Master of Science / Department of Agronomy / David B. Mengel / Over the last decade low (< 130 mg kg -1) soil test potassium (K) levels and increased crop K deficiency have become a major concern in the clay-pan soils of southeast Kansas. The use of more intense crop rotations and the increased production of high K extracting crops (e.g. soybeans (Glycine max L.)) has significantly increased K removal from these soils. In addition, the traditional use of the nutrient sufficiency-based fertilizer recommendations has resulted in K application rates being substantially lower than removal rates. Because of these practices, many soils that had naturally elevated K availability 25 years ago have declined in K content. More troubling is the extreme yearly variation of soil test exchangeable K levels reported in the region, which has many producers and consultants concerned about proper K management. This study was initiated to examine the extent of K soil test variation and to determine if the variability is impacting plant K availability by analyzing soybean leaf K content and crop yield. A major objective of our research is to identify the mechanism(s) driving these changes in soil test K levels and K availability to crops during the growing season. The long-term goal is to be able to design a soil sampling system and develop alternative K fertilizer recommendation strategies that could alleviate K deficiency impacts on crop yield. Evaluation of different K fertilizer application practices including rate of application and broadcast or surface band methods of application were studied as tools to correct soybean K deficiency. The direct and residual impacts of K fertilization and placement were also evaluated on corn (Zea mays L.) grown in the rotation with the soybeans. Results observed from this research showed that monthly soil samples taken during three crop years at multiple locations have ammonium acetate exchangeable K levels that indeed change dramatically. The data we collected together with data accumulated by farmers and crop consultants showed significant fluctuation in exchangeable K levels of up to 50% on a yearly and even on a monthly basis. Levels seem to demonstrate seasonal changes: higher in the spring months and then decline in the summer and fall. Potassium soil test levels also appear to follow a similar trend as monthly precipitation and soil moisture status. During wet months soil levels tend to increase and then decline during drier months, however, this is not a perfect relationship and other factors are likely to be involved in regulating soil test K levels. No clear effect of K fertilization or method of placement on soybean or corn yields was observed during the study. However, soybean leaf samples revealed that on very low (< 90 mg kg -1) soil test sites surface band applied fertilizer increased leaf K concentrations compared to broadcasted applications. Furthermore, the corn study revealed no distinct difference between using a split annual or biannual fertilizer application system. Maintaining soil test K levels above 130 mg kg -1 using a spring soil test appears to be a successful strategy for avoiding K deficiency. Traditionally most soil sampling occurs in late summer or fall when soil conditions are dry. Our data has demonstrated that during this period one should expect to encounter low soil test results that may not be true indicators of soil K levels during the spring planting months. With that said, spring soil sampling can be difficult to do in a timely fashion due to weather, as well as potential labor restrictions. Another critical point is to not switch back and forth between spring and fall sampling dates. Staying consistent with your sample timing will minimize the seasonal variability that is frequently experienced. Additionally, adopting a build and maintain fertilizer recommendation philosophy rather than a nutrient sufficiency-based recommendation approach is a better nutrient budgeting method to avoid having removal rates exceeding nutrient additions. The best K management proposal would be to consider using a build and maintain approach in combination with basing fertilizer rates on spring soil test K levels.

