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Showing papers on "Soil organic matter published in 1992"


Journal ArticleDOI
TL;DR: The POM fraction was isolated by dispersing the soil in 5 g L-1 hexametaphosphate and passing the dispersed soil samples through a 53-micrometer sieve as mentioned in this paper.
Abstract: Many models have been constructed in an attempt to describe the dynamics of soil organic-matter (SOM) turnover, most of which include 2 to 3 kinetically defined organic-matter pools. Physical and chemical definition of these conceptualized SOM pools has been difficult. We describe a simple method for dispersion of soil to isolate a particulate organic-matter (POM) fraction that may represent an important SOM pool in grassland soils. The POM fraction was isolated by dispersing the soil in 5 g L-1 hexametaphosphate and passing the dispersed soil samples through a 53-micrometer sieve. We compared POM and mineral-associated C among three tillage treatments (20 yr under cultivation) and an undisturbed grassland at Sidney, NE. The POM C in the native sod represented 39% of the total soil organic C. Twenty years of bare-fallow, stubble-mulch, and no-till management reduced the C content in this fraction to 18, 19, and 25%, respectively, of the total organic C. The mineral-associated organic-matter fraction showed no reduction in C content in the bare-fallow treatment compared with the grassland soil but increased in the no-till and stubble-mulch treatments. Nitrogen dynamics generally mirrored those observed for C. Analysis of the POM fraction for lignin and cellulose content indicated that this fraction was 47% lignin and had a lignocellulose index of 0.7. The stable C-isotope composition of the POM fraction suggests that wheat-derived POM turns over faster than grass-derived POM. We suggest the POM fraction closely matches the characteristics of a SOM pool variously described as slow, decomposable, or stabilized organic matter

2,259 citations


Book ChapterDOI
01 Jan 1992
TL;DR: The soil organic matter (SOM) pool encompasses plant, animal, and microbial residues in all stages of decay and a diversity of heterogeneous organic substances intimately associated with inorganic soil components.
Abstract: The soil organic matter (SOM) pool encompasses plant, animal, and microbial residues in all stages of decay and a diversity of heterogeneous organic substances intimately associated with inorganic soil components. The soil microbiota and fine roots may also be considered part of the SOM pool. The turnover of the different SOM components varies continuously due to the complex interaction of biological, chemical, and physical processes in soil. The complexity of SOM and its importance to soil fertility have challenged generations of soil scientists, and numerous studies, of which some date back more than two centuries (see historical review in Kononova, 1961), have covered a vast array of aspects of SOM.

1,095 citations


Journal ArticleDOI
TL;DR: The sensitivity of soil organic carbon (Corg) and microbial carbon measurements, and the Cm~,/Co, ratio, to reflect climatic, vegetation, cropping and management history was investigated using a range of topsoils in New Zealand.
Abstract: The sensitivity of soil organic carbon (Corg) and microbial carbon (Cmic) measurements, and the Cm~,/Co,, ratio, to reflect climatic, vegetation, cropping and management history was investigated using a range of topsoils in New Zealand. The Cmic generally comprised 1-4% of Corg, with the proportion being consistently greater under pastures, than the equivalent soil under native forest, exotic forest or arable cropping. However, absolute values differed markedly between soils and were greatly influenced by texture, mineralogy and the Corg content. The Cmic recovered more rapidly than Corg on returning to pasture following cropping. There was a generally greater Corg content in those soils from the areas with higher precipitation, but the precipitation-evaporation quotient proposed by Insam et al. (Soil Biol. Biochem. 1989, 21, 211-21) to predict the relationship between Cmic and Corg, greatly underestimated the Cmic content of New Zealand soils and there was too great a scatter in the data to derive a revised regression formula. The Cmic and the Cmic/Cor, ratio are useful measures to monitor soil organic matter and both provide a more sensitive index than COrg measured alone. However, under typical climatic and land use conditions in New Zealand, the values do not appear readily transferrable between soils. To ascertain whether a soil has achieved equilibrium in organic matter status, it will be necessary to establish reference values to which a tested soil can be compared.

