Faculty Publications
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Item Open Access Climate change resiliency in Colorado: cropping systems BMPs(Colorado State University. Libraries, 2019) Shawver, Casey, author; Ippolito, Jim, author; Waskom, Reagan, author; Udall, Brad, author; Doesken, Nolan, author; Colorado State University. Department of Soil and Crop Science, publisherItem Open Access Landscape-scale cropping changes in the High Plains: economic and environmental implications(Colorado State University. Libraries, 2019) Rosenzweigab, Steven T., author; Schipanski, Meagan E., author; IOP Publishering, Ltd, publisherA global transformation in semi-arid cropping systems is occurring as dryland (non-irrigated) farmers in semi-arid regions shift from crop rotations reliant on year-long bare fallows, called summer fallow, to more intensively cropped systems. Understanding the rate of cropping system intensification at the landscape scale is critical to estimating the economic and environmental implications of this movement. Here, we use high-resolution satellite data to quantify dryland cropping patterns from 2008 to 2016 in the US High Plains. We use these estimates to scale up our previous field-level research in this region on soil carbon, herbicide use, yields, and profitability. Over the nine year study period, the High Plains witnessed a profound shift in cropping systems, as the historically dominant wheat-fallow system was replaced by more intensified rotations as the dominant systems by land area. Out of the 4 million hectares of non-irrigated cropland in the study area, this shift coincided with a 0.5 million-hectare decline in summer fallow and a concurrent increase in alternative (non-wheat) crops. We estimate that, from 2008 to 2016, these patterns resulted in a 0.53 Tg (9%) increase in annual grain production, 80 million USD (10%) increase in annual net farm operating income, substantial reductions in herbicide use, and an increase in C sequestration that corresponds to greenhouse gas reductions of 0.32 million metric tons of CO2 equivalents per year (MMTCO2e yr-1). We project each of these implications to a scenario of potential maximum 100% intensification and estimate that, relative to 2016 levels, herbicide use would be reduced by more than half, grain production would increase by 25%, net operating income would increase by 223 million USD (26%), and greenhouse gases would be reduced by an additional 0.8 MMTCO2e yr-1. The scale of cropping intensification in the High Plains and its environmental and economic impacts has important implications for other regions undergoing similar transformations, and for policy that can either support or hinder these shifts toward more sustainable cropping systems.Item Open Access Pile burns as a proxy for high severity wildfire impacts on soil microbiomes(Colorado State University. Libraries, 2024-07-29) Fowler, Julie A., author; Nelson, Amelia R., author; Bechtold, Emily K., author; Paul, Raegan, author; Wettengel, Alexandra M., author; McNorvell, Michael A., author; Stevens-Rumann, Camille S., author; Fegel, Timothy S., author; Anderson, Erik, author; Rhoades, Charles C., author; Wilkins, Michael J., author; Elsevier B.V., publisherWildfires in the western US are increasing in frequency, size, and severity. These disturbances alter soil microbiome structure and function, with greater fire severity leading to more pronounced impacts to bacterial, archaeal, and fungal communities. These changes have implications for the provisioning of microbially-mediated ecosystem services (e.g., carbon sequestration, clean water supplies) typically associated with forested watersheds. Challenges in sampling wildfire-impacted areas immediately post-burn have limited our assessment of short-term (i.e., days to weeks) changes in the soil microbiome and understanding of how microbial populations may influence post-fire biogeochemistry and ecosystem recovery. The identification of potential high severity wildfire proxies may help address some of these knowledge gaps. One potential proxy is pile burns scars, which are produced from a set of common techniques for fuel disposal and site preparation in conifer forests throughout the western US and beyond. We sampled depth-resolved layers from fire-impacted soil and combusted litter and woody materials in a series of recent pile burn scars near West Yellowstone, Montana and nearby unburned mineral soil controls to assess whether the pile burn scars exhibited microbial signatures characteristic of forest soils impacted by recent high severity wildfire. Changes in soil carbon and nitrogen chemistry and patterns of microbial alpha and beta diversity broadly aligned with those observed following wildfire, particularly the enrichment of so-called 'pyrophilous' taxa. Furthermore, many of the taxa enriched in burned soils likely encoded putative traits that benefit microorganisms colonizing these environments, such as the potential for fast growth or utilization of pyrogenic carbon substrates. We suggest that pile burn scars may represent a useful proxy along the experimental gradient from muffle furnace or pyrocosm studies to largescale prescribed burns in the field to advance understanding