Published in Soil Sci. Soc. Am. J. 68:612-619 (2004).
© 2004 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
DIVISION S-7—FOREST & RANGE SOILS
Total Soil Nitrogen in the Coarse Fraction and at Depth
Nicol Whitney and
D. Zabowski*
Univ. of Washington, College of Forest Resources, Box 352100, Seattle, WA 98195
* Corresponding author (zabow{at}u.washington.edu).
 |
ABSTRACT
|
|---|
Historically, studies estimating total soil N are based almost exclusively on the 
2-mm soil particles (fine soil fraction), and generally have not included that portion of soil >2-mm (coarse soil fraction) or soil >1-m depth. This study examined the underestimation of the total soil N pool by following traditional or standard soil sampling and analysis. Seventeen varied soil series plus one soil classified to the level of Great Group were sampled from Alaska, Oregon, Puerto Rico, and Washington. Total soil N in each profile was quantified for the soil fine and coarse fractions, as well as for soil depths >1 m. In soils with a coarse fraction, the average percentage of total soil N contained in the coarse soil fraction ranged from 0.3 to 37%, increasing with an increase in coarse soil mass (the highest percentage of N for an individual profile was 67% in a Cryorthent with 92% coarse fragments). For soils with depths >1 m, the percentage of soil N below 1 m relative to the whole profile ranged from 7 to 35%. An average of 0.03% N concentration in the coarse soil fraction was found for all major genetic mineral horizons. Results of this study indicated that up to one-half of the total soil N of a profile would have been missed by the combined exclusion of the coarse fraction and soil below 1-m depth from analysis. The coarse soil fraction may reflect storage and/or potential sources of N not considered in traditional soil N budgets.
Abbreviations: CSM, coarse soil mass • CSNtot, coarse soil total nitrogen • Db, bulk density • Fr, percentage of coarse or fine fraction by weight • FSM, fine soil mass • FSNtot, fine soil total nitrogen • H, horizon thickness • Ncon, total nitrogen concentration • Ntot, total nitrogen
|
INTRODUCTION
|
|---|
NITROGEN CYCLING has been studied using in-depth examinations of sources, sinks, excesses, and deficiencies (Motavalli et al., 1995; Marion et al., 1981; Huntington et al., 1988; Amelung et al., 1998; Schimel and Firestone, 1985; Hackl et al., 2000; Perry et al., 1987; Dodd et al., 2000; Frank et al., 1995; Hart and Sollins, 1998; Ledgard et al., 1998). Historically, however, studies estimating total soil N have focused almost exclusively on the 2-mm soil particles and not included the >2-mm soil fraction. In this paper, soil 2 mm will be referred to as the "fine soil fraction" (including sand, silt, and clay), with soil >2 mm (including gravel, cobbles, and stones) referred to as the "coarse soil fraction." Ugolini et al. (1996) suggested that agricultural soils, which are often free of rock fragments, have received a large amount of attention, and as a result, techniques for soil analysis have been based on the fine soil fraction. While the coarse soil fraction has been evaluated more recently for its physical properties, traditionally it has been considered chemically inert and, therefore, has been discarded after initial sieving (Ugolini et al., 1996; Corti et al., 1998).
There are few researchers who have gone beyond traditional fine soil analysis to explore the potential chemical properties of soil coarse fractions (Ugolini et al., 1996; Corti et al., 1998). In the Vallombrosa Forest near Florence, Italy, Ugolini et al. (1996) studied the mineralogical, physical, and chemical properties of both the fine and coarse soil fractions of three soil profiles, all within the Inceptisol order. Following separation of the fine and coarse soil fractions through wet and dry sieving, the authors found that the coarse soil fraction averaged 20 to 29% of the total soil profile mass and increased with depth (up to 56% in lower soil horizons). Separating the coarse fraction into slightly, medially and highly altered degrees of weathering, they found that with greater weathering there was generally an increase in porosity of the coarse fraction. It is believed that these rock voids allow the infiltration of the soil solution and result in enrichment in such nutrients as C and N. In two of the profiles with rock fragments of higher porosity, total N was actually found to be higher in the coarse fraction than the fine soil fraction. Similar findings were reported in a study by Corti et al. (1998), which included two of the profiles that Ugolini et al. (1996) described above, as well as an additional profile from Italy (Inceptisol), one from France (Inceptisol), and one from Sweden (Spodosol). Both studies suggest that excluding the soil coarse fraction from analysis can result in underestimating total soil N.
