Browsing by Author "Ervin, Erik H."

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    Antioxidant metabolism variation associated with alkali-salt tolerance in thirty switchgrass (Panicum virgatum) lines
    Hu, Guofu; Liu, Yiming; Duo, Tianqi; Zhao, Bingyu Y.; Cui, Guowen; Ji, Jing; Kuang, Xiao; Ervin, Erik H.; Zhang, Xunzhong (PLOS, 2018-06-25)
    Soil salinization is a major factor limiting crop growth and development in many areas. Switchgrass (Panicum virgatum L.) is an important warm-season grass species used for biofuel production. The objective of this study was to investigate antioxidant metabolism, proline, and protein variation associated with alkali-salt tolerance among 30 switchgrass lines and identify metabolic markers for evaluating alkali-salt tolerance of switchgrass lines. The grass lines were transplanted into plastic pots containing fine sand. When the plants reached E5 developmental stage, they were subjected to either alkali-salt stress treatment (150 mM Na+ and pH of 9.5) or control (no alkali-salt stress) for 20 d. The 30 switchgrass lines differed in alkali-salt tolerance as determined by the level of leaf malondialdehyde (MDA), antioxidant enzyme activity [(superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX)], proline and protein. Alkali-salt stress increased MDA, proline, SOD, reduced CAT activity, but its effect on protein and APX varied depending on lines. Wide variations in the five parameters existed among the 30 lines. In general, the lines with higher CAT activity and lower proline content under alkali-salt stress had less MDA, exhibiting better alkali-salt tolerance. Among the five parameters, CAT can be considered as valuable metabolic markers for assessment of switchgrass tolerance to alkali-salt stress.
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    Assessment of drought tolerance of 49 switchgrass (Panicum virgatum) genotypes using physiological and morphological parameters
    Liu, Yiming; Zhang, Xunzhong; Tran, Hong T.; Shan, Liang; Kim, Jeongwoon; Childs, Kevin L.; Ervin, Erik H.; Frazier, Taylor P.; Zhao, Bingyu Y. (2015-09-22)
    Background Switchgrass (Panicum virgatum L.) is a warm-season C4 grass that is a target lignocellulosic biofuel species. In many regions, drought stress is one of the major limiting factors for switchgrass growth. The objective of this study was to evaluate the drought tolerance of 49 switchgrass genotypes. The relative drought stress tolerance was determined based on a set of parameters including plant height, leaf length, leaf width, leaf sheath length, leaf relative water content (RWC), electrolyte leakage (EL), photosynthetic rate (Pn), stomatal conductance (g s), transpiration rate (Tr), intercellular CO2 concentration (Ci), and water use efficiency (WUE). Results SRAP marker analysis determined that the selected 49 switchgrass genotypes represent a diverse genetic pool of switchgrass germplasm. Principal component analysis (PCA) and drought stress indexes (DSI) of each physiological parameter showed significant differences in the drought stress tolerance among the 49 genotypes. Heatmap and PCA data revealed that physiological parameters are more sensitive than morphological parameters in distinguishing the control and drought treatments. Metabolite profiling data found that under drought stress, the five best drought-tolerant genotypes tended to have higher levels of abscisic acid (ABA), spermine, trehalose, and fructose in comparison to the five most drought-sensitive genotypes. Conclusion Based on PCA ranking value, the genotypes TEM-SEC, TEM-LoDorm, BN-13645-64, Alamo, BN-10860-61, BN-12323-69, TEM-SLC, T-2086, T-2100, T-2101, Caddo, and Blackwell-1 had relatively higher ranking values, indicating that they are more tolerant to drought. In contrast, the genotypes Grif Nebraska 28, Grenville-2, Central Iowa Germplasm, Cave-in-Rock, Dacotah, and Nebraska 28 were found to be relatively sensitive to drought stress. By analyzing physiological response parameters and different metabolic profiles, the methods utilized in this study identified drought-tolerant and drought-sensitive switchgrass genotypes. These results provide a foundation for future research directed at understanding the molecular mechanisms underlying switchgrass tolerance to drought.
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    Biosolids as a source of soil conditioning and fertility for turfgrass
    Badzmierowski, Mike J. (Virginia Tech, 2019-11-04)
    Wastewater treatment plants are shifting towards producing exceptional quality (EQ) biosolids to increase recycling rates to land, especially urban areas. Other methods of improving the environmental impact of wastewater treatment includes additions of iron (Fe) to reduce phosphorus (P) concentrations in outgoing treated water and precipitate the P into the biosolids. Proper management of biosolids to rehabilitate anthropogenically disturbed urban soils for improved plant growth and effects on the cycling of nutrients requires further study. Our objectives were: 1) to determine whether various EQ biosolids could be managed to improve degraded soil properties and turfgrass quality while minimizing risk of P loss in a field study; and 2) to use spectral reflectance data to compare relationships of vegetation indices to soil and turfgrass parameters. We found that after an initial lag-time of one year, biosolids amendments increased turfgrass clipping biomass and aesthetic quality greater than did synthetic fertilizer. Repeated topdressing applications of biosolids reduced soil bulk density and increased soil organic carbon (OC) and nitrogen (N) stocks. Biosolids applied at the agronomic N rate did not increase water-soluble P (15 and 18 mg P kg-1 of soil) compared to biosolids applied at the agronomic P rate (9.6 mg P kg-1 of soil) and synthetic fertilizer (13 mg P kg-1 of soil) after five years. We further demonstrated at this field site that collecting continuous data improves spectral reflectance vegetation indices relationships to turfgrass quality, clipping biomass, and tissue N accumulation. Soil volumetric water content was best correlated to the water band index (r = 0.60) and the green-to-red ratio index (r = 0.54) vegetation indices. Differences in soil and turfgrass measured parameters were best detected when there was drought-stressed versus irrigated turfgrass.
