Browsing Plant Science & Landscape Architecture Theses and Dissertations by Subject "Agriculture, Agronomy"
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- ItemAlleviation of Soil Compaction by Brassica Cover Crops(2009) Chen, Guihua; Weil, Ray R; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Soil compaction is a worldwide problem in modern agriculture associated with overuse of heavy machinery and intensification of cropping systems. Though tillage is traditionally used to alleviate compaction effect, increasing concerns about environmental impacts of tillage have led to interest in conservational tillage systems and incorporation of cover crops into crop rotations. Previous study showed soybean (Glycine Max L.) roots grew through a plowpan soil using channels left by canola (Brassica napus) cover crop roots, a process termed "biodrilling" to alleviate compaction effect. However, this study did not provide any quantitative data to support the observational conclusion. We studied "biodrilling" abilities of three cover crops and the effects of "biodrilling" on corn (Zea mays)/soybean growth by conducting three experiments. The first two experiments included three surface horizon compaction treatments (high, medium and no compaction), four cover crops [FR (forage radish: Raphanus sativus var. longipinnatus, cultivar `Daikon') and rape (rapeseed: Brassica napus, cultivar `Essex') (tap-rooted species in the Brassica family), rye (cereal rye: Secale cereale L., cultivar `Wheeler') (fibrous-rooted species) and NC (no cover crop)] in Exp. 1, and three cover crops (FR, rape and NC) in Exp. 2. The third experiment was conducted on field with a legacy plowpan (subsoil compaction) using FR, rye and NC cover crops. Roots of FR were least inhibited by compaction, while rye roots were severely arrested by compaction. The order of "biodrilling" ability was FR > rape > rye. Soil bulk density, strength and least limiting water range were controlled by compaction treatments. Soil air permeability was greatly reduced by compaction. Air permeability was greater in rape/FR treatments than in rye/NC treatments under high/medium compaction. Corn/soybean root penetrations, subsoil water uptake in the compacted soils were enhanced by FR/rape treatments but not by rye/NC treatments. Compaction decreased corn yield only in Exp. 2 where soil sand fraction was greater. The yield of corn was greater in three cover crop treatments than in NC control. In terms of "biodrilling", Brassica cover crops (FR and rape) were more effective than rye cover crop, would alleviate effects of soil compaction on plant growth in no-till farming systems.
- ItemAssociation Analysis in Soybean(2008-08-29) Hwang, Eun-Young; COSTA, JOSE; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Association analysis is a new approach to identify the location of gene(s)/allele(s) of interest. There are a number of factors determining the feasibility of whole-genome association analysis which include the level of linkage disequilibrium (LD) and the magnitude of population structure in a population. The goal of this study was to evaluate the success of whole-genome association analysis in soybean germplasm accessions using DNA markers across the whole genome. Firstly, the extent of LD and the presence of population structure were estimated. Secondly, whole-genome association analysis was performed to detect the location of the allele/gene controlling flower color, pubescence color, and seed protein quantitative trait loci (QTLs) in 319 soybean [Glycine max (L.) Merr.] germplasm accessions. The soybean germplasm accessions had a relatively low level of LD which declined very rapidly to 0.8 in less than 4 Kbp as indicated by r2 as well as highly diverse population structure. Despite the low LD and the presence of high population structure, whole-genome case-control analysis successfully detected the 65 bp insertion in the GmF3'5'H (GenBank acc. AY117551) gene controlling purple vs. white flower color, as well as a single base deletion in the F3'H (GenBank acc. AB191404) gene controlling tawny vs<\em>. gray pubescence color. However, there were 28 gray pubescence lines that did not contain the deletion suggesting that there is a second mutation determining the pubescence color alteration. In the case of seed protein QTL, whole-genome regression analysis detected one of four previously reported seed protein QTLs which reside on linkage group (LG) E and a new seed protein QTL on LG K. The detection of three other previously reported seed protein QTLs on LGs A1, I and M was not successful. It is unclear why association analysis was not successful in the detection of the three previously reported QTLs. However, a number of reasons including incomplete adjustment for population structure, lack of statistical power, an inadequate number of genetic markers in light of the low level of LD, and the power of association analysis to detect alleles with relatively modest genetic effects are suggested as possible reasons.