Another common practice in soil sampling is to limit soil sampling depth. Many studies report C and/or N quantities to depths <1 m (Cole et al., 1968; Marion et al., 1981; Lamb et al., 1985; Schimel and Firestone, 1985; Perry et al., 1987; Amelung et al., 1998; Hart and Sollins, 1998; Huntington et al., 1988; Motavalli et al., 1995; Hackl et al., 2000; Prichard et al., 2000); few have carried sampling to depths >1 m (Stone et al., 1993; Frank et al., 1995; Ugolini et al., 1996; Corti et al., 1998; Dodd et al., 2000), and with the exception of Ugolini et al. (1996), these studies have included only the fine soil fraction. Sampling performed to depths >1 m increase total nutrient pools. For example, in a study of a northern Great Plains grassland Mollisol, total N for the soil fine fraction of the 0- to 30-cm depth was approximately 76 Mg ha–1 (Frank et al., 1995). The same soil profile sampled to 1.07 m resulted in a total N pool of 144 Mg ha–1, which is almost twice the total N in to the 0- to 30-cm depth. It is suggested then, that further underestimation of soil N pools may occur when soil sampling is limited to a depth <1 m when the actual total soil depth is deeper, as well as when the coarse soil fraction is not analyzed.
When considering the global land area occupied by soils containing a substantial coarse fraction and extending to a depth >1 m, the question arises as to what degree the soil total N pool is underestimated by using traditional soil sampling methods and analysis. The objectives of this study are to both: (i) quantify total soil N in the soil coarse fraction and (ii) quantify soil total N in soil >1 m, over a variety of soil types.
|
MATERIALS AND METHODS
|
|---|
Soil Sampling and Analysis
Seventeen varied soil series, and one soil classified only to the level of Great Group (hereafter referred to as the Cryorthent), from Alaska, Oregon, Puerto Rico, and Washington were chosen for sampling. These soils provide a variety of textures, coarse material quantities, parent materials, climate, and vegetative cover (Table 1). Three representative locations for each series were determined using USDA-NRCS soil surveys, while geologic and topographical maps, climate, and vegetation information were used to locate three sampling sites for the Cryorthent (Fig. 1)
. Thus, a total of 54 soil profiles (n = 3 for each series) were sampled for this study, encompassing all 12 U.S. soil order classifications. The soils ranged from very fine material with no coarse fraction, such as the Sumas silt loam formed in recent alluvium, to soils with >50% coarse material, such as the Alderwood gravelly, ashy, sandy loam formed in glacial till. Climate ranges from tropical to boreal, and includes a variety of vegetation types, such as forest, grassland, shrub-steppe, and agriculture.
View this table:
[in this window]
[in a new window]
|
Table 1. Soil classification, type of vegetation, percentage of coarse soil material, and type of parent material for 18 soil series in Alaska, Oregon, Puerto Rico, and Washington.
|
|
View larger version (19K):
[in this window]
[in a new window]
|
Fig. 1. Locations of 18 soil series sampled throughout Alaska, Oregon, Puerto Rico, and Washington. Each series included three representative profiles for a total of 54 profiles (n = 3 for each series). Series name and profile number are represented by a letter and number designation. For example, the first Athena series profile is labeled At1, the second profile is labeled At2, etc. Map units for each series are listed at the top left. Maps not drawn to scale.
|
|
Soil samples were collected in the field for chemical and physical analyses. At each location, soils pits were dug by hand and sampled by major genetic horizons to the C horizon, or to the lowest possible sampling point up to a depth of 2 m (flooding, cementation, and frozen soil prevented deep sampling in some profiles). Horizons were identified and recorded, along with horizon range and thickness, and profile depth. Photos were also taken of each site and soil profile. A representative volumetric sample of each horizon (up 3000 cm3 depending on horizon depth and size of the coarse fraction) was removed in the field to determine relative quantity of fine and coarse soil fractions. Bulk density (Db) samples were also collected using one of three methods: a soil corer of a known volume, water displacement, or wax coating of soil clods. Water displacement or wax coating of clods was used for horizons containing coarse material, cemented horizons, and the organic horizons of the Seattle. All samples were sealed in plastic bags and kept on ice until returning to the lab where they were refrigerated at 3°C until processing.