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    Chemical and biological control of silvery threadmoss on creeping bentgrass putting greens
    Post, Angela R. (Virginia Tech, 2013-07-31)
    Silvery threadmoss is a problematic weed of golf putting greens, growing interspersed with turf, decreasing aesthetic quality and playability.  Moss is typically controlled postemergence and currently only one herbicide, carfentrazone, is registered for silvery threadmoss control on greens.  Carfentrazone controls moss up to 75% applied at a three week interval throughout the growing season.  Alternatives providing longer residual or more effective control are desirable.  Studies were conducted to examine the growth of moss gametophytes from spores and bulbils and to evaluate turf protection products for pre and postemergence moss control.  Moss gametophytes develop best from spores at 30"aC and from bulbils at 23"aC.  Products which control moss equivalent to carfentrazone (>70%) both pre and postemergent include sulfentrazone, saflufenacil, flumioxazin, oxadiazon, and oxyfluorfen.  Fosamine and fosetyl-Al alone controlled moss equivalent to carfentrazone post-, but not preemergent.  14C glyphosate absorption and translocation through moss colonies was examined from 12 to 192 hours after treatment (HAT) to understand how herbicides are absorbed by silvery threadmoss.  It appears that 14C reaches equilibrium by 24 HAT in capillary water of the moss colony and inside moss tissues.  Subsequently, 14C is lost to the system presumably through microorganism degradation of 14C glyphosate in capillary water.  The final objective of this work was to identify and evaluate two fungal organisms observed to cause disease of silvery threadmoss on putting greens in efforts to develop a biological control.  The organisms were identified by morphology and ITS sequence as Alternaria sp. and Sclerotium rolfsii.  Alternaria sp. causes a leaf disease of silvery threadmoss and Sclerotium rolfsii causes Southern blight of silvery threadmoss.  Host specificity testing demonstrated moderate pathogenicity of S. rolfsii to annual bluegrass but not to "¥Penn A4"" creeping bentgrass.  Both organisms have potential to be effective biological controls for silvery threadmoss; however, host specificity indicates Alternaria sp. may be a better choice.  Data from these experiments suggest herbicides in two chemical classes control mosses both pre and postemergence, and sulfentrazone, fosetyl-Al, and Alternaria sp. may be new alternatives to carfentrazone for use on golf putting greens.  
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    Controlling Growth in Echinacea Hybrids
    Grossman, Mara Celeste (Virginia Tech, 2017-05-02)
    New hybrid Echinacea cultivars, based on crosses of Echinacea purpurea (L.) Moench with several other Echinacea species, have generated interest and excitement in the marketplace due to novel flower colors and forms. However, these cultivars vary significantly in their growth habits and requirements from the species. We examined factors in the production of Echinacea hybrid cultivars to provide guidance to growers. Foliar sprays 600 mg·L⁻¹ benzyladenine (BA) increased numbers of branches between 19% and 83% in Echinacea cultivars while 400 mg·L⁻¹ dikegulac sodium or 500 mg·L⁻¹ ethephon did not improve branching. Of several height control PGRs applied to E. ‘Marmalade,’ only plants treated with two applications of 5000 mg·L⁻¹ daminozide were shorter (24%) compared to untreated controls although flowering was also reduced by 70%. Echinacea ‘Harvest Moon’ plants were shorter in response to all of the PGRs applied, with the best results seen in plants treated with foliar sprays of uniconazole (one application of 30 mg·L⁻¹ or two applications of 15 mg·L⁻¹ ), two applications of 5000 mg·L⁻¹ daminozide, or 4 mg·L⁻¹ paclobutrazol applied once as a drench. Supplying N at 150 mg·L -1 during the growing season provided Echinacea cultivars adequate nutrition and maximized numbers of branches and flowers and shoot dry weight. In overwintering, fertilization treatments that resulted in low substrate electrical conductivity going into dormancy, 5.0 kg·m controlled release fertilizer 15N-3.9P-10K or 150 mg·L⁻¹ N using 15N-2.2P-12.5K applied using constant liquid feed, resulted in the highest survival rates of Echinacea cultivars. As a monitoring tool, SPAD measurements were not successful in predicting tissue N levels in Echinacea hybrids. Twenty-one hybrid cultivars acquired as stage 3 tissue culture plantlets were grown under one of three photoperiods (10-hour, 16-hour, or 24-hour) for 10 weeks before being transplanted to larger containers and grown under natural daylength until flowering. Providing Echinacea hybrid cultivars with a 16-hour photoperiod during liner production resulted in plants which flowered soonest without negative effects on growth. The need for height control PGRs varied by cultivar; however, overall height control PGRs controlled flower stalk height and increased market rating.
