Browsing by Author "Kern, James D."
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- Cover crop/dairy manure management systems: Water quality and soil system impactsKern, James D.; Wolfe, Mary Leigh (American Society of Agricultural and Biological Engineers, 2005)A field study was conducted to determine impacts of corn silage production systems that included a rye cover crop and application of liquid dairy manure in the spring and fall on water quality and soil characteristics. Four management systems were each replicated four times: traditional, double-crop, roll-down, and undercut. Manure was applied below the soil surface during the undercutting process; otherwise, manure was surface applied. In the roll-down system, the rye crop was fattened with a heavy roller after manure application. Rainfall was simulated within 48 h of manure application to produce runoff events. Grab samples of runoff were collected and composited for analysis. Soil samples were collected prior to treatments in the fall and spring. The roll-down system had no significant effect on water quality (sediment, nutrients, bacteria) as compared to the traditional system. While the roll-down system may require an occasional tillage operation to prevent surface compaction, it is recommended in situations where reduction of residual herbicide applications is a primary concern. The undercut system displayed evidence of a compaction layer developing below the disturbed soil layer. The undercut system reduced loadings of all nutrients, but increased losses of total suspended solids, as compared with all other systems. Mean volume of runoff from the undercut system was less than half that from any other system. Overall, the undercut system is recommended over the other systems analyzed for preventing transport of manure constituents to surface water, but should be evaluated in a complete dairy system before it is implemented by producers.
- Energetics of a sustainable crop-livestock systemKern, James D. (Virginia Tech, 1994-05-15)This study compares the energy utilization of two systems for producing cattle of desirable slaughter weight and grade from weanlings. Both systems produce beef cattle as a primary output; various types of baled hay are produced as a secondary output. One system uses generally accepted, "best management practices" while the other uses experimental, sustainable agriculture techniques. Since the adoption of new practices in agriculture often hinges on economics, an economic comparison is also presented. Beef produced in the sustainable system required 32% less energy per kilogram than that produced in the conventional system. However, baled alfalfa produced in the sustainable system required 8% more energy per kilogram than the alfalfa grown in the conventional system. When all types of hay were considered, the sustainable system used 7% more energy to produce one kilogram of baled hay. To compare the energetics of the two systems on a whole farm basis, the amount of energy required to produce one dollar of return was calculated. The sustainable system required 12.4 megajoules to produce one dollar of return, while the conventional system required 17.1 megajoules to produce the same return. Although economic returns on beef and alfalfa production were comparable in the two systems studied, the conventional system showed greater returns on the whole farm, due to a greater export of baled hay.
- Identifying Sources of Fecal Pollution in the Appomattox River WatershedMcKinney, Julie Michelle (Virginia Tech, 2004-05-20)Sources of E. coli were determined from impaired waterways in the Appomattox River watershed (in the lower Piedmont and South-Central Virginia) for the development of bacterial Total Maximum Daily Loads (TMDLs). The Appomattox River watershed is primarily undeveloped with 70.8% of the land forested, 17.0% used for agriculture (mainly livestock production), and 7.7% classified as water, wetland or barren land. The remaining 4.5% is developed for residential, commercial, and industrial land uses (mainly within the city of Petersburg). Using Antibiotic Resistance Analysis, a known source library of 1,280 E. coli isolates (320 isolates per source) was constructed. Water samples were collected monthly for between eleven and fourteen months (11/02-12/03) from 40 locations throughout the Appomattox watershed and analyzed for fecal coliforms, E. coli, and resistance to 7 antibiotics of varying concentrations. A total of 486 water samples (9,907 isolates) were analyzed during the study. The objectives of this study were verify that each sampling site exceeded state bacterial count standards (using fecal coliform data), to compare the Discriminate Analysis and Logistic Regression statistical models for use in the classification of isolates, and finally to determine the source of contamination at each site. The fecal coliform and E.coli data was used to determine if each site exceeded state standards during the assessment period. Thirty-eight of the sites exceeded the fecal coliform standard at least 10% of the time, and thirty-three exceeded the E.coli standard at least 10% of the time. Discriminate Analysis (DA) is typically used to classify isolates, but the results obtained from the DA model were unrealistic based on the watershed land uses. By statistically analyzing the original 1,280 E.coli isolates six different ways, a more appropriate classification of isolates was determined. The six analyzing methods were Regular DA and Logistic Regression (LR); DA and LR where each isolate whose probability fell below 80% was deleted; DA and LR where each isolate whose probability fell below 80% was used to create an Unknown category. The Logistic Regression model with an Unknown category proved to be the most appropriate. By using the Logistic Regression model, with Unknown category, to classify isolates, twenty five of the forty sites were discovered to be contaminated predominately with Livestock and fourteen of the sites predominately by Wildlife. One site was equally divided between these two categories. Human and Pet contamination were not dominant at any of the forty sites. This comparison of the DA and LR statistical methods could change the analysis standard for Bacterial Source Tracking and suggests that the model required to classify isolates depends on the watershed characteristics.
- Water Quality Impacts of Cover Crop/Manure Management SystemsKern, James D. (Virginia Tech, 1997-11-19)Crop production, soil system, water quality, and economic impacts of four corn silage production systems were compared through a field study including 16 plots (4 replications of each treatment). Systems included a rye cover crop and application of liquid dairy manure in the spring and fall. The four management systems were: 1) traditional, 2) double-crop, 3) roll-down, and 4) undercut. In the fourth system, manure was applied below the soil surface during the undercutting process. In all other systems, manure was surface-applied. In the third system, the rye crop was flattened with a heavy roller after manure application. Simulated rainfall was applied within 48 h of manure application. Measured constituent concentrations in runoff were compared with water quality criteria. Costs and returns of all systems were compared. The undercut system reduced loadings of all nutrients, but increased total suspended solids (TSS) concentration as compared with all other systems. The mean volume of runoff from the undercut system was less than half that from any other system, which influenced all constituent loadings. Mean TSS concentration in runoff from the undercut system was over three times the mean of any other system. The roll-down system had no significant effect on water quality as compared to the traditional system. The undercut system was reasonably effective in keeping phosphate phosphorus levels below the criterion set for bathing water. None of the systems generally exceeded nitrate nitrogen concentration criteria. However, total phosphorus, orthophosphate, fecal coliform and e. coli criteria for drinking, bathing, shellfish harvest, and aesthetics were regularly exceeded by all of the systems. There were no differences among the treatments in effects on bacterial concentrations. The double-crop system produced significantly higher net returns than all other systems only if the value of the rye crop was $92.31/Mg or more. There were no significant differences in net returns of the traditional, roll-down, or undercut systems.