Master of Science / Department of Agronomy / Dorivar Ruiz Diaz / Two studies were conducted to evaluate phosphorus response. The first study focused on genetic improvements in corn (Zea mays) for water limited scenarios on phosphorus uptake. The object of the first study was to evaluate plant response to fertilizer and soil phosphorus for contrasting corn hybrids, including a drought tolerant (DT) and conventional hybrid. This study was established at seven locations for two years (2011 and 2012). Four locations were rain fed and three locations were under irrigation. Fertilizer treatments included phosphorus fertilizer at various rates and placements for the two different hybrids. The experimental design randomized complete block with factorial arrangement in four replications. Early growth biomass, early season whole plant tissue concentration (V6), ear leaf tissue concentration, and grain yield was measured throughout the season. Results showed differences in all measurements between hybrids. Differences in most measurements were also significant with fertilizer application. The DT hybrid had less early growth and P uptake but had higher ear leaf P concentration as well as higher yields. The second study focused on P placement, P stratification may be a concern for producers using reduced tillage systems. The objective of this study was to evaluate different placements and rates of P fertilizers in two crops, corn and soybean (Glycine max). This study is currently ongoing; however, here we are presenting data from three locations and four years (2009-2012). Two of the locations were rain fed and one was irrigated. There were four different fertilizer rates with three different placements as well as various combinations of those placements. The experimental design was randomized complete block with four replications at two locations and three replications at one location. Corn early growth biomass, whole plant tissue concentration, ear leaf tissue concentration, soybean uppermost fully open trifoliate P concentration, and yield for both crops were evaluated throughout the season. Results showed response to the phosphorus treatments in all the measured parameters. Results also showed differences in all measured parameters except yield, were significantly affected by placement.

Master of Science / Department of Agronomy / Dorivar Ruiz Diaz / The application of micronutrients to increase yields has become more popular with increased commodity prices and higher yielding crops. Two studies were completed evaluating secondary and micronutrient for soybean (Glycine max [L.] Merr.) and wheat (Triticum aestivum).The objective of the first study was to evaluate the response of soybean, under a double crop system after wheat, to soil-and foliar-applied macro and micronutrients. Macronutrients (N, P, K) were applied at 22 kg ha[superscript]-[superscript]1, micronutrients (Fe, Mn, Zn) were soil applied at 11 kg ha[superscript]-[superscript]1and S was applied at 22 kg ha[superscript]-[superscript]1. Plant response parameters were evaluated including changes in nutrient concentration, and seed yield response. Tissue samples were collected at the respective R1 growth stage. Samples were analyzed for the nutrients applied with the fertilizer treatments. Soybean seed yield slightly responded to soil-applied S, Mn, and Zn. When micronutrients were foliar-applied, seed yield was significantly decreased. The second study evaluated the application of S and micronutrients to winter wheat. The objectives were to evaluate the wheat response to sulfur and micronutrient fertilization and evaluate soil testing and tissue analysis as diagnostic tools. Fertilizer treatments consisted of sulfur, iron, manganese, zinc, boron, copper. All of the micronutrients were sulfate-based products and the sulfur treatments were applied as gypsum. Fertilizer treatments were applied as topdress in early spring. Soil samples were collected before fertilizer application and after harvest. Flag leaf samples were collected and analyzed for the nutrients applied with the fertilizer treatments. Significant increases in tissue concentration were observed when Zn, B, and S were applied. Significant increases in soil test Zn, Cu, B, and S were observed compared to the control treatment. Despite the increases in soil test concentration across locations, no significant increases in yield by any of the nutrients or combination of nutrients were observed.

Master of Science / Department of Agronomy / Mithila Jugulam / Extensive, often exclusive, use of glyphosate in crop production has resulted in evolved glyphosate resistance in several weed species globally. Kochia is a competitive summer annual weed, well adapted to the North American Great Plains and has recently evolved resistance to glyphosate by gene amplification of 5-enolpyruvyl shikimate 3-phosphate synthase (EPSPS), the target-site of glyphosate. The overall objective of this research was to investigate the genetic basis of glyphosate resistance in kochia, specifically to study 1) the inheritance of glyphosate resistance and 2) determine the chromosomal distribution of EPSPS gene copies. Homozygous resistant (R) and susceptible (S) parental lines of kochia were identified. Using these parents, reciprocal crosses were performed to produce F₁ progeny. As expected for a nuclear encoded EPSPS gene, F₁ plants from both crosses survived various doses of glyphosate application. However, F1 plants showed intermediate shikimate accumulation and EPSPS gene copies (relative to ALS reference gene) compared to parents. F₂ progeny were produced by selfing F₁ plants. In response to 870 g ae ha⁻¹ glyphosate, F₂ plants (n=115) segregated into 3:1 (R:S) implying a Mendelian monogenic segregation of glyphosate resistance in kochia. Additionally, relative EPSPS gene copies ranged from 1-10 in the F₂ progeny (n=51) with a genotypic segregation of 40:11 (plants with 3 or more EPSPS gene copies: plants with 1 EPSPS gene copy). In F₂ dose-response, a correlation between the level of resistance and relative EPSPS gene copies was observed. Genomic organization of the amplified copies using fluorescent in situ hybridization (FISH) displayed a single and larger hybridization site of the EPSPS gene on one pair of homologous chromosomes in R compared to a faint hybridization site in S samples of kochia. These results suggest possibility of amplification of EPSPS gene mediated via unequal recombination leading to the evolution of the glyphosate resistance in kochia.

