Timothy P. McDonald

ACCURACY OF TRACKING FOREST MACHINES WITH GPS

This paper describes the results of a study that measured the accuracy of using GPS to track movement of forest machines. Two different commercially available GPS receivers (Trimble ProXR and GeoExplorer II) were used to track wheeled skidders under three different canopy conditions at two different vehicle speeds. Dynamic GPS data were compared to position data established through precision surveying techniques. Maps from data collected by both receivers showed general travel patterns of the skidders. Mean position errors in data collected by the GeoExplorer (2.75 m) were significantly greater than those of the data collected by the ProXR (1.34 m). When tested under different canopy conditions, GPS position accuracy showed a decreasing trend as the canopy changed from open to heavy. Finally, the machine speeds tested did not significantly affect the accuracy of GPS positions.

Real-Time Pressure and Flow Dynamics Due to Boom Section and Individual Nozzle Control on Agricultural Sprayers

Most modern spray controllers when coupled with a differential global positioning system (DGPS) receiver can provide automatic section or swath (boom section or nozzle) control capabilities that minimize overlap and application into undesirable areas. This technology can improve application accuracy of pesticides and fertilizers, thereby reducing the number of inputs while promoting environmental stewardship. However, dynamic system response for sprayer boom operation, which includes cycling or using auto-swath technology, has not been investigated. Therefore, a study was conducted to develop a methodology and subsequently perform experiments to evaluate tip pressure and system flow variations on a typical agricultural sprayer equipped with a controller that provided both boom section and nozzle control. To quantify flow dynamics during boom section or nozzle control, a testing protocol was established that included three simulation patterns under both flow compensation and no-compensation modes achieved via the spray controller. Overall system flow rate and nozzle tip pressure at ten boom locations were recorded and analyzed to quantify pressure and flow variations. Results indicated that the test methodology generated sufficient data to analyze nozzle tip pressure and system flow rate changes. The tip pressure for the compensated section control tests varied between 6.7% and 20.0%, which equated to an increase of 3.7% to 10.6% in tip flow rate. The pressure stabilization time when turning boom sections and nozzles off approached 25.2 s but only approached 15.6 s when turning them back on for the flow compensation tests. Although extended periods were required for the tip pressure to stabilize, the system flow rate typically stabilized in less than 7 s. The tip flow rate was consistently higher (up to 10.6%) than the target flow rate, indicating that system flow did not truly represent tip flow during section control. The no-compensation tests exhibited tip pressure increases up to 35.7% during boom and nozzle control, which equated to an 18.2% increase in tip flow. Therefore, flow compensation over no-compensation had better control of tip flow rate. A consistent difference existed in dynamic pressure response between boom section and nozzle control. Increased tip pressure and delayed pressure stabilization times indicated that application variability can occur when manually turning sections on and off or implementing auto-swath technology, but further testing is needed to better understand the effect on application accuracy of agricultural sprayers.

Scheduling a log transport system using simulated annealing

The log truck scheduling problem under capacity constraints and time window constraints is an NP-hard problem that involves the design of best possible routes for a set of trucks serving multiple loggers and mills. The objective is to minimize the total unloaded miles traveled by the trucks. In this paper, a simulated annealing - a meta-heuristic optimization method - that interacts with a deterministic simulation model of the log transport system, in which the precedence and temporal relations among activities are explicitly accounted for, is proposed. The results obtained by solving a small size problem consisting of four trucks, two mills, three loggers, and four truck trips showed that the best solution could be found in less than two minutes. In addition, the solution method is tested using data provided by a log delivery trucking firm located in Mississippi. The firm operates sixty-eight trucks to deliver loads from twenty-two logging operations to thirteen mill destinations. The routes assigned by a supervisory person are used as a benchmark to compare the manual generated solution to the solution obtained using the proposed method.

Spatially Monitoring Tractor Performance to Evaluate Energy Requirements of Variable Depth Tillage and Implement Selection

Recent rises in fuel costs have started to impact the bottom line for farm managers, making them consider possible methods to achieve energy savings. Conventional subsoiling can be performed deeper than necessary to alleviate compaction layers. However, site-specific subsoiling permits a subsoiler to be operated at the depth necessary to impale the compaction layer thus, reducing draft forces while also saving fuel. The overall goal of this study was to develop a mobile data acquisition system to monitor equipment performance parameters in real-time to assess and quantify energy requirements for site-specific tillage. A data acquisition system was developed to collect and monitor slip, fuel consumption, axle torque, and draft load data on two site-specific tillage experiments. Results indicated a 54% reduction in draft forces and a 17% reduction in fuel consumption occurred with a shallow depth (9 in.) compared to a deep depth (14 in.). The three