The volumetric mineral soil samples were air-dried and separated into coarse and fine soil fractions using hand sieving with a 2-mm sieve and ensuring that all aggregates were broken. Any obvious roots remaining in the sieve were removed and discarded. All fractions were weighed to determine mass and percentage of coarse and fine material of each horizon. Subsamples of the fine fraction were ground for total C and N analysis. Coarse fraction subsamples were passed through a rock grinder (broken, first, with a sledgehammer if too large for the grinder) then finely ground with a mortar and pestle. Total C and N analysis was performed using a PerkinElmer 2400 CHN analyzer (PerkinElmer Corp., Norwalk, CT). Bulk density samples were dried to a constant weight at 105°C for a minimum of 48 h and weighed. Organic horizons were air-dried and, with the exception of the Seattle, were not separated into coarse and fine fractions. These samples were then ground to <0.5 mm using a Wiley mill and analyzed for total C and N as stated above for mineral samples. All data were corrected for moisture content and are reported on an oven-dried basis.
The quantity of total N (Ntot) in each horizon for the coarse fraction and the fine fraction was calculated from horizon thickness (H), Db, percentage of coarse fraction or percentage of fine fraction (Fr), and Ntot concentration for the coarse or fine fraction (Ncon); particle densities of the coarse and fine soil were assumed to be equal:
 | [1] |
Quantities were then summed according to major horizon designations (i.e., Bs1, Bs2, and BC would be summed as B) for the entire profile and for the portion of the profile below 1 m. When calculating Ntot below 1 m, Ntot in horizons found at depths both above and below 1 m (e.g., a Bt1 at a depth of 0.8–1.2 m) were calculated using the proportion of horizon depth below 1 m, and that value was summed with the Ntot of any additional horizons below 1 m. Percentage of coarse soil Ntot (%CSNtot) and percentage of coarse soil mass (%CSM) were calculated for major horizon designations and the entire profile:
 | [2] |
 | [3] |
where CSNtot represents coarse soil Ntot, FSNtot is fine soil Ntot (Mg ha–1), CSM is coarse soil mass (Mg ha–1), and FSM is fine soil mass (Mg ha–1). Percentage of CSNtot and %CSM were each tested for significance from zero (P = 0.05) using the statistical package SPSS (2000) and comparing means with a one-tailed t test.
|
RESULTS AND DISCUSSION
|
|---|
Total Nitrogen and Depth of Profile
With the exception of the Histosol, whole-profile Ntot ranged from 5.3 Mg ha–1 in the Tanana series to 29 and 30 Mg ha–1 in the Sumas and Athena series, respectively (Fig. 2) . The Sumas profiles developed in recent alluvial deposits, and both the Sumas and Athena were under cultivation with histories of N fertilization, which probably contributes to the total N in these soils. For individual horizons, both the Sumas and the Athena contained the largest quantities of A-horizon Ntot, with 20 and 21 Mg ha–1, respectively, constituting approximately 70% of the total profile N. Again, alluvial deposition, cultivation, and N fertilization histories might be factors in the more N-rich A horizons of these soils. Additionally, the Athena is a Mollisol, a soil characterized by humus-rich surface mineral horizons, thus higher Ntot in an A horizon would be expected.
Greater than 50% of the whole-profile Ntot for mineral soil orders was found in the B-horizons of nine soil series. Percentages of Ntot in the B horizons of these profiles ranged from 54% in the Bashaw to 75% in the Bayamon. Both of these series consisted of only A and B horizons, and the Tanana series consisted of O and B horizons, thereby explaining the large percentage of Ntot in the B horizon of these soils. C-horizon Ntot was highest in the Sumas (9.1 Mg ha–1) and the Reilly (5.0 Mg ha–1), both of which developed in alluvial deposits. The high quantity of Ntot in the C horizons of these soils may be the result of flood deposition incorporating organic matter (OM) with alluvium. The Seattle (Histosol) profile Ntot was 38 Mg ha–1, 22 to 86% greater than those series with mineral horizons, showing the potential N storage of an all-OM soil.
