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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Open Access
A comparison of humic fractions of Chernozemic and Luvisolic soils by elemental analyses, UV and ESR spectroscopy
(Colorado State University. Libraries, 1974-11) Paul, E. A., author; Anderson, D. W., author; Russell, D. B., author; St. Arnaud, R. J., author; Agricultural Institute of Canada, publisher
The Ah horizons of a Brown–Dark Brown–Black–Dark Gray–Gray Luvisolic sequence of Canadian grassland and forest soils were studied. Clay-associated humus was present in greater proportions in the grassland than in forest soils, particularly in the grassland soils of the more arid regions. Amounts of alkali-pyrophosphate-extractable humus increased in the Brown to Gray Luvisolic sequence. Alkali-pyrophosphate-extractable humic acid (HA-A) contents were greatest in the Black and Dark Gray soils. C:H ratios, extinction coefficients at 280 nm (E280), and resistance to acid hydrolysis of the HA-A and clay-associated HA-B increased in the Brown to Gray Luvisolic sequence. Free radical concentrations were least for the Brown and Dark Brown soils, moderate for the Black and greatest for the Gray Luvisolic soils. The data suggest an increase in the proportion of aromatic components in the humic acids in going from the Brown to the Gray Luvisolic soils. An objective, multivariate similarity analysis based on 22 humus characteristics showed a relationship between soil zone or soil environment and the nature of the soil's humus.
Open Access
Control of the protein content of Thatcher wheat by nitrogen fertilization and moisture stress
(Colorado State University. Libraries, 1966-06) Hutcheon, W. L., author; Paul, Eldor A., author; Agricultural Institute of Canada, publisher
Experiments are reported in which it was shown that the protein content of spring wheat, grown in the growth chamber, could be effectively controlled by nitrogen supply and soil moisture stress. Protein contents above 16% were obtained only where yields were below the maximum attainable. In the protein range from 11 to 16%, it was possible to increase both protein and yields concurrently; protein contents higher than 16% were realized only where a growth factor such as moisture was below optimum for maximum yields. Moderate moisture stresses resulted in maximum efficiency of water use by the crop. High levels of nitrogen had more influence on the growth of straw than grain; the straw/grain ratio widened with increasing increments of nitrogen.
Open Access
Decomposition of 14C-labelled plant material under field conditions
(Colorado State University. Libraries, 1973-08) Paul, E. A., author; Shields, J. A., author; Agricultural Institute of Canada, publisher
Mature, uniformly labelled (14C, 15N), chopped, wheat straw incorporated in the plow layer of a Brown Chernozemic soil and a Gray Wooded soil was allowed to decompose in the field. Labelled grass material (14C) was added to the surface of an adjacent virgin Brown Chernozemic soil. After 4 yr of normal cropping practices, one-fifth of the C of added straw remained in the Brown soil and one-sixth in the Gray Wooded. The initial decomposition rate of straw was retarded in plots under wheat as compared with those under fallow. Decomposition of labelled grass was initially dependent on sufficient rainfall to compress it to the soil surface. When winter periods are excluded from the time scale, the half-life of resistant straw components or soil organic matter derived from the straw was equivalent to 24 mo in Gray Wooded soil and 48 mo in Brown soil. Resistant grass material decomposed more slowly with a half-life of 96 growing mo. Distribution of labelled C among the various fractions of soil organic matter after different periods of time was investigated. The rapid decline of labelled straw from the fraction that floated in water, the high specific activity of fulvic acid, coupled with fluctuations in humic acid and the fraction <0.04 μ suggested a higher degree of biological activity in the Gray Wooded soil. In the Brown soil, the major transfer of labelled C was from the floated fraction to the humin (>0.2 μ) suggesting that the rate of decomposition was controlled to a greater extent by abiotic factors.