Utilizing Nutrient over Mass Distribution Patterns for Assessment of Poultry Litter Spreaders

Poultry litter can be difficult to uniformly apply because of its natural variability in moisture content, particle size, and density. It is well known that nutrient concentrations of litter tend to increase with decreasing particle size, posing a question of whether litter should be applied based on nutrient distribution over mass, which is the traditional means for spreader calibration and uniformity assessment. Therefore, a study was conducted to evaluate whether macronutrient (N, P2O5, and K2O) distribution patterns contrast with the traditional mass distribution while using the nutrient data to assess application uniformity between a closed-loop system (CLS) and an open-loop system (OLS) for controlling spinner-disc speed. Three application rates (2242, 4483, and 6725 kg ha-1) were selected for applying broiler litter. A two-dimensional collection pan matrix with four rows was used to assess pattern uniformity. Results indicated that the nutrient patterns were highly correlated (R > 0.98) with their respective mass patterns, indicating that even with the existence of particle size variability across the spread width, the distribution of mass reflected the nutrient distribution. The CLS provided more uniform nutrient patterns, with coefficients of variation (CVs) ranging from 22% to 34% compared to the 26% to 39% generated by the OLS. Overall, practical differences were found between the two control systems (p = 0.0657) with significant differences occurring at the 2242 kg ha-1 (p = 0.0303) and 6725 kg ha-1 (p = 0.0379) rates. No statistical difference (p = 0.8207) was measured at the 4483 kg ha-1 rate, which was the calibration rate for both systems. Therefore, this research concluded that the distribution of mass can be used to assess nutrient distribution of poultry litter spreaders and that the CLS for spinner speed control outperformed the traditional OLS.

Multivariate modeling of acoustomechanical response of 14-year-old suppressed loblolly pine ( Pinus taeda) to variation in wood chemistry, microfibril angle and density

The polymeric angle and concentration within the S2 layer of the softwood fiber cell wall are very critical for molecular and microscopic properties that influence strength, stiffness and acoustic velocity of wood at the macroscopic level. The main objective of this study was to elucidate the effect of cellulose, hemicellulose, lignin, microfibril angle and density on acoustic velocity and material mechanical properties of 14-year-old suppressed loblolly pine. Cellulose, hemicellulose and density are consistently the most important drivers of strength, stiffness and velocity. Cellulose and lignin are the highest and lowest contributor to velocity, respectively, with lignin acting as a sound wave dispersant, while cellulose is the most important conductor of sound wave at the molecular level, while hemicellulose acts as a special coupling agent between these components. The polymeric constituents are thus important drivers of sound wave propagation at the molecular level, while density played a subsequent role at the macroscale.

Evaluation of GPS Autoguidance Systems over Varying Time Periods

Autoguidance systems are becoming more popular to Alabama farmers for use in their cropping systems. Reported accuracies of available systems can be different from what the equipment operator experiences in the field. Absolute accuracy of any autoguidance system over a long period of time, such as from season to season, is desirable especially when implementing management strategies such as controlled traffic. The objective of this study was to assess different auto-guidance systems, using from WAAS to RTK differential correction, over various time periods. A non-GPS-based surveying practice was used to establish the absolute equipment traverse during testing. This information was then used to compute path deviations from the desired traverse. Average cross-track error and pass-to-pass error were consistent with manufacturers’ recommendations for the overall study; however, the drive paths deviated from the initial AB line established throughout the study, as represented by the range of cross-track error or pass-to-pass error values. Average RTK cross-track error illustrated a deviation of ±10 cm from the initial AB line over the 15 week testing period. Average SF2 cross-track error was 34 cm with a maximum path deviation of 0.6 m. SF1 average cross-track error was 40 cm with a maximum deviation of 1.4 m, and WAAS cross-track error averaged 24 cm with a maximum deviation of 0.6 m.

