Doctoral Dissertations

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Bond graph modeling of hydraulic circuits on a sweet sorghum harvester
Rains, Glen Christopher (Virginia Tech, 1992)
A whole-stalk harvester was developed as part of a sweet sorghum-for-ethanol production system. Gathering chains grasped the stalks as they were cut at the base with a disk-cutter. These stalks were flipped onto a cross conveyor and deposited into an accumulator. Periodically the machine stopped and the accumulator was dumped. All the components on the harvester are powered hydraulically. Five pumps on the harvester supply flow to seven actuator circuits. Power is delivered to the pumps from the tractor PTO via a universal joint driveline. Each of the six existing circuits and one proposed circuit were modeled with bond graphs and implemented for computer analysis using TUTSIM. Model validation was done by comparing simulated and measured driveline torque, line pressure, and return line flow rate in each of the six existing circuits. Data collected on the gathering chains circuit was used to analyze the effect of driveline joint angles on transmitted torque and pump output. Torque measurements at three driveline angles showed a torsional vibration with a primary harmonic at driveline rpm and a secondary at twice driveline rpm. A combination of Cardan joint characteristics, mass unbalance, the secondary couple, and non-linear driveline and V-belt stiffness was used to model the driveline. Resulting simulated torque emulated the experimental very well. Measured pressure in the gathering chains circuit showed relatively low fluctuations at the highest amplitude torsional vibration (highest driveline joint angles). It was concluded that driveline vibration would not significantly affect the gathering chains circuit performance. The cross-conveyor motor circuit simulation showed close agreement to experimental results. Mean predicted flow, pressure, and torque were within 8.9, 7.3, and 7.7 percent of mean measured values. A simulation with a stalk load on the conveyor showed that power requirement increased only 8.0 percent. The accumulator dump circuit was analyzed to determine if the load on the motor would become over-running and cavitate the pump or motor as the stalks were being dumped. Simulation showed that a bundle up to 300 kg could be dumped without over-running the motor, and since this was a larger bundle than the bin could hold, a design modification was not necessary. The disk-cutter circuit was designed based on simulation results for several combinations of motor, pump, and sheave ratio. A 7.3 cm³/rad motor, 2.53 cm³/rad pump , and 2:1 sheave ratio produced the correct disk-cutter speed, and low torsional vibration when cutting the stalks, consequently this combination was selected for the design.
Cover crop residue effects on machine-induced soil compaction
Ess, Daniel R. (Virginia Tech, 1994-07-05)
Crop production systems which utilize the biomass produced by rye (Secale cereale ) to suppress weed growth and conserve soil moisture have been developed at Virginia Tech. The success of alternative, reduced-input crop production systems has encouraged research into the potential for breaking the traffic-tillage cycle associated with conventional tillage crop production systems. The fragile residues encountered in agricultural crop production, whether incorporated into the soil or distributed on the soil surface, provide minimal protection against compaction by wheeled vehicles. The potential of an intact cover crop to reduce machine-induced effects on soil properties that affect primary crop growth was the subject of this study. A randomized complete block experiment was conducted at the Whitethorne Farm in Montgomery County, Virginia. One set of plots was arranged on a terrace adjacent to the New River in a fine, mixed, mesic, Aquic Argiudolls. Another set of plots was arranged on an upland site, a river terrace tread, in a fine-loamy, mixed, mesic, Typic Hapludults. Three rye cover crop treatments were examined. In one, a live cover crop was completely undisturbed prior to tracking by a wheel-type tractor. In another, the cover crop was chemically desiccated, and in the third treatment, all above-ground biomass was removed from plots prior to machine traffic. The treatments permitted investigation of the effects of crop condition on machine-induced soil compaction and the contribution of root reinforcement to the alteration of soil response to machine traffic. A fall-tilled fallow treatment served as an experimental control. Three levels of traffic were investigated: one pass, three passes, and five passes. Undisturbed soil core samples were analyzed to determine machine-induced effects on dry bulk density, pore size distribution, and saturated hydraulic conductivity. The treatments affected soil response to machine traffic. The cover crop treatments altered the soil-plant microenvironment, affecting soil parameters that influence compactibility. Soil compaction was attenuated by the reinforcing effect of a network of undisturbed roots within the soil. There was no convincing evidence that above-ground biomass contributed directly to the reduction of machine-induced compaction effects. Soil response to machine traffic was limited to the uppermost 15 cm of the soil profile.