Open Access
Decomposition of wheat straw and stabilization of microbial products
(Colorado State University. Libraries, 1989-02) Voroney, R. P., author; Anderson, D. W., author; Paul, E. A., author; Agricultural Institute of Canada, publisher
This research examined the effects of soil environment on the decomposition of cereal crop residues and stabilization of microbial products in the field. Microplots at semi-arid and subhumid field sites were amended with 14C-, 15N-labelled wheat straw and with 14C-labelled glucose plus 15N-labelled NH4NO3 and the fate of the residual C and N was monitored over 10 yr. Mineralization of C and N derived from wheat straw was greater at the site in the more moist environment in the short term (2 yr). In the long term (up to 10 yr), however, the residual C and N at this site decayed at a slightly slower rate, providing evidence of stabilization of organic material in chemically resistant forms, as compared to possible physical protection in the semi-arid clay-textured soil. The total recovery of labelled N was 22.5–24% in the harvested crops with 13.4–16% remaining in the surface soil by the end of the study. Mineralized labelled organic N was used with an efficiency ranging from 32 to 51%. However, after summer fallow the crop apparently used mineralized labelled N with an efficiency of only 7%. This study showed that moistness of the soil environment has a considerable effect on residue decomposition. Stabilization of humic material derived from residues relates more to the recalcitrance of microbial products and their interactions with soil mineral colloids than to the nature of the original residue.
Open Access
Defining a realistic control for the chloroform fumigation-incubation method using microscopic counting and 14C-substrates
(Colorado State University. Libraries, 1996-11) Harris, David, author; Horwath, William R., author; Paul, Eldor A., author; Horton, Kenneth A., author; Jagger, Leslie, author; Norton, Jeannette, author; Agricultural Institute of Canada, publisher
Chloroform fumigation-incubation (CFI) has made possible the extensive characterization of soil microbial biomass carbon (C) (MBC). Defining the non-microbial C mineralized in soils following fumigation remains the major limitation of CFI. The mineralization of non-microbial C during CFI was examined by adding 14C-maize to soil before incubation. The decomposition of the 14C-maize during a 10-d incubation after fumigation was 22.5% that in non-fumigated control soils. Re-inoculation of the fumigated soil raised 14C-maize decomposition to 77% that of the unfumigated control. A method was developed which varies the proportion of mineralized C from the unfumigated soil (UFc) that is subtracted in calculating CFI biomasss C. The proportion subtracted (P) varies according to a linear function of the ratio of C mineralized in the fumigated (Fc) and unfumigated samples (Fc/UFc) with two parameters K1 and K2 (P = K1Fc/UFc) + K2). These parameters were estimated by regression of CFI biomass C, calculated according to the equation MBC = (Fc − PUFc)/0.41, against that derived by direct microscopy in a series of California soils. Parameter values which gave the best estimate of microscopic biomass from the fumigation data were K1 = 0.29 and K2 = 0.23 (R2 = 0.87). Substituting these parameter values, the equation can be simplified to MBC = 1.73Fc − 0.56UFc. The equation was applied to other CFI data to determine its effect on the measurement of MBC. The use of this approach corrected data that were previously difficult to interpret and helped to reveal temporal trends and changes in MBC associated with soil depth.
Open Access
Effect of carbon additions on soil labile inorganic, organic and microbially held phosphate
(Colorado State University. Libraries, 1979-11) Chauhan, B. S., author; Stewart, J. W. B., author; Paul, E. A., author; Agricultural Institute of Canada, publisher
Investigations of the rate of P movement between soil inorganic, organic and biomass P compartments were carried out to clarify aspects of P cycling in soil systems. Organic carbon, as dried grass (33% C, 0.11% P) and cellulose (43% C), was added at a rate equivalent to 4000 kg organic material (OM)∙ha−1 every 30 days for 9 mo to the Ap horizon of a Chernozemic Black soil kept at field capacity moisture content and 24 ± 2 °C. In a third treatment, cellulose was added at the same rate with P (20 kg∙ha−1) at KH2PO4. Approximately 39% and 22% of the P added in grass and with cellulose, respectively, was found in organic P forms after 9 mo incubation. The remainder was found in NH4Cl-, NH4F- and NaOH-NaCl-extractable P forms which constituted part of the labile inorganic P pool and could be extracted by an anion exchange resin. Increases of biomass P during the first 4 or 5 days of each incubation period after residue addition were found to average 12 μg P∙g−1 in the first 3 mo incubation period. After this period, there was a smaller response in microbial P attributable to additions of grass or cellulose.