Master of Science / Department of Agronomy / J. Anita Dille / Variable-rate (VR) nitrogen (N) applications have the potential to improve efficiency of grain sorghum production. Field experiments were conducted in 2010 and 2011 in Stockton and Manhattan, KS. Four VR-N prescriptions were generated using various combinations of grid soil sampling data, soil electrical conductivity (EC) data, and yield maps, and were compared in the field with a uniform application based on a composite soil sample and whole field average yield goal. Soil EC data were used to create management zones that were individually soil sampled. Prescriptions were applied before planting and grain sorghum was harvested and recorded with a yield monitor in the fall. Grain sorghum yields responded to N at both sites with a higher response in 2010 due to more precipitation during the growing season. At Stockton in both years, greatest yields and returns were realized with prescription 4, a combination of management zone soil data and spatially-variable yield goal, while the smallest yields were realized with prescription 2 based on management zone soil data and field average yield goal. Prescription 5, which used grid-soil sampling and a spatially-variable yield goal, and prescription 2 resulted in the lowest returns in both years. At Manhattan in both years, greatest yields and returns were realized with prescription 3, combining a composite soil sample with spatially-variable yield goal. Prescription 5 was among the lowest returning treatments in both years. At Stockton, there was no correlation between yield and soil EC during the 2010 growing season, however there was a significant correlation between yield and shallow EC during the drier 2011 season. At Manhattan, yield was correlated to deep EC in 2010 and to shallow EC in 2011. Overall, increasing spatial intensity of data to develop the prescriptions did not necessarily result in an increased yield response to the application. Prescriptions that included a variable yield goal component tended to perform better across both sites and years.

Master of Science / Department of Agronomy / Scott A. Staggenborg / In Kansas, productivity of grain sorghum [Sorghum bicolor (L.) Moench] is affected by weather conditions at planting and during pollination. Planting date management and selection of hybrid maturity group can help to avoid severe environmental stresses during these sensitive stages. The hypothesis of the study was that late May planting improves grain sorghum yield, growth and development compared with late June planting. The objectives of this research were to investigate the influence of planting dates on growth, development, and yield of different grain sorghum hybrids, and to determine the optimal planting date and hybrid combination for maximum biomass and grains production. Three sorghum hybrids (early, medium , and late maturing) were planted in late May and late June without irrigation in Kansas at Manhattan/Ashland Bottom Research Station, and Hutchinson in 2010; and at Manhattan/North Farm and Hutchinson in 2011. Data on leaf area index, dry matter production, harvest index, yield and yield components were collected. Grain yield and yield components were influenced by planting date depending on environmental conditions. At Manhattan (2010), greater grain yield, number of heads per plant, harvest index, and leaf-area were obtained with late-June planting compared with late May planting, while at Hutchinson (2010) greater yield was obtained with late May planting for all hybrids. The yield component most affected at Hutchinson was the number of kernels panicle-1 and plant density. Late-May planting was favorable for late maturing hybrid (P84G62) in all locations. However, the yield of early maturing hybrid (DKS 28-05) and medium maturing hybrid (DKS 37-07) was less affected by delayed planting. The effects of planting dates on growth, development, and yield of grain sorghum hybrids were found to be variable among hybrid maturity groups and locations.

Doctor of Philosophy / Department of Agronomy / Charles W. Rice / Variable N fertilizer application recommendations would benefit from crediting the N that will be mineralized and available to the crop during the growing season. During the 1994 and 1995 growing season, the spatial and temporal pattern of N mineralization was assessed on two central Kansas corn fields. Net N mineralization was measured in the field using a buried bag and a resin core method. A 60 m sampling grid was established on the field and the N mineralization was measured at each grid point. The field N mineralization measured was then compared to three lab incubation (14 day anaerobic incubation, CO₂ evolved 1 day after rewetting, and N released on autoclaving) measurements to determine if the field N mineralization could be predicted by a laboratory test. Nitrogen mineralization in the field was highest in May and declined during the growing seasons. Patches of high N mineralization appeared and disappeared during the season, areas of high and low mineralization were not found in the same areas month after month. The semivariance of the laboratory incubations tended to be smoother near the origin than the field incubations, indicating that the field incubations were subject to more sources of variability (such as microclimatic variations) than the laboratory incubations. Crop yields were not correlated with N mineralization in these fields. Soil moisture appeared to be more important to crop yields than the N contributed by mineralization. In these fields N mineralization does not need to be included in N fertilization recommendations unless the amount of fertilizer applied is much lower than in this study. Finally, a method to estimate the initial δ¹³ C content of a soil is proposed. This method can be used if a location can be found that has had a continuous C₃, a continuous C₄crop and a C₃/ C₄rotation treatment.

