Browsing by Author "Davis, Jessica, committee member"
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Item Open Access Aerobic post-processing of digestate from a multi-stage anaerobic digester(Colorado State University. Libraries, 2017) Sandefur, Julie N., author; Sharvelle, Sybil, advisor; DeLong, Susan, committee member; Davis, Jessica, committee memberThe management of animal waste from feedlots is inconvenient and costly due to the storage and transportation involved in ensuring the waste is utilized appropriately. Anaerobic digestion is a proven method for breaking down waste with low solids content and capturing methane produced to use as renewable energy. Composting is an age-old process in which solid waste retains its nutrients and becomes a suitable, natural soil amendment. By combining these methods within multi-stage anaerobic digestion (MSAD), two valuable by-products are generated – methane and nutrient-laden compost – through a process able to handle high solids material. A laboratory-scale study was conducted to simulate aerobic composting of high solids cow manure (HSCM) in a leachate bed reactor (LBR) after anaerobic digestion from a MSAD. Analysis of the leachate and solid material were performed after each phase: anaerobic – 21 days, active aerobic – 21 days, and curing - 60 days. The effects of agricultural by-products used as bulking material in the LBRs and of compost inoculum added were also assessed. The bulking material assisted in providing uniform flow of leachate through the LBRs during the anaerobic phase and served as an additional carbon source once aeration began. Inoculum acquired from Colorado State University's (CSU) composter was added at the beginning of the aeration phase via two different methods alongside a control group in order to assess the potential contributions of including already composted organic material still containing active bacteria. Compost quality parameters monitored consisted of ammonium to nitrate ratio, carbon to nitrogen ratio, pH, soluble salts, sodium absorption ratio (SAR), percent total nitrogen, phosphorus, and potassium, and the Solvita® Maturity Index (SMI). There was a sizable volatile solids reduction (%VS) observed of the HSCM only in two of the three different bulking material reactor sequences. The bulking material study showed a 41% ± 0.12, 33% ± 0.03 and 55% average reduction in the manure for corn stover, beanstalk, and woodchip reactors respectively. The woodchips most likely contributed to the larger solids reduction due to their larger particle size and more rigid structure allowing leachate and air more pathways to access and breakdown material. VS reduction in the inoculum study showed that there was no solids reduction benefit achieved by including a 1:2 municipal solid waste (MSW)-horse manure combined inoculated compost to the reactors prior to the active aeration phase. The control reactors outperformed the reactors where inoculum was added on top or mixed in with the digestate. The quality of the matured compost from all the reactors in both studies met or exceeded required specifications. The stability and maturity of the composts were compared to Rocky Mountain Region Classification tables as well as the SMI range. In each case, the analytes measured were below the suggested limits in the classification table and most fell in the "finished compost" range on the SMI scale. The values of the major nutrients assessed were of satisfactory contents as to be useful for land application. This study seeks to encourage the process of MSAD on feedlots with HSCM in arid to semi-arid regions by demonstrating the usefulness of the by-products achieved from the process. Methane gas produced in the anaerobic phase is a valuable form of renewable energy that can be used onsite. A mature compost product meeting Class 1 Compost/ Soil Amendment Classification standards can be used onsite or sold for a variety of applications. By generating methane and beginning the composting process in the same LBR, solids are further reduced, weight is minimized and the material is more stable for transportation and storage.Item Open Access Agronomic responses of grass and alfalfa hayfields to no and partial season irrigation as part of a Western Slope water bank(Colorado State University. Libraries, 2015) Jones, Lyndsay P., author; Brummer, Joe, advisor; Cabot, Perry, committee member; Davis, Jessica, committee memberProlonged drought and increasing demand for water resources has caused growing concern over Colorado's ability to fulfill legal water obligations as identified in the Colorado River Compact. A Western Slope Water Bank, which would entail agricultural water users entering into short-term leases and temporarily withholding or reducing irrigation, could be a partial solution to free up water to fulfill these obligations. Grass and alfalfa (Medicago sativa L.) hayfields may be ideal for inclusion in a water bank as they are the primary users of agricultural water in this region and may have a greater ability to withstand water stress in comparison to other crops. This study was conducted to determine effects of withholding irrigation for a full season from high elevation grass hayfields and implementing partial season irrigation on lower elevation alfalfa hayfields on forage yield, nutritional quality, and associated recovery period to confirm if this approach is worth pursuing. In Year 1, five established grass hayfields on the Colorado Western Slope were split into side-by-side plots, one of which was irrigated according to the manager’s normal practices as the control while the other was subjected to total cessation of irrigation. Both plots were irrigated in Year 2. In Year 1, average dry matter yields in non-irrigated plots were reduced to 39% (2497 kg ha-1) of the control (6377 kg ha-1). Neutral detergent fiber (aNDF) concentration in non-irrigated plots was 5% lower while crude protein (CP) content was 30% greater than the control. In-vitro true digestibility (IVTD) was unaffected by irrigation treatment. Yields of non-irrigated plots did not fully recover when returned to irrigation in Year 2 producing 49% (3623 kg ha-1) of the control (7442 kg ha-1). When returned to irrigation, aNDF concentrations were still reduced by 8% and CP contents were similar to that of the control. In the single site sampled after returning to full irrigation for 2 years, yields had fully recovered. It is probable that participation by producers in a water bank would be largely influenced by compensation for reduced yields the season of withholding irrigation as well as the following year when irrigation is returned to grass hayfields. Three established alfalfa fields were subjected to irrigation treatments including irrigation according to the manager’s normal practices (control), irrigation stopped after the 1st cutting (SA1), and irrigation stopped after the 2nd cutting (SA2) for 2 consecutive years. Averaged over both years, SA2 plots maintained production similar to the control in the 1st and 2nd cutting while SA1 plots were reduced to 61% (2089 kg ha-1) of the control (3430 kg ha-1) by the 2nd cutting. By the 3rd cutting, SA2 and SA1 yields decreased to 53% (1804 kg ha-1) and 30% (1013 kg ha-1) of the control, respectively. On a total season basis, both plots receiving partial season irrigation were reduced with SA2 plots producing 72% (7880 kg ha-1) and SA1 plots producing 33% (3650 kg ha-1) of the control (11040 kg ha-1). aNDF concentrations were greatest in the control at 34.6% and lowest in SA1 plots at 28.2%. By the 2nd cutting, SA1 plots had the highest IVTD (80%), and by the 3rd cutting, SA2 and SA1 plots were equally greater (80%) than the control (75%). Effects on CP content were inconsistent. These results suggest that reduced irrigation may improve forage quality slightly, but will significantly reduce yields. When irrigation is returned the following year, forages may have increased quality due to reduced fiber content, but grass yields will likely not fully recover while alfalfa yields may recover depending on length and severity of reduced irrigation. Due to its ability to recover, using partial season irrigation similar to that of the SA2 treatment on alfalfa hayfields may be the most practical approach to make water available to a Western Slope water bank.Item Open Access Anaerobic digestion comparison of manure leachate by high-rate anaerobic reactors(Colorado State University. Libraries, 2013) Quiroz Arita, Carlos Enrique, author; Sharvelle, Sybil, advisor; Carlson, Kenneth, advisor; Davis, Jessica, committee memberA multi-stage anaerobic digester (MSAD) has been developed to obtain high organic leachate from high solids organic waste, thus high-rate anaerobic reactors can be fed by manure leachate, which can be obtained from a leachate bed reactor. Such configuration not only makes feasible the application of high-rate reactors to treat high solids content manure, but also the hydrolysis and the methanogenesis stages can be separated and controlled, individually. However, limited research is available on achieving ideal hydrodynamic conditions, inoculation, and performance of high-rate anaerobic reactors when manure leachate is used as the carbon source. Thus, this research is aimed not only to compare the performance of three different reactor configurations; the Upflow Anaerobic Sludge Blanket (UASB), fixed film, and a hybrid for processing manure leachate as a carbon source, but also to establish design criteria for such reactors including organic loading rates (OLRs) and hydraulic loading rates (HLRs). In the first part of this research, the influence of the hydraulic loading rates (HLR) in high-rate anaerobic reactors was investigated. The upflow anaerobic sludge blanket (UASB) reactor depicted a Morrill dispersion index (MDI) of 1.7, which is measured to evaluate the plug flow conditions of a reactor by approaching a value of 2 or less, at a HLR of 0.296 m3/m2-h. On the other hand, a MDI of 4 was observed when the HLR was increased to 0.829 m3/m2-h. The variation of the HLR had not notable impact MDI of the fixed-film and hybrid reactors; however, short circuits were observed at low HLR. Thus, the most suitable HLRs of such reactors were 10.632 m3/m2-h for the fixed-film reactor and 12.450 m3/m2-h for the hybrid reactor. To evaluate the performance of the UASB, fixed-film, and hybrid reactors to treat manure leachate, this research resulted in development of a method to inoculate such reactors in a single inoculation reactor. The accomplishment of the inoculation was measured by the redox potential, with values below -300 mV after seven days and remained steady until the day 33 with methane percentages in biogas ranging from 45% to 83%. Additionally, plastic media from the inoculation reactor was tested by the biochemical methane potential (BMP) assay, where inoculated organisms were confirmed to produce methane when supplied with glucose as a substrate. In spite that a hybrid anaerobic reactor inoculated with biomass obtained from an UASB reactor, plastic media, and manure leachate was successfully operated at an OLR of 4 kg/m3-d, when transferring the inoculated sludge and media to high-rate reactors, anaerobic digestion was not accomplished. The experiment setup did not support maintenance of anaerobic conditions. In addition, manifolds and open-channel flows were recommended in this research to enhance the reactors configurations. Moreover, results from hydrodynamic studies were applied to provide recomndations for future design parameter, which are included in this thesis.Item Open Access Comparison of soil properties and Kentucky bluegrass shoots mineral composition prior to and after 10-11 years irrigation with recycled water(Colorado State University. Libraries, 2016) Lin, Yuhung, author; Qian, Yaling, advisor; Davis, Jessica, committee member; Klett, James E., committee member; Andales, Allan, committee memberIn Colorado, fresh water is one of the most valuable and limited natural resources. Due to population growth, an increase of fresh water withdrawal has been reported by U.S. Geological Survey. Irrigation with recycled water has been utilized as a means to alleviate the stress on potable water supplies and facilitate the reuse of treated wastewater. Recycled water irrigation is taking place at landscape sites such as public parks, golf courses, and school playgrounds. Research information is needed to better understand the long-term effects of recycled water irrigation on urban landscapes. Therefore, the objectives of this research were to: 1) assess changes in soil chemical properties after 5 and 11 years of recycled water irrigation, 2) determine if there is any heavy metal accumulation in soil after 11 years of recycled water irrigation, 3) evaluate Kentucky bluegrass (Poa pratensis L.) (KBG) turf quality grown on golf courses irrigated with recycled water, and 4) determine the relationship of turf quality to shoot mineral concentrations and soil chemical properties. To address Objectives 1 and 2, soil samples were collected and analyzed at the commencement (in 2004) and 11 years after recycled water irrigation on three golf courses, 5 metropolitan parks, 1 school ground, and 1 zoo. Samples were taken at 0-20, 20-40, 40-60, 60-80, and 80-100 cm depths on golf courses and at 0-20 and 20-40 cm depths at other locations. Soil was analyzed for texture, soil pH, soil organic matter, soil salinity [soil electrical conductivity (EC)], exchangeable sodium percentage (ESP), cation exchange capacity (CEC), nitrate-N, chloride (Cl), boron (B), and AB-DTPA extracted phosphorus (P), iron (Fe), manganese (Mn), arsenic(As), chromium (Cr), cadmium (Cd), cobalt (Co), nickel (Ni), lead (Pb), zinc (Zn) and copper (Cu). Averaging over all sites, soil pH was 0.25-0.3 higher in 2015 and 2009 than in 2004. The increase was greater at deeper depths. Soil salinity (EC) was 0.84, 0.88, and 0.98 dS m-1in 2004, 2009 and 2015, respectively. The magnitude of increase in ESP after recycled water irrigation indicated potential sodicity problems. Calcium based product applications reduced ESP at soil surface depths. In contrast, significant increase in ESP was found at deeper soil