Open Access
Effect of moisture, temperature, and nitrogen on yield and protein quality of Thatcher wheat
(Colorado State University. Libraries, 1966-04-28) Paul, E. A., author; Sosulski, F. W., author; Lin, D. M., author; Agricultural Institute of Canada, publisher
Soil moisture level was the most important factor controlling plant and grain yields while nitrogen fertilizer had the greatest influence on protein content and sedimentation value. Lower temperatures and nitrogen fertilization favored plant development at medium and high soil moisture levels but did not significantly alter the yield of plants subjected to periodic moisture stress. Temperature was the only treatment to have a consistent effect on kernel weight. However, seed yields were more closely associated with total plant weight and number of culms than kernel size. The sedimentation values of the flour, which ranged from 33.8 to 70.7 ml, were highly correlated with protein content. The wide range of sedimentation values approached the maximum range reported for very weak and very strong wheats. Within treatments receiving the same nitrogen applications, the sedimentation values and protein content were inversely related to grain yield. Variations in glutamic acid and proline content of the hydrolyzed flour proteins were positively associated with protein content and sedimentation value. Amino acids which were negatively correlated with protein content included alanine, arginine, aspartic acid, cystine, glycine, and lysine. Contrary to previous reports the lysine content varied over the complete range of protein content in the flours. The significance of these variations in amino acid composition are discussed in relation to recent studies on the fractionation of flour proteins.
Open Access
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.
Open Access
Effect of soil moisture stress on uptake and recovery of tagged nitrogen by wheat
(Colorado State University. Libraries, 1971-02) Paul, E. A., author; Myers, R. J. K., author; Agricultural Institute of Canada, publisher
Labelled 15NH4NO3 was used in a growth chamber to study the effect of moisture stress on the utilization of nitrogen by wheat. This made it possible to determine the recovery of nitrogen (N) in the soil-plant system of two Chernozemic soils. Moisture stress effects were less evident in a clay soil than in a loam. Approximately 55% of the N utilized by the growing plants came from organic soil-N mineralized during the growing period. From 59 to 71% of the initial fertilizer plus soil mineral-N was utilized by the plants. Twenty to 36% remained in the soil, and 1 to 17% was lost. Losses were greatest in soils exposed to high moisture stress and were related to the residual NO3-N levels in the soil. They were attributed to denitrification. Immobilization of N was highest at low moisture stress where plant growth was the greatest, but mineralization was unaffected by the moisture stress applied. It was estimated that 5.0 to 6.2 kg N were required to produce 100 kg of wheat, the highest efficiency of N utilization being obtained at low soil moisture stress.
Open Access
Effects of cultivation on the organic matter of grassland soils as determined by fractionation and radiocarbon dating
(Colorado State University. Libraries, 1974-11) Martel, Y. A., author; Paul, Eldor A., author; Agricultural Institute of Canada, publisher
The effects of cultivation on the net mineralization of carbon and nitrogen in a lacustrine Brown clay (Sceptre) and two Orthic Black soils on glacial till (Oxbow) were assessed with the aid of fractionation and radiocarbon dating techniques. Fractionation of the soil organic matter of comparative virgin and cultivated soils by acid hydrolysis and peptization in dilute NaOH showed that the distribution of carbon and nitrogen among fractions of these soils was similar. There was no measurable alteration in the mean residence time (MRT) of the soil during the first 15 to 20 yr of cultivation, during which time the Sceptre soil had lost 19% of its carbon and the Oxbow, 35%. However, the MRT increased from 250 yr before present (BP) to 710 years BP after 60 yr of cultivation of the Oxbow soil. The losses for nitrogen were 10% lower than for carbon in the Oxbow soil due to the recycling of nitrogen in the soil. The rate of loss of carbon from the Oxbow soil during the cultivation period was simulated by expressing it as the sum of two first order reactions using fractionation and carbon dating data as the variables.