Master of Science / Department of Agronomy / Scott A. Staggenborg / Abstract Hard red winter wheat (Triticum aestivum L.) is the predominate crop grown in North Central Kansas; and no-till wheat production practices have gained popularity in this region. No-till advantages may include: increased stored soil moisture, decreased labor costs, and increased soil conservation compared with conventional cropping systems. Seeding rates and fertility rates are two important no-till management decisions for producers. Therefore, a two-year study was conducted to determine the optimum wheat seeding and fertility rates in north central Kansas comparing the winter wheat cultivars 'Overley' and '2145'. Treatments also included seeding rates (100 kg ha-1 vs. 134 kg ha-1) and fertility rates (0, 78, 112, 146 kg ha-1). A fungicide application study was also conducted with this two-year study but proved to be statistically insignificant during the two years. Overall, the variety selection and fertility rates affected grain yields. The higher fertilizer treatments increased wheat grain yields. However, the seeding rate yield differences were not significant either year of this study. In the fungicide study, 2145 responded more to fungicide applications than Overley in 2006; but in 2005 there was no statistical advantage for a fungicide treatment with either variety. For this study, wheat varieties were planted during the recommended optimum "fly-free" seeding date period (4 October through 10 October). Although this study did not record yield differences between wheat drilled at higher or lower seeding rate during the recommended seeding period, other research does indicate that seeding rates should be increased if planting dates are extended well beyond the optimum period. Further outcomes from this study indicate that nitrogen rates should be adjusted based on field yield expectations. Although timely rainfall and/or stored soil moisture are the most limiting yield factors in dryland wheat production in north central Kansas, research results indicate that wheat yields increase with higher fertility rates when moisture is not a limiting factor. This research may be applied to north central Kansas wheat fields particularly where no-till farming practices are being used in wheat following wheat fields.

Doctor of Philosophy / Department of Agronomy / William T. Schapaugh Jr / Harold N. Trick / Demands on value-added crops have been raised to improve agricultural, industrial, and economical value. Currently, transgene application is one of most effective methods to satisfy these demands. Success in herbicide-resistant soybean (Glycine max (L.) Merr.) has boosted genetic engineering to be used for biochemical, nutritional, cultural, and physiological improvements. The objectives of this study were to establish transgenic soybean lines with attenuated phospholipase D[Alpha] (PLD[Alpha]) activity in the seed, test the alteration of fatty acid profiles affected by transgene and somaclonal variation, and evaluate the physiological alteration of transgenic lines by both transgene and somaclonal variation. To change fatty acid profile in soybean seed, we attenuated PLD[Alpha] enzyme activity by an RNA interference construct using the PLD[Alpha] gene sequence. Two transgenic soybean lines were established by particle inflow gun bombardment of co-bombarding pSPLDi and pHG1 transgenes, and evaluated for the presence and expression of transgenes thoroughly through the T[subscript]5 generation. PLDα-suppressed soybean lines were characterized by decreased PLD[Alpha] enzyme activity and PLD[Alpha] protein both during seed development and in mature seeds. The PLD[Alpha]-attenuated transgenic lines, SW1-7-1-1 and SW1-7-1-2, contain 36% and 49% oleic acid in the filed and greenhouse evaluations, respectively, which are equivalent to the mid-oleic acid soybean lines improved by conventional breeding and mutagenesis. Phenotypic and genetic analysis of the transgenic lines suggested the possibility that the multi-copy transgene integration formed direct or indirect repeats by random ligation during integration and organization of transgenes in the soybean genome, and the transgene cluster with tandem repeats may consequently increase the probability of transgene silencing. Various factors, such as high humidity and temperature, result in the loss of seed viability. Fayette seed stored for two months since harvest exhibited about 95% viability; however Fayette seeds stored for 33 months at room temperature and uncontrolled relative humidity become non-viable. PLDα-attenuated transgenic soybean seeds have been produced by transformation. PLD-suppressed transgenic soybean seeds have maintained viability when stored for 33 months at room temperature. Germination of transgenic seed stored for 33 months ranged from 30 to 50%. Increased leakage of electrolytes associated with the loss of viability was observed in null-transgenic and background seeds versus transgenic seed. The increase in electrolyte leakage may have been induced by lipid peroxidation and free radical formation which can generate oxidative damage in the cell and subsequently decrease seed viability. Differences in the ultrastructure of cotyledon tissue were observed between PLD[Alpha]-suppressed soybean and the background cultivar. The loss of viability in the background cultivar was consistent with observations of the plasma membrane being detached from the cell wall complex and disorganization of oil bodies. Stresses caused by temperatures higher or lower than ambient are one of agricultural problems that reduce crop productivity in many areas and diverse species. To overcome the uncertainty of environmental fluctuations, efforts continue to improve high and low temperature tolerance in crops. PLD[Alpha]-suppressed transgenic events were produced by antisense suppression driven by constitutive and seed-specific promoters using the particle inflow gun (PIG) bombardment method. Nine fertile transgenic events suppressed the expression of PLD[Alpha] protein. PLD{Alpha] enzyme activity in T[subscript]1 seed was observed to be reduced by 25 percent compared to the non-transgenic control. When soybean seedlings were exposed to lethal freezing temperature, increased electrolyte leakage associated with oxidative damage and biophysical changes were observed in non-transgenic soybean, whereas membrane stability and integrity were maintained in transgenic soybean seedlings. The early growth of PLD[Alpha]-attenuated soybean seedlings was recovered from extreme heat-shock (45 °C) and freezing treatments (-8 °C). The disruption of the plasma membrane and organelles was observed in freeze-stressed non-transgenic control seedlings. On the other hand, the structures of the plasma membrane, oil bodies, and cell organelles in transgenic seedlings were partially sustained after enduring freezing and thawing stresses.

