Doctoral Dissertations

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Assessing the Distribution and Impact of Bean pod mottle virus (BPMV) as a Re-emerging Virus, and Soybean mosaic virus (SMV) in Soybean Grown in Virginia
Mackasmiel, Lucas A. (Virginia Tech, 2004-07-12)
Bean pod mottle virus (BPMV, Genus Comovirus, Family: Comoviridae)is an important virus in soybean (Glycine max (L.) Merrill), causing quality and yield loss due to seed coat mottling and seed weight reduction. Although BPMV has been known in Virginia since 1958 and has always been regarded as causing negligible losses, its impact is changing as BPMV incidence has increased in many soybean growing areas of Virginia and the USA in general. From 1997 to 2001, a total of five BPMV isolates (V-W1, V-W2, V-S98-1, V-S98-15 and V-S01-10) were collected in Virginia and characterized. In this study, the effects of these isolates were studied, alone or with Soybean mosaic virus (SMV, Genus Potyvirus, Family Potyviridae) strain SMV G1, and isolates S98-51 and S98-52, on selected soybean cultivars. Individual isolates of BPMV showed variable symptom severity, and resulted in yield loss of between 40.4 to 58.1%, while SMV caused 23.7% in the most severe interactions. Up to 100% yield loss was realized from double inoculations of selected BPMV and SMV isolates, BPMV V-S98-1 + SMV S98-52 and BPMV S98-15 + SMV S98-52 on Hutcheson and Hutcheson Roundup Ready® (BC5) soybeans, respectively. Time of inoculation, a critical factor in the impact of many virus diseases, affected seed coat mottling in four cultivars and seed weight in two cultivars, in tests with four BPMV isolates and three stages of soybean development. All BPMV isolates inoculated to plants at vegetative stage V1-V3 severely increased seed coat mottling and reduced seed weight than those inoculated at V4-V6 and reproductive stage R1-R3. Seedlings grown from non-mottled seeds germinated more uniformly had fewer thin-stemmed seedlings and grew faster than those grown from mottled seeds. Inoculation of various cultivars and breeding lines showed that there was no correlation between the severity of virus-induced foliar symptoms, relative accumulation of SMV, and extent of seed coat mottling. Thus, by avoiding the presence of BPMV at an early growth stage through proper timing of planting to avoid vectors, proper cultural practices like weed control, use of SMV free seeds, and chemical control, it is possible to greatly improve seed quality and reduce yield losses in soybean.
Circadian and Seasonal Variation in Pasture Nonstructural Carbohydrates and the Physiological Response of Grazing Horses
McIntosh, Bridgett J. (Virginia Tech, 2006-12-14)
Nonstructural carbohydrates (NSC), which includes sugars, starches and fructans in pasture forages, undergo circadian and seasonal variation which has direct effects on metabolism in grazing horses. Increased intake of NSC is implicated in the development of digestive and metabolic disorders, such as laminitis. A series of five studies at Virginia Tech's M.A.R.E. Center in April, May, August, and October 2005, and January 2006, examined circadian and seasonal variability in forage NSC content and metabolic and digestive variables in horses over a 36 h sampling period. Fourteen mares were randomly assigned to grazing (housed on a 5-ha predominantly tall fescue pasture; n = 10) or control (stabled within the pasture and fed timothy/alfalfa hay; n = 4) groups. Blood samples were collected hourly from the horses which corresponded to hourly pasture forage samples. In all five studies, plasma glucose and insulin were measured and proxies for insulin resistance were calculated. In the April study, plasma L-lactate and fecal pH, L-lactate, D-lactate and volatile fatty acids (VFAs) were also measured. Two approaches were used for the determination of carbohydrate profiles in pasture forage samples. For the first (LAB1), sugar was water soluble carbohydrates extracted prior to analysis for starch, and included fructans. The NSC was the sum of starch and sugar. For the second (LAB2), samples were analyzed for specific NSC fractions using hydrolytic enzymes, with the addition of HCL for the determination of fructans including graminans, the type of fructans in cool season grasses. Both the LAB1 and LAB2 analyses revealed circadian and seasonal patterns in forage NSC and its constituents. In general, pasture forage NSC content was lowest in the morning and highest in the late afternoon. April had the highest NSC content which was comprised mostly of simple sugars. Forage NSC content (LAB1) was associated with environmental variables in all months with strongest correlations in April; ambient temperature (r = 0.72, P < 0.001), solar radiation (r = 0.62, P < 0.001), and humidity (r = -0.84, P < 0.001). In the animals, plasma insulin was highest in grazing horses in April (P < 0.001) followed by May (P < 0.001). Plasma insulin was higher in grazing compared to control horses at all sample points in April, and a circadian pattern was evident (P = 0.012). In grazing horses, plasma glucose was higher in April than all months except for May, and plasma glucose was higher in grazing horses compared to controls in April. In grazing horses, plasma insulin was significantly correlated with NSC and sugar in April (r = 0.69 and r = 0.67, respectively); May (r = 0.46 and r = 0.47, respectively); and January (r = 0.44 and r = 0.46, respectively). In April only, individual mean insulin response was proportional to the increase in insulin per increase in unit of NSC (r2 = 0.033, P < 0.001). Sinusoidal circadian patterns in NSC (r2 = 0.51, P < 0.001) and insulin in grazing horses (r2 = 0.12, P < 0.001) had similar frequency (P = 0.36). Plasma L-lactate was higher in grazing horses (0.64 mmol/L) than control horses (0.40 mmol/L) (P < 0.001). Fecal pH was lower in grazing horses (pH 6.9) than control horses (pH 7.2) (P = 0.008). Fecal VFAs, including acetic acid, butyric acid, and D- and L-lactate were higher in grazing horses compared to control horses (P < 0.05). These studies identified a link between forage NSC content and alterations in carbohydrate metabolism and digestion that may increase risk of laminitis via exacerbation of insulin resistance. Strategies for management practices to decrease intakes of pasture NSC by horses at risk of developing metabolic disorders are needed.
