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Three factors were tested in an attempt to accelerate the growth of Abies fraseri seedlings grown in containers in a greenhouse: growth medium acidity. foliar application of growth regulators. and supply of nitrogen fertilizer. Sphagnum peat growth medium was adjusted with a to 8 kg dolomitic limestone/m3 compressed packaged peat to initial pH ranging from 3.9 to 6.7. Best growth (21.2 cm mean height at 19 months) was achieved with 1 kg/m³ and 2 kg/m³â ¢ with initial mean pH 4.2 and 4.5. respectively. Seedlings with 4 and 8 kg/m³ grew more slowly (17.4 and 9.5 cm. respectively. in 19 months). and many were chlorotic. with poor root development. Three growth regulators were sprayed on seedlings: benzylaminopurine (BAP). gibberellic acid (G~. and indolebutyric acid (IBA). BAP stimulated terminal bud activity. decreasing the periods of rest between active growth. BAP increased height and diameter of new shoot growth up to 19% and 32% respectively. BAP reduced root growth 22% when applied at the higher concentration (100 ppm). GA3 had no main effect on either shoot or root growth. However. GA3 did increase shoot growth slightly in the absence of BAP. IBA increased root growth up to 26%. IBA had no significant effect on shoot growth. Nitrogen fertilizer was supplied weekly in concentrations of 200. 400. and 600 ppm. At six months age there was no treatment effect on seedling growth. At nine months age 400 ppm N had produced 9% more shoot growth than either 200 or 600 ppm N. Nine-month-old seedlings with 400 ppm fertilizer averaged 8.9 cm in height. / Master of Science

Mammoth cultivars of flue-cured tobacco flower under short-day photoperiods, thereby increasing the potential number of leaves per plant. Field experiments were conducted in 1991 and 1992 at the Virginia Tech Southern Piedmont Agricultural Experiment Station near Blackstone, Virginia to determine the influence of nitrogen rate on nitrogen use efficiency and its components on two mammoth cultivars and a conventional cultivar. Experiments were also conducted to determine the effects of leaf number, time of topping, and nitrogen rate on yield, quality, and other agronomic characteristics. Nitrogen uptake, utilization, and use efficiencies decreased while nitrogen accumulation increased as nitrogen rates increased from 67 to 112 kg ha⁻¹. Mammoth cultivars were more efficient than the conventional cultivar for nitrogen uptake, utilization, and use. Only NC 27 NF benefits from increasing nitrogen above the recommended rate. Yield increased by 17 percent as the leaf number increased from 20 to 36. In contrast, both agronomic traits and chemical characteristics decreased accordingly. The ratio of nitrogen to nicotine that was unacceptable at leaf numbers above 28. Yield, value, and quality decreased as topping was delayed by seven to 21 days. Yield was reduced by 30 kg per hectare per day when topping was delayed by 21 days after the conventional cultivar reached the bud stage. Leaf lengths and widths of mammoth cultivars were larger than the conventional cultivar. Mammoth cultivars were higher yielding and had better quality at 112 kg ha⁻¹ N when compared to the conventional cultivar, although these differences were not significant. / Master of Science

Several potential pathways exist for significant nitrogen loss from nitrogen fertilizer applied to winter wheat in Virginia. A number of materials have been previously identified which inhibit steps in one or more of these loss pathways. Ammonium polyphosphate, ammonium thiosulfate, dicyandiamide, potassium chloride, and monoammonium phosphate were chosen for use in the present study. They were mixed, singly and in combinations, with UAN solution or urea solution and spring top-dressed on soft red winter wheat. Experiments were conducted over two growing seasons at two locations each season. Nitrogen uptake was measured in mid-season and yield measured at harvest. In the second season, field measurement of ammonia volatilization was performed in the experiment utilizing urea solution. Addition of monoammonium phosphate significantly reduced volatilization from urea solution applied to winter wheat at both locations; however, weather conditions were such that total volatilization was low in this season, and the reduced losses were not reflected in increased nitrogen uptake or yield. None of the treatments significantly increased yield in any experiment, nor consistently increased mid-season nitrogen uptake. / Master of Science

