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1

Electronic Resource

A global inventory of nitric oxide emissions from soils (1997)

Davidson, Eric A. ; Kingerlee, Wendy

Springer

Nutrient cycling in agroecosystems 48 (1997), S. 37-50

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ISSN: 1573-0867

Keywords: greenhouse gases ; nitrogen ; NOx ; nitrous oxide ; ozone precursors ; trace gases

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Over 60 published papers reporting field measurements of emissions of nitric oxide (NO) from soil are reviewed, and over 100 annual estimates of NO emissions were made for various types of ecosystems, including agricultural fields. These data were stratified by biome and the mean of each stratum was multiplied by an estimate of the biome area. A few strata were identified as clearly having low NO emissions: montane forests, swamps and marshes, tundra, and temperate forests that are not heavily affected by N deposition. The largest emissions were observed in tropical savanna/woodland, chaparral, and cultivated agriculture, but variation in NO emissions within these strata was also large. Although the stratification scheme fails to partition this within-stratum variation, it does clearly identify these biomes as globally important sources of NO and as areas where more research is needed to investigate within-biome variation in NO emissions. It is too early to tell whether differences in NO emissions between temperate and tropical agriculture are significant, but it is clear that agriculture is an important source of NO and that management practices affect NO emissions. The best current estimate of the global soil source of NO is 21 Tg N yr-1. Adsorption of NOx onto plant canopy surfaces may reduce emissions to the atmosphere to as low as 13 Tg N yr-1, although the absorption effect is probably smaller than this. An error term for the global estimate is difficult to determine, but it is at least ±4 and perhaps as large at ±10 Tg N yr-1. Hence, only modest progress has been made in narrowing uncertainties in the estimate of the global soil source of NO, although some published lower estimates appear unlikely. This inventory reconfirms that the soil source of NO is similar in magnitude to fossil fuel emissions of NOx. Further narrowing of the uncertainty of the estimate of global soil NO emissions will require more sophisticated and carefully chosen stratification schemes to address variation within biomes based on soil fertility, soil texture, climate, and management and will require linking this type of inventory and stratification with mechanistic models.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1009738715891

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2

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Spatial covariation of soil organic carbon, clay content, and drainage class at a regional scale (1995)

Davidson, Eric A.

Springer

Landscape ecology 10 (1995), S. 349-362

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ISSN: 1572-9761

Keywords: climate change ; FAO ; geographic information system ; global carbon cycle ; Kansas ; Montana ; soil maps ; soil organic matter ; soil taxonomy ; soil texture ; STATSGO

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Several factors affecting stocks of soil organic-C have been identified, including climate, soil texture, and drainage, but how these factors and their influence vary spatially is not well documented. The State Soil Geographic Data Base (STATSGO) was used to estimate soil organic-C stocks of Montana and Kansas and to map spatial variation of soil properties. Regressions across map units of area-weighted estimates of soil organic-C, clay content, and drainage class show that clay content is positively correlated with organic-C in Kansas, but that drainage class is a better indicator of soil with high and low organic-C stocks in Montana. About 85% of Kansas is covered by Mollisols. These grasslands of the North American Great Plains are where the paradigm relating clay content to stabilization of soil organic-C was developed. In contrast, clay content does not covary with soil organic-C across Montana. Only 30% of Montana is covered by Mollisols; the remainder includes rangeland, covered primarily by Aridisols and Entisols, and forests, covered by Inceptisols, Spodosols, and Histosols. Although other unidentified factors contribute to spatial variation in soil organic-C stocks in Montana, drainage class distinguishes the C-rich and the C-poor soils. When taken with similar results correlating soil C stocks with drainage class in a separate study of Maine, soil wetness emerges as an important controller of soil organic-C in northern states of the USA. Another objective was to compare STATSGO estimates (1:250,000 scale) of area covered by soil orders with estimates from the FAO/UNESCO Soils Map of the World (1:5,000,000). Agreement was excellent in Kansas and reasonably good in Montana. When used with regionally specific estimates for soil-C, the FAO map holds promise for regional and global extrapolation of soil C stocks.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00130212

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3

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Changes in soil carbon inventories following cultivation of previously untilled soils (1993)

Davidson, Eric A. ; Ackerman, Ilse L.

Springer

Biodegradation 20 (1993), S. 161-193

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ISSN: 1572-9729

Keywords: carbon cycle ; land-use change ; organic carbon ; tillage

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Cultivation of previously untilled soils usually results in release of carbon from the soil to the atmosphere, which can affect both soil fertility locally and the atmospheric burden of CO2 globally. Generalizations about the magnitude of this flux have been hampered by a lack of good quality comparative data on soil carbon stocks of cultivated and uncultivated soils. Using data from several recent studies, we have reexamined the conclusions of previous reviews of this subject. The data were divided into subsets according to whether the soils were sampled by genetic horizon or by fixed depths. Sampling by fixed depths appears to underestimate soil C losses, but both subsets of data support earlier conclusions that between 20% and 40% of the soil C is lost following cultivation. Our best estimate is a loss of about 30% from the entire soil solum. Our analysis also supports the conclusion that most of the loss of soil C occurs within the first few Years (even within two Years in some cases) following initial cultivation. Our analysis does not support an earlier conclusion that the fractional loss of soil carbon is positively correlated to the amount of carbon initially present in the uncultivated soil. We found no relation between carbon content of uncultivated soil and the percentage lost following cultivation.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00000786

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4

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Land-Use Change and Biogeochemical Controls of Methane Fluxes in Soils of Eastern Amazonia (2000)

Verchot, Louis V. ; Davidson, Eric A. ; Cattânio, J. Henrique ; [et al.]

