Master of Science / Department of Agronomy / Johnathon D. Holman / Kraig L. Roozeboom / Replacing fallow periods with cover crops can provide many benefits including soil quality improvements and reduced nitrogen fertilizer requirements. Field experiments were established near Garden City, KS with winter wheat and fallow phases as main plots, thirteen legume or non-legume cover crops, continuous winter wheat, and fallow as subplots, and cover crop termination method as sub-subplots. Treatments containing triticale had greatest water use efficiency (19.9 kg ha[superscript]-1 mm[superscript]-1) and aboveground biomass (3550 kg ha[superscript]-1), but subsequent winter wheat yields were reduced due to a reduction in volumetric water content. Increased soil residue through greater cover crop biomass resulted in increased precipitation storage efficiency during the fallow period, but water requirements to produce biomass depleted soil moisture more than growing a low biomass crop or fallow. In years of above-average precipitation, low biomass cover crops might be grown with little to no negative effect on subsequent wheat yields. A second field experiment was established near Manhattan, KS with fallow, double crop soybean, and four cover crop treatments planted after wheat harvest in a winter wheat-grain sorghum-soybean no-till cropping system, with five nitrogen treatments applied to the sorghum crop to estimate nitrogen contribution of the cover crops. Greatest above ground biomass production and nitrogen accumulation was observed with sorghum-sudan grass. At the 0 kg ha[superscript]-1 N rate, grain sorghum yields were reduced 1200 kg ha[superscript]-1 following sorghum-sudan grass, while all other cover crop treatments provided a 20-30 kg ha[superscript]-1 N equivalent benefit. Sorghum yields might be reduced following large biomass producing cover crops when nitrogen is limiting, but a small nitrogen benefit might be realized following low C:N ratio cover crops. Cover crop productivity and their subsequent effects on grain sorghum performance were evaluated in field studies established near Manhattan and Hutchinson, KS in 2008 and 2009. Sixteen summer or fall cover crop species were planted in no-tillage winter wheat stubble and evaluated for biomass production, nitrogen concentration, and nitrogen accumulation. Summer annual grass species produced the greatest biomass, 3392 kg ha[superscript]-1 and greater, and legume species accumulated the greatest amounts of nitrogen, averaging 43 kg ha[superscript]-1. Grain sorghum yields were 867 kg ha[superscript]-1 greater following summer cover crops compared to fall cover crops. Cover crops had a significant effect on sorghum performance, with yields 1240 kg ha[superscript]-1 greater following legume cover crops.

Current estimates of terrestrial carbon (C) fluxes overlook explicit hydrological controls. In this research project, a spatially explicit hydro-ecological model, BEPS-TerrainLab V2.0 was further developed to improve our understanding of the non-linearities associated with various hydro-ecological processes. A modeling study was conducted in a humid boreal ecosystem in north central Quebec, Canada. The sizes and nature of various ecosystem-C-pools were comprehensively reconstructed under a climate change and disturbance scenario prior to simulation in order to ensure realistic biogeochemical modeling. Further, several ecosystem processes were simulated and validated using field measurements for two years. A sensitivity analysis was also performed. After gaining confidence in the model’s ability to simulate various hydrologically controlled ecophysiological and biogeochemical processes and having understood that topographically driven sub-surface baseflow is the main process determining the soil moisture regime in humid boreal ecosystem, its influence on ecophysiological and biogeochemical processes were investigated. Three modeling scenarios were designed that represent strategies that are currently used in ecological models to represent hydrological controls. These scenarios were: 1) Explicit, where realistic lateral water routing was considered 2) Implicit, where calculations were based on a bucket-modeling approach 3) NoFlow, where the lateral sub-surface flow was turned off in the model. In general, the Implicit scenario overestimated GPP, ET and NEP, as opposed to the Explicit scenario. The NoFlow scenario underestimated GPP and ET but overestimated NEP. The key processes controlling the differences were due to the combined effects of variations in plant physiology, photosynthesis, heterotrophic respiration, autotrophic respiration and nitrogen mineralization; all of which occurred simultaneously in different directions, at different rates, affecting the spatio-temporal distribution of terrestrial C-sources or sinks (NEP). From these results it was clear that lateral water flow does play a significant role in the net terrestrial C distribution and it was discovered that non-explicit forms of hydrological representations underestimate the sizes of terrestrial C-sources rather than C-sinks. The scientific implication of this work demonstrates that regional or global scale terrestrial C estimates could have significant errors if proper hydrological constraints are not considered for modeling ecological processes due to large topographic variations of the Earth’s surface.