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    Creeping Bentgrass, Kentucky Bluegrass and Tall Fescue Responses to Plant Growth Stimulants Under Deficit Irrigation
    LaBranche, Adrienne Janel (Virginia Tech, 2005-04-20)
    A four-year drought, increasing population and shifting climate has spurred water conservation practices within Virginia. Creeping bentgrass (Agrostis palustris "L93"), Kentucky bluegrass (Poa pratensis "Midnight"), and tall fescue (Festuca arundinacea) Dominion blend were evaluated under deficit irrigation and upon exogenous application of plant growth stimulants (PGS), seaweed extract (SWE) + humic acid (HA), glycinebetaine (GB) and a commercial SWE product (PP). The objectives were to determine crop coefficients (Kc) for creeping bentgrass fairways and tall fescue home lawns, to determine if PGS application allowed for more water conservation, and to determine if they impacted physiological function and/or root morphology. A preliminary greenhouse experiment was conducted with creeping bentgrass and Kentucky bluegrass irrigated with 100%, 85% and 70% of evapotranspiration (ET). The study determined that an additional deficit irrigation level should be included for the field study and that GB application and 100% and 85% ET irrigation level produced the greatest creeping bentgrass root mass. The two–year field study evaluated creeping bentgrass and tall fescue. Tall fescue home lawns could be irrigated every five days with a Kc of 0.55 or once a week with a Kc of 0.70. Creeping bentgrass fairways could be irrigated every four days with a Kc of 0.85. Glycinebetaine application increased bentgrass rooting after planting and showed osmoprotectant properties. Another greenhouse study evaluated five GB rates on bentgrass and tall fescue. No differences were found between the five rates and concluded that the rate utilized in the field study may be appropriate for turfgrass application.
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    Drought Resistance Response of Tall Fescue Established in Disturbed Urban Soils Utilizing Biosolids
    Boyd, Adam Philip (Virginia Tech, 2016-02-18)
    Urban soils are typically degraded due to land disturbance. The poor quality physical and chemical properties of the soil can benefit from application of organic amendments. Local sources of such amendments are biosolids, which are treated domestic wastewater sludges. The objective of this experiment was to compare effects of various high quality biosolids-based soil amendments with synthetic fertilizer on the growth and quality of tall fescue (Schedonorus arundinaceus) under two different soil moisture regimes. The research site was a disturbed soil at the Virginia Tech Turfgrass Research Center in Blacksburg, Virginia. The experimental design was a split plot with irrigation regime as the main factor and soil amendments as the split factor. All treatments were arranged in four randomized complete blocks. The study was established in late summer 2013. Soil amendment treatments, applied prior to seeding in September 2013, were: 1) inorganic N, P, K applied according to soil test laboratory recommendations; 2) anaerobically digested, dewatered biosolids to supply agronomic N rate; 3) anaerobically digested, dewatered biosolids blended with sand and sawdust to supply agronomic N rate; 4) anaerobically digested, dewatered biosolids blended with sand and sawdust to supply agronomic P rate; and 5) composted biosolids to supply agronomic N rate. The agronomic N rate for the turfgrass was 224 kg of estimated plant available nitrogen (PAN) ha-1. Inorganic fertilizer was applied to supply annual P and K requirements prior to seeding in late summer, and the N was split into three application timings (September 2013, April 2014, and June 2014). Supplemental fertilizer N to achieve full agronomic N rate was applied to the treatment plots that received the agronomic P rate of blended biosolids-sand-sawdust. The area was seeded on September 13, 2013 with a tall fescue blend at a rate of 488 kg ha-1. Following full tall fescue establishment, in June 2014, two irrigation regimes, consisting of 0% and 80% evapotranspiration replacement every three days, were initiated. The study had three phases denoted as the pre-drought, drought, and recovery phases which started in April and concluded in August of 2014. Turfgrass color and quality, volumetric soil moisture percentage to a 5 cm depth, normalized difference vegetative index (NDVI), clipping yield, and turfgrass N uptake were measured bi-weekly throughout the growing season. During the first May through July 2014 irrigation season, results were that the fertilizer control consistently provided improved responses relative to the biosolids amended treatments. Clipping yield, quality, and NDVI were all significantly greater in the inorganic fertilizer treatment, but volumetric soil moisture percentages were slightly greater in the biosolids treatments. Turfgrass responses appeared to have been associated with plant available nitrogen, which was lower in the biosolids treatments than in the fertilizer treatment. Calculated PAN for the biosolids products was too low to achieve ideal turfgrass growth and quality. Improving the estimated PAN and/or splitting the organic amendment application times should improve the growth and quality of the turfgrass.
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    Ecology and Taxonomy of Leptosphaerulina spp. Associated with Turfgrasses in the United States
    Abler, Steven W. (Virginia Tech, 2003-01-31)
    Leptosphaerulina spp. are common fungi that have been reported to colonize several turfgrass species. Controversy exists regarding the relationship of Leptosphaerulina spp. and their turfgrass hosts. The fungus has been classified as a saprophyte, senectophyte, weak pathogen, and pathogen of turfgrasses. There has also been conflicting reports regarding the delineation of species within the genus Leptosphaerulina. Because of the uncertainty regarding the ecology and taxonomy of the genus in relation to turfgrasses the present study was undertaken. The ITS and EF-1á gene regions were sequenced and analyzed to compare to the multiple taxonomic schemes reported in the literature. The ITS region offered no resolution of species; however, the phylogeny of the EF-1á gene was consistent with the six-species model of Graham and Luttrell. Inoculation experiments were performed on unstressed and artificially stressed plants to determine whether the fungi are pathogens, senectophytes, or saprophytes of turfgrasses. Perennial ryegrass and creeping bentgrass plants were stressed by placing them in a dew chamber set at 38ºC, 100% R.H., and no light for two and one days respectively. Plants were inoculated with cultures of Leptosphaerulina isolated from turfgrasses, and maintained at optimum conditions reported for infection and colonization. There was no visible difference between inoculated and uninoculated plants, and examination of cleared and stained leaves with a light microscope revealed spores that germinated and produced appressoria, but failed to penetrate the epidermal cells. The lack of infection and colonization suggests that Leptosphaerulina spp. are saprophytes of turfgrasses.