depths. No increase in soil nitrate-N was observed over 5 and 11 years with recycled water irrigation, therefore, leaching of nitrogen to the groundwater was not a great concern. AB-DTPA extracted As, Co, and Ni decreased after 11 years of recycled water irrigation. Soil Cd, Cr, Cu, Pb, and Zn did not show significant change from 2004 to 2015. Results revealed that there was no sign of heavy metal accumulation. To address Objectives 3 and 4, research was conducted on eight golf courses, including three courses in Denver after 10 years of recycled water irrigation, three courses in the nearby cities receiving recycled water for more than 10 years, and two courses receiving fresh surface water for irrigation. Results indicated that Na concentration in KBG shoot tissues increased by 4.3-9.9 times, Cl by 1.5-1.3 times, B by 1.3-3.5 times whereas K/Na ratio was reduced by 74-90%. Multiple regression analysis indicated shoot Na accumulation had the highest association to turf quality decline (R2= 0.65). Soil sodium adsorption ratio (SAR) in 0-20 cm depth was highly associated with KBG shoot Na concentration (R2= 0.70).Item Open Access Evaluation of a trickle flow leach bed reactor for anaerobic digestion of high solids cattle manure(Colorado State University. Libraries, 2013) Hanif Abdul Karim, Asma, author; Sharvelle, Sybil, advisor; Carlson, Kenneth, committee member; Davis, Jessica, committee memberAnaerobic digestion (AD) of cattle manure from feedlots and dairies is of increasing interest in Colorado due to its abundant availability. Colorado is the one of the highest producer of high solids cattle manure (HSCM) in the United States. Despite the available resources, Colorado currently has only one operational anaerobic digester treating manure (AgSTAR EPA 2011), which is located at a hog farm in Lamar. Arid climate and limited water resources in Colorado render the implementation of high water demanding conventional AD processes. Studies to date have proposed high solids AD systems capable of digesting organic solid waste (OSW) not more than 40% total solids (TS). Lab tests have shown that HSCM produced in Greeley (Colorado) has an average of 89.6% TS. Multi-stage leach bed reactor (MSLBR) system proposed in the current study is capable of handling HSCM of up to 90% TS. In this system, hydrolysis and methanogenesis are carried out in separate reactors for the optimization of each stage. Hydrolysis is carried out in a trickle flow leach bed reactor (TFLBR) and methanogenesis is carried out in a high rate anaerobic digester (HRAD) like an upflow anaerobic sludge blanket (UASB) reactor or a fixed film reactor. Since leach bed reactors (LBRs) are high solids reactors, studies have indicated clogging issues in LBRs handling 26% TS. Since TFLBRs are subjected to hydrolyze upto 90% TS, obtaining hydraulic flow through the reactor is a challenge. The objective of this research is to (a) ensure good hydraulic flow through the TFLBRs and (b) evaluate and optimize the performance of the TFLBR to effectively hydrolyze the HSCM. The system was operated as a batch process with a hydraulic retention time (HRT) of 42 days without leachate recirculation. A layer of sand was added as dispersion media on top of the manure bed in the TFLBRs. This promoted good hydraulic flow through the reactor eliminating clogging issues. Organic leaching potential of a single pass (without leachate recirculation) TFLBR configuration was evaluated in terms of chemical oxygen demand (COD). Manure is naturally rich in nutrients essential for microbial growth in AD. In a typical MSLBR system, the TFLBRs are subjected to leachate recirculation, conserving the essential nutrients in the system. However, in this single pass system, the leachate removal would flush out the nutrients in the TFLBRs over time. So, nutrient solution was added to the TFLBRs to provide a constant supply of essential nutrients in the reactors for the purpose of this study and would not be necessary in a leachate recirculated TFLBR. A comparison between nutrient dosed and non-nutrient dosed TFLBRs was performed. The non-nutrient dosed and nutrient dosed TFLBRs indicated a COD reduction of approximately 66.3% and 73.5% respectively, in total in terms of dry mass. A total reduction in volatile solids (VS) of approximately 46.3% and 44.7% was observed in the non-nutrient dosed and nutrient dosed TFLBRs, respectively. Biochemical methane potential (BCMP) tests indicated a CH4 potential of approximately 0.17 L CH4/g COD leached and 0.13 L CH4/g COD leached from the non-nutrient dosed and nutrient dosed TFLBRs, respectively. Concentration of inorganics leached from the TFLBR was monitored periodically.Item Open Access Hydraulic characteristics of feedlot manure in an anaerobic leachate bed reactor(Colorado State University. Libraries, 2013) Wasserbach, Kelly, author; Sharvelle, Sybil, advisor; Shackelford, Charles, committee member; Davis, Jessica, committee memberConcentrated animal feeding operations (CAFOs) use the practice of optimizing space for the raising of livestock. By implementing space-saving techniques, these operations end up with large quantities of waste on small parcels of land. One way to utilize the waste is to integrate an anaerobic digester into the waste management approach of a CAFO. Anaerobic digesters efficiently break down waste while creating an energy source. In the Midwestern United States, water is in abundance, and therefore can be added to continuously stirred reactors or other anaerobic digestion technologies. In semi-arid climates, such as in Colorado, water is a treasured commodity. A new technology is being investigated to limit the need for water addition in anaerobic digestion. Water is trickled through a column of manure creating leachate. Leachate is continuously recycled though the leachate bed reactor, and then flows to a compositing tank and ultimately to a high rate anaerobic digester where methane is produced. This method has been used in manure, food and landfill applications. In many cases, clogging occurs either initially or after some digestion has occurred, and the pore space decreases. The objectives of this research were to gain a better understanding of what additives will aid in better flow through manure and to develop a method to characterize hydraulic flow through a column of manure. Intrinsic permeability (k) was measured with respect to compressed air as the permeant fluid on a homogenized sample of feedlot manure. The impact of compression, bulking agents (straw and wood chips), sieving out small fragments, and dispersion media were compared on the basis of the measured k. Applied force, or compression, had the greatest impact on k because the tested manure was greater than 30% air by volume. Straw showed the greatest increase in k of feedlot manure compared to wood chips and particle sieving. After determining which substrate combination would be best suited for liquid flow, experiments based on the mean residence time were set up. No substrate was added in these experiments, because the behavior of the manure was uncertain. Water with an