Master of Science / Department of Biological and Agricultural Engineering / Ronaldo G. Maghirang / Military installations in the United States may be large sources of fugitive dust emissions. Off-road vehicle training can contribute to air quality degradation resulting from increased wind erosion events as a result of soil disruption; however, limited information exists regarding the impacts of off-road vehicle maneuvering. This study was conducted to determine the effects of soil texture and intensity of training with off-road vehicles on fugitive dust emission potential due to wind erosion at military training installations. Multi-pass trafficking experiments, involving wheeled and tracked military vehicles (i.e., M1A1 Abrams tank, M925A1 water tanker and various HMMWV models), were conducted at three military training facilities with different climate and soil texture (i.e., Fort Riley, KS; Fort Benning, GA; and Yakima Training Center, WA). Dust emissions were measured on site using a Portable In-Situ Wind Erosion Laboratory (PI-SWERL) coupled with a DustTrak™ dust monitor. In addition, a top layer of soil was collected in trays and tested in a laboratory wind tunnel for dust emission potential. In wind tunnel testing, the amount of emitted dust was measured using glass-fiber filters through high-volume samplers. Also, the particle size distribution and concentration of the emitted dust were measured using a GRIMM aerosol spectrometer. Comparison of the PI-SWERL (with DustTrak™ dust monitor) and wind tunnel test (with GRIMM aerosol spectrometer) results showed significant difference and little correlation. Also, comparison of the filter and GRIMM aerosol spectrometer data showed significant difference but high correlation. The dust emission potential (as measured with the GRIMM spectrometer) was significantly influenced by soil texture, vehicle type and number of passes. For the light-wheeled vehicle, total dust emissions increased from 66 mg m-2 for undisturbed soil to 304 mg m-2 (357%) and 643 mg m-2 (868%) for 10 and 50 passes, respectively. For the tracked vehicle, an average increase in total dust emission of 569% was observed between undisturbed conditions and 1 pass, with no significant increase in emissions potential beyond 1 pass. For the heavy-wheeled vehicle, emissions increased from 75 mg m-2 for undisturbed soil to 1,652 mg m-2 (1,369%) and 4,023 mg m-2 (5,276%) for 10 and 20 passes, respectively. Soil texture also played an important role in dust emission potential. For all treatment effects, there was a 1,369% difference in emissions between silty clay loam soil and loamy sand soil.

Doctor of Philosophy / Department of Agronomy / Charles W. Rice / Nitrogen is critical for plant growth and is a major cost of inputs in production agriculture. Too much nitrogen (N) is also an environmental concern. Agricultural soils account for 85% of anthropogenic N₂O which is a major greenhouse gas. Management strategies for N fertilization and tillage are necessary for enhancing N use efficiency and reducing negative impacts of N to the environment. The different management practices induce changes in substrate availability for microbial activity that may result in increasing or reducing net N₂O emitted from soils. The objectives of this research were to (1) integrate results from field studies to evaluate the effect of different management strategies on N₂O emissions using a meta-analysis, (2) quantify N₂O-N emissions under no-tillage (NT) and tilled (T) agricultural systems and the effect of different N source and placements, (3) perform sensitivity analysis, calibration and validation of the Denitrification Decomposition (DNDC) model for N₂O emissions, and (4) analyze future scenarios of precipitation and temperature to evaluate the potential effects of climate change on N₂O emissions from agro-ecosystems in Kansas. Based on the meta-analysis there was no significant effect of broadcast and banded N placement. Synthetic N fertilizer usually had higher N₂O emission than organic N fertilizer. Crops with high N inputs as well as clay soils had higher N₂O fluxes. No-till and conventional till did not have significant differences regarding N₂O emissions. In the field study, N₂O-N emissions were not significantly different between tillage systems and N source. The banded N application generally had higher emissions than broadcasted N. Slow release N fertilizer as well as split N applications reduced N₂O flux without affecting yield. Simulations of N₂O emissions were more sensitive to changes in soil parameters such as pH, soil organic carbon (SOC), field capacity (FIELD) and bulk density (BD), with pH and SOC as the most sensitive parameters. The N₂O simulations performed using Denitrification Decomposition model on till (Urea) had higher model efficiency followed by no-till (compost), no-till (urea) and till (compost). At the regional level, changes in climate (precipitation and temperature) increased N₂O emission from agricultural soils in Kansas. The conversion from T to NT reduced N₂O emissions in crops under present conditions as well as under future climatic conditions.

