at high pH in all soil types, with 5, 25, and 125 mg kg⁻¹ metalaxyl. Only the 125 mg kg⁻¹ metalaxyl treatment caused NO₂⁻ accumulation at the high pH in all soils beyond the second week after treatment, with the peak occurring in most cases between weeks three and four. Nitrate accumulation proceeded normally in all soil types and pH levels except with treatments of 25 and 125 mg kg". Nitrate accumulations with 25 mg kg⁻¹ were similar to those for nitrapyrin. The 125 mg kg⁻¹ rate was consistent in causing near total inhibition of NO₃⁻ accumulation at all pH levels in all soils. Nitrate accumulation tended to be lower at lower soil pH levels compared to the highest pH for all soils. Little difference in nitrification due to soil appears to be evident. Use of metalaxyl at recommended rates of 0.25 to 1.5 mg kg⁻¹ would not be expected to inhibit nitrification.

Browsing by Author "Wolf, Dale D."

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