Doctor of Philosophy / Department of Human Nutrition / Delores H. Chambers / Vegetables are popular among consumers because of their versatility of preparation, unique sensory characteristics, and exceptional health benefits. Trends such as organic farming and breeding to increase nutrition and functional health components have increased interest in understanding the flavor of vegetables, such as leafy greens. A lexicon of thirty-two flavor attributes was created to help describe the flavor of fresh leafy vegetables. This lexicon includes five “green” attributes; mouth feel characteristics such as pungent, bite, tooth-etch, and heat/burn; fundamental tastes including bitter and umami; seven terms that describe unique flavors related to specific vegetables such as cabbage, celery, lettuce, spinach, parsley, beet, and radish leaves; and a group of other terms including citrus, piney, woody, water-like, musty/earthy, floral, sulfur, metallic, soapy, petroleum-like, and overall sweet. In addition, our study encompassed a series of sensory tests which will aid in better understanding the effects of several production variables on the sensory characteristics of pac choi and tomato. Variables evaluated were production systems (i.e. organic and conventional), fertilizer amount (i.e. high, low, and no fertilizer), environment (i.e. field and high tunnel), maturity level (i.e. 2.5, 4.5, and 6.5-week old plants at the time of harvest), and shelf life (i.e. 1, 4, 9, 18 days of refrigerated storage). Samples were grown at the Kansas State University Horticulture Research Center located in Olathe, Kansas. Highly trained descriptive panelists from the Sensory Analysis Center at Kansas State University evaluated the samples. There do not appear to be major sensory differences between organic and conventional products specific to the crops and seasons studied. Furthermore, when differences were present, they generally were quite small and showed no clear trends or patterns favoring one production system over the other even after refrigerated storage. However, it is suggested that differences in flavor and volatile composition between organic and conventional pac choi may be more evident at early stages of growth.

Doctor of Philosophy / Department of Entomology / Raymond A. Cloyd / James R. Nechols / Raymond A. Cloyd / James R. Nechols / Greenhouse studies were conducted to examine direct effects of light intensity and nitrogen source on primary and secondary metabolism of pac choi (Brassica rapa L. var. chinensis cv. ‘Mei Qing Choi’) and indirect effects on diamondback moth (Plutella xylostella L.)(DBM). In the first study, plants were exposed to high and low light intensities during different times of the year, resulting in a range of light intensities. From four experiments, plants exhibited higher phenolic content, greater shoot biomass, and higher C:N ratios under high light intensity, whereas plants under low light intensity contained higher protein. Ferulic acid increased under high light intensity, and this increase was negatively correlated with male DBM body weights. However, DBM developed faster on plants in the August experiment (high light), compared to the July experiment (lower light). This implies that light intensity may not be affecting DBM through plant-mediated changes unless reduced male weights confer a reduction in larval consumption. In the nitrogen source study, application of an organic source of nitrogen (fish hydrolysate fertilizer) was compared to a conventional fertilizer to determine whether nitrogen source directly impacts pac choi chemistry and biomass, thus indirectly impacting DBM fitness. In two experiments, there was no significant effect of fertility treatment on pac choi nutrients or biomass, with the exception of percent leaf phosphorus, which was significantly higher in the conventional fertility treatment. For DBM, percent survival and cohort development were significantly reduced on pac choi receiving the organic fertilizer. Calcium and magnesium were significantly higher in pac choi infested with DBM larvae than plants without DBM. In addition, calcium was negatively correlated with female DBM body weights in one experiment for the organic treatment. Overall, this study demonstrated that pac choi plants that received the organic fertilizer were similar to pac choi plants that received a conventional fertilizer with the exception of phosphorus. Furthermore, female DBM body weights were negatively impacted by calcium in the organic treatment. As multiple fitness traits for DBM were negatively affected in the organic treatment, pac choi crops grown with fish hydrolysate fertilizer may experience less feeding from DBM.

Master of Science / Department of Horticulture, Forestry, and Recreation Resources / Rhonda R. Janke / Petiole sap nitrate-nitrogen (NO3-N) analysis with handheld meters is a valuable tool in applying in-season nitrogen (N) for many crops. Sufficiency levels have been determined for several leafy green crops, including lettuce (Lactuca sativa L.) and cabbage (Brassica oleracea L.), but not for pac choi (Brassica rapa L.). The response of pac choi to different fertilizer rates and sources [conventional and organic] has established optimal soluble N application rates and Cardy meter sufficiency ranges. Greenhouse experiments were conducted during summer and fall of 2008 in Manhattan, KS. Conventional soluble fertilizer was formulated from inorganic salts with a 4 NO3-N: 1 ammonium ratio. Phosphorus was held at 1.72mM and K at 0.83mM for all treatment levels. The organic soluble fertilizer, fish hydrolyzate (2N:1.72P:0.83K), was diluted to provide the same N levels as with conventional treatments. Both fertilizers were applied at rates of 0, 32, 75, 150, 225, 300, and 450 mg. L-1. Seedlings were transplanted and fertilizer application began at 18 days. Plants were harvested at seven weeks (five weeks post transplanting) after receiving 15 fertilizer applications during production. Samples of the most recently matured leaves were harvested weekly and analyzed for petiole sap NO3-N and leaf blade total N concentration. Leaf count, leaf length, and chlorophyll content were also measured weekly. Fresh and dry weights were determined on whole shoots and roots. Optimum yield was achieved at the 150 mg. L-1 fertility rate with both conventional and organic fertilizers. Field and high tunnel experiments were conducted during fall 2008 to validate the sufficiency ranges obtained from the greenhouse studies. Based on field and high tunnel results, sufficiency levels of NO3-N for pac choi petiole sap during weeks 2 to 3 of production were 800-1500 mg. L-1, and then dropped to 600-1000 mg. L-1 during weeks 4 through harvest for both conventional and organic fertilizers sources. These ranges could vary based on the variety of the crop, the fertility of soil, and certain environmental factors such as photoperiod, light intensity. However, we found that petiole sap nitrate always increased to the point associated with the maximum biomass, followed by a plateau where sap nitrate remained constant. This characteristic of the Cardy meter can provide the growers with a practical methodology to generate their standard curves under specific conditions to guide in-season N applications. Total N in leaf tissue showed fewer fertilizer rate effects than petiole sap NO3-N. Chlorophyll content was not useful in evaluating pac choi N status.