Community Decision Making Aids for Improved Pasture Resources in the Madiama Commune of Mali
El Hadj, Meriem (Virginia Tech, 2004-11-29)
The lack of forage resources in the Sahelian region of Mali is a major constraint to food production and food sufficiency. Madiama commune is located in northern Mali, in the Niger Delta region. Three separate experiments were conducted to investigate ways to improve pasture resources and productivity. The first experiment (2003) was designed to investigate the influence of sheep grazing tethered at two different residual heights on botanical composition, forage biomass and animal performance. Young sheep weighing approximately 18-24 kg were tethered for a certain period of time depending on residual canopy height. Two treatments 3 or 6 cm residual height were each replicated 4 times. Animals were rotated based on canopy height and each tethered animal followed an 8 paddock rotation. Measurements included forage biomass, plant diversity, animal performance, and botanical composition. The forage species found on these pastures were primarily Schoenfeldia gracilis, Panicum laetum, Setaria palludefusca, Eragrostis turgida, Eragrostis tremula, Zornia glauchidiata, Tephrosia pedicellata, and Cynodon spp. Accumulated seasonal forage biomass increased while forage quality declined as the growing season progressed. Treatment had only a slight effect on animal weight gains (1 to 3kg season-1). These results suggest that residual height may not affect livestock gain. The second experiment was designed to investigate the potential of Cassia tora (C. tora) which is an invasive weed in the region as a supplemental feed for livestock. Cassia tora was harvested within the Madiama commune and ensiled with or without additives (water and or honey/sugar) for 60 or 90 days. Harvest occurred at the vegetative stage in year 1 and mature growth stage in year 2. Prior to placing the chopped material in the bags for ensiling, sub-samples of fresh C. tora were obtained for dry matter (DM) and chemical analysis (NDF, ADF, CP, IVDMD and TDN). In year 1, the ensiled material/fresh material across treatments and locations had NDF varying from 48 to 56 %/ 56 to 57%, ADF from 34 to 41 %/40 to 42%, CP from 9 to 10 %/9 to 23%, and IVDMD from 53 to 64 %/52 to 54%. In year 2, CP averaged twice as much as year 1 with significantly less fiber probably due to the fact that harvest occurred at the vegetative stage. Addition of water or sugar/honey improved the nutritive values of the ensiled material. These results suggest that C. tora can be a reliable feed source during the dry season. A greenhouse experiment was conducted using various P sources (Tilemsi phosphate rock (TPR), North Carolina phosphate rock (NCPR), Aluminum phosphate (AlP), Iron phosphate (FeP), and Triple superphosphate (TSP) and rates (0, 20, 40, 60, and 80 mg P kg-1 soil). Plants were grown for 10 wks, harvested and separated into above and below ground plant parts. The root and plant material were dried, ground and analyzed for elemental P. The result showed variable P solubility and uptake by the plant. Overall, addition of P resulted in an increase in above ground biomass as well as root mass compared with the untreated control. Field and greenhouse experiments showed that in the Sahel region of Africa where feed resources are scarce 8 out of 12 months a year, anything we can do to increase pasture resources and animal productivity while maintaining a healthy ecosystem, could improve the quality of life in the community.
Cotton Yield as Related to Selected Physical and Chemical Properties of Soils of the Coastal Plain of Virginia and North Carolina
Adcock, Clyde Wesley (Virginia Tech, 1998-08-28)
Cotton (Gossipium hiristum, L) is a warm season perennial with indeterminant growth habit. In 1995, 42,500 and 300,000 hectares were grown in Virginia and North Carolina, respectively. Soil physical and chemical properties may limit cotton yields. The objective of this study was to; 1) determine influences of soil physical and chemical properties on yield, 2) validate existing preharvest yield estimators, and 3) determine the effect of subsoiling and/or subsurface liming on cotton development and root growth. Two hundred sites were sampled across the Coastal Plain of Virginia and North Carolina to a depth of 92 cm representing 5 major soil series. Soil samples were analyzed for selected physical and chemical properties from each horizon. Boll and plant counts were obtained while harvesting a 3-meter length of row at each site to determine yield for the 1996 and 1997 growing season. Cotton was grown in the greenhouse on 30 cm diameter cores of a soil with low subsoil pH and a hard pan to determine the effects of subsoiling and/or subsurface liming. Ninety days after planting, the cotton plants were harvested and the above ground biomass and rootmass were analyzed. Physical and chemical properties explained 52% of yield variability in 1996 and 27% in 1997. Physical and chemical properties that were significant to yield were surface bulk density, available water holding capacity, depth of the water table and Bt horizon, Mg, K, Ca, and Al content. Soil analysis for nutrient status at depths up to 45 cm were better indicators of cotton yield. Subsoiling with or without subsurface liming increased rooting depth over the untreated check. The subsurface liming reached first flower 11 days prior to the other treatments. The additional period for flowering and boll set in Virginia and North Carolina could increase potential yield.