Open Access
Effects of fertilizer N and soil moisture on mineralization, N recovery and A-values, under spring wheat grown in small lysimeters
(Colorado State University. Libraries, 1978-02) Paul, E. A., author; Campbell, C. A., author; Agricultural Institute of Canada, publisher
The influence of rate of fertilizer N and soil moisture on N uptake by spring wheat, N mineralization, A-values and N recovery was determined in small lysimeters on stubble land by means of 15N-labelled KNO3. Net mineralization was enhanced by frequent irrigations but depressed by cropping. In contrast to most growth chamber results, N uptake was not linearly but logarithmically related to rate of application; uptake from fertilizer was positively related to rate, but only up to a point beyond which it levelled off; uptake from native soil N was generally negatively related to rate; A-values were not constant but negatively related to rate except at the highest rates (123–164 kg N/ha) when they were positively related especially under dry conditions. These differences in results were credited to the fact that the pot system does not adequately simulate the field situation. On dryland an average of 68, 20 and 12% of the plant N was located in the grain, straw and roots, respectively; under irrigation the corresponding values were 75, 16 and 9%. Average recovery of fertilizer N on dryland was: soil 34.6%, grain 37.3%, straw 12.2%, roots 2.6%, error 6.0%, and unaccounted 7%; under irrigation it was 15.4, 58.3, 13.0, 3.5, 6.0 and 4.0%, respectively. On dryland about 28% of the fertilizer N was left in the soil at rates up to 82 kg N/ha, while 57% was left at 164 kg N/ha; under irrigation the corresponding values were 15 and 21%, respectively. On dryland > 70% of the residual N was located in the 0- to 30-cm soil segment at fertilizer rates < 82 kg N/ha; at higher rates > 50% was in the 30- to 60-cm segment. Only at 164 kg N/ha was there appreciable residual N in the 30- to 60-cm segment under irrigation. There was negligible fertilizer N below 60 cm in all treatments.
Open Access
Effects of vesicular-arbuscular mycorrhiza on 14C and 15N distribution in nodulated fababeans
(Colorado State University. Libraries, 1980-05) Paul, Eldor A., author; Pang, P. C., author; Agricultural Institute of Canada, publisher
A two-compartment growth chamber in which the aboveground plant materials were exposed to 14CO2 and the belowground portion was exposed to 15N2 under normal atmospheric pressure was designed for carbon and nitrogen transfer studies. Vicia faba infected with vesicular-arbuscular fungus Glomus mossae and non-mycorrhizal plants fixed similar quantities of N2 at an age of 6½ wk. Approximately 0.10 mg N was fixed ∙ g−1 dry plant materials ∙ day−1 and 40 mg C • g−1 dry matter day−1 were synthesized by mycorrhizal and non-mycorrhizal fababeans during 48 h exposure to 14CO2 at 6½ wk with no apparent difference in yield of dry matter. The non-mycorrhizal plants transferred 37% of the fixed 14C beneath ground. The mycorrhizal ones transferred 47% of the fixed 14C beneath ground. Most of the difference could be accounted for in the belowground respiration. The 14CO2 produced by root-microbial systems of the mycorrhizal fababeans was twice as great as that of the nonmycorrhizal; both contained active rhizobium.