Doctor of Philosophy / Department of Agronomy / Charles W. Rice / Increasing atmospheric CO2 concentrations and other greenhouse gases have been linked to global climate change. Soil organic C (SOC) sequestration in both agricultural and native ecosystems is a plausible option to mitigate increasing atmospheric CO2 in the short term. Laboratory and field studies were conducted to (1) understand the influence of soil water content on the temperature response of SOC mineralization (2) investigate burn and nutrient amendment effects on biogeochemical properties of tallgrass prairie and (3) assess perennial and annual plant management practices on biophysical controls on SOC dynamics. The laboratory study was conducted using soils collected from an agricultural field, currently planted to corn (C4 crop), but previously planted to small grain (C3) crops. The changes in cultivated crops resulted in a δ¹³C isotopic signature that was useful in distinguishing older from younger soil derived CO2-C during SOC mineralization. Soils were incubated at 15, 25 and 35 oC, under soil water potentials of -1, -0.03 and -0.01 MPa. Soil water content influenced the effect of temperature on SOC mineralization. The impact of soil water on temperature effect on SOC mineralization was greater under wetter soil conditions. Both young and older SOC were temperature sensitive, but SOC loss depended on the magnitude of temperature change, soil water content and experiment duration. Microbial biomass was reduced with increasing soil water content. The first field experiment investigated burn and nutrient amendment effects on soil OC in a tallgrass prairie ecosystem. The main plots were burned (B) and unburned (UB) tallgrass prairie and split plots were nutrient amendments (N, P or N+P including controls). Vegetation was significantly altered by burning and nutrient amendment. Treatment effects on either TN or SOC were depth-specific with no impact at the cumulative 0-30 cm depth. The P amendment increased microbial biomass at 0-5 cm which was higher in unburned than burned. However, at 5-15 cm depth N amendment increased microbial biomass which was higher in burned than unburned. In conclusion, soil OC in both burned and unburned tallgrass prairie may have a similar trajectory however; the belowground dynamics of the burned and unburned tallgrass prairie are apparently different. Another field experiment assessed SOC dynamics under perennial and annual plant management practices. The main plots were grain sorghum (Sorghum bicolor) planted in no-tillage (NT) or continuous tillage (CT), and replanted native prairie grass, (Andropogon gerardii) (RP). The spit plots were phosphorus (+P) and control without P (-P). The P amendment was used to repress arbuscular mycorrhizal fungi (AMF), known to influence soil aggregation. The macroaggregate >250 µm, SOC and TN were higher in RP and NT than CT. The relative abundances of AMF and saprophytic fungi were greater with less soil disturbance in RP and NT than in CT. Therefore, less soil disturbance in RP and NT increased AMF and fungal biomasses. The higher relative abundances of AMF and fungi with less soil disturbance increased macroaggregate formation in RP and NT, which resulted in higher SOC sequestration in RP and NT than CT.