The Effect of Three Fescue Types and Lakota Prairie Grass on Copper Status, Dry Matter Intake, and Alkaloid Appearance of Beef Steers
Stewart, Robert Lawton Jr. (Virginia Tech, 2006-10-27)
Tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] is an important forage crop in the United States and covers over 14 million ha. The presence of Neotyphodium coenophialum, an endophytic fungus in tall fescue, is associated with several disorders in grazing livestock, but also increased persistence of tall fescue. These disorders, commonly called fescue toxicosis, are responsible for large economic losses in the beef cattle industry each year. This research examined the effect of three fescue types [endophyte-infected Kentucky 31 tall fescue (E+), endophyte-free Kentucky 31 tall fescue (E-), non-ergot alkaloid-producing endophyte Q4508-AR542 tall fescue (Q)], and Lakota prairie grass (L; Bromus catharticus Vahl.) on animal response, alkaloid appearance, DMI, and copper status. Ergovaline (EV) is the most abundant ergot alkaloid in tall fescue and has previously been considered the causative toxin in fescue toxicosis. More recently it is simpler ergot alkaloids, such as lysergic acid amide (LSA) have been implicated. The objective of the first project was to evaluate animal performance and alkaloid (EV and LSA) appearance in forage and ruminal fluid of steers grazing E-, Q, E+, and L. Average daily gains were greater (P < 0.05) on E-, Q and L compared to E+, and there was a trend (P = 0.11) for gains on E- to be higher than with Q. The seasonal appearance of LSA in ruminal fluid was similar to the seasonal pattern of alkaloids in E+ forage. Ergovaline was not detectable in ruminal fluid of steers grazing E+. Alkaloids were not detectable in forage or ruminal fluid of steers grazing E-, Q, or L. The appearance of LSA in ruminal fluid of steers grazing E+ suggests that this alkaloid may contribute to fescue toxicosis. Low DMI of animals grazing E+ tall fescue is considered a key factor in decreased animal performance compared to other fescue types. The objective of the second project was to evaluate DMI of steers grazing E-, E+, Q, and L pastures using the alkane technique. Dry matter intake of steers grazing E- was greater (P < 0.001) than Q, E+, and L and DMI of steers grazing Q and E+ were similar (P > 0.10) in 2004. In 2005, DMI did not differ (P = 0.23) among fescue types. These results suggest that decreased DMI effects ADG of steers grazing E+ compared to those grazing E-, and lower DMI of Q suggests that the fescue variety Q4508 may not be the optimal variety for the incorporation on non-ergot alkaloid-producing endophytes. Reactive oxygen metabolites such as superoxide (O₂⁻) are produced by both endogenous and exogenous sources and an accumulation of these compounds can result in oxidative stress. Copper/zinc superoxide dismutase (SOD) is a Cu-based antioxidant metalloprotein that acts as a defense against oxidative stress by the scavenging of O₂⁻. Neotyphodium-infected tall fescue is typically lower in Cu which could potentially increase oxidative stress of animals grazing this forage. Therefore the objective of the third project was to investigate the Cu and SOD status of steers grazing E-, E+, Q, and L forages. Copper levels of all forages were below the dietary requirement (10μg Cu/g DM) of growing cattle. In 2004, steers grazing E+ exhibited lower (P <0.05) liver Cu compared to E- and Cu intake was lower (P < 0.001). Cu/Zn SOD enzymatic activity and mRNA relative expression did not differ (P > 0.10) among treatments. Copper intake of steers grazing E+ tall fescue was sufficient to maintain, but not replenish liver Cu, and SOD status did not appear compromised by grazing E+ at these Cu levels.
Effects of Biofertilizers and Organic Amendments on Nutrient Availability in Soil and Plant Growth
Mott, Joshua Darell (Virginia Tech, 2022-04-28)
Applications of fertilizers derived from non-renewable resources, along with improved land management practices have contributed greatly increased crop yields in the past 70 years. Biofertilizers and organic amendments, provide alternative sources of nutrients for increased plant yields and resistance against abiotic stress. The objective of this work was to evaluate the effectiveness of various biofertilizers and an organic amendment on improve plant health and/or crop yield. The first study focused on the organic amendment, glucoheptonate and found that applications of 800-1600 kg/ha can increase available water capacity in fine textured soils by up to 3%. The second study evaluated the effectiveness of dual-inoculating biofertilizers Mung beans (Vigna radiata (L.) Wilczek) with two, bradyrhizobium spp. and arbuscular mycorrhizal fungi. Dual inoculation significantly increased grain yield (+33%) compared to a synthetic N fertilizer application but did not significantly increase grain yield compared to the control (+22%). Dual inoculation may increase grain yields of mung beans compared to synthetic fertilizer regime but does not show evidence of improving N fixation. The final study was a greenhouse experiment focused on evaluating some mung bean cultivars to determine their susceptibility to salt stress while also evaluating the effect of inoculation in combating saline soils. Germination was significantly decreased at 6 dS/m in all cultivars by about 36% when compared to the control treatment (0 dS/m). Seed yields, pods per plant and seeds per plant, increased as salt concentration increased. No factors recorded where affected by inoculation. Overall, our research suggests that the use of biofertilizers and organic amendments can improve crop health, but other management and environmental considerations need to be accounted for when reporting effectiveness of such alternative soil amendments
Estimating forage mass of tall fescue pastures and dry matter intake and digestibility of fescue forage by beef steers
Lopez-Guerrero, Isaias (Virginia Tech, 2005-01-13)
A series of three experiments were conducted to evaluate different methods of estimating forage mass of tall fescue pastures, and dry matter intake and digestibility in beef steers under indoor and grazing conditions. Forage mass was estimated with the herbage cutting method (HCM) and three indirect methods; the pasture capacitance meter (PCM), the plate meter (PPM), and the visual estimation (VE). The coefficients of determination from the calibration equations were 0.686, 0.751, and 0.862 for the PCM, PPM, and VE, respectively. There were differences in forage mass estimates due to sampling method, sampling date, and their interaction. The second experiment was a digestion trial conducted with confined animals to determine the recovery rate of chromic oxide and alkanes from controlled release capsules and to evaluate the accuracy of the concurrent estimations of intake and digestibility. No difference was found in the recovery rate of either alkanes or chromic oxide during the 7 d of the collection period. Likewise, actual fecal output, dry matter intake, and digestibility were not different from the estimated values. However, estimated values had to be adjusted for the respective recovery rate. The third experiment was conducted under grazing conditions to evaluate the chromic oxide controlled release capsule technique in estimating intake and digestibilty. In this trial, although the recovery rate of the marker was extremely high (avg. = 1.89), the actual and estimated values of dry matter fecal output, intake, and digestibility were not different. Again the recovery rate had to be used as a correction factor.
