Faculty Publications

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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, author
Two-page summary of findings of a social network study to explore conservation practices among farmers in Iowa.
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, author
Iowa'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.
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, publisher
The 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.
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, publisher
Nitrate (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.
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, publisher
With 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).
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, publisher
This 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.
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, publisher
The 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.
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], publisher
Soil 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.
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], publisher
The 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.
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, publisher
A 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.
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, publisher
Agriculture 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.
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., publisher
An 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.
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, publisher
Measurement 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.
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., publisher
The 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.
Open Access
Comparisons between P-fertilized and mycorrhizal plants
(Colorado State University. Libraries, 1986-01) Paul, Eldor A., author; Bethlenfalvay, G. J., author; Pacovsky, R. S., author; Crop Science Society of America, publisher
In experimentation with vesicular-arbuscular mycorrhizal (VAM) fungi, the availability of non-VAM control plants of equal size to VAM plants is a fundamental requirement. The purpose of this work was to determine nutrient regimes needed to achieve growth equivalence between VAM and non-VAM plants. Soybean [Glycine max (L.)Merr.] cv. Amsoy 71 and sorghum [Sorghum bicolor (L.) Moench] cv. Bok 8 plants were grown under controlled conditions in a soil (Josephine silty clay loam, mesic Typic Haploxerult) low in plant-available P. Soybeans were inoculated with one of four species and sorghum with one of two species of VAM fungi. Non-inoculated control plants received nutrient solutions that contained 0.0, 0.2, 0.4, or 1.0 mM P. while the growth of P-supplemented controls may be equivalent to VAM plants, an important question remains: Are these plants also equivalent in terms of such functional parameters as leaf development, dry matter partitioning, and nutrient assimilation? The objective of this experiment was to answer these questions. The response to VAM colonization was similar in both hosts, although less extensive colonization was observed in sorghum. Dry weight, leaf area, and P content increased exponentially with nutrient solution P level. Plants colonized with VAM fungi grew 3 to 6 times larger than the P-free controls but attained only 35 to 65% of maximum growth possible with high fertilizer P input. Host response to VAM colonization was equivalent to that of plants receiving between 0.12 and 0.22 mM P for phytomass, leaf area, and N content. Mycorrhizal plants contained less P, Mn, and root Fe but more Zn and Cu than comparable plants fertilized with P. It was concluded that P-treated, non-VAM plants differed physiologically and anatomically from VAM plants of equivalent size grown under P stress. It may therefore be necessary to establish the comparability of VAM plants and of "VAM-equivalent controls" separately for each plant parameter of interest. Even then, differential growth responses in VAM-host associations may prevent complete comparability between VAM and P-fertilized plants.
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, publisher
The 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.
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., publisher
Afforestation 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.
Open Access
Soil organic carbon pool changes following land-use conversions
(Colorado State University. Libraries, 2004-07) Paustian, Keith, author; Paul, Eldor A., author; Morris, Sherri J., author; Merck, Roel, author; Six, Johan, author; DeGryze, Steven, author; Blackwell Publishing Ltd., publisher
Carbon (C) can be sequestered in the mineral soil after the conversion of intensively cropped agricultural fields to more extensive land uses such as afforested and natural succession ecosystems. Three land-use treatments from the long-term ecological research site at Kellogg biological station in Michigan were compared with a nearby deciduous forest. Treatments included a conventionally tilled cropland, a former cropland afforested with poplar for 10 years and an old field (10 years) succession. We used soil aggregate and soil organic matter fractionation techniques to isolate C pools that (1) have a high potential for C storage and (2) accumulate C at a fast rate during afforestation or succession. These fractions could serve as sensitive indicators for the total change in C content due to land-use changes. At the mineral soil surface (0–7 cm), afforesting significantly increased soil aggregation to levels similar to native forest. However, surface soil (0–7 cm) C did not follow this trend: soil C of the native forest site (22.9 t C ha-1) was still significantly greater than the afforested (12.6 t C ha-1) and succession (15.4 t C ha-1) treatments. However, when the 0–50 cm soil layer was considered, no differences in total soil C were observed between the cropland and the poplar afforested system, while the successional system increased total soil C (0–50 cm) at a rate of 0.786 t C ha-1 yr-1. Afforested soils sequestered C mainly in the fine intra-aggregate particulate organic matter (POM) (53–250 μm), whereas the successional soils sequestered C preferentially in the mineral-associated organic matter and fine intra-aggregate POM C pools.