Defining farm-safety research priorities and adjusting farm insurance premiums by a risk analysis approach
Zhao, Wei (Virginia Tech, 1992)
A risk analysis approach for farm work-related injuries was proposed. For this study, risk is defined as the Expected Injury Cost (EIC) index per farm worker per year. Four steps are involved in the risk assessment analysis of farm injuries: (1) determination of risk factors, (2) injury severity classification, (3) cost estimation, and (4) risk characterization. Farm variables were examined to determine their influences on the rates of occurrence as well as the severity of injuries. Farm injuries were correlated with the risk factors of employment status, gender of farm worker, age of farm worker, hours of exposure, type of agricultural operation, and various hazardous conditions on a farm. By combining the probability of injuries due to a particular risk factor with the estimated costs of injuries, the EIC indices were derived for farm workers and activities. Agricultural safety education and research priorities were defined based upon the risk model developed in this study. A sensitivity analysis was conducted to determine the impact of the assumptions on the research priorities established. It was found that the research priorities were not affected by the uncertainty on the magnitude of injury costs and other variables used in this study. The risk-based approach can also provide input to farm insurance ratings. By combining the EIC index for each worker with the number of workers employed on a farm, a composite risk factor could be obtained for the farm enterprise. This composite risk factor can be used as a basis for adjusting farm insurance premiums. Adjustment of insurance premiums or related benefits could be used as an economic incentive to encourage adoption of safer farming practices so that preventable farm accidents and human suffering can be reduced. Other potential applications of the risk model presented in this study include safety management and loss control for a farm enterprise, and serving as a guide for the systematic collection of farm injury data.
Development of a continuous, physically-based distributed parameter, nonpoint source model
Bouraoui, Faycal (Virginia Tech, 1994-04-18)
ANSWERS, an event-oriented, distributed parameter nonpoint source pollution model for simulating runoff and sediment transport was modified to develop a continuous nonpoint source model to simulate runoff, erosion, transport of dissolved and sediment-bound nutrients, and nutrient transformations. The model was developed for use by nonpoint source pollution managers to study the long-tenn effectiveness of best management practices (BMPs) in reducing runoff, sediment, and nutrient losses from agricultural watersheds. The Holtan's infiltration equation used in the original version of ANSWERS was replaced by the physically-based Green-Ampt infiltration equation. Soil evaporation and plant transpiration were modeled separately using the Ritchie equation. If soil moisture exceeds field capacity, the model computes percolation based on the degree of soil saturation. Nutrient losses include nitrate, sediment-bound and dissolved ammonium; sediment-bound TKN, and sediment-bound and dissolved phosphorus. A linear equilibrium is assumed between dissolved and sediment-bound phases of ammonium and phosphorus. Nutrient loss is assumed to occur only from the upper cm of the soil profile. The model simulates transformations and interactions between four nitrogen pools including stable organic N, active organic N, nitrate and ammonium. Transformations of nitrogen include mineralization simulated as a combination of ammonification and nitrification, denitrification, and plant uptake of ammonium and nitrate. The model maintains a dynamic equilibrium between stable and active organic N pools.