Doctor of Philosophy / Department of Agronomy / Ganga M. Hettiarachchi / Urban soils may contain harmful levels of potentially toxic contaminants. These contaminants transfer to humans via two exposure pathways: direct transfer (soil-humans by soil ingestion, dermal exposure and inhalation) and food chain transfer (soil-plant-humans). Soil amendments alter the speciation of the contaminants in soils and thereby modify their bioavailability. The objectives of this research were to access the plant availability of lead (Pb), arsenic (As), and polycyclic aromatic hydrocarbons (PAHs); bioaccessibility and speciation of soil Pb, and As; and dermal absorption of soil PAHs in contaminated urban soils; and effectiveness of soil organic amendments on reducing contaminant bioavailability. Two field experiments were conducted in Kansas City, MO and Indianapolis, IN. Both sites had elevated concentrations of Pb in soils (Kansas City site: 30-380 mg kg⁻¹ and Indianapolis site: 200-700 mg kg⁻¹) . Indianapolis site’s soils also had elevated concentrations of As (40-100 mg kg⁻¹) and PAHs (benzo[a]pyrene: 1-10 mg kg⁻¹) . A control treatment (no-compost) and compost-types (leaf compost and/or composted biosolids, non-composted biosolids, mushroom compost) were used as treatments. A leafy vegetable, a fruiting vegetable and a root crop were grown for two growing seasons. The treatments were arranged in split-plot design (main plot factor: compost; sub-plot factor plant-type). An in vitro steady fluid experiment was conducted using human skins to examine the dermal transfer of soil PAHs. The concentrations of Pb, As, and PAHs in the vegetables were low, except Pb in root crops. Compost reduced the bioaccessibility of Pb, but did not change the bioaccessibility of As. Selected soil samples were analyzed for speciation of Pb using extended x-ray absorption fine structure spectroscopy. The predominant Pb species were Pb sorbed to Fe oxy(hydr)oxide and to organic C. Stable Pb phosphates (pyromorphite) was formed during the in vitro extraction. Dermal transfer experiments showed PAHs in the contaminated soils did not transfer through the skin. Stratum conium of the skin acted as a barrier for dermal transfer of soil PAHs. In general, the risk of food chain transfer of soil Pb, As, and PAHs were low in the studied sites and can be further reduced by compost addition. Bioaccessibility of Pb and As in urban soils were low. Dermal absorption of soil PAHs was insignificant.

Master of Science / Department of Agronomy / DeAnn Presley / Steve Thien / Interest and participation in urban agriculture is growing in many cities throughout the United States. Urban gardeners and farmers produce food on various types of urban lands. Common soil contaminants of urban areas limit the amount of land on which food may safely be grown. The objective of this study was to assess and meet the informational and technical assistance needs of urban gardeners and farmers as well as students enrolled in the introductory soils science course at Kansas State University on the topics of urban soil quality and contamination. A needs assessment survey of urban gardeners and farmers was conducted in four communities; Tacoma and Seattle, Washington, Kansas City, Kansas and Missouri, Manhattan, Kansas, and Gary, Indiana. The survey generated information about what urban gardeners and farmers know, think they know, and want to know about urban soil quality and contamination. Eighty-eight percent of respondents indicated that they do not have knowledge of the best management practices to minimize health risks involved when growing food crops on soils contaminated with lead, cadmium, arsenic or organic contaminants. Our results suggest that urban gardeners and farmers require and want information and guidance on soil testing for common contaminants, interpretation of testing results, and best management practices for growing food on mildly contaminated soils. The students enrolled in the introductory soil science course at Kansas State University are future agricultural and environmental professionals who need skills to address urban soils issues. Most of the students in the Agronomy 305: Soils course are not Agronomy majors. Furthermore, an increasing number of Agronomy 305 students come from urban and suburban communities and/or have interest in working in urban environments upon completion of their undergraduate degree. An urban soils laboratory was developed in response to the future workforce demands as well as the demographics of students enrolled in the Agronomy 305 course. Throughout the semester students evaluated the physical, chemical, and biological properties of a soil from this urban community garden. Reaction of students to the new urban soils lab offering has been positive with 72% of students enrolled in the course reporting that they have interest and need in learning about the urban soil issues covered in the lab course. Overall, student responses about their learning experience in the urban soils laboratory course were positive, indicating that incorporating urban soil principles enhanced their soil science education. Students who participated in the urban soils lab are better prepared, as future agricultural and environmental professionals, to address the educational and technical assistance needs of urban growers.