oxidation reduction potential (ORP) of less than -500 mV was used to mimic anaerobic conditions. Three replicate columns were constructed and operated for six weeks. Three tracer tests, each with a hydraulic loading rate of 0.88 m/d, using sodium bromide (NaBr) as the tracer salt were conducted for three replicate columns. Variability in effluent concentrations and flows was observed in the columns, which was expected due to variability in packing within the column. The average mean residence time was approximately 6 hours. Also, the majority of the tracer (60% of the output) leached from the columns in less than one pore volume. Thus, the columns likely experienced preferential flow in that large pulses of water would exit at random times and the majority of the tracer exited the column in less than one pore volume. Tailing of residence time distribution curves and inability to recover all injected salt indicates the likelihood of dead zones within reactors. A ratio (further referred to as ratio R) of the superficial velocity to the hydraulic loading rate was calculated. The ratio R was greater than one for every tracer test indicating that water flows through the column slowly. This indicates retardation through the column consistent with the observation of tailing in residence time distribution curves, also indicating the presence of dead zones. The free drain volume was a small fraction of the pore volume in the total column. The fact that so few pore volumes exited the column indicates severe retardation within the column that can be attributed to dead zones. Each tracer test also showed that very few pore volumes exited the column. This could possibly indicate a retardation in flow.Item Open Access Identifying grass-legume bicultures to increase above and belowground biomass production and improve traditional fallows in crop rotations of the Andean Highlands(Colorado State University. Libraries, 2021) Meza Retamozo, Katherin Paola, author; Fonte, Steven, advisor; Schipanski, Meagan, committee member; Davis, Jessica, committee memberIn the high Andes of Peru, intensification of crop rotation and agricultural land-use is reducing the practice and duration of traditional fallow (based on natural establishment of native vegetation). These fallows represent one of the main traditional soil management practices to sustain long-term productivity, while also providing key forage resources in these mixed crop-livestock systems. Improved forage-based fallows, with the intentional seeding of more productive annual and perennial forages, offer great potential for producing forage and contributing to soil restoration under intensified contexts; however, there remains a gap in knowledge about which plant species can best optimize tradeoffs between forage production and belowground inputs to support long-term soil fertility and contribute to the multifunctionality of Andean agroecosystems. To address this issue, a pot study was conducted with two contrasting soils to evaluate the above and belowground productivity of all possible grass-legume pairs involving five grasses (oat (Avena sativa), ryegrass (Lolium multiflorum), festulolium (Lolium x Festuca genera), brome grass (Bromus catharticus), and orchardgrass (Dactylis glomerata), and four legumes (vetch (Vicia dasycarpa ), red clover (Trifolium pratense), black medic (Medicago lupulina), and alfalfa (Medicago sativa)) in comparison to the performance of each species in monoculture. Grass-legume bicultures resulted in significant overyielding, producing 65% and 28% more total dry biomass and total N uptake on average than species in monoculture, respectively. Grass-legume shoot biomass production yielded 67% more compared to monocultures, while root biomass was on average 58% higher in bicultures than in monocultures. For aboveground biomass, production differences between grass-legume bicultures were significantly influenced by the species of legume present, while belowground biomass was more affected by the grass species present in the bicultures. Roughly 80% of the mixtures achieved a mean land equivalent ratio (LER) > 1.0. When examining total biomass production, the most successful bicultures were oat-vetch (LER=1.87), vetch-festulolium (LER=2.31), vetch-orchardgrass (LER=1.87), oat-red clover (LER=1.62), and red clover-ryegrass (LER=1.46). When examining partial LERs (the component of the LER attributed to each species), we found that overyielding in bicultures was mainly driven by increases in the biomass of the component grass species. Our findings suggest that mixtures of key functional species (e.g. grass and legume, annual and perennial species) offer greater promise in improved fallows compared to monocultures of the respective species. Additionally, I suggest that strategically designed improved fallow mixtures, with emphasis on perennial species that support long-term root inputs, can best support soil health and the multifunctionality of Andean agroecosystems.Item Open Access Impacts of black soldier fly larval frass on vegetable crop production(Colorado State University. Libraries, 2023) Chavez, Maria, author; Uchanski, Mark, advisor; Davis, Jessica, committee member; Tomberlin, Jeff, committee member; Ode, Paul, committee memberThe "insects as food and feed" movement is gaining considerable momentum as a novel way to provide protein to human and animal diets. Insects require significantly fewer resources, such as water and land, to produce, process and distribute as a food source. Food, service, and restaurant partners often donate their waste to insect producers. This converts landfill destined waste into high protein food sources. The left-over waste product from mass rearing insects, known as frass, creates a problem for insect producers. However, across the food system numerous industries are involved, and this research examines how waste from the hospitality and insect industries can be utilized in vegetable crop production. Peat is the most common medium for plant growth in greenhouse and gardening operations; however, peat extraction has severe environmental consequences for marsh ecosystems, surrounding environments, and climate change. Partially replacing peat with insect frass could reduce industrial waste from insect and food producers and decrease peat consumption. Greenhouse studies were designed to investigate the use of frass in vegetable production. In pot studies with arugula, lettuce, and tomato different ratios of peat and vermicompost and peat and insect frass were compared to a 100% peat control. Arugula and lettuce grown in distillery grain frass, all BSFL treatments were equal or better in yield than the 100% peat control, regardless of season. For brewery grain frass, most treatments in arugula and lettuce were worse or comparable to the peat control in yield, regardless of season. The diet of the larvae (distillery grain vs. brewery grain) was a significant factor in determining the impacts on vegetable yield. Arugula and lettuce leaf tissues were analyzed for nutrient concentrations. Primary macronutrient (NPK) concentrations were higher in frass