- ItemBiology of Ophiosphaerella agrostis, epidemiology of dead spot, and a molecular description of the pathogen(2004-10-21) Kaminski, John; Dernoeden, Peter H.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ophiosphaerella agrostis is a newly described pathogen that incites dead spot disease of creeping bentgrass (Agrostis stolonifera) putting greens throughout the eastern United States. The objectives of this research project were to: 1) monitor environmental conditions and develop a predictive model for disease progress and pathogen dispersal under field conditions; 2) determine the effect of various fertilizers on dead spot recovery in bentgrass; and 3) develop molecular methods to diagnoses the disease and determine genetic variation among O. agrostis isolates. Field studies showed that the appearance of dead spot infection centers was influenced predominantly by air (greater than or equal to 18 degrees Centigrade) and soil (greater than or equal to 20 degrees Centigrade) temperature, but other factors including low relative humidity (less than or equal to 80%), shortened periods of leaf wetness (less than or equal to 14 hours), and high levels of solar radiation (greater than or equal to 230 W m to the minus 2) were associated with the development of dead spot epidemics. Patch diameter of O. agrostis infection centers and pseudothecia production generally increased at a linear rate between mid-June and early to mid-August. In a growth chamber study, ascospores were released from pseudothecia following a sharp decrease in relative humidity. Field studies revealed that ascospore release occurred primarily at dawn and dusk or during precipitation events. During precipitation events, ascospores may be forcefully discharged during the entire event, but most ascospores are released within the first 10 hours after precipitation begins. O. agrostis successfully over-wintered in bentgrass leaf sheaths, crowns, roots, and stolons, but little or no reactivation of the disease occurred in the second year. Plots treated with ammonium sulfate and isobutylidene diurea were among the fastest and slowest to recover from dead spot, respectively. In the second year (2003), dead spot recurred in plots treated since 2002 with KNO3, Ca(NO3)2, urea, and a complete fertilizer (20-20-20), but disease symptoms did not recur in plots receiving ammonium sulfate. Species-specific primers capable of detecting O. agrostis at very low concentrations (5 pg DNA) were developed and can be used to assist in diagnosing dead spot. Amplified fragment length polymorphism (AFLP) DNA fingerprinting resulted in placement of isolates (n=77) into three distinct clades that were greater than or equal to 69% similar.
- ItemDOLLAR SPOT AND GRAY LEAF SPOT SEVERITY AS INFLUENCED BY IRRIGATION PRACTICE AND PLANT PROTECTION MATERIALS(2005-11-23) McDonald, Steven James; Dernoeden, Peter H; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Agrostis stolonifera and Lolium perenne are widely used turfgrass species grown on golf fairways, however, they are susceptible to dollar spot (Sclerotinia homoeocarpa) and gray leaf spot (Pyricularia grisea) diseases, respectively. Two field studies were conducted to assess: 1) the influence of two irrigation regimes and seven chemical treatments on dollar spot and gray leaf spot severity; and 2) the effects of two spray volumes (468 and 1020 L water ha-1), two fungicides (chlorothalonil and propiconazole) and three application timings (dew present or displaced and dry canopy) on dollar spot control. Dollar spot was more severe in A. stolonifera subjected to infrequent irrigation; whereas, gray leaf spot was more severe in frequently irrigated L. perenne. The plant growth regulator and wetting agent evaluated suppressed dollar spot, but they had no effect on gray leaf spot. Chlorothalonil was most effective when applied to a dry canopy in 468 L water ha-1.