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    The Effect of Fe-sulfate on Annual Bluegrass, Silvery Thread Moss, and Dollar Spot Populations Colonizing Creeping Bentgrass Putting Greens
    Reams, Nathaniel Frederick (Virginia Tech, 2013-06-05)
    Annual bluegrass (Poa annua L.) is the most problematic weed to control in creeping bentgrass (Agrostis stolonifera L.) putting greens.  The objective of this study was to transition a mixed putting green stand of annual bluegrass and creeping bentgrass to a monoculture by using fertilizers and plant growth regulators that selectively inhibit annual bluegrass.  A 25 year old loamy sand rootzone research green, planted with \'Penn-Eagle\' creeping bentgrass, with roughly 45% initial annual bluegrass coverage was utilized.  The biweekly application of ammonium sulfate (4.8 kg ha-1) with treatments of ferrous sulfate at rates of 0, 12.2, 24.4, and 48.8 kg ha-1 and in combination with seaweed extract (12.8 L ha-1) or paclobutrazol (0.37 L ai ha-1 spring and fall; 0.18 L ai ha-1 summer) were applied March to October, 2011 and 2012.  Plots receiving the highest rate of ferrous sulfate resulted in annual bluegrass infestation declines from an early trial amount of 45% to a final average of 20% but also resulted in unacceptable late-summer events of annual bluegrass collapse.  The ferrous sulfate medium rate resulted in a smooth transition from early-trial annual bluegrass infestation of 45% to an end of trial infestation of 20% and had the highest putting green quality.  Previous research has reported that consistent use of paclobutrazol can effectively and safely reduce annual bluegrass infestations.  In this trial annual bluegrass was reduced to 9% infestation after three months of application.  Two unexpected observations from this trial were that ferrous sulfate, applied at medium to high rates, significantly reduced silvery thread moss (Bryum argentum Hedw.) populations and occurrences of dollar spot (Sclerotinia homoeocarpa F. T. Bennett) disease.  Dollar spot control with ferrous sulfate has not previously been reported in the literature, so additional studies were designed to investigate this phenomenon further.  A creeping bentgrass putting green study was conducted to determine if sulfur, iron, or the two combined as ferrous sulfate decreases dollar spot activity.  Ferrous sulfate resulted in the highest turf quality and suppressed S. homoeocarpa infection, even during high disease pressure.  Fe-EDTA suppressed dollar spot infection as well as ferrous sulfate but quality declined to unacceptable levels during the summer, due to Fe-EDTA only.  Sulfur did not affect or increased S. homoeocarpa infection, indicating that a high and frequent foliar rate of iron is responsible for dollar spot control.  An in-vitro study was conducted to determine if agar pH in combination with iron concentrations affects mycelial growth of S. homoeocarpa.  Results from this trial indicated that 5.4 agar pH is an optimal pH for mycelial growth.  The 10 to 100 mg iron kg-1 concentration had little effect on mycelial growth at 5.0 and 5.5 pH, but increased growth at 4.5 and 6.5 pH.  As the iron concentration was increased from 10 to 100 to 1000 mg kg-1, mycelial growth decreased or stopped.  Our final conclusions are that seasonal biweekly foliar applications of the medium rate of ferrous sulfate (24.4 kg ha-1) safely and effectively reduced annual bluegrass infestation out of a creeping bentgrass putting green, while also effectively suppressing silvery thread moss and dollar spot incidence.
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    Effect of Golf Course Turfgrass Management on Water Quality of Non-tidal Streams in the Chesapeake Bay Watershed
    Wilson, Chantel (Virginia Tech, 2015-04-09)
    Turfgrass management activities on golf courses have been identified as a possible source of Chesapeake Bay nutrient pollution. Total Maximum Daily Load goals are in place to reduce nutrient amounts entering the Bay. Dissertation investigations include (1) the role of golf course turfgrass management in nutrient deposition or attenuation in local streams, (2) estimations of total nitrogen (N) discharging to the watershed from stream outlet points as a function of land use and watershed area, and (3) other factors potentially affecting water quality on golf courses, including soil characteristics and use of best management practices (BMPs). Total N, nitrate-N, ammonium-N, phosphate-phosphorus (P), streamwater temperature, specific conductance (SpC), pH and dissolved oxygen (DO) were sampled at 12-14 golf course stream sites in the James River and Roanoke River watersheds during baseflow conditions. Discharge was determined at outflow locations. Unit-area loads (UALs) were calculated from monitoring data. These UALs were then compared to UALs from Chesapeake Bay Watershed Model land use acreages and simulated loads for corresponding watershed segments. Virginia golf course superintendents were also surveyed to determine BMP use. No consistent impairment trends were detected for streamwater temperature, SpC, pH, or DO at any of the sites. Outflow NO3-N was below the 10 mg L-1 EPA drinking water standard. However, some sites may be at increased risk for benthic impairment with total N concentrations >2 mg L-1, as suggested by VADEQ. Significant increases in nitrate-N at OUT locations were measured at four sites, whereas decreases were measured at two sites. Ammonium-N significantly decreased at two sites. Golf course N UALs calculated from baseflow monitoring were lower than or similar to UALs estimated for forested areas in the associated watershed segment at seven out of the 12 sites. Golf course UALs ranged from 1.3-87 kg N ha-1 yr-1. Twenty-one of 32 surveyed BMPs had an adoption rate ≥50% among survey respondents. In most cases, presence of golf courses generally does not appear to significantly degrade baseflow water quality of streams in this study. Management level appears to be an influencing factor on water quality and concerns may be heightened in urban areas.