Master of Science / Department of Agronomy / David B. Mengel / Research has shown that nitrogen fertilizer is needed most years to optimize winter wheat yields in Kansas. Anhydrous ammonia (AA) has long been a favorite N fertilizer of producers as it has proven to be a reliable and economical source of N. Anhydrous application methods and equipment have changed little over the past 70 years. Recently John Deere has developed their 2510 HSLD (2510H) anhydrous ammonia applicator designed to improve efficiency and performance in no-till systems. The 2510H is designed to be run at high speed with low soil disturbance and low draft. This is achieved by using a rolling coulter type injection unit, designed much like modern single disk opener grain drill units, to apply AA at relatively shallow depths. With this low soil disturbance design, topdress AA applications may also be possible. Due to the environmental risks associated with wheat production, many Kansas producers prefer an N management system that consists of a “starter” application at planting with the majority of the N fertilizer applied in the spring. This approach makes certain that the crop survives the winter before the investment in N is made and eliminates the potential for fertilizer N being lost over the winter months. It has not been feasible to use AA for topdressing in the past due to the damage to the growing crop from application with traditional knife style applicators. The first part of this research revisits traditional preplant AA application methods by evaluating proper unit spacing and the use of nitrification inhibitors as well as comparing these AA treatments to common topdress applications of N. Over three site years, few consistently significant advantages between unit spacing, use of nitrification inhibitor or N management method were found. Unit spacing did show a notable trend favoring 50 cm spacing. The second part of this research was a two-year experiment conducted with the objective of assessing the feasibility of topdressing with AA using the 2510H as compared with topdressing with granular urea. A number of factors such as application direction in relation to crop row, speed of application and timing as a function of crop development were examined to minimize crop injury and maximize crop yield. The initial 2010 study was promising, showing no significant yield loss topdressing with AA compared to topdressing with urea. The experiment was repeated at two locations in 2011. Results were mixed, indicated that soil conditions and the plants ability to recover from the AA application injury were important for the success of topdressing with AA. Lastly, an economic evaluation of the production economics of preplant and topdress AA was compared to the traditional practice of topdressing winter wheat with urea. Through evaluation of the agronomic and economic factors affecting the feasibility of uses of AA and the 2510H, three main conclusions can be made: 1. Preplant application of AA has no agronomic advantage and only a small economic advantage over topdressing with urea when yields are the same. 2. Topdressing with AA is agronomically feasible but is at an economic disadvantage when compared to topdressing with urea, due to the yield reduction associated with the AA method. 3. Further research focused on reducing yield loss with topdress AA applications is needed before this N management strategy can be promoted on a large scale.

Master of Science / Department of Agronomy / William T. Schapaugh / Heat and drought stress are common problems for crops grown in Kansas. Rarely do these problems occur separately, more often than not they occur in tandem if not simultaneously. The interaction of heat stress and pollen germination was investigated in order to determine if a physiological screen was a feasible method of determining heat tolerance in soybean [Glycine max (L.) Merr]. Ten soybean lines (Group A) from the 2006 Northern Region Uniform Soybean Tests were analyzed over two years in four locations consisting of irrigated and dryland field environments, with an additional twenty lines (Group B) analyzed in the second year. Pollen was collected from plants and incubated at either 28o, 34o, or 38o C to determine pollen germination for optimal and stress-inducing temperatures. A three-way interaction of entry x incubation temperature x environment was observed, as well as significant differences among entries, incubation temperatures and environments. Average pollen germination for soybean entries ranged from 25% to 38% across three incubation temperatures and four environments in Kansas during 2006 – 07. The average environment effect for pollen germination ranged from 29% (dryland, 2006) to 34% (irrigated, 2007), while the average incubation temperature effect on pollen germination ranged from 25% (38oC) to 44% (28oC). This experiment has shown that increasing incubation temperatures significantly decreases pollen germination in vitro. It has also shown that soybean genotypes differ in pollen germination and that an in vitro screen can be used to characterize these differences. Further studies are needed to establish the relationship between pollen germination, seed set and seed yield in soybean. Work also needs to be completed to determine the proper sample size to adequately characterize differences in pollen germination so that performance differences among genotypes can be used as selection criteria in a plant breeding program.

Master of Agribusiness / Department of Agricultural Economics / Kevin Dhuyvetter / This thesis was commissioned by Cooperative Producers, Inc. (CPI) of Hastings, Nebraska in order to better understand the preferences and uses of precision agriculture by customers within the company’s trade territory. With the rapid increase of precision agriculture (hardware, software, services, etc.) it is necessary to get a better understanding of what drives growers to adopt and implement precision agriculture practices. A paper survey was sent out in CPI’s monthly statements to patrons that also included instructions to be able to fill out an online survey if that was preferred. From that offering there were a total of 114 responses providing data from which several technology adoption models were estimated. Based on prior experience with precision agriculture and the development of services offered to growers, it is hypothesized that there are three primary variables influencing a grower’s decision to adopt precision agriculture. If the operation is managed by a younger grower (<40 years old), farms with a larger number of acres, and if a high percent of the operation’s acres are irrigated they will be more likely to adopt precision agriculture practices. The survey results generally revealed that younger farmers, larger farm size, and a higher percentage of irrigated acres did not increase the likelihood of utilizing precision agriculture. The questions asked in the survey were designed to provide information for the development of a tool that salespeople offering precision agriculture services could use to determine if a potential customer with be inclined to adopt and utilize precision agriculture. While some of the results were contrary to expectations they do offer insight into what type of customer adopts precision agriculture and a direction for CPI to move in order to maximize market penetration.