816 citations


Journal ArticleDOI
TL;DR: Light fraction (LF) material, comprised largely of incompletely decomposed organic residues, may provide a sensitive indicator of the effects of cropping practices on soil organic matter. as discussed by the authors found that the LF content of the surface soil (0-7.5 cm) accounted for 2.0 to 5.4%, 3.3 to 7.1%, and 7.5% of the organic C at Indian Head, Melfort, and Scott, respectively.
Abstract: Light-fraction (LF) material, comprised largely of incompletely decomposed organic residues, may provide a sensitive indicator of the effects of cropping practices on soil organic matter. The objective of our study was to determine the influence of agronomic variables on soil LF content, and to evaluate the LF as a measure of labile organic matter. Soils from three long-term crop rotation studies in Saskatchewan, Canada, were analyzed for LF content and composition. The experiments, established at Indian Head (Udic Boroll), Melfort (Udic Boroll), and Scott (Typic Boroll), included wheat (Triticum aestivum L.) based rotations varying in fertilizer application, frequency of summer fallow, and cropping sequence. The LF of the surface soil (0–7.5 cm) accounted for 2.0 to 5.4%, 3.3 to 7.1%, and 7.1 to 17.5% of the organic C at Indian Head, Melfort, and Scott, respectively. Within each site, the LF content was generally highest in treatments with continuous cropping or perennial forages and lowest in those with a high frequency of summer fallow. Fertilizer application generally favored LF accumulation. Differences in LF content among sites and treatments were attributed to variable residue inputs and rates of substrate decomposition. The respiration rate and microbial N content of soils was strongly correlated with the LF content, suggesting that the LF is a useful indicator of labile organic matter. Nitrogen mineralization was also correlated with LF content, though the relationship was less consistent, presumably because the high C/N ratio of the LF induced temporary N immobilization. The LF content is a sensitive indicator of the effects of cropping on soil organic matter content and composition but, because of its transient nature, probably reflects primarily short-term effects. LRS Contribution no. 3879163.

699 citations


Journal ArticleDOI
TL;DR: In this article, the authors examined the importance of decomposition in the removal of dissolved organic matter (DOM) and DON in a tree canopy and forest floor of an oak (Quercus spp.)-hickory (Carya spp.).
Abstract: High concentrations of dissolved organic matter (DOM) were leached into rainwater passing through the canopy and forest floor of an oak (Quercus spp.)-hickory (Carya spp.) forest in the southern Appala-chian Mountains. More than 95% of this dissolved organic C (DOC) and N (DON) was removed as water percolated through the soil profile and left the ecosystem in stream water. Our objective was to examine the importance of decomposition in the removal of DOC and DON. Samples of DOM front throughfall, forest floor water, soil water from A and B soil horizons, and stream water were all adjusted to a common initial DOC concentration, inoculated with soil and stream microbes , and incubated in solution for 134 d. In general, only 14 to 33% of the DOC in forest floor, soil solution, and stream samples decomposed during the incubation. The relative order of average decomposition of DOC from the various strata was, from fastest to slowest: throughfall, Oi horizon (forest floor), Oa horizon (forest floor), B horizon, stream, AB horizon, isolated fulvic acid, and upper A horizon. In short, biodegradability of DOM in the ecosystem profile declined vertically from throughfall to the A horizon and then increased with depth. The DON generally did not decay faster than the DOC — results consistent with the idea that hydrolysis of organic N is linked to mineralization of DOC rather than occurring selectively in response to the biochemical need for N. Throughfall DOM could be decomposed during its passage through the upper soil, but decomposition seems too slow to be responsible for the bulk of removal of DON and DOC that occurs in the mineral soil. Adsorption, rather than biodegradation, is more likely responsible for maintaining low DOC substrate concentrations in the mineral soil and preventing its loss into stream water. T HE BIODEGRADABILITY of xenobiotic compounds in soil and water has been the focus of much research. The biodegradability of naturally occurring DOM has received less attention, though there has been considerable research on the fate of fresh autumn leaf litter leachate and on the ability of stream and lake DOM to support the growth of bacteria in those At the same time, there is a widespread belief that dissolved humic substances , which make up much of natural DOM, are quite resistant to decomposition. For obvious reasons, DOM in soil has received much less attention than that in lakes and streams. The …

630 citations


Journal ArticleDOI
TL;DR: A review of recent developments on assessing the effect of agricultural systems on long-term productivity of soils is provided in this paper, which reaffirms the continuing need for the maintenance of existing longterm experimental sites and establishment of new studies in major agroecosystems throughout the world.