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    Effects of Biosolids on Tall Fescue-Kentucky Bluegrass Sod Production and Soil Chemical and Physical Properties
    Cataldi, Joseph Derik (Virginia Tech, 2013-07-02)
    Composted biosolids have been shown to enhance turfgrass establishment and growth more than fertilizer alone, but few studies have investigated the production of turfgrass using uncomposted biosolids. Increasingly employed treatment methods that generate pathogen-free, low pollutant-containing biosolids are creating alternative products for use in urban settings.  Understanding the effects of these uncomposted and alternative biosolids products on turfgrass culture and soil chemical and physical properties is essential to understanding the benefits these products may provide in sod production systems. The objectives of this study were to compare processing methods, application and N mineralization rates of two biosolids products and an inorganic fertilizer control for sod fertilization on 1) agronomic parameters related to turfgrass quality, 2) the amount of soil, C and P exported at harvest, and 3) chemical and physical properties of the soil following sod harvest as an indicator of the benefits of biosolids use. The study was conducted on a sod farm in Remington, Virginia on a silt loam Ashburn-Dulles complex from 2009 to 2012. The biosolids products were applied at estimated plant available nitrogen (PAN) rates of 98 kg N ha-1  (0.5X), 196 kg N ha-1 (1.0X) and 294 kg N ha-1  (1.5X) for a tall fescue (Festuca arundinacea Schreb. \'Rebel Exeda\' \'Rebel IV\' and \'Justice\')/ Kentucky bluegrass (Poa pratensis L. \'Midnight\') mixture. One biosolids product was an anaerobically digested dewatered cake applied at 15, 30.5 and 46 wet Mg ha-1. The second biosolids product was the same cake blended with wood fines applied at 17, 34 and 51 wet Mg ha-1. The biosolids treatments were compared to an inorganic fertilizer control that supplied 196 kg N ha-1 through three applications over the production cycle. There were no differences in establishment between the cake biosolids treatments and the inorganic fertilizer control, but all of the blended biosolids were slower to establish. Only the 1.0X and 1.5X PAN rates from the cake biosolids matched the inorganic fertilizer control in producing an acceptable quality sod in ten months. Lower nitrogen uptake between the blended biosolids treatments compared to the inorganic fertilizer control and lower although acceptable sod quality ratings at harvest of the 1.0X cake biosolids indicate our PAN estimates of 30% organic nitrogen mineralization overestimated the PAN for both materials. There were no differences in sod tensile strength between the 1.5X cake biosolids and inorganic fertilizer control. There were no differences in transplant rooting strength among all treatments. After repeat applications of biosolids, the 0.5X rates did not increase soil extractable phosphorus, while the 1.0X rates steadily increased soil extractable phosphorus at. The 1.0X and 1.5X biosolids rates increased soil organic matter content, but only the 1.5X rate of cake biosolids reduced soil bulk density and mineral matter export at harvest. Overall results indicate that the cake biosolids are an acceptable fertility alternative to inorganic fertilizer, and applications of biosolids for sod production can improve soil quality. Sod growers should consider using biosolids in a rotational system to offset rising production costs and improve production field soil quality.
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    Effects of Nitrate and Cytokinin on Nitrogen Metabolism and Heat Stress Tolerance of Creeping Bentgrass
    Wang, Kehua (Virginia Tech, 2010-07-23)
    Creeping bentgrass (Agrostis stolonifera L.) is a major low-cut cool-season turfgrass used worldwide. The objectives of this research were to: 1) to gain insight into the diurnal fluctuation of N metabolism and effects of cytokinin (CK) and nitrate; 2) to characterize the impacts of N and CK on creeping bentgrass under heat stress; 3) to investigate the simultaneous effects of CK and N on the antioxidant responses of heat stressed creeping bentgrass; and 4) to examine the expression pattern of the major heat shock proteins (HSPs) in creeping bentgrass during different heat stress periods, and then to study the influence of N on the expression pattern of HSPs. The transcript abundance of nitrate reductase (NR), nitrite reductase (NIR), plastidic glutamine synthetase (GS2), ferredoxin-dependent glutamate synthase (Fd-GOGAT), and glutamate dehydrogenase (GDH) and N metabolites in shoots were monitored during the day/night cycle (14/8 h). All the measured parameters exhibited clear diurnal changes, except GS2 expression and total protein. Both NR expression and nitrate content in shoots showed a peak after 8.5 h in dark, indicating a coordinated oscillation. Nitrate nutrition increased diurnal variation of nitrate content compared to control and CKHowever, CK shifted the diurnal in vivo NR activity pattern during this period. Grass grown at high N had better turf quality (TQ), higher Fv/Fm, normalized difference vegetation index (NDVI), and chlorophyll concentration at both 15 d and 28 d of heat stress than at low N, except for TQ at 15 d. Shoot NO3-, NH4+, and amino acids increased due to the high N treatment, but not water soluble proteins. High N also induced maximum shoot nitrate reductase activity (NRmax) at 1 d. CK increased NDVI at 15 d and Fv/Fm at 28 d. In addition, grass under 100 µM CK had greatest NRmax at both 1 d and 28 d. Under high N with 100 µM CK, root tZR and iPA were 160% and 97% higher than under low N without CK, respectively. Higher O2- production, H2O2 concentration, and higher malonydialdehyde (MDA) content in roots were observed in grass grown at high N. The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and guaiacol peroxidase (POD) in roots were enhanced by high N at 19, 22, and 24% levels, respectively, relative to low N. Twenty-eight days of heat stress resulted in either the development of new isoforms or enhanced isoform intensities of SOD, APX, and POD in roots compared to the grass responses prior to heat stress. However, no apparent differences were observed among treatments. No CK effects on these antioxidant parameters were found in this experiment. At week seven, grass at medium N had better TQ, NDVI, and Fv/Fm accompanied by lower shoot electrolyte leakage (ShEL) and higher root viability (RV), suggesting better heat resistance. All the investigated HSPs (HSP101, HSP90, HSP70, and sHSPs) were up-regulated by heat stress. Their expression patterns indicated cooperation between different HSPs and that their roles in creeping bentgrass thermotolerance were affected by N level.