Development of phenomenologically-based distribution fitting procedures and spatial processes for mixed population soil properties
Cooke, Richard (Virginia Tech, 1993-11-08)
In the literature, two distinct flow phenomena, namely, flow through the main body of the soil, and flow through preferential flow paths, have been identified. Models which try to incorporate the effects of these two phenomena require either an explicit or an implicit knowledge of the probability distribution functions associated with the soil properties affecting flow. In keeping with the fact that these properties are influenced by two distinct phenomena, it is postulated that they should be represented by heterogeneous distribution functions. These distribution functions are, by design, suitable for representing mixed population data. Procedures were developed for fitting heterogeneous distribution functions to data. These procedures are encoded in Microsoft QUICKBASIC with some additional FORTRAN routines. The fitting procedures do not utilize any moment above the second order, and are markedly different from the use of regression methods for fitting multiple parameter distributions. Procedures were developed for two types of mixtures. One type is suitable for instances where a measured quantity is the sum of values from two populations, while the other is applicable when a measured quantity may be from one population or from another, but not from both at the same time or location. The procedures were applied to several data sets, including flow data, infiltrability data, and pH data. In many instances, the use of heterogeneous distributions resulted in an improvement in fit quality as compared to the fit quality for homogeneous distributions. The most dramatic improvement are observed in the fit to extreme data values. Procedures were also developed to incorporate heterogeneous distribution functions into three common processes in Soil and Water Engineering, namely, Monte Carlo simulation, stochastic field generation, and interpolation. In these procedures, data which are best represented by heterogeneous distributions are transformed to Gaussian space and existing Gaussian-based procedures are applied. In several validation efforts the modified processes were found to as good as, or better than, conventional procedures. In the process of developing the modified spatial processes mentioned above, a robust trend surface procedure and a new matrix decomposition procedure were developed. These ancillary procedures were shown to be useful in other engineering applications.
Mechanization of the selective harvest of broccoli
Wilhoit, John Hiram (Virginia Polytechnic Institute and State University, 1989)
An investigation was made of concepts for mechanizing the selective harvest of broccoli. Selective harvesting has advantages over once-over harvesting because of greater yield and reduced handling requirements. Results of a preliminary experiment measuring broccoli stalk cutting forces indicated that the blade speed for a broccoli cutting mechanism should be as fast as possible to minimize the required cutting force. A manually-directed, powered cutting device was designed to fit readily into existing broccoli harvest systems. In tests the first year with the device, the harvest rate was substantially faster than hand harvest rates measured at commercial farms, but the level of leaf-stripping achieved with the device was unacceptably low. A new cutting device included an added leaf-stripping mechanism and had a mounting arrangement that allowed the harvesting of two double rows at once. In tests the second year, leaf-stripping was much improved, but the overall harvest rate was only marginally better because of extra manipulation required to activate the leaf-stripping mechanism. Measurements related to mechanical harvesting were made on broccoli plants both years. Head height, stalk diameter, and head weight were strongly affected by harvest time and in-row plant spacing. Height and stalk diameter were moderately correlated to head diameter. A regression model for predicting head diameter from height and stalk diameter indicated that potential exists for using a combination of the two parameters for sizing broccoli heads. Head weight was highly correlated to height and stalk diameter. Two concepts for automatic mature head selection were evaluated. The results of an experiment measuring the force required to uproot broccoli plants indicated that physically sizing broccoli heads using spaced fingers would only be feasible if late season irrigations could be incorporated in a harvest system. Digital image processing for head selection appears more promising. An image processing algorithm based on the gray level run length method of textural analysis was developed for predicting broccoli head area. Accurate head classification was obtained with the model. For an automatic selective harvester, an image processing system can be coupled with a cutting device with the major advantage that leaf~stripping can be accomplished automatically during the harvesting action.