627 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used solid-state cross-polarization/magic-angle-spinning 3C NMR spectroscopy to characterise semi-quantitatively the organic materials contained in particle size and density fractions isolated from five different mineral soils.
Abstract: Solid-state cross-polarisation/magic-angle-spinning3C nuclear magnetic resonance (CP/MAS13C NMR) spectroscopy was used to characterise semi-quantitatively the organic materials contained in particle size and density fractions isolated from five different mineral soils: two Mollisols, two Oxisols and an Andosol The acquired spectra were analysed to determine the relative proportion of carboxyl, aromatic, O-alkyl and alkyl carbon contained in each fraction Although similar types of carbon were present in all of the fractions analysed, an influence of both soil type and particle size was evident The chemical structure of the organic materials contained in the particle size fractions isolated from the Andosol was similar; however, for the Mollisols and Oxisols, the content of O-alkyl, aromatic and alkyl carbon was greatest in the coarse, intermediate and fine fractions, respectively The compositional differences noted in progressing from the coarser to finer particle size fractions in the Mollisols and Oxisols were consistent with the changes noted in other studies where CP/MAS13C NMR was used to monitor the decomposition of natural organic materials Changes in the C:N ratio of the particle size fractions supported the proposal that the extent of decomposition of the organic materials contained in the fine fractions was greater than that contained in the coarse fractions The increased content of aromatic and alkyl carbon in the intermediate size fractions could be explained completely by a selective preservation mechanism; however, the further accumulation of alkyl carbon in the clay fractions appeared to result from both a selective preservation and anin situ synthesis The largest compositional differences noted for the entire organic fraction of the five soils were observed between soil orders The differences within orders were smaller The Mollisols and the Andosol were both dominated by O-alkyl carbon but the Andosol had a lower alkyl carbon content The Oxisols were dominated by both O-alkyl and alkyl carbon A model describing the oxidative decomposition of plant materials in mineral soils is proposed and used to explain the influence of soil order and particle size on the chemical composition of soil organic matter in terms of its extent of decomposition and bioavailability

594 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of organic matter and fertilizer additions on soil organic-matter dynamics were analyzed using the CENTURY model, using results from a 30yr-old Swedish field experiment, using the Century model.
Abstract: To study the effects of organic matter and fertilizer additions on soil organic-matter (SOM) dynamics, we analyzed results from a 30yr-old Swedish field experiment, using the CENTURY model. Field treatments on a sandy clay loam included biannual addition (up to 4000 kg C ha ) of straw, sawdust, and no organic additions, with and without N fertilizer (80 kg N ha), and green manure, farmyard manure, and bare fallow. Soil C and N, crop production (small-grain and root crops), N uptake, and mineralization and immobilization of N were modeled and compared with field measurements. Changes in soil C and N, as much as 30% after 30 yr, were generally well represented by the model. Most of the treatment differences in SOM could be explained by the rate of organic-matter input, its lignin content, and C/N ratio, plus the effect of N fertilizer on belowground C inputs. However, there appeared to be additional positive effects of N supply on SOM accumulation that were not fully explained by the model. The quality of organic amendments strongly influenced N uptake and crop productivity, through controls on N mineralization and immobilization. Mean annual N uptake ranged from a low of 3.1 g m 2 in sawdust-amended soil to a high of 9.2 g m 2 in fertilized, strawamended soil. Simulated N losses accounted for 7 to 20% of total N inputs. Nitrogen-balance estimates by the model were consistent with the observed data for four of the treatments, but treatments with low N availability appeared to have additional, unexplained N inputs. View complete article To view this complete article, insert Disc 5 then click button8

574 citations


Journal ArticleDOI
TL;DR: The literature on soil C change with forest harvesting, cultivation, site preparation, burning, fertilization, N fixation, and species change is reviewed in this paper, showing no significant change (± 10%) with harvesting only, a few studies showed large net losses, and a few cases showed a net gain following harvesting.
Abstract: The literature on soil C change with forest harvesting, cultivation, site preparation, burning, fertilization, N fixation, and species change is reviewed. No general trend toward lower soil C with forest harvesting was apparent, unless harvesting is followed by intense burning or cultivation. Most studies show no significant change (± 10%) with harvesting only, a few studies show large net losses, and a few studies show a net gain following harvesting. Cultivation, on the other hand, results in a large (up to 50%) loss in soil C in most (but not all) cases. Low-intensity rescribed fire usually results in little change in soil C, but intense presribed fire or wildfire can result in a large loss of soil C. Species change can have either no effect or large effects on soil C, depending primarily upon rooting patterns. Fertilization and (especially) nitrogen fixation cause increases in soil C in the majority of cases, and represent an opportunity for sequestering soil C and causing long-term improvements in site fertility.