Doctor of Philosophy / Department of Agronomy / P.V. Vara Prasad / Productivity of grain crops is highly sensitive to changing climates and crop management practices. Response of finger millet [Eleusine coracana (L.) Gaertn.] to high temperature stress, and intensive management practices such as increased seeding rates and fertilizer application are not clearly understood. The objectives of this research were to determine the effects of (a) season-long, and short episodes of high temperature stress on growth and yield traits of finger millet, (b) seeding rates and nitrogen fertilizer application rates on grain and biomass yield, and (c) to evaluate the finger millet minicore collection for high grain and biomass yield. Controlled environment studies were conducted to determine the effects of high temperature stress on physiological, growth and yield traits. Field studies were conducted in Manhattan and Hays (Kansas) and Alupe (Kenya) to determine the effects of seeding and nitrogen fertilizer rates on growth and yield traits. Finger millet minicore collection was evaluated under field conditions in India, for phenology, growth and yield traits. Season long high temperature stress of 36/26 or 38/28°C compared to 32/22°C decreased panicle emergence, number of seeds per panicle, grain yield and harvest index. Finger millet was most sensitive to short episodes (10 d) of high temperature (40/30°C) during booting, panicle emergence and flowering stages, resulting in lower number of seeds, and grain yield. Finger millet responded to the interaction between environmental (locations) and temporal (years) factors. In general, locations with higher rainfall had greater grain and biomass yield than those with low rainfall. There was no influence of seeding rates (3.2 or 6.0 kg ha[superscript]-1) at Hays and Alupe. However, in one of the two years in Manhattan, higher seeding rate of 6.0 kg ha[superscript]-1 increased grain yield compared to 3.2 kg ha[superscript]-1. There was no influence of nitrogen rates (0, 30, 60 or 90 kg ha[superscript]-1) on grain or biomass yield at all three locations. However, higher fertilizer rates had greater percentage lodging. The finger millet minicore collection displayed large ranges for most quantitative traits including days to flowering, plant height, number of fingers panicle[superscript]-1, grain yield, biomass yield, and lodging; and had >60% heritability. Some of the genotypes from the minicore collection have the potential to increase grain and biomass yield and abiotic stress tolerance of finger millet.

Master of Science / Department of Agronomy / Charles W. Rice / Declining soil health is the underlying cause of decreasing agricultural productivity and environmental degradation. To address this challenge, research was conducted to determine how: (1) cover crops affect soil health in Kansas, USA and (2) direct seeding mulch–based cropping (DMC) systems affect soil health in Nyankpala, Ghana. Soil health indicators assessed include: biomass yield (kg ha[superscript]-1), soil microbial respiration (SMR), soil microbial C and N (MBC & MBN), potentially mineralizable N (PMN), dissolved organic carbon (DOC), soil organic C (SOC), soil total nitrogen (TN), phospholipid fatty acid analysis (PLFA), water stable aggregate (WSA), bulk density, pH, N, P, K, Ca and Mg. DMC systems from Ghana yielded significantly greater biomass compared to the control. High biomass produced by DMC systems did not increase SOC and PMN relative to the control. Fertilizer application had a significant impact on biomass production, which resulted in a significant increase in SOC and PMN in the 0-5 cm soil layer. Soil pH was significantly reduced by cropping systems and fertilizer in the 0-5 cm soil layer. Microbial biomass N, TN, SMR, N, P, Ca and Mg were not affected by the DMC cropping systems. Application of mineral fertilizer increased SMR, MBN, TN, N, and P. Soil K was also significantly affected by cropping systems and mineral fertilizer. The combination of mineral fertilizer and plant residues would be needed to improve soil health and increase crop productivity in the Guinea Savanna Zone of Ghana. Liming would be required to address low soil pH. In the USA, of all the soil health indicators examined, actinomycetes, gram-positive bacteria, fungi-bacteria ratio (F:B), SMR, MBN and WSA, were those significantly influenced by cover crops. The interactive effect of cover cops and N fertilizer also affected gram-positive bacteria, total PLFA, MBN, F:B ratio and WSA. Cover crop residues contributed to the observed differences in these indicators. The low response of soil health indicators suggest further evaluations are needed to determine the effectiveness of the indicators.