Master of Science / Department of Agronomy / Humberto Blanco / DeAnn Presley / The U.S. agricultural sector is in a prime position to provide crop residues such as corn (Zea mays L.) stover as feedstock for large-scale bioenergy production. While producing renewable energy from biomass resources is a worthy initiative, excessive removal of corn stover from agricultural fields has the potential to increase soil erosion, degrade soil properties, and reduce corn yields. A need exists to objectively assess stover removal impacts on agriculture and the environment on regional scales. This project assessed the effects of removing various rates of corn stover on runoff and erosion and changes in soil physical properties and corn yields on a regional scale across three soils at Colby, Hugoton, and Ottawa in Kansas, USA. The soils were Ulysses silt loam (Fine-silty, mixed, superactive, mesic Aridic Haplustolls) at Colby, Hugoton loam (Fine-silty, mixed, superactive, mesic Aridic Argiustolls) at Hugoton, and Woodson silt loam (Fine, smectitic, thermic Abruptic Argiaquolls) at Ottawa, all with slopes [less than or equal to] 1%. Five stover treatments were studied that consisted of removing 0, 25, 50, 75, and 100% of stover after harvest from no-till and strip-till continuous corn plots. Simulated rainfall was applied in spring 2010 at rates representing 5 yr return intervals at each site and included a dry and wet run. Runoff increased with an increase in stover removal at Colby and Hugoton, but not at Ottawa. At Colby, stover removal rates as low as 25% caused runoff to occur 16 min sooner and increased sediment loss. At this site, runoff and sediment-carbon (C) loss increased as removal rates exceeded 25%. At Hugoton, complete stover removal increased loss by total N by 0.34, total P loss by 0.07, PO[subscript]4-P by 0.003 and NO[subscript]3-N by 0.007 kg ha-[superscript]1. At Ottawa, PO[subscript]4-P loss decreased by 0.001 kg ha-[superscript]1 with 25% removal and by 0.003 kg ha-[superscript]1 with 50% removal. Mean weight diameter (MWD) of wet aggregates decreased with an increase in stover removal on all soils. At Ottawa, stover removal at 75% reduced soil C in the top 5 cm by 1.57 Mg ha-[superscript]1. Soil volumetric water content decreased with stover removal at Colby and Ottawa, but was variable at Hugoton. Soil temperature tended to increase with stover removal during summer months and decrease during winter months. Soil temperature also fluctuated much more widely with stover removal, resulting in more freeze-thaw events compared to no stover removal. No effect of stover removal on soil water retention was observed on any of the soils. In 2009, removal rates [greater than or equal to]50% resulted in greater grain yield at Colby, while removal rates [greater than or equal to]75% resulted in greater grain yields at Ottawa in 2009 and 2010. Results from the first two years of stover management suggest that stover removal at rates above 25% for bioenergy production increased water erosion, degraded soil structural properties, and altered soil water and temperature regimes. Higher rates of removal ([greater than or equal to]75%) can also reduce soil C concentration in the short-term in rainfed regions. However, grain yields may be enhanced by stover removal from irrigated soils and from rainfed soils with adequate moisture. Overall, the increase in water erosion and alteration in soil properties in the short-term suggest that stover removal can detrimentally affect water quality and soil productivity in Kansas. Further long-term monitoring is warranted to conclusively discern stover removal implications.

There have been no landscape-scale studies on earthworm populations in Canada comparing vegetation types; previous studies on edge habitats have been conducted in agricultural systems. I examined the spatial variations of earthworm populations by measuring abundance based on regional municipality, vegetation type, and edge habitat. Earthworms were sampled throughout the season across a gradient of vegetation types including meadow, forest edge, and interior at a local-scale; and at the landscape level with vegetation types including meadow, deciduous forest, pine plantation and mixed forest. Regional effects were more significant than vegetation type likely due to a gradient of soil characteristics in southern Ontario; edges had intermediate earthworm abundance and a higher proportion of epigeic species. My research provides insight into the patterns of earthworm populations in southern Ontario and the possible effects of edge creation through landscape fragmentation. Field sampling of earthworm parasitoid cluster-flies (Calliphoridae: Pollenia) using synomones was also discussed.

There have been no landscape-scale studies on earthworm populations in Canada comparing vegetation types; previous studies on edge habitats have been conducted in agricultural systems. I examined the spatial variations of earthworm populations by measuring abundance based on regional municipality, vegetation type, and edge habitat. Earthworms were sampled throughout the season across a gradient of vegetation types including meadow, forest edge, and interior at a local-scale; and at the landscape level with vegetation types including meadow, deciduous forest, pine plantation and mixed forest. Regional effects were more significant than vegetation type likely due to a gradient of soil characteristics in southern Ontario; edges had intermediate earthworm abundance and a higher proportion of epigeic species. My research provides insight into the patterns of earthworm populations in southern Ontario and the possible effects of edge creation through landscape fragmentation. Field sampling of earthworm parasitoid cluster-flies (Calliphoridae: Pollenia) using synomones was also discussed.