Spodosols sampled by Huntington et al. (1988) at the Hubbard Brook Experimental Forest in New Hampshire contained 5.9 Mg ha–1 Ntot in the fine soil fraction sampled to the base of the B horizon. Our Chinkmin series, within the order Spodosol, averaged 3.6 Mg ha–1 Ntot in the fine fraction and 1 Mg ha–1 Ntot in the coarse fraction when calculating Ntot to the base of the B-horizon, totaling 4.6 Mg ha–1. The smaller quantity of Ntot found in our study relative to that of Hubbard Brook might have been due to sampling depth, which averaged 48 cm to the base of the B horizon in the Chinkmin compared with 54 cm at Hubbard Brook. Variations in horizon depths and environmental factors also likely affected total N storage. When soil Ntot was extrapolated to 54 cm for the Chinkmin, the result was 5 Mg ha–1 when both fine soil and coarse soil fractions were totaled. The Hubbard Brook sites were under deciduous and mixed forests, which might have been influenced by OM to a greater degree than the coniferous forest of this study. However, there was often great variability among the replicate profiles of each soil series reported in this paper, therefore, differences found between the Hubbard Brook Spodosol and the Chinkmin of this study are not surprising.
The average sampling depth was >1 m for 13 of the 18 soil series, and the greatest average sampling depth was reached in the Sagehill Series (1.7 m, Fig. 3)
. Average A-horizon thickness was greatest for the Athena (110 cm), of the order Mollisol. Thirteen of the 18 soil series had >50% of their profile depths in the B horizons, ranging from 51% in the Lickskillet to 92% in the Tanana. Nine of the 13 series with the greatest percentages of B-horizon thickness were also those series having the greatest percentage of Ntot in the B horizon. The C horizons were thickest for the Sumas and the Reilly. Orders with the thickest A, B, and C horizons also had the largest quantities and percentages of Ntot for those same A, B, and C horizons. Horizon thickness is used to calculate soil Ntot (1), therefore thicker horizons would result in larger calculations of Ntot. Of the mineral soil profiles with O horizons present, O-horizon thickness was greatest in the Tanana, which is located in central Alaska where temperatures can inhibit decomposers. The Seattle profiles had an average depth of 1.3 m, with Oi, Oe, and Oa horizon thickness averaging 31, 47, and 50 cm, respectively. Despite mapped surveys estimating depths of 6.1 to 15 m for the Seattle profile locations (Rigg, 1958), greater sampling depths during our study were not possible due to shallow water tables.
View larger version (44K):
[in this window]
[in a new window]
|
Fig. 3. Average soil profile depth and horizon thickness sampled for 18 soil series. Thirteen of the 18 series were sampled to a depth >1 m. Percentage of total N found below 1-m depth is shown below each bar.
|
|
In soils deeper than 1 m, total N below 1-m ranged from 0.48 Mg ha–1 in the Jonas to 10.2 Mg ha–1 in the Athena (Fig. 3). It is interesting to note that although the Jonas was lowest in Ntot below 1-m depth, both the Kerby and the Langellain were sampled to an equal or shallower depth (120 and 102 cm, respectively) than the Jonas (120 cm), yet contained more Ntot below 1-m depth with 1.1 Mg ha–1. Of those orders with mineral soil horizons, the percentages of whole-profile Ntot deeper than 1 m ranged from 5.4% found in the Jonas to 35% in the Sagehill, and all were significantly greater than zero at the 0.05 confidence level. Thus of the soils sampled, up to one-third of the soil Ntot would have been missed in this study by sampling to 1 m only, and reports of total soil N in studies that limit sampling to 50 cm could be missing more than half of the total soil N (see Fig. 3). Similar results were found by Stone et al. (1993) who reported an overall average of 40% of total N below 1 m in Florida Spodosols. Dodd et al. (2000) also found approximately 25% of total soil N below 1 m in a Colorado Aridisol.