Evaluation of florpyrauxifen-benzyl for use in pastures and hayfields
Greene, Wykle (Virginia Tech, 2021-12-07)
Weed control is a critical component in pastures and hayfields in order to ensure maximum forage yields. Typically, broadleaf weed control in pastures and hayfields is achieved through the use of synthetic auxin. However, these herbicides also control desirable broadleaf species such as forage legumes, including white clover. Use of herbicides can lead to severe injury and often complete elimination of white clover, making it difficult for producers to maintain legumes in mixed grass-legume swards while controlling weeds. It is often desirable to have legumes present in the sward due to their high nutritive forage value and ability to fix nitrogen compared to grass only swards. Florpyrauxifen-benzyl + 2,4-D is a new herbicide which is reported to control broadleaf weed species, while preserving white clover. Little published research exists on this herbicide, particularly for use in pastures and hayfields. Research evaluating sward composition indicates that florpyrauxifen-benzyl + 2,4-D is effective in controlling broadleaf weed species while also preserving greater amounts of white clover than any other herbicide treatments. Florpyrauxifen-benzyl + 2,4-D also resulted in significantly more forage grass production than the nontreated control. Florpyrauxifen-benzyl + 2,4-D was less effective than other herbicides when applied via fertilizer impregnation. Additional research assessing the spectrum of broadleaf weed control found that florpyrauxifen-benzyl + 2,4-D is a viable herbicide for the control of several broadleaf weed species including bulbous buttercup, Canada thistle, broadleaf plantain, plumeless thistle, and common ragweed. However, florpyrauxifen-benzyl + 2,4-D was less effective than other herbicides for controlling certain weeds, such as horsenettle. White clover was injured from florpyrauxifen-benzyl + 2,4-D, but was able to fully recover in 90 to 120 days. There were no differences in white clover response between the four varieties tested. When evaluating establishment of forage species, florpyrauxifen-benzyl + 2,4-D did not injure or reduce biomass of tall fescue or orchardgrass plantings, indicating a high level of safety. Florpyrauxifen-benzyl + 2,4-D was also safe to both drilled and frost seeded clover when applied prior to and at planting. Greenhouse trials revealed that flowering white clover is more sensitive to herbicides compared to vegetative white clover, and that safety of white clover to florpyrauxifen-benzyl + 2,4-D is dependent upon use rate. Considerations such as weed species present, and the amount of white clover injury that is considered acceptable will dictate the decision to utilize florpyrauxifen-benzyl + 2,4-D in pastures and hayfields. This research demonstrates the effectiveness and overall utility of florpyrauxifen-benzyl + 2,4-D for use in pastures and hayfields due to the effectiveness of weed species as well as the level of safety to white clover.
Exploring Teaching Practices of the Agricultural Education at Bangladesh Agricultural University (BAU)
Kuri, Subrato Kumar (Virginia Tech, 2021-06-29)
The purpose of this study was to understand the teaching practices of the Agriculture Faculty at Bangladesh Agricultural University (BAU). This study is at the intersection of the critical assessment and examination of assumption and exploring options and plans stages of transformative learning theory (Mezirow, 2000) and the environment factor of Astin's I-E-O model. Previous studies showed that tertiary education of Bangladesh fails to develop critical thinking abilities among the students. Higher order teaching practices help to develop critical thinking abilities among the students. Thus, it is important to explore the level of teaching practices at the Agriculture Faculty of BAU to understand how it supports critical thinking abilities among the students. Graduates being able to use critical thinking skills to solve agricultural issues will increase total food production and reduce national poverty. This study was an instrumental single case study. Faculty of Agriculture of BAU was the unit of analysis for this study. The findings of this study were only generalizable to the Agriculture Faculty at BAU and only relevant for Summer 2020. The phenomenon of this study was teaching practices at the Agriculture Faculty of BAU. Data sources included a census survey of active faculty members and content analysis of course syllabi. Findings from this study suggested that both teaching methods and course learning outcomes of the courses of the Agriculture Faculty at BAU were related the lower order of Revised Bloom's Taxonomy (RevBT). Moreover, faculty members from biological science and engineering used more teaching practices from evaluating level of RevBT than social science disciplines. Evaluating level is considered as higher level of RevBT. Male faculty members also used more teaching practices related to analyzing level than female faculty members. Analyzing level is also considered as higher level of RevBT. Faculty members identified that they have lack of training, standard teaching resources to use higher order teaching practices. Moreover, they also said that students of the Agriculture Faculty at BAU are more interested in job preparation than classroom education. However, faculty members also felt that higher order teaching practices can improve the creativity and critical thinking abilities for students and brings enthusiasms in teaching. Faculty members recommended that BAU revise its curriculum, syllabi, and assessment strategies to create higher order teaching practices in classrooms. As a result of this study, there is opportunity for faculty to increase their use of higher order teaching practices and develop course outcomes that support higher order learning. In addition, the university should revise their existing curricula and assessment techniques and give more freedom to the faculty members to choose their teaching and assessment methods. Finally, training should be organized to support higher order teaching by female faculty members.
Fatty Acid Composition of Diets, Metabolism, and Deposition in Subcutaneous Adipose Tissue of Pasture and Feedlot Finished Cattle
Guay, Jennifer Fincham (Virginia Tech, 2005-04-06)
An experiment was conducted to evaluate the effects of pasture finishing versus high-concentrate finishing, over time, on fatty acid metabolism in Angus crossbred (n = 24) beef steers. Ruminal fluid, serum, and adipose tissue biposies were obtained on d 0, 28, 84, and 140. Pasture forages and diet ingredient samples were obtained at 14 d intervals to determine nutritive value and fatty acid composition. The high-concentrate diet consisted of corn silage, cracked corn, soybean meal, and a vitamin and mineral supplement. The pasture-finished steers grazed sequentially on triticale (Triticale hexaploide)/annual ryegrass (Lolium multiflorum), alfalfa (Medicago sativa)/orchardgrass (Dactylis glomerata), and a cool-season grass/legume mixture. The high-concentrate diet consisted of 57 % linoleic acid and 7 % linolenic acid (of total fatty acids). The pasture forages contained an average 9 % linoleic acid and 66 % linolenic acid (of total fatty acids). Adipose tissue concentrations of 18:2 cis-9, trans-11 CLA were higher (P < 0.05) in the pasture-finished steers than high-concentrate finished steers. Concentrations of 18:2 cis-9, trans-11 CLA declined in the high-concentrate finished steers (P < 0.05) from d 0 to 28 and d 28 to 84. In the pasture-finished steers concentrations peaked (P < 0.10) on d 28, and remained high throughout the duration of the study. Concentrations of linolenic acid were higher (P < 0.05) in adipose tissue, ruminal fluid, and serum of the pasture-finished steers, compared to the high-concentrate finished steers. In the pasture-finished steers linolenic acid concentrations peaked (P < 0.05) on d 28, and remained high throughout the study. Concentrations of linolenic acid gradually decreased (P < 0.05) over time within the high-concentrate finished steers. Thus, it appears that only a short time is needed to alter the omega-3 and CLA composition of adipose tissue in cattle finished on pasture.