- ItemDouble-Cropped Soybean Response to Various Wheat Stubble Managements(2005-08-12) Pearce, Justin Tyler; Kratochvil, Robert J; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Varying responses to wheat (Triticum aestivum L.) stubble management preceding double-crop soybean [Glycine max (L.) Merr.] have been reported; however, little work has been done in the Mid-Atlantic region of the United States. The objectives of this study were to observe the effects of wheat stubble management (WSM) on physiological growth and yield characteristics for double-cropped glyphosate-resistant soybean, soil moisture retention and soil surface shading, monitor weed response characteristics, and to perform a simple economic analysis comparing the four WSM treatments. Soybean plant height, lowest pod height, and soil surface shading were greater in the 30 cm stubble treatment; however, there was no plant lodging or yield response to WSM, and soil moisture contents were unaffected due to the ample rainfall that was received during 2003 and 2004. As a result, 15 cm stubble with the straw removed via baling was found to be the most economically profitable treatment.
- ItemThe Establishment and Persistence of American Ginseng (Panax quinquefolius L.) in Maryland Forests.(2005-05-26) Slak, David; McIntosh, Marla; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)American ginseng (Panax quinquefolius L.) is a profitable non-timber forest product with the potential of improving the sustainability of Maryland forests. In order to determine factors affecting Maryland ginseng production, ginseng seeds and roots were planted in forests in Eastern, Central, and Western Maryland in plots amended with no treatment, lime, or gypsum. The response variables measured included soil nutrients and ginseng persisence and establishment. In general, soil lime treatments improved establishment at the Eastern but not the Central or Western sites. The gypsum soil treatments did not significantly affect populations. Establishment of American ginseng grown from seed ranked by site was Western>Central>Eastern. Conversely, root establishment was best at the Eastern site. Across sites, soil pH, Ca, Mg, and K were positively correlated with establishment and persistence. Thus, American ginseng was grown throughout Maryland and ginseng production was enhanced by lime addition at the Eastern site.
- ItemEVALUATION OF LABILE SOIL CARBON TEST FOR PREDICTION OF SOIL PRODUCTIVITY RESPONSE TO ORGANIC MATTER MANAGEMENT(2005-01-05) Lucas, Shawn Thomas; Weil, Ray R; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A KMnO4 oxidation method for estimating labile soil C (CL) was evaluated for use in a soil testing mode to identify soils where soil quality and productivity is likely or unlikely to respond positively to increased levels of CL. Four sets of paired fields of the same soil series (within each set) but contrasting soil management history (continuous cropping vs. long-term sod) were studied. Fields with sod history initially tested higher in total soil C and CL than fields with cropped management history. Within each field two treatments (winter rye cover crop or no cover crop) were applied in each of four blocks. Crop and soil functional responses to rye, when significant, were higher in fields that initially tested lower in CL indicating that the KMnO4 method used has some predictive value as a soil test. The method could be used in field testing kits for evaluation of soil C.
- ItemFACTORS AFFECTING MEDIA pH AND NUTRIENT UPTAKE IN GERANIUMS(2004-08-30) Raymond, Carinne A.; MCINTOSH, MARLA S; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Consumer demand has prompted an increase in geranium breeding efforts to produce new cultivars each season. It is hypothesized that the breeding for unique morphological traits has inadvertently resulted in changing the plant's ability to competitively take up nutrients. Under certain conditions, nutrient uptake of these novelty cultivars is less efficient, possibly caused by the influence of the geranium itself. Information collected from the container media is a good indicator of the container nutritional status and can be used as a diagnostic tool for early identification of nutritional problems and prevent plant loss. Severe nutrient deficiencies and toxicities have been associated with plants fertigated with low alkalinity water, suggesting that an unsteady pH in the rhizosphere coupled with low buffering capacity of irrigation water may cause preferential nutrient uptake. Maintaining a media pH that optimizes nutrient solubility while preventing interactions or precipitation is the goal for ensuring proper plant nutrition. Three experiments were performed to address the following objectives: 1.) Evaluate the effects of the geranium cultivar and class on the container media. 2.) Determine if media type affects nutrient availability and uptake by geraniums. 3.) Identify if preferential nutrient uptake occurs in response to changing pH and water alkalinity levels in the container media. Results indicate that a significant reduction in media pH occurs for zonal and ivy geraniums during a specific stage of growth and that the effects of pH and water alkalinity on nutrient uptake and are highly specific to the nutrient tested and the media type. Significant interactions between water alkalinity and pH contributed to preferential uptake of several of the tested nutrients especially at low water alkalinities. Overall, the differences in uptake were in most cases specific to cultivar, the stage of growth and nutrient tested and should be considered when determining optimal fertility requirements for specific geranium cultivars.