Nitrogen transport and dynamics in grass filter strips
Mendez-Delgado, Aida (Virginia Tech, 1996-02-01)
Field research was conducted to investigate the impact of vegetative filter strips (VFSs) on surface runoff water quality and to determine if this impact decreases with time. The field research provided information for the development and testing of a model to describe the dynamics and fate of nitrogen (N) in VFSs. The experiment had a completely randomized design, with 3 treatments and 2 replicates per treatment. The treatments were 3 VFS lengths: 0, 4.27, and 8.5 m VFSs. The distribution free Kruskal-Wallis test indicated that the runoff, TSS, NO₃⁻-N, NH₄⁺-N, and TKN yields and concentrations from the 8.5 m VFSs were significantly less (α = 0.05) than the influent values. The TSS and NH₄⁺-N yields and concentrations and the TKN concentration from the 4.27 m VFSs were significantly less than the influent yields and concentrations. The Mann-Kendall test indicated that the yields of TSS, NO₃⁻-N, NH₄⁺-N, and TKN from the filters did not significantly increase from 1992 to 1993 and neither did the FTKN yield nor the FTKN concentration from the beginning to the end of 1993. The mean percentage reductions in influent runoff, TSS, NO₃⁻-N, NH₄⁺-N,, and TKN yields from the 8.5 m filters were 73, 91, 79, 86, and 83%, respectively. The mean percentage reductions in influent TSS, NO₃⁻-N, NH₄⁺-N, and TKN concentrations from the 8.5 m filters were 88, 50, 66, and 75%. The mean percentage reductions in influent runoff, TSS, NO₃⁻-N, NH₄⁺-N, and TKN yields from the 4.27 m filters were 43, 83, 55, 40, and 56%, respectively. The mean percentage reductions in influent TSS, NO₃⁻-N, NH₄⁺-N, and TKN concentrations from the 4.27 m filters were 81, 45, 26, and 41%. Based on the information gathered from the experiment results and the literature, a continuous, long-term, field scale model (Grass Filter Strip Model, GFSM) was developed to describe N transport and dynamics in VFSs. The model was based on GRAPH (GRAssed-strip-PHosphorus), a field scale, event-based model that describes sediment and P transport in runoff. The model simulates sediment, nitrate, sediment-bound and dissolved ammonium, and sediment-bound organic N transport during a runoff event. The model simulates the daily percolation and evapotranspiration and dynamics of nitrate, sediment-bound and dissolved ammonium, and sediment-bound organic N in the filter between runoff events. The model predicts the amount of N and sediment exiting the VFSs, and it can be used to estimate the site specific effectiveness and length of VFSs. The model can also be run for an event to assess the effectiveness of VFSs in reducing nonpoint source pollution loading from a single design storm. The model was validated using runoff, sediment, NO₃⁻ and NH₄⁺ yield field data gathered from April to December, 1993. The model predicted reasonably well (within a factor of 2) the cumulative runoff volume and the yields of TSS. NO₃⁻ and NH₄⁺. The model was most sensitive to the runoff rate, depth of the EDI, soil water storage depth, field capacity, and the steady-state infiltration rates. The model was used to determine the minimum length of VFS required for a 1.3 ha field in Georgia to achieve 75% and 40% sediment and nutrient reductions, respectively, over a 10-year period. The model results indicated that a buffer length of 6.3 m was sufficient to reduce sediment and nitrogen losses by the specified percentages.
Non-invasive quality evaluation of fruits and vegetables using ultrasound
Cheng, Yanling (Virginia Tech, 1993-02-05)
Ultrasonic techniques were investigated for non-invasive quality evaluation of selected fruits and vegetables. An ultrasonic non-destructive evaluation system was developed and used to investigate physical and acoustical property changes for the selected fruits and vegetables non-invasively. The system included a high power burst pulser, a broadband receiver, a digital storage oscilloscope, two pairs of transducers of 250 kHz and 1 MHz, and a microcomputer system, which was interfaced with the ultrasonic equipment through a General Purpose Interface Board (GPIB), for data acquisition and analysis. Using potatoes and apples, several forms of the acoustic indices were investigated using the system. Investigation of “Yukon-Gold’ potatoes concentrated on the physical and acoustical property changes during the storage period of approximately five months. The tests were conducted at regular intervals. Ultrasonic velocity, attenuation coefficient, modulus of elasticity, and tissue density were determined for each potato along two different orientations — longitudinal and transverse. Three varieties of apples, ‘Golden Delicious’, ‘Red Delicious’, and ‘Granny Smith’, were tested to detect their