Fine and Coarse Soil Fractions
Fine soil Ntot was greater than coarse soil Ntot in all soil series (Fig. 4a)
. The Sumas and the Athena had the highest quantity of Ntot among the mineral soils, averaging 29 and 30 Mg ha–1, respectively, while the Tanana was lowest with 5.3 Mg ha–1. Each of these three soil series consisted solely of a fine soil fraction.
View larger version (30K):
[in this window]
[in a new window]
|
Fig. 4. (a) Total soil N (Mg ha–1) by quantity contained in the fine and coarse soil fractions with O horizon N included with the fine soil; (b) Soil mass (Mg ha–1) of fine and coarse soil fractions with mass of O horizons included with the fine soil.
|
|
Total coarse soil N in soil series with mineral coarse soil fractions ranged from 0.02 Mg ha–1 in the Sagehill to 3.2 Mg ha–1 in the Alderwood. The Seattle, a Histosol, averaged 33 Mg ha–1 Ntot for the fine fraction, and 5 Mg ha–1 Ntot for the coarse fraction. As Histosols are characterized by their high organic matter content, it was not surprising that the quantity of Ntot in the Seattle was similar to that found in the fine soil fraction of the Sumas and Athena, and of a greater quantity in the coarse soil fraction (woody material >2 mm) than any other soil series. All other soil orders where multiple series were sampled showed variability in the quantity of Ntot found in the coarse fraction.
Total soil mass of orders with mineral horizons ranged from 4500 Mg ha–1 in the Tanana to 31000 Mg ha–1 in the Athena, which represent the shallowest and one of the deepest soils sampled (Fig. 4b). Fine soil mass was greater than CSM in all soil series that contained a coarse soil fraction, with the exception of the Cryorthent, Alderwood, Chinkmin, and Lickskillet. The Alderwood series had the greatest average CSM, containing 12000 Mg ha–1, while the lowest CSM was found in the Sagehill series with 110 Mg ha–1. Because of its low bulk density, the Seattle, though highest in soil Ntot, was lowest of all soil series in total mass.
Percentage of CSNtot was lower than percentage of CSM of each soil series containing a coarse soil fraction, ranging from 0.3 to 37% of the total soil profile for mineral soils with coarse fragments (Fig. 5)
. The percentage of CSNtot for all soil types examined was significantly different from zero (p = 05) suggesting that excluding the coarse fraction from soil analysis would omit a significant quantity of soil Ntot.
View larger version (22K):
[in this window]
[in a new window]
|
Fig. 5. Average percentage of total coarse mineral soil N compared with mineral soil mass of the coarse fraction (O horizons are not included with the exception of the Histosol) (n = 3). Standard deviations are indicated by error bars.
|
|
The Alderwood contained the greatest quantity of CSNtot and CSM, and had the highest percentages of CSNtot and CSM of any soil series. In contrast, the Sagehill contained the smallest quantity of CSNtot and CSM, and was the lowest in percentage of CSNtot. The average percentages of CSNtot for the Alderwood and Kerby series, both Inceptisols, were somewhat higher than total N found in three Inceptisols of Tuscany, Italy, which were reported to contain an average of 23, 14, and 21% Ntot for washed rock fragments throughout three profiles (Ugolini et al., 1996). Of the soils included in this study that had a coarse fraction, on average one-fifth of Ntot and one-third of the soil total mass would have been excluded from analysis if standard soil sieving procedure had been used.
A comparison of CSNtot with percentage of CSM for all soils by profile suggested that N concentration (Ncon) might change depending on percentage of CSM. Therefore, three categories of percentage of CSM were created: <10%, between 10 and 60%, and >60%. Coarse soil Ntot concentrations of master horizons within these categories were then averaged and standard deviations were calculated (see Table 2). Those horizons for each series without coarse soil fraction, and therefore without CSNtot, were excluded. E horizons were also excluded due to the limited number of samples. Average FSNtot is also shown in Table 2 for comparison. Concentrations of CSNtot across all percentage CSM categories approached 0.3 g kg–1 for each horizon. A horizons had the highest average concentration of CSNtot for percentage of CSM <60%, undoubtedly due to the high organic matter content of the surface horizons. The reason for a low N concentration of A horizons in the >60% CSM category was unclear. One factor may have been the limited number of soils with this percentage of coarse soil material (n = 3), which was also the case for those C horizons in the <10% CSM category (n = 1). It is possible that extent of pedogenic development, physical, chemical, and/or biological processes also influenced A horizon results.