Master of Science / Department of Agronomy / William T. Schapaugh Jr / The soybean cyst nematode (Heterodera glycines) (SCN) is an important pathogen of soybean in the United States. Annual yield losses from SCN are estimated to be over $2 billion worldwide. However, SCN virulence or the ability of a nematode to grow on resistant soybean genotypes varies widely among SCN populations. Fortunately there are several genetic sources of resistance to decrease the virulence of the pathogen on soybean. The objectives of this research were to: 1) characterize the genetic diversity of soybean cyst nematode populations in Kansas, 2) determine the frequency of Kansas SCN populations virulent on PI88788, 3) determine which plant introductions used in the HG Type Test provide the best level resistance, and 4) compare the performance of commercial soybean cultivars to the plant introduction from which their SCN resistance was derived. Soil samples were collected from SCN-infested fields across the state. Each soil sample was taken to the greenhouse and planted to a susceptible soybean cultivar to increase SCN population. Following an SCN population increase, a HG Type Test was planted. H. glycines field populations were highly variable, not only in population densities, but also in their abilities to develop on soybean genotypes. Collected from a diverse range of environments, ten HG types were identified. About 50% of the H. glycines populations were virulent on PI 88788, and most of the populations were virulent on commercial SCN resistant lines which derived their resistance from PI 88788. The commercial lines tended to be more susceptible to SCN than the lines from which they derived their resistance, but few HG populations were virulent on PI 437654 or the commercial line that derived its resistance from PI 437654. These results suggest that sources other than PI 88788 should be used in the development of H. glycines resistant cultivars for Kansas. One possible source of resistance is PI 437654. Information about SCN diversity in Kansas will improve decisions regarding cultivar development and selection for SCN management.

Doctor of Philosophy / Department of Agronomy / Johanna A. Dille / Success of plants depends largely on their environment. A survey, field and greenhouse studies were conducted from 2006 to 2010 to characterize the dynamics of giant ragweed (AMBTR) and common sunflower (HELAN) in KS through determining their distribution, plant-soil feedback response and demography. The survey revealed a distinct distribution pattern within the state with HELAN being more dominant than AMBTR. Populations of AMBTR and HELAN from KS could be grouped by their emergence characteristics. Plant-soil feedback response of AMBTR and HELAN varied across sites with HELAN having a consistent positive feedback response while AMBTR had negative feedback response in IL, KS, MI-a, MI-B, OR and SD but not in MT. Interaction coefficient analysis was neutral for IL, KS and MI-b while positive for OR and SD and negative for MI-a and MT. Plant-soil feedback response of KS-derived populations of AMBTR and HELAN indicated that both KS-AMBTR and KS-HELAN seemed to grow best in soil preconditioned by another species. Seed survivorship over winter and summer, emergence, and population growth rates of both weed species varied over three years with HELAN having higher growth rates that AMBTR. This study showed that demographic success of HELAN and AMBTR was greatly influenced by the climatic conditions more than any other factors. AMBTR from IL, if introduced to the state can adapt to KS conditions. Further studies including impacts of soil biota, nutrient dynamics and biochemical processes such as allelopathy are needed to better understand the mechanism behind the plant-soil feedback response of the two weed species and its contribution to the demographic success of AMBTR and HELAN.