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    Effects of Organic Soil Amendments on Soil Physiochemical and Crop Physiological Properties of Field Grown Corn (Zea mays) and Soybean (Glycine Max)
    Bowden, Chandra Lynndell (Virginia Tech, 2006-04-28)
    Water stress is the most critical environmental factor limiting crop production in the US Piedmont. The presence of humic substances in composted organic amendments may increase crop tolerance to water stress through their hormone-like effects on plant metabolism. The objectives of this study were to calculate N mineralization rates of composted and non-composted organic materials used in this long-term field study, and to determine differences in soil physiochemical properties, corn and soybean leaf physical and biochemical properties yield and seed quality between organically amended and inorganically fertilized treatments. Nitrogen mineralization rates were greatest in the poultry litter (21%) and Panorama yard waste compost (4.5%) amended plots. Nitrogen uptake (120 mg/pot, 133 mg/pot, respectively) in these treatments were greater than that in the control (0N) (91.3 mg/pot) treatment. Wolf Creek biosolids compost and Huck's Hen Blend yard waste compost induced N immobilization (-5.0% and 0.18%, respectively), and had N uptake values similar to the control (92.6 mg/pot and 95.7 mg/pot). Rivanna biosolids compost immobilized N (-14.8%) but N uptake (136 mg/pot) was greater than that in the control due to the relatively high inorganic N content in the amendment. The total N concentration and C:N values were less reliable variables in predicting N mineralization when a significant portion of the total N was in the inorganic form. The annual application of poultry litter, Rivanna biosolids compost, and Panorama yard waste compost at 100% agronomic nitrogen and 30 % agronomic nitrogen rates in the field study improved soil fertility and increased total organic and humified carbon contents relative to the inorganically fertilized and control treatments. The amended treatments had slightly greater plant available water contents (average 10.0 cm/15 cm) than the control (8.38 cm/15 cm). Leaf water potential measurements revealed that neither crop experienced water stress during the sampling season. Treatment differences in leaf antioxidant activity were only observed in corn. All corn plants that were fertilized with amendments supplying the crop's nitrogen needs, regardless of the source, had greater leaf nitrogen (+29%), chlorophyll (+33%), and protein contents (+37%), lower superoxide dismutase (-29%) and ascorbate peroxidase (-17%) activities, and lower malondialdehyde (-33%) contents relative to the control and low nitrogen treatments. There were no observed differences in catalase activity, which was likely due to the evolutionary advantage of C4 metabolism. Yield was strongly related to midseason leaf nitrogen contents (R2=0.87, p<0.0001) and not soil humified carbon (R2=0.02, p=0.0543). There were no observed treatment differences in soybean leaf physiology and metabolism. Differences, however, were observed over time. As the leaves senesced, leaf chlorophyll, protein, superoxide dismutase and catalase activities decreased, and the malondialdehyde content increased. Ascorbate peroxidase activity slightly increased with time. Catalase activity in soybean was primarily driven by the oxidation of glycolate, a product of photorespiration, and not the formation of reactive oxygen species in the chloroplasts. The organically amended treatments had higher yields (9-21% increase), greater protein contents (4-9% increase), and seed weights (5-14% increase) relative to the fertilizer and control treatments. It was concluded that differences in soybean yield and seed quality were due to non-nutritive benefits of the organic amendments and not available water or plant nutrition.
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    Elucidating Influence of Temperature and Environmental Stress on Turfgrass Response to Mesotrione and Evaluation of Potential Synergistic Admixtures to Improve Mesotrione Efficacy
    Ricker, Daniel (Virginia Tech, 2006-12-14)
    Mesotrione is under evaluation for registration in turfgrass for weed control, but often requires repeat treatments. Previous research in agricultural crops indicates tank mixtures with mesotrione may improve weed control. Three field trials were conducted in 2005 and 2006 in Blacksburg, VA on smooth crabgrass in perennial ryegrass and tall fescue. Data indicate mesotrione applied in combination with bentazon, bromoxynil, or carfentrazone, controlled smooth crabgrass better than any of these herbicides applied alone at all sites. Adding mesotrione to MSMA and quinclorac improved smooth crabgrass on of three sites. Sequential mesotrione applications improved long term weed control.