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 grazing sheep and cattle together and separately on soils, plants and animals
Abaye, Azenegashe Ozzie (Virginia Tech, 1992-02-25)
Angus cows (Bos taurus) with calves and 1/2 Dorset, 1/4 Finn and 1/4 Rambouillet ewes (Ovis aries) with lambs grazed Kentucky bluegrass (Poa pratensis) - white clover (Trifolium repens) in a randomized block design with three replications during 3 yr, to investigate effects of grazing cattle and sheep together and separately on soils, plants and animals. Additionally, changes in stocking rate, seasonal distribution of cool-season forages and varying nutritional requirements of animals were examined. There were 6 cow-calf pairs or 6 ewes with 11 lambs per replication of cattle alone and sheep alone treatments. Six cows plus six ewes, with their offspring, were allotted to each replication of mixed grazed pastures. Initial stocking rates were equilibrated among treatments to 1 cow and calf per .45 ha. Grazing sheep alone increased (P < .05) percentage bluegrass (58%) but decreased white clover (6%) and weeds (36%), compared to pastures grazed only by cattle (30, 16 and 53%, respectively, which was similar to initial composition). Soils in mixed grazed pastures remained higher (P < .05) in plant nutrients, pH, and percent organic matter and were less (P < .05) compacted, compared to soils where sheep or cattle grazed alone. Total forage mass and quality were higher (P < .05) in mixed grazed pastures, compared to pastures grazed by cattle and sheep alone. Daily gain (.23 kg/d), total gain (23 kg), and weaning weights (43 kg) of lambs were higher (P < .01) in pastures grazed by both animal species, compared to sheep alone (.18 kg/d, 19 and 38 kg, respectively). These animals also reached target weaning weights (43 kg) 14 d earlier (P < .05) than those grazed alone. Body condition of ewes was improved by the breeding season, compared to ewes grazed alone. Five measuring techniques were investigated to determine forage mass and botanical composition. Measurements based on small plots permanently located within pastures were as accurate as those based on the entire pasture. Visual estimations of forage mass were lower, compared to hand clipping, but reflected canopy height. Visual evaluations more accurately estimated presence of individual plant species than hand separated samples. Grazing ewes and cows with associated spring-born offspring on bluegrass-white clover improved the balance between plant growth and animal forage requirements and improved sustainability of the soil-plant-animal system.
Manure and Nutrient Accretion, Partitioning, and Excretion in Holstein Heifers
Hill, Stephanie R. (Virginia Tech, 2006-11-10)
Considerable changes have occurred in environmental regulations in recent years, only one of which is the requirement of stand alone heifer operations and feedlots to carry environmental permits. While growth of heifers is a widely researched topic, publications concerning nutrient utilization, partitioning, and excretion are scarce and are becoming necessary. That combined with the fact that feeding programs for heifers are highly variable from region to region and even from farm to farm indicated the need to examine the effects of diet on nutrient utilization. Therefore, the objective of this work was to evaluate how differences in levels of dietary protein and energy will affect growth and nutrient utilization in heifers from birth to calving. Two projects were conducted, one in 20 month old bred heifers where forage level in the diet was altered to provide the required nutrients in less feed and one in young calves where energy and protein content of the milk replacer was altered. Three diets were fed to 18 (n=6), 20 month old heifers who were in late gestation; the first was the high forage (HF) ration which was 90.7% forage and 9.3% concentrate, the second was a by-product (BP) ration which was designed to have the same level of fiber as the HF ration, however soybean hulls and cottonseed hulls were added at the sacrifice of the grain mix which increased the fiber content; the last ration was the low forage (LF) which was 54.7% concentrate and 45.3% forage and was fed at ~89% of the ad libitum intake of heifers fed the HF ration. Heifers fed the HF ration had greater fecal excretion compared to those fed LF, however heifers fed the LF ration exceeded the heifers fed HF and BP by 4.5 and 2.5 times, respectively, in urine volume excretion (40.2 vs. 8.9 and 16.9 kg/d, respectively). Although total N excretion (kg/d) was not different, heifers fed the LF ration tended to partition more N to urine than to feces. Phosphorus excretion in the feces was not different, however heifers fed HF and BP tended to have greater fecal P (P < 0.06). Urinary P excretion was less in heifers fed HF and BP compared to LF, however these heifers were excreting as much urinary P as a lactating cow. Calves were purchased from a commercial dairy at 3 d old (± 1d) and transported to the VT Dairy Center. They remained on study until 63 d when they were harvested for body composition. Four treatment diets were fed; a control milk replacer (24/17; 24% CP, 17% Fat), a high protein, low fat (32/17; 32% CP, 17% Fat), a high protein, high fat (31/24, 31% CP, 24% fat), and that same 31/24 milk replacer fed at 1460 g/d powder (31/24+). Calves were offered a 20% cottonseed hull starter at 1 d after arrival to the VT Dairy Center. Calves fed 24/17 consumed more starter than those fed the other milk replacers and therefore had a lower apparent digestibility and greater fecal excretion. Fecal N excretion was not different, although calves fed 24/17 tended to have greater fecal N excretion. Urinary N excretion was higher in calves fed 31/24+ compared to those fed 31/24. Total N excretion and N retention were not different. Empty body weight (EBW) gain was greater in calves fed 31/24+ compared to 31/24, however those same calves also had a higher percent of EBW as fat. Calves fed 32/17 had the most lean gain (in the form of N gain) compared to those fed extra energy (31/24) and also had a higher N as a percent of EBW. Limit feeding Holstein heifers late in gestation did not reduce nutrient excretion, however, more digestible nutrients were available to the heifer and fetus. Heifers in late gestation are likely over fed P and therefore excrete nearly everything they consume which has negative implications for nutrient management planning. Calves fed a low protein, low fat milk replacer did not grow as well as calves fed higher protein. Nitrogen retention and CP gain were higher when protein was at least 31% and fat was at least 17%. Feeding fat over 17% only increased fat gain and not CP gain. Overall, paying for extra nutrients in bred heifer diets seemed to be beneficial, however, feeding above 31% CP and 17% fat increased nutrient loss to the environment.
