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Paul (Eldor A.) Collection

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https://hdl.handle.net/10217/100513
This digital collection includes articles by Eldor A. Paul, a Senior Research Scientist at the Natural Resource Ecology Laboratory and a Professor in the Department of Soil and Crop Sciences at Colorado State University, Fort Collins. Eldor has had a lifelong interest in teaching and research in both grassland ecology and agroecosystems, ranging from wheat fields in Canada, through corn-belt rotations in the Great Lakes region of the US, into the afforested systems in California and Colorado.

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Browsing Paul (Eldor A.) Collection by Subject "15N"

Now showing 1 - 5 of 5
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    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.
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    Effect of nitrification inhibitor on N immobilization and release of 15N from nonexchangeable ammonium and microbial biomass
    (Colorado State University. Libraries, 1983-05) Paul, E. A., author; Juma, N. G., author; Agricultural Institute of Canada, publisher
    The disposition of 15N-aqua NH3 and 15N-solution urea in the presence and absence of a nitrification inhibitor [4-amino-1,2,4-triazole (ATC)] was measured under field conditions. ATC caused a 15% greater recovery of fertilizer N in the soil-plant system (95 vs. 80%) but no changes in wheat N uptake (37%). The 0- to 15-cm layer of ATC-treated soils contained 52–55% of the fertilizer N. The same layer of the non-ATC-treated soils contained 28–30%. The recovery of fertilizer N in the soil profile was 55–59% in ATC treatments compared to 40–42% in non-ATC treatments. Five to eight percent of fertilizer N was recovered in the non-exchangeable NH4+ fractions of A horizons of ATC-treated soils compared to ~ 1% in non-ATC treatments. Laboratory incubations and isotopic analysis of the 15N-enriched soil, a Dark Gray Chernozem, showed that the nonexchangeable 15NH4+ was released at rates equivalent to a half-life of 38 wk (k = 0.018 wk−1) at 28 ± 1 °C and soil pore water potential of 34 kPa. Particle size and mineralogical analyses showed that the coarse clay fraction composed of mica, vermiculite and smectites contained 49% of the labeled nonexchangeable NH4+; the coarse silt fraction contained 26% of the labeled nonexchangeable NH4+. After growth of wheat fertilized with NH4OH treated with ATC, the microbial biomass accounted for 41% of the organic 15N remaining in soil. Soil samples from the ATC-treated plots contained almost two times the amount of 15N in the microbial biomass compared to non-ATC treatments; this accounted for 46% of the organic 15N remaining in the soil. The average half-life of microbial biomass 15N was 27.6 wk in all the treatments. Thus, ATC caused a greater immobilization of fertilizer 15N but no change in the rate of release of 15N-microbial biomass. The conserved fertilizer would be slowly released over a long period of time.
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    Fate of legume and fertilizer nitrogen-15 in a long-term cropping systems experiment
    (Colorado State University. Libraries, 1994-09) Janke, Rhonda R., author; Peters, Steven E., author; Paul, Eldor A., author; Hesterman, Oran B., author; Harris, Glendon H., author; American Society of Agronomy, publisher
    Relying more on biological N2 fixation has been suggested as a way to meet one of the major challenges of agricultural sustainability. A 15N study was conducted to compare the fate of applied legume and fertilizer N in a long-term cropping systems experiment. Nitrogen-15-1abeled red clover (Trifolium pratense L.) and (NH4)2SO4 ere applied microplots within the low-input and conventional cropping systems of the Farming Systems Trial at the Rodale Institute Research Center in Pennsylvania. The 15SN was applied to soil and traced into corn (Zea mays L.) in 1987 and 1988. Residual 15SN was also traced into second-year spring barley (Hordeum vulgare L.). Legume and fertilizer 15SN remaining in soil was measured and loss of N was calculated by difference. More fertilizer than legume N was recovered by crops (40 vs. 17% of input), more legume than fertilizer N was retained in soil (47 vs. 17% of input), and similar amounts of N from both sources were lost from the cropping systems (39% of input) over the 2-yr period. More fertilizer than legume N was lost during the year of application (38 vs. 18% of input), but more legume than fertilizer N was lost the year after application (17 vs. 4% of input). Residual fertilizer and legume 15SN was distributed similarly among soil fractions. Soil microbial biomass was larger in the legume-based system. A larger, but not necessarily more active, soil microbial biomass was probably responsible for the greater soil N supplying capacity in the legume-based compared with fertilizer-based system.
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    Injection of nitrogen-15 into trees to study nitrogen cycling in soil
    (Colorado State University. Libraries, 1992-01) Pregitzer, Kurt S., author; Paul, Eldor A., author; Horwath, William R., author; Soil Science Society of America, publisher
    Most 15N dilution techniques disturb either the soil or N-pool size. The objective of this study was to develop a method of labeling the roots of Populus trees with 15N without physically disturbing the soil. Such a method would enable the direct measurement of the flux of 15N from dead roots into the soil organic matter. Leaf and root biomass were labeled by injection of 15N directly into the vessel elements of hybrid Populus trees during their second growing season. The 15N was uniformly distributed throughout the canopy and root system. The rate and amount of 15N turnover from plant tissue can be determined by pool transfer or through differences in plant 15N concentrations. The 15N was detected in the dead-root pool 8 wk after injection, indicating root turnover. Results demonstrate the ability to measure the contribution of fine-root litter to N-cycling processes without disturbing the soil environment.
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    Natural nitrogen-15 abundance of soil and plant samples
    (Colorado State University. Libraries, 1976-02) Rennie, D. A., author; Johns, L. E., author; Paul, E. A., author; Agricultural Institute of Canada, publisher
    Nitrogen isotope analysis of total soil N and soil-derived nitrate for nine selected Chernozemic and Luvisolic Ap horizons showed mean δa15N values based on atmospheric abundance of 8.8. Luvisolic soils were characterized by a relatively low level of the heavier isotope. Isotope enrichment of the total N reached a maximum in the lower B horizon. Subsoil nitrate (180-cm depth) had a δa15N value 1/3 that of the Ap horizon. The δa15N of subsurface soil horizons containing residual fertilizer N were low (−5.2) compared to the surface horizon (7.0). The δa15N of NH4-N in commercial fertilizers is close to that of atmospheric-N whereas the NO3-N has higher values. The data suggest that variations in δ15N abundance between horizons of the same soil, or between different soils, may be of real use in evaluating stresses which have been placed in the nitrogen cycle due to man's activities in the past. Similarly, differences in 15N abundance of soil, legume and air samples may provide an integrated estimation of symbiotic nitrogen fixation under field conditions. More detailed understanding of biological and other processes which control the N isotope concentrations must be obtained before the data reported can be further interpreted.