physiological changes with ripeness. The tests were conducted at two different stages of ripeness. In each test, ultrasonic velocity, attenuation coefficient, modulus of elasticity, and tissue density were determined along longitudinal and radial directions of the apples. Frequency analysis of the transmitted ultrasonic signals through potato and apple samples was also conducted using Fast Fourier Transform (FFT) techniques. The experimental results for the potatoes and apples indicated the measured acoustical and physical properties differed along different orientations; i.e., potato and apple tissues are anisotropic materials. Apple tissues transmitted much lower frequency components than potato tissues and the transmitted frequency range was much narrower due to the much higher percentage of intercellular void space in apple tissues (24%) than in potato tissues (2%). The ultrasonic measurements were able to detect physiological changes and physical heterogeneities in fruit and vegetable tissues. Therefore, the ultrasonic technique can be a useful and quick method for evaluating firmness as well as textural and rheological property changes during storage of fruits and vegetables. Hollow hearts in ‘Atlantic’ potatoes were successfully detected using the ultrasonic nondestructive evaluation system at 250 kHz. A objective this work was to develop a quantitative, non-invasive method for hollow heart detection in potatoes, and to provide information for designing evaluation equipment which could serve as an automatic quality control step in the production process. The analysis of the transmitted ultrasonic signals through the potatoes was carried out in both time and frequency domains. The results of the investigation of ‘Atlantic’ potatoes showed that the waveform of transmitted ultrasonic signals through a hollow heart potato differed significantly from that of a normal potato. Further, the defective potatoes could be separated on the basis of the amount of ultrasonic power transmitted through a potato. By means of digital Fourier analysis, the 0^th spectral moment, M₀, was determined from the power spectral density curve of a transmitted ultrasonic signal. The spectral moment represents the amount of ultrasonic power transmitted through a tested potato, and was chosen as the basis for quantitative, non-invasive method for hollow heart detection, since power transmission of ultrasonic wave was affected by the presence of hollow heart in potatoes. Potatoes with hollow heart transmitted much less ultrasonic power than normal potatoes — approximately 89% less on average. There was a distinct separation between the normal potatoes and hollow heart potatoes. The reliability of this method was confirmed. Among 41 ‘Atlantic’ potatoes tested, all 26 hollow-heart potatoes were identified without exception. Therefore, the parameter M₀ could provide an effective method of analyzing the ultrasonic measurements for quantitative, non-invasive evaluation of hollow hearts in potatoes. This non-invasive method could be used to identify internal quality of potatoes that is difficult to evaluate from external appearance. Such a measurement offers promises for the development of equipment that would sort potatoes with hollow heart automatically.
Simulation of a swine nursery to facilitate economical management
Harmon, Jay David (Virginia Polytechnic Institute and State University, 1989)
Two deterministic simulation models were developed to assess the economics of swine nurseries. The first model assessed the emergency needs of swine nurseries by simulating the temperature response during a short term power failure. The failure model accounted for heat exchange by conduction, convection, radiation, and air infiltration. An existing sub-model was used to predict swine heat and moisture loss. The failure model was validated using a nursery constructed of concrete block. It performed well for cases with constant solar load, but tended to overpredict temperature changes during periods of no solar load. Validation indicated accurate wall-characteristic and wind velocity estimations were crucial to obtain accurate model results. The second model was developed to describe the normal operation of swine nurseries by predicting pig growth and feed consumption, building fuel consumption, and cost per unit of gain produced. lt was based on an existing swine model that was converted to an hourly basis. An optimization option was incorporated into the operational model to allow minimization of the cost per unit of gain. The operational model was validated and found to accurately predict feed consumption and growth during a one week time frame. Fuel consumption was less accurate. The optimization mode predicted considerable cost savings for operation at lower temperatures.