treatments for both crops. Secondary macronutrients and micronutrients did not show clear trends on the effect of distillery or brewery grain frass. Tomatoes did not produce any significant differences across insect frass treatments, though average individual fruit weight was significantly higher in low percentages of vermicompost. Emergence, germination, and seedling vigor of arugula, lettuce, and tomato seeds were negatively impacted by brewery grain frass in the absence of vermicompost. In the presence of vermicompost, low concentrations of insect frass in a germination mixture produced comparable results to a 100% peat control. There are many components of insect frass yet to be fully explored, such as the impact on cation exchange capacity and microbial activity. More research to understand the physical, chemical, and microbial components of the medium will be essential in pushing the field forward, improving the material as an amendment, and closing gaps in the cycle of production.Item Open Access Investigation of substrate selection and finishing protocols for nursery container production of 13 plant taxa native to the southwestern United States(Colorado State University. Libraries, 2023) Linfield, Allisa, author; Bousselot, Jennifer, advisor; Gu, Mengmeng, committee member; Davis, Jessica, committee member; Shonle, Irene, committee memberNursery-produced native plant taxa are a tool for habitat restoration, and their use extends beyond wildlife areas as urban residents seek to create wildlife corridors. Water conservation concerns and understanding of pollinator decline further motivates use of native plants in cultivated and designed landscapes. Furthermore, increasing awareness around degradation of peatlands, drives consumer interest in sustainably produced plant material using peat-alternative substrates. Growers attempt to meet the demand for native plant material, but protocols for growing these taxa, which are not adapted to thrive in peat-based substrates, are limited. Without finishing protocols for sizing up propagules to retail size, growers, who are limited by time and resources, amend peat-based substrates using trial and error in hopes of achieving favorable growing outcomes. We identified grower practices through a survey of nationwide Plant Select® growers. Based on survey results, we evaluated survivability and plant growth in response to partially replacing peat-based substrate with sand, field soil, a microbial-inoculated compost (MIC), and a green waste compost (GWC). Our results indicated that plant growth response to these substrates is taxon specific. However, only one of the 13 taxa evaluated resulted in a significantly higher plant growth index (PGI) increase in the control group. Thus, our findings suggest that 12 of the investigated taxa may respond to peat-reduced substrates during the finishing period without significant negative impacts on PGI or dry weight.Item Open Access Role of rhizosphere bacteria and root exudates on the assimilation of phosphorus(Colorado State University. Libraries, 2022) Pantigoso Guevara, Hugo A., author; Vivanco, Jorge M., advisor; Fonte, Steven, committee member; Davis, Jessica, committee member; Manter, Daniel, committee memberDeficient phosphorus (P) bioavailability in soils is a major challenge for sustainable food production as effective strategies to access unavailable P are limited. Solubilizing-bacteria and root exudate metabolites that solubilize P are promising approaches to increase available P for plants. We hypothesized that compounds in root exudates could elicit the P-solubilization activity of bacteria. To test this hypothesis, the root exudates of Arabidopsis grown in vitro under sufficient and deficient P conditions were characterized using GC-MS. We tested the ability of previously screened root exudates to solubilize plant-unavailable P in vitro. In parallel, potential P-solubilizing bacteria were isolated from the rhizosphere of wild potatoes using conventional microbiology techniques. The bacteria strains were tested, both individually and in consortia, for their ability to solubilize organic (phytin) and inorganic (calcium) P sources in vitro and in planta. Lastly, selected root exudate compounds were incubated together with P-solubilizing bacteria, and bacterial growth, P solubilization activity, and plant growth were evaluated. Our results demonstrate that malic, nicotinic, and 3-hydroxypropionic acids improved solubilization of P as compared to a control. Likewise, the bacterial strains E. cloacae, P. pseudoalcaligenes, and B. thuringiensis enhanced plant growth and P content with additions of plant-unavailable P. Furthermore, we found that threonine and 4-hydroxybutyric acid elicit P solubilization in all bacteria, under both organic and inorganic sources, independent of bacterial growth. Subsequent exogenous application of threonine to soils improved plant root growth, enhanced nitrogen and phosphorus content in roots and increased available levels of potassium, calcium, and magnesium in soils. Altogether, our findings expand on the function of exuded specialized compounds and suggest approaches to effectively recover residual P from soil, improving crop growth and nutrition.Item Open Access Simultaneous phosphorus and nitrogen removal using aluminum based water treatment residual(Colorado State University. Libraries, 2011) Liang, Qian, author; Carlson, Kenneth, advisor; Davis, Jessica, committee member; Sharvelle, Sybil, committee memberIn this study, an aluminum-based water treatment residual (Al-WTR) from a local water treatment facility was investigated for its capacity for phosphorus (P) and nitrogen (N) removal in wastewater. Characterization results indicated that Al-WTR had a high content of amorphous aluminum hydroxide, which is able to bond phosphorus in solution mainly via ligand exchange. Also, Al-WTR was found to be rich in bio-available carbon, which can facilitate biological denitrification for N removal. Batch equilibrium tests analyzed the P sorption parameters according to Langmuir and Freundlich isotherms. The results of the maximum sorption capacity were 4.498, 3.258 and 2.038 g/kg at pH values of 4, 7, and 9 respectively, indicating that P sorption was favored at lower pH conditions. However, the sorption capacity results may not reflect that in continuous-flow conditions. Al-WTR was shown to be a more effective sorbent for orthophosphate phosphorus (ortho-P) than total phosphorus (TP), but still had promising removals (greater than 90%) to both. Simultaneous P and N removal in wastewater was tested in column experiments in a continuous-flow mode. 95.9% removal of ortho-P and 90.0 % removal were achieved. Also, NO3- removal was highly efficient (99.6%). In sum, using Al-WTR as a P and N mitigation agent is a feasible and sustainable technology, and could be applied in P and N control practices in point-sources and non-point sources.Item Open Access Soil phosphorus availability and transformations following biosolids applications(Colorado State University. Libraries, 2020) McDaniel, Jacob