Springer

Ecosystems 3 (2000), S. 41-56

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ISSN: 1435-0629

Keywords: Key words: CH4; Amazon basin; Brazil; methanotrophy; methanogenesis; deforestation; rainforests; tropical forests; tropical pastures.

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: ABSTRACT Tropical soils account for 10%–20% of the 15–35 Tg of atmospheric methane (CH4) consumed annually by soils, although tropical deforestation could be changing the soil sink. The objectives of this study were (a) to quantify differences in soil CH4 fluxes among primary forest, secondary forest, active pasture, and degraded pasture in eastern Amazonia; and (b) to investigate controlling mechanisms of CH4 fluxes, including N availability, gas-phase transport, and soil respiration. At one ranch, Fazenda Vitória, annual uptake estimates (kg CH4ha−1 y−1) based on monthly measurements were: primary forest, 2.1; secondary forest, 1.0; active pasture, 1.3; degraded pasture, 3.1. The lower annual uptake in the active pasture compared with the primary forest was due to CH4 production during the wet season in the pasture soils, which is consistent with findings from other studies. In contrast, the degraded pasture was never a CH4 source. Expressing uptake as a negative flux and emission as a positive flux, CH4 fluxes were positively correlated with CO2 fluxes, indicating that root and microbial respiration in the productive pastures, and to a lesser extent in the primary forest, contributed to the formation of anaerobic microsites where CH4 was produced, whereas this productivity was absent in the degraded pasture. In all land uses, uptake rates of atmospheric CH4 were greater in the dry season than in the wet season, indicating the importance of soil water content and gas transport on CH4 fluxes. These clay soils had low annual uptake rates relative to reported rates on sandy soils, which also is consistent with gas transport within the soil being a limiting factor. Nitrogen availability indices did not correlate with CH4 fluxes, indicating that inhibition of CH4 oxidation was not an important mechanism explaining differences among land uses. At another ranch, Fazenda Agua Parada, no significant effect of pasture age was observed along a chronosequence of pasture ages. We conclude that land-use change can either increase or decrease the soil sink of CH4, depending on the duration of wet and dry seasons, the effects of seasonal precipitation on gas-phase transport, and the phenology and relative productivity of the vegetation in each land use.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s100210000009

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5

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Effects of soil water content on soil respiration in forests and cattle pastures of eastern Amazonia (2000)

Davidson, Eric A. ; Verchot, Louis V. ; Cattânio, J. Henrique ; [et al.]

Springer

Biogeochemistry 48 (2000), S. 53-69

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ISSN: 1573-515X

Keywords: Brazil ; carbon cycle ; CO2 ; deforestation ; land use change

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Geosciences

Notes: Abstract The effect of soil water content on efflux of CO2 from soils has been described by linear, logarithmic, quadratic, and parabolic functions of soil water expressed as matric potential, gravimetric and volumetric water content, water holding capacity, water-filled pore space, precipitation indices, and depth to water table. The effects of temperature and water content are often statistically confounded. The objectives of this study are: (1) to analyze seasonal variation in soil water content and soil respiration in the eastern Amazon Basin where seasonal temperature variation is minor; and (2) to examine differences in soil CO2 emissions among primary forests, secondary forests, active cattle pastures, and degraded cattle pastures. Rates of soil respiration decreased from wet to dry seasons in all land uses. Grasses in the active cattle pasture were productive in the wet season and senescent in the dry season, resulting in the largest seasonal amplitude of CO2 emissions, whereas deep-rooted forests maintained substantial soil respiration during the dry season. Annual emissions were 2.0, 1.8, 1.5, and 1.0 kg C m-2 yr-1 for primary forest, secondary forest, active pasture, and degraded pasture, respectively. Emissions of CO2 were correlated with the logarithm of matric potential and with the cube of volumetric water content, which are mechanistically appropriate functions for relating soil respiration at below-optimal water contents. The parameterization of these empirical functions was not consistent with those for a temperate forest. Relating rates of soil respiration to water and temperature measurements made at some arbitrarily chosen depth of the surface horizons is simplistic. Further progress in defining temperature and moisture functions may require measurements of temperature, water content and CO2 production for each soil horizon.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1006204113917

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6

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Estimating regional carbon stocks and spatially covarying edaphic factors using soil maps at three scales (1993)

Davidson, Eric A. ; Lefebvre, Paul A.