Simulation of deep-bed drying of Virginia peanuts to minimize energy use
Kulasiri, G. Don (Virginia Tech, 1990-11-05)
A deep-bed drying model simulating the drying of peanuts in a fixed bed is required for designing energy-efficient and automatically controlled dryers. A deep-bed drying model consists of a thin-layer drying model to calculate the moisture release from the material and a set of mass and energy balances. An experimental setup was constructed to determine drying rates of Virginia-type peanuts under 14 different drying air conditions. Selected empirical and semi-theoretical models available for modeling thin-layer drying rates were fitted to the collected data using nonlinear regression techniques. The modified Page's model and the two-term exponential model fitted the data better than other models considered. A deep-bed drying model PEATECH based on four coupled partial differential equations consisting of four variables, air temperature, peanut temperature, air humidity, and peanut moisture content was developed. Validation of the model was accomplished by using the data collected from 36 deep-bed drying experiments conducted using three laboratory dryers during 1987, 1988, and 1989. PEATECH predicted the variables within a peanut bed with an accuracy of less than ± 6%. The energy saving potential of exhaust-air recirculation was established by conducting simulated experiments using a modified version of PEATECH.
Simulation of weight gain and feed consumption of turkeys
Parmar, Rajbir Singh (Virginia Polytechnic Institute and State University, 1989)
Like most agricultural production systems, effective decision making in turkey production systems requires the prediction of future status of the system and evaluation of alternative management policies. A simulation model of a turkey production system was developed to predict values of flock performance indicators of significant economic importance, namely body weight and feed consumption. Existing weather simulation models were combined and modified in order to develop a model that predicted daily dry-bulb temperature and humidity ratio outside the turkey house. The weather simulation model was validated using twenty years of daily observed weather data from Roanoke, Virginia. Thermal environment inside the turkey house was predicted from simulated outdoor weather using energy and mass balance equations. House environment prediction part of the model was validated using observed inside and outside temperature data collected at a turkey farm in Virginia. A discrete event simulation model was developed to simulate the effects of house thermal environment, feed energy, sex, and age on weight gain and feed consumption of growing turkeys. The model was validated using temperature, body weight, and feed consumption data collected at a turkey farm in Virginia. The observed average bird weights at marketing age were within 95% confidence intervals of the predicted values. However, the model underpredicted energy consumption values. The sensitivity of the model to variations in R-value, ventilation rate, and feed energy concentration was evaluated. The model was more sensitive to feed energy concentration.
Stochastic dynamic optimization approach for revegetation of reclaimed mine soils under uncertain weather regime
Mustafa, Golam (Virginia Polytechnic Institute and State University, 1989)
This study presents a comprehensive physically based stochastic dynamic optimization model to assist planners in making decisions concerning mine soil depths and soil mixture ratios required to achieve successful revegetation of mined lands at different probability levels of success, subject to an uncertain weather regime. A perennial grass growth model was modified and validated for predicting vegetation growth in reclaimed mine soils. The plant growth model is based on continuous relationships between plant growth, air temperature, day length, leaf area, photoperiod and plant-soil-moisture stresses. A plant available soil moisture model was adopted to estimate daily soil moisture for mine soils. A general probability model was developed to estimate the probability of successful revegetation in a 5-year bond release period. The probability model considers five possible bond release criteria ir1 mine soil reclamation planning. A stochastic dynamic optimization model (SDOM) was developed to find the optimum combination of soil depth and soil mixture ratios that met the successful vegetation standard under non-irrigated conditions with weather as the only random element of the system. The SDOM was applied for Wise County, Virginia, and the model found that 2:1 sandstone/siltstone soil mixture required the minimum soil depth to achieve successful revegetation. These results were also supported by field data. The developed model allows the planners to better manage lands drastically disturbed by surface mining.