Mungbean [Vigna radiata (L.) Wilczek]: Protein-rich Legume for Improving Soil Fertility and Diversifying Cropping Systems
Diatta, Andre Amakobo (Virginia Tech, 2020-04-21)
Drought, salinity, and low soil fertility have negative impacts on agricultural productivity, resulting in food scarcity and nutritional insecurity, particularly in Sub-Saharan Africa. Mungbean [Vigna radiata (L.) R. Wilczek] has seen increased interest as a short-duration and drought tolerant legume crop, capable of atmospheric N₂ fixation. Mungbean is a protein and iron-rich legume and can be used as vegetable or grain for human consumption or multipurpose crop. At present, few studies have simultaneously explored the best agronomic practices for mungbean cultivation and evaluated its potential for increasing crop yields via intercropping systems and improving soil fertility through biological N₂ fixation. To understand the agronomic practices and soil physical properties limiting mungbean production, the impacts of two mungbean cultivars (Berken and OK2000) with and without inoculation with Bradyrhizobium spp. grown in loamy sand and silt loam soils on mungbean growth and yield were investigated under glasshouse conditions. Promising results from this study led to the introduction of mungbean into pearl millet systems in Senegal and evaluation of the effects of intercropping on growth, yields, land equivalent ratio (LER), canopy cover estimates, and normalized difference vegetation index (NDVI). Finally, we evaluated plant growth and N₂ fixation of five mungbean genotypes grown in two soil textures using the ¹⁵N natural abundance technique leading to recommendations for those with the greatest overall benefit to the cropping system. The literature review shows mungbean often proposed as a strategic crop for increasing legume diversification within current cropping systems and providing increased food security as well as market diversification and economic sustainability. The greenhouse study revealed that OK2000 cultivar produced significantly higher yield when inoculated and planted on a silt loam soil than other treatments, indicating the importance of inoculation and soil texture in mungbean establishment. Intercropping mungbean and millet significantly (p≤ 0.05) increased combined yields (35% to 100% increase) and LER compared to sole millet cropping systems. Canopy cover estimates and NDVI values significantly increased up to 60% and 30%, respectively, in millet-mungbean intercropping over millet alone. The N2 fixation study showed that %Ndfa of mungbean was higher when grown in the loamy sand soil (27% increase). However, soil N uptake (235 mg plant⁻¹) and amount of N fixed (67 mg plant⁻¹) were greater in the silt loam soil. Among genotypes, IC 8972-1 significantly (p≤ 0.05) derived less N from the atmosphere (23%) but took more soil N (155 mg plant⁻¹) which yielded significantly greater dry biomass (7.85 g plant⁻¹) and shoot N content (200 mg plant⁻¹). The results from the N₂ fixation study indicated that choice of mungbean genotype can contribute to reducing N needs of agricultural systems. Overall, this research project demonstrated that mungbean has the potential for diversifying smallholder agriculture and adding biologically fixed N into soils, in line with transformative adaptation strategies being promoted for sustainable agriculture. Further research and development programs on good cultural practices, adaptation to cropping systems, and nutritional benefits for human consumption can promote mungbean cultivation in SSA.
Nitrogen and Sulfur Management in Soybean and Edamame Production in the Mid-Atlantic Coastal Plain
Brooks, Keren Ruth (Virginia Tech, 2023-01-23)
The United States is a world leader of soybean [Glycine max (L.) Merr.] production, but to maintain quality production at this level, soybean management needs to be continually monitored and improved. Sulfur (S) deficiencies in soybean have become more frequent in the U.S. due to fertilizer purity, emissions regulations, and higher yields. We completed a study for soybean grown in sandy loam soils in the mid-Atlantic coastal plain system to determine proper S fertilizer rate and application timing. Yields ranged from 1,236-4,051 kg ha-1. Neither S rate nor application timing influenced yield. S treatments increased methionine concentration (methionine = -0.0001 S rate2 + 0.002 S rate + 5.60). Sulfur fertilization can improve soybean quality and may impact marketability. Another study was conducted to determine optimal source and rate of S application for soybeans in the Mid-Atlantic coastal plain system. Yields ranged from 1,316-4,914 kg ha-1. While sulfur rate did not influence yield and fertilizer source responses were site-specific. Sulfur leaf tissue concentrations were directly related to S rate (S concentration = 0.004S rate + 2.103). Nutrient uptake responses to S fertility indicate the potential for S yield responses in the future when soils become S depleted and contain less available S. Soybean producers and retailers in the United States are interested in capitalizing on new edamame markets to provide a domestic product. To aid the shift from oilseed production to vegetable production, a study was conducted to determine the optimal N rate and N application timing for edamame yield and quality in the Mid-Atlantic coastal plain system. Nitrogen rate significantly increased yield one out of three years (Yield = 29.9N Rate + 3387) when all N was applied at planting but was not significant with split applications. Fertilizer rate and timing did not impact edamame maturity or final pod/bean quality. N fertilizer applied at-planting may aid edamame yield and profit for sandy loam soils in the mid-Atlantic, USA. Currently, mid-Atlantic coastal plain soils, coupled with S deposition, are able to supply enough S for soybean growth and development, but without fertilization soybean soils are being mined of S and will eventually become depleted. Sulfur must be monitored if future deficiencies are to be avoided. Nitrogen fertilizers may improve yield in vegetable soybean production. Both oilseed and vegetable soybean farmers should continue to monitor soil nutrient levels to ensure proper nutrition for soybean growth and development.