Determining the effects of felling method and season of year on the regeneration of short rotation coppice

There is increasing interest in plantations with the objective of producing biomass for energy and fuel. These types of plantations are called Short Rotation Woody Crops (SRWC). Popular SRWC species are Eucalypt (Eucalyptus spp.), Cottonwood (Populus deltoides) and Willow (Salix spp.). These species have in common strong growth rates, the ability to coppice, and rotations of 2–10 years. SRWC have generated interest for many forest products’ companies (seeking for diversification or energy self-sufficiency) and private landowners, and although they might help with the supply for the expected growth on the bioenergy and biofuels market, there are still several concerns about how and when to harvest SRWC to maximize their ability to coppice. SRWC have elevated establishment and maintenance costs if compared to other type of plantations, but due to the coppicing ability, the same plantation may be harvested up to 5 times without the need of establishing a new one. Study plots were installed at six locations in Florida, Mississippi and Arkansas, and were cut with a chainsaw and a shear head during summer and winter, to determine the effects of felling method and season on coppice regeneration. Thus, plots were divided into areas of four different treatments: shear-winter, saw-winter, shear-summer, saw-summer. Harvesting eucalypt and cottonwood trees during winter resulted in better survival rates than harvesting during summer; however, there was no effect of felling method on coppice regeneration. Finally, no statistically significant difference was found on coppice regeneration of black willow when harvested during winter or summer with a chainsaw or a shear head.

Modeling sediment transport from an off-road vehicle trail stream crossing using WEPP model

There is a limited information available pertaining to the adverse effects of Off-Road- Vehicle (ORV) use and trail impacts. As a result, this study was initiated in 2003 to (a) quantify water quality impacts of an ORV trail stream crossing through monitoring of total suspended solids, and (b) conduct WEPP (Water Erosion Prediction Project) simulations to determine longterm sediment loads contributed by the ORV trail stream crossing. To collect suspended sediment samples from the ORV trail stream crossing, ISCO6 6700 water samplers were installed. Data was collected from November 2003 through July 2004. During this time suspended sediment samples were collected for three different operational conditions (open, closed, maintenance). When the study began the trail was open to traffic. The trail was then closed to traffic on January 1, 2004 and went through a two-week maintenance regime in early March. The trail was then opened to ORV traffic on April 1, 2004. The largest suspended sediment load contributed by the stream crossing during this study occurred during the trail closed condition. This storm event had a recorded rainfall of 49 mm, and contributed a suspended sediment load of 109 kg. Since there were no storm events sampled with return intervals of more than one year, the WEPP model was used to estimate the potential long term effects of ORV trail stream crossing. A thirty-year synthetic weather data (generated by CLIGEN) was used to predict sediment yield from the ORV trail stream crossing. The WEPP model suggested that average annual sediment load from the stream crossing is about 126.8 tons/ha, which is much higher than what is allowed by the USDA Forest Service-National Forests in Alabama for temporary roads. The model also suggested that most of the sediment load to the stream is contributed by a steep hillslope section that flows directly to the stream. Hence the modeling study suggests that a BMP needs to be implemented to control sediment loss from ORV trail section that contributes sediment directly to the stream. In addition, the ORV trail stream crossing should be located on as flat a slope as possible.

Nozzle Uniformity for Agricultural Sprayers Operating Under Field Operation when Using Automatic Section Technology

The adoption of automatic section control technology is increasing since it reduces application overlap and application in unwanted areas leading to input savings and improved environmental stewardship. Spray controllers attempt to maintain the desired target application rate when implementing auto-section control but concerns exist about whether intended nozzle flow rates are sustained at all times. Therefore, a study was conducted to evaluate nozzle flow rate and control system response in maintaining target application rates during field operation. Specific objectives were to: 1) map real-time nozzle uniformity CV (%) during field operation and 2) quantify the difference between target and actual nozzle (% off-rate) flow rate. Field experiments were conducted using common self-propelled sprayers equipped with commercially available controller systems with automatic section control and guidance capabilities. High frequency pressure sensors were mounted across the spray boom to record nozzle pressure with data stamped with GPS locations. Nozzle pressure were converted to nozzle flow rate using manufacturers calibration curves and nozzle CV, off-rate and flow rate settling times were calculated. Results indicated that target application rate changed frequently with ASC engagement and ground speed changes on irregular field boundaries with no-spray zones. The nozzle off-rate beyond ±10% occurred for approximately 60% and nozzle uniformity CVs for 25% of the time when operating in irregular shaped fields using auto-nozzle control sprayer. Static experiments during ASC engagement and sprayer acceleration and deceleration demonstrated that nozzle off-rate can vary from -27.6% to 37.2%, thus complimenting the field results. Auto-boom and auto-nozzle control sprayers results indicated that ASC engagement plus sprayer acceleration will result in under-application whereas ASC engagement and deceleration will over-application. Nozzle flow stabilization time up to 20.0 s during ASC engagement and/or speed change was irrationally high and needs to be investigated further. Overall, irregular fields can amplify application errors though extent and magnitude may vary with selection of type of section control strategy selected (boom or nozzle control), control algorithms, and controller response.