Nutrient loadings to the Chesapeake Bay are a source of concern for water quality agencies. In particular, excess nitrogen loadings from agricultural production activities threaten water quality in the Bay. Questions have been raised about how effectively traditional BMPs can control nitrogen loss from crop production. This study examines agricultural nitrogen pollution control from an input management perspective. Using an economic and physical model, seven production systems and nitrogen management strategies are compared in terms of input use, profitability, and nitrogen loss potential. Results suggest that several of the production systems will reduce residual nitrogen without reducing profits. However, it is recognized that factors in addition to profitability will influence producers' nitrogen management decisions. Therefore, using the results of a farmer survey, adoption models are estimated to examine the impact of production system characteristics and producer characteristics on the decision to use an alternative production system and nitrogen management strategy. Finally, a sensitivity analysis is conducted to examine the impact of alternative policy tools on adoption incentives. Both financial incentives and education and information programs are found to be important tools for influencing producers' decisions. Producers' interest in the alternative systems and desire for information on the systems suggest that agricultural research will contribute by assuring that producers have access to adequate information on the alternative systems. / Ph. D.

Two experiments were conducted with field- and container-grown 'Delicious' apple trees to evaluate the effect of nitrogen fertilization on the physiology of apple leaves subjected to European red mite feeding, and the subsequent recovery of leaf function following mite removal. Nitrogen (N) fertilization affected the visual damage, and the photosynthetic response of 'Imperial Delicious' apple leaves to mite feeding. Visual damage occurred first, and remained greatest on the low N treatment throughout the experiment. High N trees exhibited a linear decline in Pn with increasing MD, in contrast to the quadratic decline found under low N treatment. With equal mite populations, high N trees retained higher Pn rates. Transpiration, dark respiration, relative water content, leaf nitrogen, and total chlorophyll were negatively related to MD, but specific leaf weight was positively related to MD. No interaction was found between N treatment and mite feeding for these parameters. Following removal of ERM populations, 'Redchief Delicious' leaves subjected to greater than 4000 MD exhibited recovery in Pn by 28 days after mite removal. Leaves receiving less MD (1500-3000) demonstrated an inconsistent response over time. Transpiration and diffusive resistance showed no recovery. Relative water content, specific leaf weight, leaf nitrogen, and total chlorophyll linearly declined with mite feeding, and were unaffected by foliar urea treatment. / Master of Science

Optimum spring N fertilizer rates for winter wheat in Virginia vary widely from field to field, but traditionally spring N is applied at a uniform rate to all fields. A recently-developed tissue test procedure provides a field-specific evaluation of crop N status and predicts optimum N rate for the second spring N application in a split spring application management system. However, this procedure is based on a small number of researcher-planted experiments utilizing a single cultivar; it fails to provide field-specific rate recommendations for the first spring N application; and it is not accessible to farmers who are unwilling to split their spring N applications. Our objectives were: to evaluate the reliability of the tissue test procedure in a large number of farmer fields; to develop a method for making field-specific N rate recommendations for the first spring application in a split-application management system; and to develop a method for making field-specific N rate recommendations in a single-application management system. Forty-five spring N rate experiments were established in farmer fields over a five-year period. A range of N fertilizer rates was applied in early spring (Zadoks growth stage 25) and again in mid-spring (Zadoks growth stage 30) in all possible combinations. Yield data were used to calculate economic optimum N rates at growth stage (GS) 25 and GS 30 with split-application management, and at GS 25 with single-application management. These optima were regressed against a variety of predictor variables measured in the same fields. The reliability of the previously-developed tissue test procedure for making GS 30 N rate recommendations was confirmed. Tiller density was the best predictor of optimum GS 25 N rate with split-application management, while soil nitrate to 90 cm was the best predictor of optimum GS 25 N rate with single-application management. These three relationships fit together to form a flexible and powerful system for making spring N rate recommendations for winter wheat. This system increased estimated profit and apparent fertilizer efficiency in these experiments. / Ph. D.