Nutritional and PGR effects on lipid unsaturation, osmoregulant content, and relation to bermudagrass cold hardiness
Munshaw, Gregg C. (Virginia Tech, 2003-07-30)
Winter injury of bermudagrass (Cynodon spp.) continues to be a problem across the transition zone. In an attempt to delay or induce winter dormancy while maintaining cold hardiness, applications of seaweed extract (SWE) (0.54 kg ha-1), ethephon (16 L ha-1), Fe (1 kg ha-1), and N (49 kg ha-1) took place every three weeks during the fall of 2001 and 2002. Cultivars examined included 'Riviera', 'Midiron', 'Princess', and 'Tifway'. Tifway exhibited greatest fall color retention in both years of the study. Ethephon promoted early senescence and turfgrass quality during fall ratings in both years of the study while N, Fe, and SWE increased quality over the control in 2001 and only N showed better quality and color retention over the control in 2002. Samples removed from cold acclimated plots were artificially frozen as a measure of cold hardiness. Treatments did not have an effect on post freeze regrowth, however, cultivar was significant in both years. Midiron showed best regrowth followed by Riviera, Tifway, and Princess. In both years Riviera and Midiron displayed the quickest and greatest amount of spring greenup followed by Tifway and then Princess. Ethephon reduced greenup in both years and SWE, Fe, and N showed no differences from the control in 2001 and Fe showed significantly better greenup in 2002. Proline and Linolenic acid levels were highest in Midiron, followed by Riviera, Tifway, and Princess. Nitrogen, SWE, and Fe generally did not have an effect on linolenic acid and no consistent effects were noted on proline concentration. Ethephon treatments did not have an effect on linolenic acid levels, however, there was a negative effect on proline concentrations. The results of this study indicate that judicial N applications during the fall can promote color retention and do not have a negative effect on bermudagrass cold-tolerance. Linolenic acid and proline findings also help to explain differences in cold-tolerance between different bermudagrass cultivars.
Spatial Allocation of Forages and Its Impact on Grazing Behavior, Diet Selection and Dry Matter Intake of Beef Steers
Boland, Holly Terry (Virginia Tech, 2009-01-26)
Previous research on grazing behavior has shown that ruminants will select a mixed diet. The use of adjacent monocultures is an essential tool for determining dietary preference of forages. Much of the work to date has been conducted with white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.). Partial preference for white clover over ryegrass has been reported consistently and partial preference for legumes is thought to occur regardless of the legume and grass species being evaluated. Two forage species, tall fescue (Festuca arundinacea Schreb. or Lolium arundinaceum (Schreb.) S.J. Darbyshire) and alfalfa (Medicago sativa subsp. sativa L.), which had not been evaluated together previously as adjacent monocultures were grazed by beef steers in the present set of experiments. Steers exhibited a partial preference for alfalfa of 61 to 65% when given a choice of grazing alfalfa or tall fescue as adjacent monocultures, regardless of the ground area proportion of the two forages offered. Steers grazing tall fescue monocultures spent more time ruminating (P = 0.02) and tended to graze less time (P = 0.06) than steers in adjacent monoculture treatments. Time spent idling, number of prehensions and mastications, and bite rate were similar (P > 0.05) among treatments. Steers grazing tall fescue monocultures spent less time standing, more time lying, were less active and took fewer steps (P ≤ 0.05) than steers in adjacent monoculture treatments. Grazing behavior was examined when alfalfa had not been in the previous diet of the steers. Cattle without previous experience grazing alfalfa spent 78% of the time grazing alfalfa, whereas after having experience grazing it they spent a lower (P = 0.04) proportion of their time grazing alfalfa (72%). Overall proportion of the day spent grazing both forages was lower (P = 0.0001) when alfalfa was novel (40%), compared to when steers were experienced grazing both forages (46%). Proportion of the day spent idling was greater (P < 0.0001) when alfalfa was novel (35%), compared to when both forages were familiar to the steers (26%). Previous research has reported that ruminants exhibit a diurnal pattern of preference by decreasing the proportion of white clover consumed from morning to late afternoon while increasing the proportion of perennial ryegrass in the diet. This is thought to be a strategy to increase fiber intake before nightfall or as a response to higher carbohydrate levels in grass in the afternoon. In the present study, proportion of grazing time in alfalfa was higher (P = 0.02) in the afternoon (76.8 %) than in the morning (72.1 %). While fiber concentration was higher in the tall fescue, carbohydrate concentrations were similar. Steers were not attempting to increase fiber intake in the afternoon in the present study. Dry matter intake of steers grazing adjacent monocultures of alfalfa and tall fescue was estimated with n-alkanes. Diet composition was estimated using n-alkanes and long chain alcohols (LCOH) in several different combinations. The use of LCOH added additional characterization of the forages, but diet composition estimates were not different (P ≥ 0.22) than when estimated using four different n-alkanes. Laboratory analysis costs may be reduced if n-alkanes alone can adequately characterize the forages being consumed, depending on the forage species in question. Meteorological conditions impacted DMI with intake being less in hotter conditions. Steers had similar partial preferences for alfalfa over tall fescue (P = 0.13, 79% and 70% alfalfa in yr 1 and 2, respectively) even though total DMI differed between years (P = 0.002, 9.4 kg d-1 and 4.5 kg d-1 in yr 1 and 2, respectively). Lower DMI in yr 2 was attributed to hotter air temperatures. When animals are consuming two different forages as adjacent monocultures such as in the current experiments, it is important to determine the proportion of each forage in the diet before calculating DMI using odd chain n-alkanes of the forage along with a dose even chained n-alkane. Dry matter intake can be overestimated if the proportion of the forages consumed is not estimated and accounted for in the equation. This would apply to other studies utilizing mixed swards or any diet containing multiple components that differ in concentration of the n-alkane being used for DMI estimation. Analysis of n-alkane concentration should be performed on each item in the diet and the proportion of each item in the diet estimated so that the right value can be used in the calculation. Differences in marker concentrations between years also indicate the importance of analyzing those concentrations in the feed or forage at the time of fecal collection and not using values reported from previous research.