View this table:
[in this window]
[in a new window]
|
Table 2. Average total soil N concentrations and standard deviations by horizon and separated by percentage of coarse soil material found in the total soil mass along with combined average total soil N for all mineral horizons with a coarse fraction. Average N concentration of the fine soil fraction is given for comparison. No C horizon with <10% coarse soil mass was sampled.
|
|
B and C horizons were similar despite the variety of subordinate designations (i.e., Bt, Bk, Cg, Ck) found within those horizons and despite changes in the percentage of CSM (Table 2). B horizons contained the largest concentration of CSNtot for CSM > 60%, though the reasons for this are not obvious. One possible answer may have been found in the study by Ugolini et al. (1996), where the authors investigated mineralogical, chemical, and physical properties of the soil coarse fraction. They found that for two of the three soil profiles sampled in the study, total porosity of the rock fragments exceeded 50% of that in the fine soil, and in one of these profiles porosity of the rocks actually reached that of the fine soil in the deepest horizon sampled (BCb2). The authors suggested that the porosity (which changes according to lithology and degree of weathering) of these rocks allowed for the collection of N-bearing organics, and may ultimately have resulted in a coarse fraction with the same or higher Ntot than the surrounding fine earth, which was the case for two of their profiles. It is possible that N-bearing organics moving in solution through the soil profiles in our study may have been intercepted within the weathered voids of the B-horizon coarse soil fraction before reaching the C horizon. This, combined with a large percentage of CSM (>60%), could explain the higher concentration of CSNtot in some B horizon. Nevertheless, variability of Ncon in the coarse fraction of the B and C horizons was much less than that of the A horizon.
|
CONCLUSIONS
|
|---|
The common practice of excluding the coarse soil fraction and soil below 1-m depth from analysis is challenged by the data presented in this study. Where rocks and deep soils were present, the percentage of total soil N contained in the coarse soil fraction (0.3–37%) as well as in soil >1-m depth (7–34%) was significantly different from zero (P = 0.05). The percentage of total N found in the coarse soil fraction increased with an increase in coarse soil mass. Up to one-half of the total soil N in a profile would have been unmeasured by the combined exclusion of the coarse fraction and soil below 1 m from analysis. An average concentration of 0.3 g kg–1 of total N in the coarse soil fraction was estimated for all major genetic mineral horizons, with less variability in the B and C horizon than in A horizons.
These results indicate that to obtain a true value of total soil N, the entire soil must be sampled, including the coarse soil fraction and soil below 1 m. This accurate appraisal of total soil N is important as it may reflect enhanced storage and/or a potential source of available N not generally accounted for in soil N research.
|
ACKNOWLEDGMENTS
|
|---|
Our sincere thanks to all of the gracious land managers and land owners who allowed us to sample their soils. This study would not have been possible without funding provided by the USDA-NRI Soil and Soil Biology Program, Grant # 99-35107-7781.
|
NOTES
|
|---|
Funding for this study was provided by the USDA-NRI Soil and Soil Biology Program.
Received for publication September 17, 2002.
|
REFERENCES
|
|---|
- Amelung, W., W. Zech, X. Zhang, R.F. Follett, H. Tiessen, E. Knox, and K.-W. Flach. 1998. Carbon, nitrogen, and sulfur pools in particle-size fractions as influenced by climate. Soil Sci. Soc. Am. J. 62:172–181.[Abstract/Free Full Text]
- Cole, D.W., S.P. Gessel, and S.F. Dice. 1968. Distribution and cycling of nitrogen, phosphorous, potassium and calcium in a second-growth Douglas-fir ecosystem. p. 197–233. In H.E. Young (ed.) Primary productivity and mineral cycling in natural ecosystems. University of Maine Press, Orono.