of the soil (and related layers, like ash) microbiome following high severity wildfires, particularly when coupled with experimental manipulation. Finally, we discuss existing research gaps that experimentally manipulated pile burns could be utilized to address.Item Open Access Climate change resiliency in Colorado: grazing systems BMPs(Colorado State University. Libraries, 2019) Shawver, Casey, author; Ippolito, Jim, author; Waskom, Reagan, author; Udall, Brad, author; Doesken, Nolan, author; Colorado State University. Department of Soil and Crop Science, publisherItem Open Access How social networks impact agricultural land stewardship in Iowa(Colorado State University. Libraries, 2024) Luxton, India, author; Ellis, Ellie, author; Arnold, Parker, author; Shakya, Prasiddha, author; Lee, Juliet, author; Ravetta, Emilia, author; Toombs, Ted, author; Mook, Anne, author; Cross, Jeni, authorTwo-page summary of findings of a social network study to explore conservation practices among farmers in Iowa.Item Open Access Agricultural conservation networks in Iowa(Colorado State University. Libraries, 2023-09) Luxton, India, author; Ellis, Elizabeth, author; Arnold, Parker, author; Shakya, Prasiddha, author; Lee, Juliet, author; Ravetta, Emilia, author; Toombs, Ted, author; Mook, Anne, author; Cross, Jeni, authorIowa's farmlands, celebrated for their remarkable agricultural productivity, are facing pressing environmental challenges, including soil erosion, waterway nitrogen pollution, and vulnerability to extreme weather events. These issues imperil the state's agricultural sector's long-term sustainability and economic stability. Despite substantial investments from governmental and non-governmental entities to encourage conservation practice use, adoption rates remain persistently low. In this report, we use quantitative, qualitative, and social network analysis on a sample of 38 farmers to understand how social networks shape their adoption of conservation practices. We analyze data through a systems framework and compare counties with high- and low-adoption of conservation practices to assess influences from the individual farmer level to the broader societal context. We conclude with a discussion of strategic implications to promote conservation adoption.Item Open Access Quantifying proximity, confinement, and interventions in disease outbreaks: a decision support framework for air-transported pathogens(Colorado State University. Libraries, 2021-02-19) Bond, Tami C, author; Bosco-Lauth, Angela, author; Farmer, Delphine K., author; Francisco, Paul W., author; Pierce, Jeffrey R., author; Fedak, Kristen M., author; Ham, Jay M., author; Jathar, Shantanu H., author; VandeWoude, Sue, author; Environmental Science & Technology, publisherThe inability to communicate how infectious diseases are transmitted in human environments has triggered avoidance of interactions during the COVID-19 pandemic. We define a metric, Effective ReBreathed Volume (ERBV), that encapsulates how infectious pathogens, including SARS-CoV-2, transport in air. ERBV separates environmental transport from other factors in the chain of infection, allowing quantitative comparisons among situations. Particle size affects transport, removal onto surfaces, and elimination by mitigation measures, so ERBV is presented for a range of exhaled particle diameters: 1, 10, and 100 μm. Pathogen transport depends on both proximity and confinement. If interpersonal distancing of 2 m is maintained, then confinement, not proximity, dominates rebreathing after 10–15 min in enclosed spaces for all but 100 μm particles. We analyze strategies to reduce this confinement effect. Ventilation and filtration reduce person-to-person transport of 1 μm particles (ERBV1) by 13–85% in residential and office situations. Deposition to surfaces competes with intentional removal for 10 and 100 μm particles, so the same interventions reduce ERBV10 by only 3–50%, and ERBV100 is unaffected. Prior knowledge of size-dependent ERBV would help identify transmission modes and effective interventions. This framework supports mitigation decisions in emerging situations, even before other infectious parameters are known.Item Open Access Vulnerability assessments of Colorado ground water to nitrate contamination(Colorado State University. Libraries, 2004-07-06) Ceplecha, Z., author; Waskom, R., author; Bauder, T., author; Sharkoff, J., author; Khosla, R., author; Water, Air, and Soil Pollution, publisherNitrate (NO3-N) contamination of ground water aquifers is an important problem in the United States and throughout the world, particularly as ground water resources become increasingly relied upon to support human needs. Cost effective methodologies are needed to facilitate decision-making for ground water protection. To aid ground water protection organizations, we designed two tools to assess aquifer vulnerability to NO3-N contamination in Colorado. The first tool is a statewide aquifer vulnerability map (VM) that identifies regions vulnerable to ground water contamination. The VM uses five factors that influence aquifer vulnerability on a regional scale: aquifer locations, depth to water, soil drainage class, land use, and recharge availability. We