Master of Science / Agronomy / Johanna A. Dille / Mithila Jugulam / Common lambsquarters (Chenopodium album L.) is an annual broadleaf weed species that competes with more than 40 crop species around the world. A biotype of common lambsquarters in north central KS (DK) was not controlled by a glyphosate application. Plant growth stage and temperature have been related to overall glyphosate efficacy on common lambsquarters. The objectives were to determine the: 1) tolerance of two biotypes of common lambsquarters to glyphosate, 2) efficacy of glyphosate on common lambsquarters at different growth stages, and 3) efficacy of glyphosate on common lambsquarters when grown at different temperatures. Greenhouse dose-response experiments, shikimate accumulation assay, and glyphosate uptake and translocation experiments were conducted using DK biotype and a known susceptible biotype (RL) of common lambsquarters for comparison. Dose-response results indicated elevated tolerance of the DK biotype to glyphosate based on the GR₅₀ (a dose causing 50% biomass reduction) values (373 g ae/ha for RL vs. 552 g ae/ha for DK). Similarly, the DK biotype accumulated slightly less shikimate in the leaf discs compared to the RL biotype. Minimal differences were observed in ¹⁴C-glyphosate uptake and translocation between the two biotypes. Greenhouse-grown common lambsquarters were treated with glyphosate at a field dose (1x) of 840 g ae/ha when they were 5-7, 10-12, 15-17 or 19-21 cm tall. Common lambsquarters were also grown in growth chambers for 1 wk maintained at d/n temperatures of 25/15, 32.5/22.5, or 40/30 C and then treated with 0-, 0.125-, 0.25-, 0.5-, 0.75, 1.0-, and 2.0-x rates of glyphosate at 8-10 cm tall. Visual injury was recorded 1 WAT and biomass was determined 2 WAT. Common lambsquarters plants treated at 5-7 cm were more susceptible than larger plants to glyphosate. Furthermore, plants were more susceptible to glyphosate when grown under lower temperatures of 25/15 C than higher temperatures. Overall, these results suggest that the DK biotype of common lambsquarters appears to have elevated tolerance to glyphosate. Additionally, glyphosate should be applied early in the season when plants are small and temperatures are cooler for optimal control of common lambsquarters.

Doctor of Philosophy / Agronomy / Charles W. Rice / Substitution of cellulosic biofuel in place of gasoline or diesel could reduce greenhouse gas (GHG) emissions from transportation. However, emissions of nitrous oxide (N₂O) and changes in soil organic carbon (SOC) could have a large impact on the GHG balance of cellulosic biofuel, thus there is a need to quantify these responses in cellulosic biofuel crops. The objectives of this study were to: (i) measure changes in yield, SOC and microbial communities in potential cellulosic biofuel cropping systems (ii) measure and characterize the temporal variation in N₂O emissions from these systems (iii) characterize the yield and N₂O response of switchgrass to N fertilizer and to estimate the costs of production. Sweet sorghum, photoperiod-sensitive sorghum, and miscanthus yielded the highest aboveground biomass (20-32 Mg ha⁻¹). The perennial grasses sequestered SOC over 4 yrs, while SOC stocks did not change in the annual crops. Root stocks were 4-8 times higher in the perennial crops, suggesting greater belowground C inputs. Arbuscular mycorrhizal fungi (AMF) abundance and aggregate mean weight diameter were higher in the perennials. No consistent significant differences were found in N₂O emissions between crops, though miscanthus tended to have the lowest emissions. Most N₂O was emitted during large events of short duration (1-3 days) that occurred after high rainfall events with high soil NO₃₋. There was a weak relationship between IPCC Tier 1 N₂O estimates and measured emissions, and the IPCC method tended to underestimate emissions. The response of N₂O to N rate was nonlinear in 2 of 3 years. Fertilizer induced emission factor (EF) increased from 0.7% at 50 kg N ha⁻¹ to 2.6% at 150 kg N ha⁻¹. Switchgrass yields increased with N inputs up to 100-150 kg N ha⁻¹, but the critical N level for maximum yields decreased each year, suggesting N was being applied in excess at higher N rates. Yield-scaled costs of production were minimized at 100 kg N ha-1 ($70.91 Mg⁻¹). Together, these results show that crop selection and fertilizer management can have large impacts on the productivity and soil GHG emissions biofuel cropping systems.