P., author; Butters, Gregory, advisor; Barbarick, Kenneth, advisor; Davis, Jessica, committee member; Frasier, Marshall, committee memberLand application of biosolids has many benefits such as providing nutrients for plant growth as well as adding organic matter to soil. However, there is the potential for negative impacts due to the high concentration of phosphorus (P) relative to nitrogen (N). Much work has been done looking at the effects of over application of P and best management practices for the application of biosolids in the eastern United States. However, little work has been done in the western United States where the environment is very different due to lower rainfall and higher soil pH and calcium (Ca) concentrations. This study was composed of four parts to help understand how P reacts in the western United States and to look at the implications for plant growth. These parts included: (1) fractionation of P in biosolids, (2) vertical distribution of P following long-term biosolids applications, (3) seasonal soil P cycling, and (4) plant uptake of P. The fractionation of P was designed to look at several biosolids and determine a method to be able to characterize the P that is present. This information would have the potential to aid in decision making about best managing the P from various sources. The vertical distribution of P following long-term application was designed to characterize the P in the soil profile. It is usually assumed that P is not mobile, but over long periods of time and with high application rates it can move. Seasonal changes of the different pools of P were studied to better understand how time of year affects the amount of P available in soil samples, and potentially to plants and the environment. The last study was designed to show how different sources of organic amendments supply different amount of P to a plant. The objective was to be able to better determine the amount of plant available P from an amendment. The results of the different studies begin to show the similarities and differences in the behavior of P in the western United States and in the east. The fractionation study found that the assumptions that are used for manure cannot be applied to all factions of P in biosolids and that a longer shaking time is needed. This study also found that there are differences among wastewater treatment plants that is mostly related to differences in treatment methods in an individual wastewater treatment plant. The vertical distribution of P study found that over time with repeated applications of P in dryland wheat (Triticum aestivum L.)-fallow rotations there is a significant effect on occluded P. Even with repeated applications most of the accumulations of P were limited to the plow layer and in a system where P chemistry is dominated by Ca, Fe still plays an important role. The seasonal change in the fractions of soil P study showed the changes in soil P were greatly affected by soil properties, water availability, climate, and application rates of biosolids. The high concentration of Ca in the soils favored the formation of Ca bound P, and saturated soils affected the forms of Fe bound P. The addition of organic matter and Fe with biosolids applications increased the concentration of soluble P, microbial biomass P, and Fe bound P. The plant uptake study found that there is a much larger effect of the soil on plant uptake than the source of the amendment. There is an inverse relationship between a soil's ability to adsorb P and the concentrations of plant tissue P when the plants are young. As the plants age and develop large root masses they can increase their tissue P concentrations. This work shows that in the western United States there is more of a need to focus on the soils than the biosolids being applied to be able to make the best management decision. All the studies that looked at the P after it had been added to soil found that Ca affects the transformations and uptake of P by plants. In the western United States, there are areas that have large amount of Ca in the soil and areas that do not. As a result, interactions of Ca and P need to be focused on and further studied to ensure adequate plant nutrition as well as being a steward of the environment.Item Open Access The development and demonstration of a multiple stage anaerobic digester for the treatment of high solids wastes(Colorado State University. Libraries, 2018) Loetscher, Lucas H., author; Sharvelle, Sybil, advisor; De Long, Susan, committee member; Davis, Jessica, committee memberThe semi-arid Great Plains of the central United States is home to numerous high-density, confined animal feeding operations (CAFOs) that utilize outdoor animal pens. These facilities generate a desiccated manure very different from the wastes generated from similar enclosed facilities in other parts of the country. These high-solids wastes present challenges to the conventional digestion systems commonly used on wastes with lower solids contents. Therefore, it was determined that there was a need in the industry for a new technological approach to improve feasibility of the digestion of these challenging wastes. A first principle design technique was applied to the conceptual design of an innovative technology better suited to such a challenging substrate. This system, named the CSU multiple-stage anaerobic digester (MSAD) technology, is a promising technical alternative to existing AD technologies. The CSU MSAD technology demonstrated the ability to overcome various limitations in previous anaerobic digestion technologies and ultimately demonstrated the ability to be used in the digestion of a wider variety of substrates. A demonstration-scale CSU MSAD system was constructed and operated for a duration of four months. The demonstration-scale equipment was constructed as a stand-alone mobile pilot lab that could function with various substrates and hydrolysis reactor configurations. In addition to the demonstration of the MSAD system on manure wastes, experiments were conducted on the digestion and inoculation of food wastes. Findings from these experiments indicated that substrate inoculation became less important as the digestion system operated for a longer duration. Inferring from these findings, it is expected that commercial MSAD digesters will not benefit from substrate inoculation after the system completes a successful startup process. An analysis of the existing state of the MSAD technology was completed based on review of previous research efforts. To prioritize future research efforts, a modified technology development risk analysis using qualitative scores was applied to development needs of the technology that currently have unknown and potentially risky outcomes. This approach has led to a series of recommended future development efforts for the commercialization of this technology.Item Open Access The effects of effluent water irrigation and salinity on soil chemical properties and three species of perennial grass(Colorado State University. Libraries, 2017) Isweiri, Hanan F., author; Qain, Yaling, advisor; Barbarick, Ken, committee