- ItemForage Radish Cover Crop Effects on Mycorrhizal Colonization and Soil Test Phosphorus(2009) White, Charles Macaulay; Weil, Ray R; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Forage radish (Raphanus sativus L. var. longipinnatus) and cereal rye (Secale cereale L.) cover crops were examined for their effects on arbuscular mycorrhizal colonization and P acquisition of a subsequent corn (Zea mays L.) silage crop. Soil test P following these cover crops was also measured in bulk soil collected at three depths in the surface soil and in soil sampled within 3 cm of forage radish tap root holes. Forage radish never decreased mycorrhizal colonization and rye sometimes increased colonization of the subsequent crop compared to growing no cover crop. The extent of colonization of corn roots by arbuscular mycorrhizal fungi was positively correlated with corn shoot tissue P concentrations. Slight vertical soil test P stratification in the bulk soil occurred following both forage radish and rye cover crops at some sites. A large increase in soil test P occurred within 3 cm of forage radish tap root holes.
- ItemNitrogen Mineralization from Brassica Cover Crops(2006-07-27) Kremen, Amy; Weil, Ray; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The potential of forage radish (Raphanus sativus L.), rape (Brassica napus L.), and rye (Secale cereale L.) cover crops to capture residual nitrogen and then provide early season N to subsequent main crops via mineralization from their residues was compared. At four field experiments established in Maryland (2003-2005), N uptake by radish and rape equaled or exceeded that by rye. No differences in soil inorganic N due to cover crop type were observed during spring 2004. In spring 2005, greatest N release from forage radish residues (March-May) was followed by that from rape residues (May-June). Brassica decay significantly increased growth of immature corn and soybean plants. In a 48-day incubation study comparing N mineralization in fine and coarse textured soils from Brassica and rye root or shoot residues, N mineralization was greatest from forage radish and rape shoots. Compared with rye, the Brassica cover crops showed environmental and agronomic promise.
- ItemSoil Nematode Communities as Influenced by Cover Crops, with a Focus on Brassicaceae(2007-06-11) Gruver, Lisa Stocking; Weil, Ray R.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The effect of brassicaceous cover crops (Brassica juncea/Sinapis alba, B. napus, and Raphanus sativus) on plant-parasitic and free-living soil nematode communities, in grain agroecosystems, was evaluated in three experiments, at two sites in Maryland. Brassicaceous cover crops alone did not suppress plant-parasitic nematodes, however when combined with rye (Secale cereale) or clover (Trifolium incarnatum), juvenile (J2) Heterodera glycines populations were lower in June, soybean yields were higher, or free-living nematode abundance was higher. Indices of free-living nematode community structure suggested that winter-kill of N-rich radishes activated the bacterivore community in early spring resulting in high populations of bacterivore dauer larvae and high community structure by summer. In contrast, nematode communities in spring-terminated rapeseed and rye plots had high abundances of fungivore nematodes and a plant associate/fungal feeder, Coslenchus. Brassicaceous cover crops in Maryland grain rotations may be more useful for managing soil ecology than for biofumigation of plant-parasitic nematodes.