Open Access
Extraction and charaterization of humus with reference to clay-associated humus
(Colorado State University. Libraries, 1974-08) Anderson, D. W., author; Paul, E. A., author; St. Arnaud, R. J., author; Agricultural Institute of Canada, publisher
An extraction-fractionation method was developed with which it is possible to isolate 60–67% of the humus of Chernozemic and Luvisolic soils. Two humic acid fractions were obtained: (1) a conventional alkali-pyrophosphate extractable HA-A; (2) a clay-associated HA-B fraction isolated after ultrasonic dispersion, in water, of the residue of the alkali-pyrophosphate extraction. As compared to the HA-A, the HA-B fractions had lower C contents but greater N contents, narrower C:H ratios, higher molecular weights, and less resistance to hydrolysis in 6 N HCl. It was concluded that the HA-B is a weakly humified, potentially labile humic constituent stabilized by adsorption to clay. Spectral measurements on low-ash (< 2 %) humic acids showed a positive correlation between extinction coefficient at 280 nm (E280) and C:H ratio, and negative correlations between E280 and percent of hydrolyzable C and N. The E4:E6 ratio was related to molecular weight, as determined by agar gel filtration, increasing with decrease in molecular weight.
Open Access
Fractionation of soil and 15N nitrogen to separate the organic and clay interactions of immobilized N
(Colorado State University. Libraries, 1976-08) McGill, W. B., author; Paul, Eldor A., author; Agricultural Institute of Canada, publisher
Labelled 15N was added to two soils in cylinders in the field, and allowed to equilibrate for two summers of crop growth. The labelled soils were fractionated to provide information on the effect of organic and inorganic colloids on the stabilization of immobilized, 15N. Organic materials removed by 0.5 N NaOH without pretreatment contained more 15N than those extracted by the same reagent following decalcification and removal of sesquioxides with dithionite and HCl. Both extracts had similar amino acid (contents) and similar degrees of hydrolability. A fractionation system using an initial 0.1 M NaOH–0.1 M Na4P2O7 extraction followed by sonication and peptization in H2O yielded a humic acid fraction and a sedimentation fraction (< 0.04 μm) which differed markedly in degree of hydrolyzability, 15N content and amino acid-N content. The N associated with inorganic colloids < 0.04 μm, and that remaining in solution after the removal of larger particles accounted for 50% of the amino acid-N in a clay soil, and 40% in a fine sandy loam soil. Removal of sesquioxides followed by a second 0.5 N NaOH extraction reduced the N content of the colloidal size fractions of both soils, indicating that amorphous iron and aluminum compounds on the surface of clays are probably the active agents in bonding organic N to inorganic colloids. It is suggested that the nonhydrolytic technique, based largely on dispersion of the inorganic–organic colloids and analyses of the sediment, could be used to interpret the fate of microbiologically immobilized N compounds in the soil. Materials removed by 0.1 M Na4P2O7 were associated with polyvalent cations in the soil. Materials such as cytoplasmic constituents, released from the biomass during ultrasonic vibration or as lytic products would be expected to be adsorbed to inorganic colloids. They should be concentrated in the < 0.04 μm-size fraction. Cell wall and other particulate debris with a faster setting velocity would be expected to appear in larger-sized sedimentation fractions.
Open Access
Gaseous nitrogen losses from cropped and summer-fallowed soils
(Colorado State University. Libraries, 1982-02) Aulakh, M. S., author; Rennie, D. A., author; Paul, E. A., author; Agricultural Institute of Canada, publisher
A study designed to assess gaseous losses of N as N2O and N2 from soils of conventional till fields seeded to wheat in the Chernozemic soil region of Saskatchewan, together with limited supporting laboratory investigations, has confirmed that for the May-November period losses were in the vicinity of 3 kg N∙ha−1 or less. In contrast, total losses from a summer-fallowed field were approximately 300% higher. Comparisons at one site were made of N losses from a conventionally tilled and zero-tilled Dark Brown Chernozemic soil seeded to wheat; the total losses of N were twice as high for the zero till as the conventional till treatments. The N2O fluxes were shown to be the result of both reductive (denitrification) and oxidative (nitrification) processes and generally, under the conditions of these field experiments, both occurred simultaneously. This experiment also confirmed that C2H2 inhibited nitrification in a manner very similar to N-serve, a well-known nitrification inhibitor.