Springer

Biodegradation 22 (1993), S. 107-131

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ISSN: 1572-9729

Keywords: clay ; drainage class ; geographic information systems ; Histosols ; Maine ; Podzols ; soil carbon ; soil maps ; soil organic matter ; Spodosols ; SSURGO ; STATSGO ; temperate forests

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Most estimates of regional and global soil carbon stocks are based on extrapolations of mean soil C contents for broad categories of soil or vegetation types. Uncertainties exist in both the estimates of mean soil C contents and the area over which each mean should be extrapolated. Geographic information systems now permit spatially referenced estimates of soil C at finer scales of resolution than were previously practical. We compared estimates of total soil C stocks of the state of Maine using three methods: (1) multiplying the area of the state by published means of soil C for temperate forests and for Spodosols; (2) calculating areas of inclusions of soil taxa in the 1:5,000,000 FAO/UNESCO Soils Map of the World and multiplying those areas by selected mean carbon contents; and (3) calculating soil C for each soil series and map unit in the 1:250,000 State Soil Geographic Data Base (STATSGO) and summing these estimates for the entire state. The STATSGO estimate of total soil C was between 23% and 49% higher than the common coarse scale extrapolations, primarily because STATSGO included data on Histosols, which cover less than 5% of the area of the state, but which constitute over one-third of the soil C. Spodosols cover about 65% of the state, but contribute less than 39% of the soil C. Estimates of total soil C in Maine based on the FAO map agreed within 8% of the STATSGO estimate for one possible matching of FAO soil taxa with data on soil C, but another plausible matching overestimated soil C stocks. We also compared estimates from the 1:250,000 STATSGO database and from the 1:20,000 Soil Survey Geographic Data Base (SSURGO) for a 7.5 minute quadrangle within the state. SSURGO indicated 13% less total soil C than did STATSGO, largely because the attribute data on depths of soil horizons in SSURGO are more specific for this locality. Despite localized differences, the STATSGO database offers promise of scaling up county soil survey data to regional scales because it includes attribute data and estimates of areal coverage of C-rich inclusions within map units. The spatially referenced data also permit examination of covariation of soil C stocks with soil properties thought to affect stabilization of soil C. Clay content was a poor predictor of soil C in Maine, but drainage class covaried significantly with soil C across the state.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00002707

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7

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Soil carbon cycling in a temperate forest: radiocarbon-based estimates of residence times, sequestration rates and partitioning of fluxes (2000)

Gaudinski, Julia B. ; Trumbore, Susan E. ; Davidson, Eric A. ; [et al.]

Springer

Biogeochemistry 51 (2000), S. 33-69

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ISSN: 1573-515X

Keywords: carbon ; dynamics ; isotope disequilibrium ; radiocarbon ; soil respiration ; temperate forests

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Geosciences

Notes: Abstract Temperate forests of North America are thought to besignificant sinks of atmospheric CO2. Wedeveloped a below-ground carbon (C) budget forwell-drained soils in Harvard Forest Massachusetts, anecosystem that is storing C. Measurements of carbonand radiocarbon (14C) inventory were used todetermine the turnover time and maximum rate ofCO2 production from heterotrophic respiration ofthree fractions of soil organic matter (SOM):recognizable litter fragments (L), humified lowdensity material (H), and high density ormineral-associated organic matter (M). Turnover timesin all fractions increased with soil depth and were2–5 years for recognizable leaf litter, 5–10 years forroot litter, 40–100+ years for low density humifiedmaterial and 〉100 years for carbon associated withminerals. These turnover times represent the timecarbon resides in the plant + soil system, and mayunderestimate actual decomposition rates if carbonresides for several years in living root, plant orwoody material. Soil respiration was partitioned into two componentsusing 14C: recent photosynthate which ismetabolized by roots and microorganisms within a yearof initial fixation (Recent-C), and C that is respiredduring microbial decomposition of SOM that resides inthe soil for several years or longer (Reservoir-C).For the whole soil, we calculate that decomposition ofReservoir-C contributes approximately 41% of thetotal annual soil respiration. Of this 41%,recognizable leaf or root detritus accounts for 80%of the flux, and 20% is from the more humifiedfractions that dominate the soil carbon stocks.Measurements of CO2 and 14CO2 in thesoil atmosphere and in total soil respiration werecombined with surface CO2 fluxes and a soil gasdiffusion model to determine the flux and isotopicsignature of C produced as a function of soil depth. 63% of soil respiration takes place in the top 15 cmof the soil (O + A + Ap horizons). The average residencetime of Reservoir-C in the plant + soil system is8±1 years and the average age of carbon in totalsoil respiration (Recent-C + Reservoir-C) is 4±1years. The O and A horizons have accumulated 4.4 kgC m−2above the plow layer since abandonment by settlers inthe late-1800's. C pools contributing the most to soilrespiration have short enough turnover times that theyare likely in steady state. However, most C is storedas humified organic matter within both the O and Ahorizons and has turnover times from 40 to 100+ yearsrespectively. These reservoirs continue to accumulatecarbon at a combined rate of 10–30 gC mminus 2yr−1. This rate of accumulation is only 5–15% of the total ecosystem C sink measured in this stand using eddy covariance methods.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1006301010014

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