A subsurface water quality evaluation system for assessing NPS pollution potential by pesticides
Li, Weiping (Virginia Tech, 1993-05-05)
A watershed scale water quality evaluation system was developed for assessing spatial variation of subsurface pesticide movement. The system consists of a linked-transport model component for performing simulation and a GIS component for processing spatially-related data. The surface heterogeneity caused by agricultural activities, topographic, hydrologic, and soil type variations in a watershed was handled by partitioning the watershed into homogeneous subfields. The subsurface soil profile and aquifer heterogeneities were considered by dividing the subsurface domain into root zone, intermediate vadose zone, and saturated zone, respectively. On each of the homogeneous subfields, the physically-based models, PRZM and VADOFT, were linked to simulate pesticide transport in the root and intermediated vadose zones. Pesticide movement in groundwater underneath the watershed was simulated by linking the other two models with SUTRA. An irregular shape finite element mesh generator was developed for fitting the irregular shape watershed boundary and reducing the number of nodes of the finite element mesh. Either transient or steady state flow and transport simulation could be performed with the system. The system is able quantitatively to produce detailed spatial variation maps of pesticide concentrations at any desired depth in the unsaturated zone and in groundwater. The system requires spatially-distributed information as inputs. Management of large volumes of spatially-referenced data which represent the heterogeneous properties of the watershed were facilitated by a developed GIS component. The GIS data processing component was composed of spatial data manipulation and display, attribute database management, and model input information extraction subcomponents. The spatial data processing component consists of data format conversion, map registering, map editing, new information generation, and map display subcomponents.
A systems analysis of sweet sorghum harvest for a Piedmont ethanol industry
Worley, John Wright (Virginia Tech, 1990)
The Piedmont System is a collection of equipment for efficiently removing the juice from sweet sorghum stalks for the production of ethanol. The concept is to separate the whole stalks into pith and rind-leaf fractions, pass only the pith fraction through a screw press, and thus achieve an improvement in juice expression efficiency and press capacity. The operation of three alternative harvesting/processing systems were modeled and compared using computer simulation to determine which system could produce sweet sorghum juice and deliver it to a central plant at the lowest cost per liter of potential ethanol produced. In addition, an energy analysis was done to determine the net energy gain. System A cut the sorghum stalks and hauled them to a crossroads site where they could be stored up to 30 days before juice expression. System B separated the pith and rind-leaf fractions in the field, and juice expression was accomplished at a nearby site. No storage was possible for System B. System C cut the stalks like System A, but then a mobile processor moved through the field to separate the pith and rind-leaf fractions. It was found that the cost of producing feedstock with System C ($0.87/L) was significantly higher than either System A ($0.56/L) or System B ($0.63/L). While the System A cost was slightly lower than that of System B, it is recommended that both Systems A and B should be studied further since small adjustments to the model could eliminate the advantage of System A over System B. Increases in whole-stalk yield and juice sugar level would lower the cost of all three systems by as much as 43%. As the price of energy rises, sweet sorghum is expected to gain an economic advantage over com as a feedstock for ethanol, because of its higher energy ratio. If the by-products are used to produce ethanol through cellulose conversion, the overall energy ratio for sweet sorghum was calculated to be 1.1 compared to 0.8 for corn. The energy ratio if only liquid fuels are considered was 7.9 for sweet sorghum compared to 4.5 for corn.
Tillage effects on soil-water-air matrix and prediction of soil bulk density from cone index data
Jayatissa, Dangallage Nimal (Virginia Tech, 1990-02-05)
Conventional farming systems create socio-economic problems through increased production costs and loss of the soil and chemicals that are washed from the farmlands. Even though no-till farming systems can increase farm profit and reduce environmental degradation, soil compaction can negate the advantages of no-till farming when no-till systems are used continuously under certain soil and climatic conditions. One objective of this study was to evaluate the long-term effects of the no-till method on bulk density, capillary porosity, noncapillary porosity, void ratio, and cone index of the soil. Although tillage affected cone index significantly, moisture variations caused difficulty in interpreting the results. No statistically significant differences in other parameters were found among no-till, conventional till, and control fallow treatments within each of three cropping seasons. However, within each tillage treatment these parameters showed significant variations between test seasons. When the soil bulk density data is required at close depth intervals, the core sample method becomes laborious while its use is limited by soil type and moisture conditions. The neutron probe densitometer is difficult to use in tillage studies due to practical problems. Among the predictive models for bulk density, some require parameters determined through expensive laboratory procedures while others have not been proven to work in field conditions. Therefore, the second objective was to develop a model to predict soil bulk density using cone index and moisture content data for a Virginia soil. Two separate models have been developed for top and subsoil layers using remolded natural soil samples. The topsoil model predicted bulk density close to the actual data taken in recently disturbed soils. One cropping season after plowing, predicted values were about 10% higher than the actual, a result which could be due to the aging effect. The subsoil model, on the other hand, under-predicted soil bulk density by about I5% After the model coefficients for a particular soil are determined through laboratory tests, cone index and moisture data can be used to predict bulk density in that soil. This procedure may save time and expense in future research on soil compaction.