Open Access
The microbial efficiency-matrix stabilization (MEMS) framework integrates plant litter decomposition with soil organic matter stabilization: do labile plant inputs form stable soil organic matter?
(Colorado State University. Libraries, 2013-04) Wallenstein, Matthew D., author; Denef, Karolien, author; Boot, Claudia M., author; Cotrufo, M. Francesca, author; Paul, Eldor A., author; Blackwell Publishing Ltd., publisher
The decomposition and transformation of above- and below-ground plant detritus (litter) is the main process by which soil organic matter (SOM) is formed. Yet, research on litter decay and SOM formation has been largely uncoupled, failing to provide an effective nexus between these two fundamental processes for carbon (C) and nitrogen (N) cycling and storage. We present the current understanding of the importance of microbial substrate use efficiency and C and N allocation in controlling the proportion of plant-derived C and N that is incorporated into SOM, and of soil matrix interactions in controlling SOM stabilization. We synthesize this understanding into the Microbial Efficiency-Matrix Stabilization (MEMS) framework. This framework leads to the hypothesis that labile plant constituents are the dominant source of microbial products, relative to input rates, because they are utilized more efficiently by microbes. These microbial products of decomposition would thus become the main precursors of stable SOM by promoting aggregation and through strong chemical bonding to the mineral soil matrix.
Open Access
Leaching and mass balance of 15N-labeled urea applied to a Kentucky bluegrass turf
(Colorado State University. Libraries, 1996-11) Rieke, P. E., author; Paul, Eldor A., author; Branham, B. E., author; Miltner, E. D., author; Crop Science Society of America, publisher
The fate of urea applied to Kentucky bluegrass (Poa pratensis L.) turf was studied over a 2-yr period using a combination of intact monolith lysimeters and small plots. Soil type was a Marlette fine sandy loam (fine-loamy, mixed mesic Glossoboric Hapludalfs). Urea was applied at a rate of 196 kg N ha−1 yr−1 in five equal applications of 39.2 kg N ha−1, using two application schedules. Treatments were fertilized at approximately 38-d intervals with the "Spring" treatment fertilized from late April through late September and the "Fall" treatment from early June through early November. In 1991 only, the April and November applications used 15N-labeled urea (LFN). For the Spring treatment, 31% of LFN was recovered from thatch at 18 DAT. This value remained constant for the next year, then gradually declined to 20% after 2 yr. Only 8% of the LFN was recovered from soil at 18 DAT and increased to only 20% 2 year after application. Approximately 35% of the LFN was harvested in clippings over 2 yr. Through May 1993 (748 DAT), LFN in leachate totaled 0.18% of the amount applied. For the Fall treatment, 62% of the LFN was recovered from thatch at 18 DAT. This value declined to 35% by the following June. LFN in soil increased from 12% to25% over 2 yr. Approximately 38% of the LFN was harvested in clippings over 2 yr. Total leachate LFN recovery was 0.23% over the 2-yr period. Total recovery of LFN was 64 and 81% for the Spring and Fall treatments, respectively, suggesting volatile losses of N. Whether the N was applied in the spring or late fall, rapid uptake and immobilization of the LFN resulted. A maximum of 25% of applied LFN was recovered in the soil from either application timing at any time over the 2 year of the experiment. A well-maintained turf intercepts and immobilizes LFN quickly making leaching an unlikely avenue of N loss from a turf system.