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    Environmental Best Management Practices for Virginia's Golf Courses
    Schoenholtz, Stephen H.; Goatley, Michael; Ervin, Erik H.; Hodges, Steven C.; Hipkins, Perry L.; McCall, David S.; Askew, Shawn D.; Youngman, Roger R.; Hipkins, Patricia A.; Grisso, Robert D.; Muckley, Glenn; George, Lester; Ballard, Mike; Roadley, Chuck; Lajoie, Matt; Rodriguez, Mark; Habel, Robert; Sexton, Tim; Buchen, Terry (Virginia Cooperative Extension, 2019-01-09)
    Provides recommendations for Virginia golf courses, emphasizing water quality protection.
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    Environmental Best Management Practices for Virginia's Golf Courses
    Schoenholtz, Stephen H.; Goatley, Michael; Ervin, Erik H.; Hodges, Steven C.; Hipkins, Perry L.; McCall, David S.; Askew, Shawn D.; Youngman, Roger R.; Hipkins, Patricia A.; Grisso, Robert D.; Muckley, Glenn; George, Lester; Ballard, Mike; Roadley, Chuck; Lajoie, Matt; Rodriguez, Mark; Habel, Robert; Sexton, Tim (Virginia Cooperative Extension, 2013-02-27)
    Provides recommendations for golf courses in the Commonwealth that emphasize water quality protection and have been specifically adapted for courses in Virginia using the results of current research, the experience of golf course superintendents in implementing best management practices, golf industry representatives, and state regulators.
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    Evaluating methiozolin programs for golf putting greens and investigating potential modes of action
    Venner, Katelyn (Virginia Tech, 2015-10-06)
    Annual bluegrass is a winter annual grass that is problematic on golf putting greens due to its light green color, prolific seedhead production and intolerance to stress. On creeping bentgrass putting greens, herbicides for annual bluegrass control are limited. A new herbicide, methiozolin, developed by Moghu Research Center, LLC, in Daejeon, South Korea, safely and selectively controls annual bluegrass in creeping bentgrass and several other turfgrass species. Methiozolin typically controls annual bluegrass over several weeks, allowing desirable turfgrass time to grow into areas previously infested by annual bluegrass with little surface disruption. The mode of action of methiozolin is unknown, but has been proposed to act as either a cell wall biosynthesis inhibitor (CBI) or an inhibitor of tyrosine aminotransferase (TAT). Field studies were conducted at Virginia Tech to investigate strategies promoting surface recovery on putting greens following atypically rapid annual bluegrass loss resulting from methiozolin application, intensive core-cultivation as well as potential interactions with plant growth regulators (PGR's), like ethephon. In the rapid annual bluegrass removal study, all treatments receiving additional fertility via synthetic fertilizer with or without trinexapac-ethyl or biostimulant recovered 1 to 3 weeks more quickly than treatments that did not include additional fertility. Addition of the PGR trinexapac-ethyl inconsistently regulated speed of canopy recovery, both increasing and decreasing recovery speed. Under normal maintenance conditions, methiozolin does not negatively influence putting green recovery, however, if the putting green is exposed to droughty conditions, methiozolin can reduce recovery time by several weeks. Core-cultivation should be avoided in conjunction with methiozolin and ethephon applications because when this procedure was conducted on the same day as herbicide application it significantly damaged creeping bentgrass, reducing cover to 19% at 2000 g ai ha⁻¹, compared to the non-treated at 62%. Regarding the question of methiozoling mode of action, laboratory studies supported the claim that addition of exogenous 4-hydroxyphenylpyruvate (4-HPP) alleviates symptoms of methiozolin exposure in lesser duckweed, a model monocot species, but feeding various turfgrass species and annual bluegrass exogenous 4-HPP did not alleviate symptoms. Creeping bentgrass secondary root length and density was not affected by methiozolin, although annual bluegrass, Kentucky bluegrass and perennial ryegrass secondary root lengths were reduced. Based on these data, it does not appear that TAT inhibition is a primary mode of action of methiozolin in turfgrass. Studies were conducted to determine if methiozolin inhibited cell wall biosynthesis in desirable turfgrass species and annual bluegrass. All species exhibited decreased enrichment of ¹³C in cell-wall sugars form ¹³C-glucose in response to methiozolin and a known cell wall biosynthesis inhibitor, indaziflam. Indaziflam and methiozolin at 0.01 µM inhibited ¹³C enrichment of all sugars less than methiozolin at 1.0 µM, for xylose, arabinose and glucose, but not galactose. Addition of 4-HPP increased incorporation of ¹³C into xylose, but had no other influence on ¹³C incorporation into other cell wall sugars. Lack of species specific response indicates that cell wall biosynthesis inhibition is probably not the source of interspecific species responses observed in the field.