member; Davis, Jessica, committee member; Hughes, Harrison, committee member; Koski, Anthony, committee memberTo view the abstract, please see the full text of the document.Item Open Access The intensification revolution in dryland cropping systems: implications from field to landscape scale(Colorado State University. Libraries, 2017) Rosenzweig, Steven, author; Schipanski, Meagan, advisor; Stromberger, Mary, committee member; Carolan, Michael, committee member; Davis, Jessica, committee memberA global transformation in semi-arid cropping systems is occurring as dryland (non-irrigated) farmers shift from crop rotations reliant on year-long periods of bare fallow to more intensively cropped systems. Bare fallow has reduced year-to-year variability in crop yields, but it has also constrained crop productivity and, therefore, reduced carbon (C) inputs to soils. Exposure to tillage and erosion, combined with C limitation, has gradually degraded dryland soils and reduced their capacity to capture water and supply plant nutrients, requiring dryland farmers to rely on external inputs to support plant growth. However, the emergence of no-till has enabled dryland farmers to save enough water to replace bare fallows with crops, a practice called cropping system intensification. Cropping intensification has potential implications for the environment and economy of dryland agriculture as it impacts every aspect of the agroecosystem – from soil health, to weed and nutrient management, to crop yields. This dissertation seeks to unravel the economic and environmental implications of cropping system intensification at both the field and landscape scale in the US High Plains, and to understand the social dynamics underpinning this revolution. I quantified the impacts of cropping system intensification on a range of soil health parameters on 96 dryland, no-till fields in the High Plains. Three levels of cropping system intensity – wheat-fallow, mid-intensity, and continuous – were represented along a potential evapotranspiration gradient that increases from northwestern Nebraska to southeastern Colorado. I conducted in-depth interviews with farmers to examine the motivations, perceptions, and social interactions that influence decisions about whether and how much to intensify, and to collect detailed field histories including input use and crop yields. To scale up the implications of these field-level analyses, and to assess the current extent of the cropping revolution in the High Plains, I conducted a spatial analysis using high-resolution satellite crop data to examine changes in cropping patterns over time at the landscape scale. I found that cropping system intensification was positively associated with soil organic carbon, aggregation, and fungal biomass, and these effects were robust amidst variability in environmental and management factors. I also found that intensified systems were associated with greater potentially mineralizable and total nitrogen (N), and arbuscular mycorrhizal fungal colonization of wheat roots, suggesting that cropping intensity enhances internal cycling of N and phosphorus (P). Continuous dryland farmers also achieved greater total crop production using fewer external inputs than wheat-fallow farmers, leading to enhanced profitability. To explain the social dynamics underpinning the cropping system revolution, I build on Carolan's application of Bourdieusian social fields to agriculture, and find several overlapping fields within Carolan's more general fields of sustainable and conventional agriculture, which are reflected in different degrees of intensification. I identify strategies for change, some of which would serve to reshape social fields, and others which leverage existing social positions and relationships, to enable farmers to overcome the barriers constraining cropping system intensification. Results from the spatial analysis suggest that, from 2008 to 2016, the High Plains witnessed a profound shift in cropping systems, as the historically dominant wheat-fallow system was replaced by intensified rotations as the dominant systems across the landscape. I estimated that these patterns over the 9-year study period increased annual grain production and annual net farm operating income, slightly reduced herbicide use, and increased C sequestration, contributing to greenhouse gas reductions. I projected each of these implications to a scenario of 100% continuous cropping adoption to estimate the potential environmental and economic impacts of cropping system intensification in the High Plains. Overall, my findings suggest that dryland cropping systems are gradually intensifying in the High Plains, and these trends are likely reversing historical negative environmental and economic trends to enhance the profitability and environmental sustainability of dryland agroecosystems.Item Open Access Understanding the dynamics and management of organic nutrient sources in smallholder farming systems: an interdisciplinary approach(Colorado State University. Libraries, 2021) Magonziwa, Blessing, author; Fonte, Steven, advisor; Davis, Jessica, committee member; Carolan, Michael, committee member; Paustian, Keith, committee memberSmallholder farmers often face challenges in managing soil fertility due to limited inputs and high spatial variability on their farms. In many places, soil fertility, and overall soil health, is on the decline, and management of organic nutrient sources (ONS) can play a vital role in sustaining the productivity of soils. However, in mixed smallholder crop-livestock systems there is often competition for crop residues between retaining residues within fields versus feeding them to livestock. Understanding how ONS produced on-farm are managed, and the flows and drivers of this essential resource is critical for the restoration and sustainable management of soil fertility and health in smallholder agroecosystems. The objectives of this study were to: i) validate a soil health tool kit developed to facilitate smallholder research and management involving the use of ONS and other soil management strategies; ii) evaluate how different maize-based ONS (shoot, roots, manure) influence soil organic carbon (SOC) dynamics; iii) understand socio-cultural, economic, and environmental drivers of ONS allocation and use; and iv) understand management and environmental drivers SOC and nutrient (N, P and K) balances across various management scenarios. To address these objectives, a soil health tool kit to provide in-field quantitative data that are comparable to formal laboratory methods was assembled. I then validated methods used in this tool kit against standard analyses conducted at national laboratories on soils collected from 36 smallholder farms in Kenya and 115 farms in Peru. My results showed that permanganate oxidizable C and pH measured with the tool kit from Kenyan and Peruvian soils were highly correlated to the same variables measured by a standard laboratory. The tool kit and standard laboratory measures of available P were less well correlated, but also showed a significant positive relationship. Both tool