validated the VM using 576 discrete ground water sample points from throughout the state and found that the VM was able to delineate areas of increased aquifer vulnerability to NO3-N contamination (r2= 0.78). The second aquifer assessment tool is a vulnerability matrix (VMX) developed to help practitioners determine relative aquifer vulnerability to NO3-N contamination on a field scale. The VMX consists of a series of factors that are rated and combined for a particular field. This rating is used to give landowners an index of general aquifer vulnerability to NO3-N contamination for a specific field, and inform them of changes in management practices to reduce the vulnerability. The VMX can be used in conjunction with the VM to determine NO3-N contamination potential from intensive agriculture.Item Open Access Infrared thermometry to estimate crop water stress index and water use of irrigated maize in northeastern Colorado(Colorado State University. Libraries, 2012) Taghvaeian, Saleh, author; Chávez, José L., author; Hansen, Neil C., author; Molecular Diversity Preservation International, publisherWith an increasing demand of fresh water resources in arid/semi-arid parts of the world, researchers and practitioners are relying more than ever on remote sensing techniques for monitoring and evaluating crop water status and for estimating crop water use or crop actual evapotranspiration (ETa). In this present study, infrared thermometry was used in conjunction with a few weather parameters to develop non-water-stressed and non-transpiring baselines for irrigated maize in a semi-arid region of Colorado in the western USA. A remote sensing-based Crop Water Stress Index (CWSI) was then estimated for four hourly periods each day during 5 August to 2 September 2011 (29 days). The estimated CWSI was smallest during the 10:00-11:00 a.m. and largest during the 12:00-13:00 p.m. hours. Plotting volumetric water content of the topsoil vs CWSI revealed that there is a high correlation between the two parameters during the analyzed period. CWSI values were also used to estimate maize actual transpiration (Ta). Ta estimates were more influenced by crop biomass rather than irrigation depths alone, mainly due to the fact that the effects of deficit irrigation were largely masked by the significant precipitation during the growing season. During the study period, applying an independent remotely sensed energy balance model showed that maize ETa was 159 mm, 30% larger than CWSI-Ta (122 mm) and 9% smaller than standard-condition maize ET (174 mm).Item Open Access Biological and molecular structure analyses of the controls on soil organic matter dynamics(Colorado State University. Libraries, 2008-09) Magrini, K., author; Follett, R. F., author; Conant, R., author; Paul, Eldor A., author; Morris, S. J., author; Lomonosov Moscow State University, Department of Chemistry, publisherThe dynamics of soil organic carbon (SOC) are controlled by the interaction of biological, physical, and chemical parameters. These are best measured by a combination of techniques such as long-term field sites with a C3↔C4 plant switch. Acid hydrolysis and 14C- dating measure the mean residence time (MRT) of the resistant fraction. Long-term incubation allows the in situ biota to identify and decompose the labile SOC components. Statistical analysis (curve fitting) of the CO2 release curves, determines the pool size and of the two labile fractions (1). The effect of chemical structure is measured with pyrolysismolecular beam mass spectrometry (py-MBMS). The dynamics of charcoal, clay and silt are measured with both 13C and 14C.Item Open Access Agriculture's role in greenhouse gas mitigation(Colorado State University. Libraries, 2006-09) Paul, Eldor A., author; Sheehan, John, author; Antle, John M., author; Paustian, Keith, author; Pew Center on Global Climate Change, publisherThis report describes opportunities for U.S. agriculture to contribute to reducing net greenhouse gas emissions. The Pew Center on Global Climate Change was established by the Pew Charitable Trusts to bring a new cooperative approach and critical scientific, economic, and technological expertise to the global climate change debate.Item Open Access Analytical determination of concentric carbon gradients within stable soil aggregates = Détermination analytique de gradients concentriques de carbone au sein d’agrégats stables de sol(Colorado State University. Libraries, 1998-08) Paul, Eldor A., author; Smucker, Alvin J. M., author; [ISSS-AISS-IBG-SICS], publisherSoil aggregation dynamics directly control agricultural production and reduce environmental contamination by convection-dispersion sequestrations of most ions. Greater containment and longer residence times of most plant nutrients, pesticides, and water would better sustain most agricultural production systems without polluting nearby groundwater supplies. In short, the large surface areas associated with the plethora of porosities within each natural soil aggregate provide dynamically interactive areas for chemical sequestration. Once known, it is these active/inactive centers which can be modified to improve plant productivity and water quality.Item Open Access Analytical determination