Studies on the Plasticity of Dormancy and on Aging in Switchgrass Seeds
Shen, Zhengxing (Virginia Tech, 1997-07-02)
The dormancy of switchgrass (Panicum virgatum L.) seeds may be broken by a variety of treatments, including after-ripening and stratification. This study was conducted to investigate and characterize more systematically factors affecting both after-ripening and stratification effectiveness, and the aging that can occur concomitantly with after-ripening. More than one year of after-ripening at ambient temperature and humidity was necessary for germination of newly harvested seeds to increase from as low as 5% to around 80%. After-ripening was not accelerated at temperatures above ambient for seeds stored in paper bags, which permitted the loss of seed moisture at the increased temperatures. Both after-ripening and aging accelerated with increases in temperature (5 to 60°C) and seed moisture content (50 to 130 g kg⁻¹), except that there was evidence of a moisture optimum for after-ripening that shifted downward as temperature increased. For many seedlots, storage at 60°C and 50 g kg⁻¹ seed moisture content for about 1 mo broke most of the dormancy and resulted in acceptably low numbers of abnormal (aged) seedlings. Decreases in germinability caused by post-stratification drying of switchgrass seeds (described herein as "reversion", in which the reverted seeds could be made germinable again by further stratification) increased as the desiccation increased. Revertibility decreased as stratification or after-ripening time increased. Stratification and after-ripening worked additively to release switchgrass seeds from dormancy. Reversion (germination with stratification minus germination after stratification followed by drying) may reveal seedlot differences and changes over time and moisture content that can not be seen otherwise. Imbibed, dormant seeds placed at 21 or 30°C were induced into deeper dormancy, as indicated by length of stratification needed to break the dormancy. Dormancy deepened more as storage temperature and time increased for imbibed seeds. There are transitional temperature and seed moisture ranges where opposing processes (aging vs. after-ripening, stratification vs. dormancy deepening) appeared to overlap or surpass one another. Switchgrass seeds, either on a single seed level, or on the population level, responded continuously to changing temperature and moisture conditions. Less aging was observed for switchgrass seeds stored in N₂. After-ripening of switchgrass seemed not to be influenced by N₂ or air. In sum, switchgrass is revealed to be remarkably plastic in its ability to move toward both greater germinability and greater dormancy.
Switchgrass as an Energy Crop: Fertilization, Cultivar, and Cutting Management
Lemus, Roque Wilson (Virginia Tech, 2004-01-09)
Switchgrass (Panicum virgatum L.) has potential as a biofuels feedstock. Major management questions include cultivar selection, cutting management, and optimizing N fertilization. Four cultivars of switchgrass were evaluated under two cutting regimes at eight locations within KY, NC, TN, VA, and WV in 2000 and 2001. Harvests were made once (in early November) or twice (midsummer and early November). Biomass yields averaged 15 Mg ha-1 and ranged from 10 to 22 Mg ha-1 across locations and years. There was no yield advantage to taking two harvests of the lowland cultivars ("Alamo" and "Kanlow"). If harvested twice, the upland cultivars ("Cave-in-Rock" and "Shelter") provided yields equivalent to the lowland ecotypes. A closer look at Alamo revealed much higher N removal in the midsummer harvests, late-season N translocation out of tillers, and fewer tillers developing under one-cut management. Switchgrass appears to be capable of truly perennial productivity in the upper Southeast USA with 50 kg N ha-1 yr-1 and a single harvest. A second field study was conducted on "Cave-in-Rock" switchgrass at Orange and Blacksburg, VA to examine N dynamics. For the 3-yr study, N fertilizer was applied once in May 2001 at 0, 90, 180, or 270 kg N ha-1. Switchgrass was harvested once (early November) in 2001 and twice (early July and early November) in 2002 and 2003. Tissue, root, and soil samples were collected in May, July, September, and November each year. Nitrogen fertilization had no effect on yield in 2001 and small residual effects in 2002 and 2003. Higher N removal was observed with two-cut management, where a high-yielding July cut had high shoot N concentrations. The amount of N removed as biomass from the 0 N treatments over 3 yr was 227 kg N ha-1; obviously significant amounts of N can be made available by these soils without any fertilizer applied. During the growing season, higher mineral N in soil was observed in July and September, when warmer temperatures increase microbial activity and N mineralization. Nitrogen use efficiency declined with increasing N rates. The low N response could be due to "native" N, to microbiological interactions, and/or to the ability of the plants to create internal N reserves. Proper N management of switchgrass must take into account the dynamics of several N pools. Greenhouse studies were conducted to establish switchgrass' responses to N and P under well-defined, soilless conditions and to examine two N sources. Shoot biomass increased with N fertilization with an observed inflection point at 210 kg N ha-1. In these pot studies, root biomass increased with N only to 115 kg N ha-1. No significant effect of P above 30 kg ha-1 was observed in shoot or root biomass. Biomass yield and tiller number were highly correlated. Biomass production was two times greater with ammonium sulfate than with urea when each was applied at equivalent N rates. Taken together, these findings suggest soils in the upper Southeast USA can supply significant amounts of the N needs of switchgrass, especially when harvested once at the end of the season.

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