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1. Mechanisms of urea adsorption by soils Physically adsorbed urea may be easily desorbed by dilution. Chemisorbed urea existing primarily in the form of relatively stable soil organic matter-urea complexes may, in part, be slowly dissociated upon dilution. Differences between soil types with respect to urea adsorption were primarily related to organic matter contents; the effects of CEC, pH, and clay mineral content were found to be insignificant. Wet soils had a lower capacity for urea adsorption than dry soils. Considering the amounts of urea adsorbed it appears that soils have a weak affinity for the urea molecule. 2. Mechanisms of urea hydrolysis and volatilization in soils The biological or catalytic hydrolysis of urea is rapid and can be related to soil microbial activities. The reaction rate of the chemical hydrolysis of urea is very slow and insignificant in comparison with the biological or catalytic hydrolysis. Urea-nitrogen loss through ammonia volatilization may immediately follow urea hydrolysis and proceeds rapidly. Urea hydrolysis and ammonia volatilization from ammonium carbonate are first order reactions. 3. Mechanism of foliar absorption and subsequent utilization of urea The mechanism of foliar absorption of urea solution is suggested to be a simple physical diffusion phenomenon. The absorbing capacity of the foliage for urea solution is relatively lover during the day than during the night. It is suggested that rapid evaporation at high temperature and low humidity conditions may increase the concentration of the urea solution on the leaf thereby decreasing the rate of diffusion of foliar applied urea into the leaf. The absorbing capacity of the leaf for urea solution is independent of its position, but the younger leaves have a higher capacity to metabolize the absorbed urea. Urea in foliage cannot be translocated, but more than 90%of the absorbed urea can be rapidly and directly transformed into other soluble nitrogenous compound(s). The mechanism of the biochemical reactions and their related enzymatic systems are not yet known. Sucrose does not influence the urease activity, and no urease activity was detected in the tobacco leaves used. The reduction of urea injury from foliar applied urea solutions containing sucrose was associated with decreased urea absorption and increased urea utilization. A relationship was found to exist between the urea concentration in the leaf and the incidence of injury. Plasmolysis resulting from increased urea concentrations in the leaf may be the cause of foliage burning resulting from foliar application of urea. 4. Methodology The principle of the newly developed methods for the determination of urea in fertilizers, urine, and blood and the estimation of urease activity is based on the difference in electric conductivity of urea and ammonium carbonate produced from urea by urease in solution. These methods are rapid, simple and accurate. They have very wide testing ranges, and the values of the standard curves are constant at a specified temperature. Interference due to the presence of colored impurities are eliminated. However, these methods will not be applicable if heavy metal ions such as Ag, Hg, and the protein-destroying substances are present in the testing solution. / Ph. D.

Equine gastric glandular mucosal ulceration can have a prevalence of 58%, yet its etiology is poorly understood. In man Helicobacter pylori is the most common cause of gastritis and peptic ulcer disease. Helicobacter is uniquely able to colonize the stomach, via the action of cytoplasmic urease. Different Helicobacter species have been isolated from many mammals but none has yet been cultured from the horse. Three tests used to identify human Helicobacter infection were applied to the horse. Test 1: PCR amplification of Helicobacter specific DNA, n=12. Test 2: the Pyloritek™ rapid urease test (RUT), n=15. Test 3: the 13C-urea blood test, n=8. Gastroscopy and antral biopsy was performed in all horses. All horses demonstrated the presence of Helicobacter specific gene material by PCR. Biopsy specimens from 7/15 horses were urease positive by RUT. Significant 13C enrichment of the body CO2 pool was found in all horses after intragastric administration 13C-urea (p<0.05). As Helicobacter is currently the only known gastric urease positive microorganism, the demonstration of this activity in horses positive by PCR strongly supports the presence of an equine gastric Helicobacter species. Variations of 13C-urea blood test were further examined and a single protocol was found to be most applicable. As the horse is a hind gut fermenter, the effect of cecal urease on the test was examined by laparoscopic intracecal administration of 13C-urea. Significant cecal urease activity was demonstrated however the timing of peak 13C enrichment may limit any effect on the gastric test to 90 minutes onwards. / Master of Science