Water management for lowland rice irrigation
Siddeek, Fathima Zeena (Virginia Polytechnic Institute and State University, 1986)
A procedure was developed to estimate optimum irrigation requirements for lowland rice cultivation in Southeast Asia. The procedure uses a water balance equation of semi-stochastic nature to maintain minimum desired water depths in paddy fields at the end of each irrigation period. The procedure estimates weekly pan evaporation (EV) and rainfall (RF) at different probability levels, which is then used to determine weekly irrigation requirements at different probability levels. To illustrate the use of the method, the Kalawewa irrigation scheme in Sri Lanka was selected for demonstration purposes. Different transformations were applied to Rf and EV data in an attempt to normalize these variates and to obtain a unique distribution to describe their variations. Statistical analysis of weekly EV arid RF showed that the power transformation was best able to transform the weekly RF and EV data to normality. Comparison of the use of the model and current system practices showed that a significant amount of water could be saved even when the system was operated at high probability levels (90% reliability). The irrigation water required when the system was operated at the 72% probability level was about 21% less than the amount required when the system was operated at 90% probability level during some weeks. The EXTRAN flow routing model was used to simulate water flow in the upper reaches of the main canal system for varying discharges at the head gate each day. The simulated water depths were used to determine the gate settings required at the turnout structures to divert the desired amount of irrigation water into the turnout areas. The flow simulation for the demonstration area, showed that it was not possible to regulate irrigation water from the main reservoir to meet daily demands at all the turnouts. This was due to the large distances between the regulating reservoir and turnouts that caused appreciable time lag for the flow to reach the turnouts farthest from the regulating reservoir.
Watershed nonpoint source management system: a geographic information system approach
Kleene, J. Wesley (Virginia Tech, 1995-03-05)
A comprehensive, distributed parameter, annual, watershed nonpoint source management system (WATNPS) was developed for land management planning. WATNPS simulates annual sediment, nitrogen (chemical and livestock organic), and phosphorus (chemical and livestock organic) yields from nonpoint sources. The system is linked to a GIS platform to reduce the input required by personnel during analysis. WATNPS predicts potential impacts of land management practices on surface water quality. Data were compiled for the Middle Fork Holston River (MFHR) drainage basin, Owl Run and Nomini Creek watersheds in Virginia. WATNPS utilizes annual screening models for the prediction of pollutant yields. Overland delivery ratio, phosphorus yield, and animal waste models were modified for use in the system. In-stream delivery ratio, and pollutant routing procedures were developed as a part of the overall system functionality. Development and calibration of individual in-stream delivery ratio parameters was performed based on single year data from Nomini Creek and Owl Run. A procedure was developed to rank individual watersheds and sites based on predicted pollutant yields during screening. Simulation results and individual watershed characteristics were used during the development of a drainage quality index (DQI). The DQI was developed using statistical analysis to link a water quality indicator to predicted yields and watershed characteristics. The DQI was developed to assess the impact of management within individual watersheds and among watersheds within a drainage basin. WATNPS was validated using observed data. During simulations WATNPS predicted sediment yields within 50% of observed values. Nutrient yields were predicted within a order of magnitude. Simulation of alternative livestock management practices in Owl Run reflected the same trends identified in the observed data. The Hutton Creek simulation was also consistent with water quality observations. A watershed ranking based on the DQI assessment was compared to one provided by local personnel to compare predicted trends to observed watershed conditions. A demonstration of WATNPS selected a single watershed based on watershed rankings. Critical sites were identified during WATNPS site assessment and BMPs were developed. Following BMP implementation the watershed was simulated to determine the impact on sediment, nitrogen, and phosphorus yields.

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