of soil C dynamics = Détermination analytique de la dynamique du carbone du sol(Colorado State University. Libraries, 1998-08) Haile-Mariam, Shawel, author; Collins, Harold P., author; Paul, Eldor A., author; [ISSS-AISS-IBG-SICS], publisherThe significance and possible management of soil organic C (SOC) in ecosystem functioning, global change and sustainable agriculture is best determined through a knowledge of its dynamics. This requires analytically determined measurements of SOC pool sizes and flux rates. The amount and quality of plant residues inputs, biotic activity, site characteristics and management are reflected in the size of the pools and their turnover rates. Some constituents are decomposed during periods of weeks; some persist for centuries and millenia. Fractionation of the soil and the use of tracers such as 14C and 13C makes possible the determination of the dynamics of the pools involved such that more meaningful estimates of the role of SOC in the many functions in which it plays a role can be calculated.Item Open Access The extraction and measurement of adenosine triphosphate from marine sediment(Colorado State University. Libraries, 1976-05) Paul, E. A., author; Bancroft, K., author; Wiebe, W. J., author; American Society of Limnology and Oceanography, publisherA technique has been developed, using boiling sodium bicarbonate buffer, to extract adenosine triphosphate (ATP) from marine sediments and has been tested on a variety of sediments, including those with high organic content, clay, and carbonate. Recovery of ATP, as measured by the addition of bacteria of known ATP content to sediment, varied from 64-100%. The technique also was as effective as the conventional Tris buffer for extraction of ATP from both pure cultures of bacteria grown in broth and natural seawater samples.Item Open Access Greenhouse gases in intensive agriculture: contributions of individual gases to the radiative forcing of the atmosphere(Colorado State University. Libraries, 2000-09-15) Harwood, Richard R., author; Paul, Eldor A., author; Robertson, G. Philip, author; American Association for the Advancement of Science, publisherAgriculture plays a major role in the global fluxes of the greenhouse gases carbon dioxide, nitrous oxide, and methane. From 1991 to 1999, we measured gas fluxes and other sources of global warming potential (GWP) in cropped and nearby unmanaged ecosystems. Net GWP (grams of carbon dioxide equivalents per square meter per year) ranged from 110 in our conventional tillage systems to -211 in early successional communities. None of the annual cropping systems provided net mitigation, although soil carbon accumulation in no-till systems came closest to mitigating all other sources of GWP. In all but one ecosystem, nitrous oxide production was the single greatest source of GWP. In the late successional system, GWP was neutral because of significant methane oxidation. These results suggest additional opportunities for lessening the GWP of agronomic systems.Item Open Access Automated analysis of 15N and 14C in biological samples(Colorado State University. Libraries, 1989) Paul, Eldor A., author; Harris, D., author; Marcel Dekker, Inc., publisherAn automated method for the simultaneous analysis of total N, total C, 15N and 14C in small plant and soil samples is described. A commercial C-N analyser - continuous flow isotope ratio mass spectrometer (ANCA-MS) has been extended to also measure CO2 and collect 14CO2 produced by sample combustion. Samples containing 20 - 200 μg N and up to 5 mg C can be analysed directly with no sample preparation other than drying and fine grinding. The precision of total elemental analysis is comparable to that by conventional methods. The average standard deviation of 15N analyses of plant material at natural abundance was ±1 ‰. This is accurate enough for all 15N studies except those using natural abundance and possibly long term studies of soil organic matter. Recovery of 14C in test samples was 100%. The instrument can be operated by graduate students under supervision and operating costs are primarily for sample cups, combustion catalyst and quartz tubes.Item Open Access Continuous flow isotope ratio mass spectrometry of carbon dioxide trapped as strontium carbonate(Colorado State University. Libraries, 1997) Paul, Eldor A., author; Porter, L. K., author; Harris, D., author; Marcel Dekker, Inc., publisherThe isotopic signal provided by differential discrimination against atmospheric carbon dioxide (13CO2) by C3 and C4 plant photosynthetic pathways is being widely used to study the processes of carbon (C) fixation, soil organic matter formation, and mineralization in nature. These studies have been facilitated by the availability of automated C and nitrogen (N) combustion analyzers (ANCA) combined with continuous flow isotope ratio mass spectrometers (CFIRMS). Analysis of 13CO2 in these instruments requires consistent sample mass for best precision, a requirement that is easily satisfied for soil and tissue samples by adjusting sample weight. Consistent CO2 sample size is much more difficult to achieve using gas handling systems for samples of headspace gases when CO2 concentrations vary widely. Long storage of gaseous