Vineyards in the Eastern United States are often prone to excessive vegetative growth. In order to suppress excessive vine vigor, many viticulturists have employed cover cropping strategies. Cover crops provide a myriad of agronomic benefits, however they are known to compete with the vine for water and nutrients. Due to the widespread use of cover crops in Eastern vineyards, many vineyards experience nitrogen (N) deficiencies in both the vegetative vine tissue and yeast assimilable nitrogen (YAN) in the juice. Soil applications of calcium nitrate and foliar applications of urea were assessed as a means of vineyard N amelioration at cover cropped sites comprised of Petit Manseng and Sauvignon blanc (Vitis vinifera L.). Perennial White and Crimson clover cover crops and foliar urea applications were also used in a Vidal blanc (Vitis spp.) vineyard. Treatments were imposed in the Sauvignon blanc vineyard for five years. The Petit Manseng and Vidal blanc vineyards were subjected to treatments for two years. Soil-applied N at bloom was most effective at increasing leaf petiole N at véraison, season-long chlorophyll content index (CCI), vine capacity and fruit yield. Fruit yield was increased due to more berries per cluster and greater berry weights. Increased rates of soil-applied N decreased the fruit weight:pruning weight ratio. Clover cover crops offered little to no benefit as a N source in the two-year period of evaluation. None of the N management schemes negatively impacted canopy density, fruit zone light interception, or botrytis bunch rot incidence. The combination of both a soil-applied and foliar-applied N fertilizer may be the most effective means to increase both vine capacity and YAN in vineyards where vineyard floor cover crops are compromising vine N status. / Master of Science

To combat excessive vine vigor, many vintners have employed intensive cover cropping techniques. While cover crops provide a multitude of benefits to the farming system, they can compete for nutrients and water. The seemingly ubiquitous adoption of cover crops in the Eastern United States has led to vines and grape musts which are deficient in nitrogen (N). A must that is deficient in yeast assimilable nitrogen (YAN) can lead to the production of off aromas and stuck or sluggish fermentations. It has also been suggested that musts with limited amino nitrogen sources can result in wines with less fruity aromas than those with a higher starting amino acid content. Varying rates of calcium nitrate were applied to the soil at bloom and foliar urea was sprayed at a Sauvignon blanc and Petit Manseng (Vitis vinifera L.) vineyard. Perennial White and Crimson clover as well as foliar urea applications at véraison were utilized at a Vidal blanc (Vitis spp.) site. Foliar urea was effective at significantly increasing YANs in all experiments with some year to year variation in efficacy. Foliar urea applications slightly favored the production of ammonia over primary amino nitrogen. While most of the measured amino acids in fruit increased in concentration with the application of either soil or foliar N, foliar applications were more effective at increasing fruit amino acids. Of the amino acids measured, arginine and glutamine were the most increased by foliar urea applications, whereas proline was relatively unaffected. The use of clover as a perennial under-vine cover crop did not increase berry YAN. The application of foliar urea sprays may present an effective means by which vintners can easily increase must YANs and amino acid contents. / Master of Science in Life Sciences

Increased nitrogen (N) costs and environmental concerns have created a need to reevaluate current sidedress N application recommendations for corn. Injection of Urea Ammonium-Nitrate (UAN) may reduce N-loss via ammonia (NH?) volatilization compared to current surface application methods. This study evaluated injection and surface-banding application techniques of UAN in two ways: (1) by conducting a laboratory experiment where NH?-N loss was measured from UAN applied by both techniques across varying residue covers; and (2) by performing a field study where the application methods were compared by their effect on corn grain yield, ear leaf tissue N content, and stalk nitrate (NO3). The laboratory system used to compare the NH?-N loss from the UAN application methods was evaluated and found to be capable of providing rapid, accurate, and precise measurements of N loss throughout a range of N rates and conditions. In the laboratory study, injection of UAN reduced NH?-N losses to <1% of applied N. Surface-banding of UAN resulted in NH?-N losses between 15.3 and 32.5% of applied N. Results from the field study suggest that differences between application methods were commonly seen in ear leaf tissue N, where injection of UAN was often found to increase tissue N compared to surface-banding. Also, injection of UAN reduced the optimal N rate by 25 kg N ha?? compared to surface-banding. The results suggest that injection of UAN reduces the potential of NH?-N losses and is a practice worth considering in developing an efficient N fertilizer program. / Master of Science