kit and standard lab analyses displayed similar abilities to predict maize grain yield in Kenya. My findings suggest that the tool kit methods proposed in this study have broad applicability to smallholder farms for explaining variability in crop yields, assessing soil properties of different plots and quantifying management-induced changes in soil health. In the next study, I used a mesocosm experiment and a 13C natural abundance approach, where organic residues (maize shoots, ex-situ maize roots, in-situ maize roots and cattle manure) were incubated for 11 months to trace maize-derived C into different SOC pools. My findings indicated that there was greater stabilization of shoot-derived C (2 X more than manure and 1.6 X more than ex-situ root C) in the mineral-associated organic matter fraction. At the same time, mineral additions of N, P and S (aimed at adjusting the stochiometry of the added residue inputs) led to a 60% decrease in C stabilization in the mineral-associated fraction, compared to a control with no nutrient additions. My study highlights the potential importance of residue retention as a strategy to maintain SOC and therefore soil health and did not support the idea that strategic N, P, and S additions can facilitate C stabilization in soil over the long-term. I then used focus group discussions and conducted a survey of 184 farming households to understand socio-economic, socio-cultural, and environmental drivers of ONS allocation and use at farm scale in three contrasting agroecological zones of western Kenya. I found that the more resource endowed a farmer is, the more ONS are allocated to the main production plot within a farm. However, beyond resource endowment I observed that agroecological location, and tenure, perceived soil fertility, gender and social connections also had important influences on ONS allocation. Lastly, I examined case studies from three representative farm types within three agroecological zones in western Kenya and used a modelling approach to estimate nutrient and C flows in and out of fields. Based on the estimated flows, I then examined different scenarios representing alternative possibilities for ONS management in the region. I noted differences in inputs and allocation between the three zones, but these did not affect the overall balances, which were largely influenced by fertilizer inputs, as well as nutrient export in harvest and soil erosion. Overall nutrient balances were variable, but largely negative across the zones, farm types and field types. When exploring the different management scenarios, reducing erosion led to significantly less negative N balances in all locations. A full residue retention scenario indicated the greatest impact on K balances, while for SOC scenarios with full residue retention and lablab (a high biomass legume) incorporation resulted in at least 50 % more SOC compared to current practices. Scenarios indicate that retaining residues as well as implementing erosion control measures have the potential to effectively reduce nutrient losses as well as improve SOC stocks and that these practices should be encouraged. As research and development organizations continue to engage with smallholder farmers to reduce the burden of global food insecurity, the insights gained by this research will allow for better anticipation of drivers and obstacles to improved nutrient management in these farming landscapes and communities.Item Open Access When the wells run dry: soil organic carbon dynamics during the transition from irrigated to dryland cropping systems(Colorado State University. Libraries, 2021) Núñez, AgustÃn, author; Schipanski, Meagan, advisor; Cotrufo, M. Francesca, committee member; Davis, Jessica, committee member; Paustian, Keith, committee memberIn many parts of the world, irrigation must decrease due to declining water availability and increased demand from other water users. The Ogallala Aquifer, one of the biggest aquifers in the world, is one example where declining groundwater levels threaten agricultural productivity and social communities across large parts of the semiarid High Plains. In this semiarid region, irrigation is not only fundamental for crop productivity, but it also has positive effects on soil organic carbon (SOC). However, little is known about the changes in SOC dynamics during the transition from irrigated to dryland cropping systems, which has important potential implications for the long-term productivity of these agricultural systems as well as the potential for the soils of the region to be a net sink or source of CO2. The general objective of my dissertation was to study how irrigation retirement affects SOC dynamics in semiarid agricultural systems of the Ogallala Aquifer Region. I used field experiments to quantify the early changes in crop productivity and C inputs, soil microbial communities, C outputs and SOC formation and turnover during the transition from irrigated to dryland cropping systems. Irrigation retirement had a stronger influence on C inputs than on C outputs because plants responded faster and to a greater magnitude than soil microorganisms to water limitations. Given intrinsic differences in growing season and water requirements, crops vary in their sensitivity to water stress, and wheat agroecosystems were less affected by irrigation retirement than maize agroecosystems. After three growing seasons, there was lower microbial activity and SOC formation in dryland (retired) than irrigated maize, but we did not find changes in the decomposition rate of old SOC. In winter wheat, low differences in soil moisture and crop productivity resulted in almost no changes in microbial activity and SOC dynamics after irrigation retirement. These short-term study results suggest that large losses of crop productivity and C inputs without changes in C outputs will decrease the formation of new SOC, thus affecting SOC storage on the longer term. I confirmed this outcome with on-farm observations of the longer-term effect of irrigation retirement on SOC stocks under different management options. After 7-10 years, sites that used to be irrigated and transitioned back to dryland systems had lower SOC than long-term irrigated sites and had the same SOC stocks as long-term dryland fields, confirming the relatively short legacy effect of irrigation. An exception to this was the transition from irrigated agriculture to perennial, ungrazed grasslands enrolled in the Conservation Reserve Program (CRP). Fields that transitioned into CRP were able to maintain intermediate SOC levels that did not differ from the currently irrigated controls. Taken together, the results of my dissertation indicate that there will be rapid and significant losses of SOC during the transition from irrigated to dryland cropping systems in the Ogallala Aquifer Region. These losses will occur mainly in response to changes in C inputs. Therefore, comparison of biomass and residue production could be used to rapidly identify crop and vegetation management strategies with higher potential to minimize the negative impact of irrigation retirement on SOC.