Open Access
Measurement of microbial biomass N:C by chloroform fumigation-incubation
(Colorado State University. Libraries, 1997-11) Harris, D., author; Voroney, R. P., author; Paul, Eldor A., author; Agricultural Institute of Canada, publisher
We present a calculation for soil microbial biomass N:C ratio determined from a 10-d incubation following chloroform fumigation. The calculation is based on a mathematical model of the N content of the pre- and post-fumigation soil microbial biomass and the growth yield of the biomass that develops after fumigation. Biomass N is calculated from the N:C ratio and biomass C. The mineralization of bacteria and fungi, with different N contents, added to fumigated soils was used to establish the model parameters. The model was tested against an independent set of measurements and considers two assumptions: 1) The ratio of N:C mineralized from killed biomass is equal to the ratio of N:C mineralized from soil non-biomass constituents. 2) More realistically, the N and C mineralization in the fumigated soil, from sources other than killed biomass, is a residual fraction of the N and C mineralization in the unfumigated soil. Biomass C:N ratios calculated without a control correction (assumption 1) were, on average, 20% wider than corrected values (assumption 2). Biomass N calculated as the product of N:C and biomass C was compared with published values for several data sets. The new calculation method was robust even when net immobilization of N followed fumigation.
Open Access
Measurement of soil color
(Colorado State University. Libraries, 1966-02) Paul, E. A., author; Shields, J. A., author; St. Arnaud, R. J., author; Clayton, J. S., author; Agricultural Institute of Canada, publisher
The color of cultivated surface samples from Chernozemic and Gray Wooded soils were measured by visual and spectroreflectance methods. Variations in visual color measurements among different observers were of sufficient magnitude to represent serious errors in the application of the soil color criteria outlined in the Canadian soil classification system. Spectroreflectance measurements facilitated the accurate measurement and characterization of the Munsell renotations of Chernozemic and Gray Wooded soils sampled within their respective soil zones. The ratio of renotation value: renotation chroma of the Chernozemic samples (air-dry) were distinctly lower than those of the Gray Wooded samples. The presence of moisture caused a greater decrease in the renotation value of the Gray Wooded samples than it did in the Chernozemic samples. The renotation hue of most of the measured samples occurred midway between the 10YR and 2.5Y hue charts currently available in the Munsell soil color chart series. Color measurement of cultivated surface soil samples taken within the various soil zones of Saskatchewan indicated discrepancies between their renotation values and the color criteria currently suggested by the National Soil Survey Committee of Canada for the respective soils at the Order and Great Group levels.
Open Access
Measurement of the polysaccharide content of soils
(Colorado State University. Libraries, 1963-01) Acton, C. J., author; Paul, E. A., author; Rennie, D. A., author; Agricultural Institute of Canada, publisher
The polysaccharide content of two soils, measured by precipitating and weighing the microbial gums from the fulvic acid fraction of soil organic matter, and by colorimetric analyses using anthrone, was increased appreciably during the incubation of samples with straw. Applications of nitrogen and phosphorus altered only slightly the amount of polysaccharides present. The polysaccharide content of the amended soils increased rapidly during the first week of incubation and then levelled off. Peptization of the soil with dilute alkali prior to acid hydrolysis substantially increased the carbohydrates measured with anthrone. The anthrone reagent which measures primarily hexoses indicated a soil carbohydrate content of 10–15 per cent occurring in a range of Saskatchewan soils. Thirty-five per cent more carbohydrate carbon was found using the less specific phenol-sulphuric acid reagent. The acetone precipitated fraction from the fulvic acids accounted for only 10 per cent of the soil carbohydrates and contained a large proportion of ash and other non-carbohydrate materials. The total acid-soluble base-soluble fraction, fulvic acids, contained 15–25 per cent; the remainder was distributed in the alkali insoluble humin — 55–70 per cent and the humic acid fraction 4–12 per cent.
Open Access
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.
Open Access
Nitrate ion electrode method for soil nitrate nitrogen determination
(Colorado State University. Libraries, 1968-10) Paul, Eldor A., author; Myers, R. J. K., author; Agricultural Institute of Canada, publisher