- Corti, G., F.C. Ugolini, and A. Agnelli. 1998. Classing the soil skelton (greater than two millimeters): Proposed approach and procedure. Soil Sci. Soc. Am. J. 62:1620–1629.[Abstract/Free Full Text]
- Dodd, M.B., W.K. Lauenroth, and I.C. Burke. 2000. Nitrogen availability through a coarse-textured soil profile in the shortgrass steppe. Soil Sci. Soc. Am. J. 64:391–398.[Abstract/Free Full Text]
- Frank, A.B., D.L. Tanaka, L. Hofmann, and R.F. Follett. 1995. Soil carbon and nitrogen of Northern Great Plains grasslands as influenced by long-term grazing. J. Range Manage. 48:470–474.
- Hackl, E., S. Zechmeister-Boltenstern, and E. Kandeler. 2000. Nitrogen dynamics in different types of pasture in the Austrian Alps. Biol. Fertil. Soils 32:321–327.
- Hart, S.C., and P. Sollins. 1998. Soil carbon and nitrogen pools and processes in an old-growth conifer forest 13 years after trenching. Can. J. For. Res. 28:1261–1265.
- Huntington, T.G., D.F. Ryan, and S.P. Hamburg. 1988. Estimating soil nitrogen and carbon pools in a northern hardwood forest ecosystem. Soil Sci. Soc. Am. J. 52:1162–1167.[Abstract/Free Full Text]
- Lamb, J.A., G.A. Peterson, and C.R. Fenster. 1985. Wheat fallow tillage systems' effect on a newly cultivated grassland soils' nitrogen budget. Soil Sci. Soc. Am. J. 49:352–356.[Abstract/Free Full Text]
- Ledgard, S.F., S.C. Jarvis and D.J. Hatch 1998. Short-term nitrogen fluxes in grassland soils under different long-term nitrogen management regimes. Soil Biol. Biochem. 30:1233–1241.
- Marion, G.M., J. Kummerow, and P.C. Miller. 1981. Predicting nitrogen mineralization in chaparral soils. Soil Sci. Soc. Am. J. 45:956–961.[Abstract/Free Full Text]
- Motavalli, P.P., C.A. Palm, E.T. Elliott, S.D. Frey, and P.C. Smithson. 1995. Nitrogen mineralization in humid tropical forest soils: Mineralogy, texture and measured nitrogen fractions. Soil Sci. Soc. Am. J. 59:1168–1175.[Abstract/Free Full Text]
- Perry, D.A., C. Choquette, and P. Schroeder. 1987. Nitrogen dynamics in conifer-dominated forests with and without hardwoods. Can. J. For. Res. 17:1434–1441.
- Prichard, S.J., D.L. Peterson, and R.D. Hammer. 2000. Carbon distribution in subalpine forests and meadows of the Olympic Mountains, Washington. Soil Sci. Soc. Am. J. 64:1834–1845.[Abstract/Free Full Text]
- Rigg, G.B. 1958. Peat resources of Washington. State of Washington Dep. of Conserv., State Printing Plant, Olympia.
- Schimel, J.P., and M.K. Firestone. 1989. Nitrogen incorporation and flow through a coniferous forest soil profile. Soil Sci. Soc. Am. J. 53:779–784.[Abstract/Free Full Text]
- SPSS. 2000. SPSS Version 10.1 [computer software]. SPSS, Inc., Chicago, IL.
- Stone, E.L., W.G. Harris, R.B. Brown, and R.J. Kuehl. 1993. Carbon storage in Florida Spodosols. Soil Sci. Soc. Am. J. 57:179–182.[Abstract/Free Full Text]
- Ugolini, F.C., G. Corti, A. Agnelli, and F. Piccardi. 1996. Mineralogical, physical and chemical properties of rock fragments in soil. Soil Sci. 161:521–542.
This article has been cited by other articles:
|
|
|
|
 
C. M. Flint, R. B. Harrison, B. D. Strahm, and A. B. Adams
Nitrogen Leaching from Douglas-fir Forests after Urea Fertilization
J. Environ. Qual.,
August 8, 2008;
37(5):
1781 - 1788.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
ABSTRACT
INTRODUCTION