- ItemSoil Properties and Native Plant Communities in a Kansas Prairie(2004-08-18) Gordon, Carol Sue; Weil, Ray R.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)I hypothesized that the relative proportion of grasses and legumes in native prairie communities are associated with physical and chemical soil properties. In a greenhouse study, I determined species responses to differences in soils ex situ by individually growing three grasses, two legumes, and two composites in soils from four sites on a never-plowed prairie at The Land Institute in Saline County, KS. The highest organic matter (OM) soil produced the highest plant dry matter for five of the species. In a field study, I measured 20 soil properties in 24 quadrats (0.5 m2) with high, low, or no legume cover on the same four sites. After incubation, NH4 in subsurface soils was lower for high legume cover suggesting higher nitrification. Discriminant multivariate analysis showed the ratio, active C as a percent of total C, and percent OM were the most closely associated surface soil variables with percent legume cover.
- ItemSpatial Distribution of Surface Soil Moisture under a Cornfield(2004-12-03) Fisher, Jackson; Hill, Robert L; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Autocorrelation within surface soil moisture (SSM) data may be used to produce high-resolution spatial maps of SSM from point samples. The objective of this study was to characterize the temporal and spatial properties of SSM (0-5 cm) in a Beltsville, MD cornfield using capacitance probes. The range of spatial autocorrelation was approximately 10 m and the highest sill values were found at water contents (theta) between 20-27%. Nugget values represented a significant portion of the total variance (up to 50% for theta > 20% and 73% for theta < 12%). The patterns of SSM under wet conditions exhibited large, continuous polygons while drier conditions resulted in smaller, discreet regions. Early season (< 60 days) Auto-Regressive Moving-Average (ARMA) forecasts of SSM plotted against observed data resulted in R2 values from 0.15-0.26, while late season (>80 days) forecasts improved to 0.46-0.65. Forecasts were improved by autoregressive coefficients and additional SSM datasets.
- ItemTHATCH AND SOIL PESTICIDE DEGRADATION AND MICROBIAL ACTIVITY AS INFLUENCED BY TURF CULTIVATION PRACTICES(2009) MU, YUSONG; Carroll, Mark J; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Pesticide degradation in turf is complicated by presence of an organic matter enriched layer called thatch. It is not well understood how the extensive pesticide sorption capacity of thatch may affect the aerobic degradation of pesticides in thatch. Hollow tine cultivation and vertical mowing are two commonly used cultivation practices used to control thatch. Two studies were conducted to determine how these two cultural practices may affect microbial activity and pesticide degradation within thatch and soil. Hollow tine cultivation briefly enhanced microbial activity within thatch while vertical mowing had no consistent effect on thatch or soil microbial activity. Neither cultivation practice consistently altered the aerobic degradation of 2,4-D, flutolanil or chlorpyrifos. Thatch and soil aerobic degradation constants obtained for flutolanil and chlorpyrifos supported the hypothesis that strongly adsorbed pesticides are shielded from microbial populations that degrade pesticides within thatch.
- ItemWATER QUALITY IN MANAGEMENT INTENSIVE GRAZING AND CONFINED FEEDING DAIRY FARM WATERSHEDS(2005-07-12) Gilker, Rachel Esther; Weil, Ray R.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dairy farm size has increased in the United States, while the profit margin has decreased. An alternative to confined feeding dairy farming is management intensive grazing (MIG), a grass-based system relying on rotational grazing for most of the herd's dietary requirements. Previous research has measured high levels of nitrate leaching under MIG, citing the liquid nature and high nitrogen (N) content of urine. However, this research included heavy N fertilizer applications or was conducted on monolith lysimeters with artificial leaching processes and did not accurately represent mid-Atlantic MIG dairy farms. Phosphorus (P) losses have typically been attributed to runoff and erosion but are now being ascribed to leaching as well. To measure the magnitude of N and P losses to groundwater, we sampled shallow groundwater and pore water on one confined feeding and two MIG-based Maryland dairy farms between 2001 and 2004. Transects of nested piezometers and ceramic-tipped suction lysimeters were installed in two watersheds on each farm. Two streams running through two of the grazed watersheds were also sampled to measure the effects of grazing on surface water. For three years, groundwater and surface water samples were collected biweekly and pore water was collected when conditions made it possible. Samples were analyzed for inorganic N and dissolved reactive P and were digested for determination of dissolved organic N and P, pools previously not considered major sources of nutrient loss. Seasonal mean nitrate concentrations under the grazed watersheds remained below the EPA maximum contaminant load of 10 mg L-1 with only two exceptions on the grazed watersheds. Mean nitrate concentrations in the four grazed watersheds ranged from 3 to 7.44 mg L-1. Nitrogen losses were closely correlated to farm N surpluses. Groundwater P concentrations exceeded the EPA surface water critical levels in all six watersheds. Geologic factors, rather than dairy farm management, played a large role in P losses. In all watersheds, substantial pools of dissolved organic N and P were measured in groundwater. Low nitrate losses under MIG as well as the environmental advantages inherent in a grass-based system make grazing a viable Best Management Practice.