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    Evaluation of novel techniques to establish and transition overseeded grasses on bermudagrass sports turf
    Mittlesteadt, Tyler Lee (Virginia Tech, 2009-04-29)
    Most professional turf in Virginia is comprised of bermudagrass (Cynodon dactylon L.) or (Cynodon dactylon x C. transvaalensis Burtt Davy) as a monoculture in summer and overseeded with perennial ryegrass (Lolium perenne L.) (PR) in winter, during bermudagrass dormancy. Two transitions are required in an overseeding program, fall establishment of PR and spring control of PR. During each transition, turf quality suffers as one grass dies or enters dormancy while another grass is promoted to fill voided areas. Field studies at various locations in Virginia were conducted to investigate methods of improving spring and fall transition. Bermudagrass green cover in August was influenced by duration of PR competition variably between three bermudagrass cultivars. For example, "Midiron", "Patriot", and "Riviera" bermudagrass required 218, 139, and 327 cumulative growing degree days at base 18.3 C (GDD) to reach 95% cover. Bermudagrass biomass was also positively correlated with increasing duration of noncompetitive GDD. Total nonstructural carbohydrates were not correlated to duration of PR competition. Novel application methods were invented and tested at Virginia Tech. Drip, sponge, and strip application methods were used to create patterns of PR control using selective herbicides. Controlling a portion of PR with these methods maintained acceptable turfgrass quality throughout the spring transition and improved bermudagrass cover 12 to 20%, speeding transition by 20 or more days. Efforts to improve PR establishment in dense bermudagrass suggest chemicals that injure existing bermudagrass can improve PR establishment, but cause unacceptable turf discoloration. Mechanical methods to disrupt the bermudagrass canopy had less effect on PR establishment than chemical treatments.
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    Expanding the Application of Spectral Reflectance Measurement in Turfgrass Systems
    McCall, David S. (Virginia Tech, 2016-04-25)
    Light reflectance from plants can be used as a non-invasive predictor of health and yield for many cropping systems, and has been investigated to a lesser extent with managed turfgrass systems. The frequent agronomic inputs associated with maintaining golf course grasses allow for exceptional stand quality under harsh growing conditions, but often expend resources inefficiently, leading to either stand loss or unnecessary inputs in localized areas. Turfgrass researchers have adopted some basic principles of light reflectance formerly developed for cropping systems, but field radiometric-derived narrow-band algorithms for turfgrass-specific protocols are lacking. Research was conducted to expand the feasibility of using radiometry to detect various turfgrass stressors and improve speed and geographic specificity of turfgrass management. Methods were developed to detect applied turfgrass stress from herbicide five days before visible symptoms developed under normal field growing conditions. Soil volumetric water content was successfully estimated using a water band index of creeping bentgrass canopy reflectance. The spectral reflectance of turfgrass treated with conventional synthetic pigments was characterized and found to erroneously influence plant health interpretation of common vegetation indices because of near infrared interference by such pigments. Finally, reflectance data were used to estimate root zone temperatures and root depth of creeping bentgrass systems using a gradient of wind velocities created with turf fans. Collectively, these studies provide a fundamental understanding of several turfgrass-specific reflectance algorithms and support unique opportunities to detect stresses and more efficiently allocate resources to golf course turf.
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    Factors governing zoysiagrass response to herbicides applied during spring green-up
    Craft, Jordan Michael (Virginia Tech, 2021-03-29)
    Zoysiagrass (Zoysia spp.) is utilized as a warm-season turfgrass because of its density, visual quality, stress tolerance, and reduced input requirements. Turf managers often exploit winter dormancy in warm-season turfgrass to apply nonselective herbicides such as glyphosate and glufosinate to control winter annual weeds. Although this weed control strategy is common in bermudagrass (Cynodon spp.), it has been less adopted in zoysiagrass due to unexplainable turf injury. Many university extension publications recommend against applying nonselective herbicides to dormant zoysiagrass despite promotional language found in a few peer-reviewed publications and product labels. Previous researchers have used vague terminology such as "applied to dormant zoysiagrass" or "applied prior to zoysiagrass green-up" to describe herbicide application timings. These ambiguous terms have led to confusion since zoysiagrass typically has subcanopy green leaves and stems throughout the winter dormancy period. No research has sought to explain why some turfgrass managers are observing zoysiagrass injury when the literature only offers evidence that these herbicides do not injure dormant zoysiagrass. We sought to explore various herbicides, prevailing temperatures surrounding application, heat unit based application timings, and spray penetration into zoysiagrass canopies as possible contributors to zoysiagrass injury. The results indicated that a wide range of herbicides may be safely used in dormant zoysiagrass. However, as zoysiagrass begins to produce more green leaves, herbicides such as metsulfuron, glyphosate, glufosinate, flumioxazin, and diquat become too injurious. Glufosinate was consistently more injurious regardless of application timing than glyphosate and other herbicides. When temperatures were 10 °C for 7 d following treatment, a delayed effect of glyphosate and glufosinate effect on digitally-assessed green cover loss was noted on zoysiagrass sprigs. In subsequent studies on turf plugs, a 14-d incubation period at 10 °C reduced glyphosate but not glufosinate effects on turf green color reduction. Glyphosate applied at 125, and 200 GDD5C can safely be applied to zoysiagrass while glufosinate applied at the same timings caused inconsistent and often unacceptable zoysiagrass injury in field studies conducted at Blacksburg, VA, Starkville, MS, and Virginia Beach, VA. Zoysiagrass green leaf density was described as a function of accumulated heat units consistently across years and locations but variably by turf mowing height. Turf normalized difference vegetative index was primarily governed by green turf cover but reduced by herbicide treatments, especially when applied at greater than 200 GDD5C. Substantial spray deposition occurred to subcanopy tissue regardless of nozzle type, pressure and height above the zoysiagrass canopy based on spectrophotometric assessment of a colorant admixture. However, increasing nozzle height above the turf canopy and avoiding air induction type nozzles significantly reduced the percentage of green tissue exposed at lower canopy levels. Absorption of radio-labeled glyphosate and glufosinate was up to four times greater when exposed to zoysiagrass stems compared to leaves. Glyphosate translocated more than glufosinate and both herbicides moved more readily from stem to leaf than from leaf to stem