Doctor of Philosophy / Department of Agronomy / Ganga M. Hettiarachchi / Constructed wetland treatment systems (CWTSs) are an alternative adaptation for flue-gas desulfurization (FGD) wastewater purification. A series of laboratory-based soil column studies mimicking a pilot-scale CWTS was carried out to evaluate the performance of the treatment system in detail. The main objectives of studies were to (1) understand the transport characteristics, retention capacity and transformation of selenium and other FGD constituents in the CWTS, (2) evaluate the effectiveness of soil treatments and influent flow rate on the performance of the CWTS, and (3) develop a mechanistic understanding of the CWTS performance through monitoring interrelationships of selenium (Se), arsenic (As), iron (Fe), and sulfur (S). Ferrihydrite (1% w/w), and labile organic carbon (OC) were used as soil treatments. Different influent flow rates, X (1.42 mL/hour), 2X, or 1/2X were used depending on the objectives of each study. Deoxygenated 1:1 mixture of FGD: raw water was the influent. It was delivered to the saturated columns with an upward flow. Effluent samples were collected continuously, and analyzed for constituents of concern. End of these experiments, soil from sectioned columns were used for total elemental analysis, sequential extraction procedure (SEP) for Se, and synchrotron-based X-ray spectroscopy analyses. Results indicated a complete Se retention by the columns. Boron, and fluorine partially retained whereas sodium, sulfur, and chlorine retention was weak, agreeing with field observations. Some of the initially-retained Se (~ 4 to 5%) was mobilized by changing redox conditions in the soil. Selenium fed with the wastewater accumulated in the bottom 1/3 (inlet) of the soil columns and was mainly sequestrated as stable forms revealed by SEP. Bulk-, and micro-XANES analyses suggested the retention mechanism of Se from the FGD wastewater was via the transformation of Se into reduced/stable forms [Se(IV), organic Se, and Se(0)]. Under wetland conditions, native soil As was mobilized by reductive dissolution of As associated minerals. However, the ferrihydrite amendment suppressed the native soil As mobility. Micro-XRF mapping integrated with As, and Fe-XANES suggested that the mechanism of native soil As retention was the sequestration of released As with newly precipitated secondary Fe minerals. A long-term study carried out with X, 1/2X flow rates, and OC source indicated enhanced S retention by the slow flow rate (1/2X), most likely due to the time dependency of biogenic S reduction. Further, bulk S-, As-, and Fe-XANES revealed that long submergence period and the slow flow rate increased the formation of reduced and/or biogenic S, realgar-like, and greigite-like species. These observations indicated that modified flow rates could have a significant impact on the long-term trace element (such as As) sequestration in the CWTS. Our studies provide useful information to improve the performance, and longevity of a full-scale CWTS for FGD wastewaters.

Master of Science / Department of Biology / Brett K. Sandercock / Cattle-grazing is a dominant land use in the United States, with more than 300 million hectares of land grazed each year. The habitat changes facilitated by cattle grazing can influence resource availability and habitat selection for associated wildlife. To investigate the potential for changes in traditional livestock management to restore native grassland and riparian habitat, we evaluated biological community responses to winter-grazing and livestock exclusion at the Kansas Army Ammunition Plant in southeastern Kansas. In grassland habitats, we combined winter-grazing by domestic cattle and discontinued fertilization in an attempt to restore pastures dominated by tall fescue to native tallgrass prairie and improve habitat for grassland-breeding birds. We observed a decrease in tall fescue and an increase in native, warm-season grasses in winter-grazed pastures compared to fertilized, year-round grazed pastures. Grassland-breeding bird responses to winter-grazing were species-specific. Dickcissels preferred winter-grazed pastures, while Eastern Meadowlarks and Grasshopper Sparrows tended to prefer year-round grazed pastures. Dickcissels were negatively correlated with the presence of cattle during the breeding season and the abundance of tall fescue. Grasshopper Sparrows were negatively correlated with native, warm-season grass abundance and visual obstruction, but were positively correlated with forb abundance. Henslow’s Sparrows and Common Yellowthroats were detected breeding in low numbers on pastures that had been winter-grazed for five years. Our results suggest that winter-grazing and discontinued fertilization of agricultural grasslands can direct semi-natural plant communities toward tallgrass prairie and benefit some grassland-breeding birds. In riparian habitats, livestock were excluded from 1996 to 2005. We measured bird community responses in grazed and ungrazed sites using baseline data collected in 1996-97 and post-treatment data collected in 2004-05. Riparian bird community data were analyzed using robust design mark-recapture models that allowed us to evaluate changes in bird species richness while accounting for differences in detectability among species. We detected increases in species richness in both ungrazed and grazed treatments. We observed few differences in community vital rates between treatments; however, we did detect differences in guild responses. The changes observed within both grazed and ungrazed riparian bird communities were likely influenced by regional fluctuations in species richness and composition.