- ItemWeed Suppression By Forage Radish Winter Cover Crops(2010) Lawley, Yvonne Elizabeth; Weil, Ray R; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Forage radish (Raphanus sativus L. var. longipinnatus) is a new winter cover crop in the Mid-Atlantic region. This study had three objectives: 1) to characterize the repeatability, amount, and duration of weed suppression during and after a fall-planted forage radish cover crop 2) to quantify its subsequent effect on direct seeded corn, and 3) to identify the mechanisms of this weed suppression. Forage radish cover crops were grown in ten site-years and followed by a corn crop in seven site-years in the coastal plain of Maryland. Forage radish was compared to rye (Secale cereale L.), oat (Avena sativa L.), and no cover crop treatments. Early and typical corn planting dates along with contrasting herbicide management strategies were compared over four site-years. Forage radish did not reduce population or yield in subsequent corn crops. Forage radish provided complete suppression of winter annual weeds in the fall and early spring but the suppression did not persist into the following cropping season. When forage radish cover crops were used in place of pre-plant burn down herbicide treatments to control weeds in early planted corn, some weeds were present at the time of corn emergence but corn yields were not reduced if emerged weeds were controlled with a postemergence herbicide. Controlled environment bioassays involving cover crop amended soil, aqueous plant extracts, and aqueous soil extracts along with a field experiment involving planted weed seeds did not provide evidence of allelopathy. In a residue moving experiment, no difference in spring weed suppression was observed if forage radish residues were removed prior to killing frost in November or left in place to decompose in three of four site-years. These results were supported by planting date experiments where fall ground cover and spring weed suppression was greatest for earlier planting dates of forage radish cover crops. Thus, rapid and competitive fall growth, rather than allelopathy, is the most likely mechanism of weed suppression by forage radish winter cover crop. Strategies to utilize the weed suppression of forage radish cover crops should focus on fall weed suppression and the early spring pre-plant window of weed control.
- ItemWinter annual rye cover crops in no-till grain crop rotations: impacts on soil physical properties and organic matter(2007-07-31) Bilek, Meredith; Coale, Frank J; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Winter annual cover cropping (WCC) is a common management practice subsidized by Maryland to protect water and soil quality. The affect of long-term incorporation of WCC on soil physical properties (SPP) is not well established. We hypothesized by increasing organic inputs WCC would improve SPP. To evaluate the effect of WCC and wheel traffic (WT) on SPP, we studied two long term rotations (corn/rye and corn/fallow) at two locations on the Coastal Plain (CP) and one on the Piedmont. WCC improved SPP, but only during the winter at the CP. High levels of WT compacted soil in both rotations. WCC and wheel traffic had no effect on SPP or organic matter at the Piedmont. We conclude, only during the winter did WCC improve SPP; however, due to the drastic annual changes, we hypothesize this improvement is due to soil disturbance caused by the grain drill planting the rye.