samples also is difficult. Extended respiration studies are most easily conducted by trapping CO2 in alkali and conversion to an insoluble carbonate. Thermal decomposition of the carbonate in an on-line ANCA allows consistent and optimal CO2 sample mass to be obtained. The use of precipitated carbonates also facilitates storage of samples and enables full automation of sample analysis using an ANCA interfaced to a CFIRMS. Calcium (Ca), strontium (Sr), and barium (Ba) carbonates were tested. Strontium carbonate (SrCO3) with the addition of vanadium pentoxide (V2O5) as a combustion catalyst was found most suitable.Item Open Access Carbon flow in plant microbial associations(Colorado State University. Libraries, 1981-07-24) Kucey, R. M. N., author; Paul, Eldor A., author; American Association for the Advancement of Science, publisherMeasurement of the distribution of the photosynthesis product in the symbiotic association of a legume, a mycorrhizal fungus, and nitrogen-fixing bacteria showed that the fungus incorporated 1 percent of the photosynthesis product and respired 3 percent. The nodules of a 5-week-old plant utilized 7 to 12 percent of the photosynthesis product. The legume compensated in part for the needs of its microbial partners through increased rates of photosynthesis.Item Open Access Evaluation of carbon accrual in afforested agricultural soils(Colorado State University. Libraries, 2007-06) Morris, Sherri J., author; Haile-Mariam, Shawel, author; Bohm, Sven, author; Paul, Eldor A., author; Blackwell Publishing Ltd., publisherAfforestation of agricultural lands can provide economically and environmentally realistic C storage to mitigate for elevated CO2 until other actions such as reduced fossil fuel use can be taken. Soil carbon sequestration following afforestation of agricultural land ranges from losses to substantial annual gains. The present understanding of the controlling factors is inadequate for understanding ecosystem dynamics, modeling global change and for policy decision-makers. Our study found that planting agricultural soils to deciduous forests resulted in ecosystem C accumulations of 2.4 Mg C ha-1 yr-1 and soil accumulations of 0.35 Mg C ha-1 yr-1. Planting to conifers showed an average ecosystem sequestration of 2.5 and 0.26 Mg C ha-1 yr-1 in the soils but showed greater field to field variability than when planted to deciduous forest. Path analysis showed that Ca was positively related to soil C accumulations for both conifers and deciduous afforested sites and played a significant role in soil C accumulations in these sites. Soil N increases were closely related to C accumulation and were two times greater than could be explained by system N inputs from atmospheric deposition and natural sources. Our results suggest that the addition of Ca to afforested sites, especially conifers, may be an economical means to enhance soil C sequestration even if it does not result in increasing C in aboveground pools. The mechanism of N accumulation in these aggrading stands needs further investigation.Item Open Access Acid hydrolysis of easily dispersed and microaggregate-derived silt- and clay-sized fractions to isolate resistant soil organic matter(Colorado State University. Libraries, 2006-08) Conant, R. T., author; Paustian, K., author; Paul, Eldor A., author; Plante, A. F., author; Six, J., author; British Society of Soil Science, publisherThe current paradigm in soil organic matter (SOM) dynamics is that the proportion of biologically resistant SOM will increase when total SOM decreases. Recently, several studies have focused on identifying functional pools of resistant SOM consistent with expected behaviours. Our objective was to combine physical and chemical approaches to isolate and quantify biologically resistant SOM by applying acid hydrolysis treatments to physically isolated silt- and clay-sized soil fractions. Microaggegrate-derived and easily dispersed silt- and clay-sized fractions were isolated from surface soil samples collected from six long-term agricultural experiment sites across North America. These fractions were hydrolysed to quantify the non-hydrolysable fraction, which was hypothesized to represent a functional pool of resistant SOM. Organic C and total N concentrations in the four isolated fractions decreased in the order: native > no-till > conventional-till at all sites. Concentrations of non-hydrolysable C (NHC) and N (NHN) were strongly correlated with initial concentrations, and C hydrolysability was found to be invariant with management treatment. Organic C was less hydrolysable than N, and overall, resistance to acid hydrolysis was greater in the silt-sized fractions compared with the clay-sized fractions. The acid hydrolysis results are inconsistent with the current behaviour of increasing recalcitrance with decreasing SOM content: while %NHN was greater in cultivated soils compared with their native analogues, %NHC did not increase with decreasing total organic C concentrations. The analyses revealed an interaction between biochemical and physical protection mechanisms that acts to preserve SOM in fine mineral fractions, but the inconsistency of the pool size with expected behaviour remains to be fully explained.