518 citations


Journal ArticleDOI
TL;DR: The data suggest that sorption of organic pollutants onto soil organic matter significantly affects biodegradability as well as biotoxicity.
Abstract: Polycyclic aromatic hydrocarbon (PAH) biodegradation was investigated in contaminated soils from two different industrial sites under simulated land treatment conditions. Soil samples from a former impregnation plant (soil A) showed high degradation rates of PAHs by the autochthonous microorganisms, whereas PAHs in material of a closed-down coking plant (soil B) were not degraded even after inoculation with bacteria known to effectively degrade PAHs. As rapid PAH biodegradation in soil B was observed after PAHs were extracted and restored into the extracted soil material, the kind of PAH binding in soil B appears to completely prevent biodegradation. Sorption of PAHs onto extracted material of soil B follows a two-phase process (fast and slow); the latter is discussed in terms of migration of PAHs into soil organic matter, representing less accessible sites within the soil matrix. Such sorbed PAHs are suggested to be non-bioavailable and thus non-biodegradable. By eluting soil B with water, no biotoxicity, assayed as inhibition of bioluminescence, was detected in the aqueous phase. When treating soil A analogously, a distinct toxicity was observed, which was reduced relative to the amount of activated carbon added to the soil material. The data suggest that sorption of organic pollutants onto soil organic matter significantly affects biodegradability as well as biotoxicity.

470 citations


Journal ArticleDOI
TL;DR: Soil quality can be defined as an inherent attribute of a soil that is inferred from its specific characteristics and observations (e.g., compactability, erodibility, and fertility).
Abstract: Different chemical, physical, and biological properties of a soil interact in complex ways that determine its potential fitness or capacity to produce healthy and nutritious crops. The integration of these properties andine resulting level of productivity often is referred to as “soil quality.” Soil quality can be defined as an inherent attribute of a soil that is inferred from its specific characteristics and observations (e.g., compactability, erodibility, and fertility). The term also refers to the soil's structural integrity, which imparts resistance to erosion, and to the loss of plant nutrients and organic matter. Soil quality often is related to soil degradation, which can be defined as the time rate of change in soil quality.Soil quality should not be limited to soil productivity, but should encompass environmental quality, human and animal health, and food safety and quality. There is inadequate reliable information on how changes in soil quality directly affect food quality, or indirectly affect human and animal health. In characterizing soil quality, biological properties have received less emphasis than chemical and physical properties, because their effects are difficult to measure, predict, or quantify. Improved soil quality often is indicated by increased infiltration, aeration, macropores, aggregate size, aggregate stability, and soil organic matter, and by decreased bulk density, soil resistance, erosion, and nutrient runoff. These are useful, but future research should seek to identify and quantify reliable and meaningful biological/ecological indicators of soil quality, such as total species diversity or genetic diversity of beneficial soil microorganisms, insects, and animals.Because these biological/ecological indexes of soil quality are dynamic, they will require effective monitoring and assessment programs to develop appropriate databases for research and technology transfer. We need to know how such indexes are affected by management inputs, whether they can serve as early warning indicators of soil degradation, and how they relate to the sustainability of agricultural systems.

Journal ArticleDOI
TL;DR: In this paper, an empirical approach to establish the existence of a universal calibration function for TDR soil moisture measurement is presented. But the practical aspects of the measurement calibration are discussed, and an empirical method to establish a universal calibrator for soil moisture measurements is discussed.
Abstract: SUMMARY The paper is addressed to soil scientists who use Time-Domain Reflectometry (TDR) technology to measure soil moisture. The practical aspects of the measurement calibration are discussed, and an empirical approach to establishing the existence of a universal calibration function is presented. Samples of 11 mineral soil horizons and seven organic soil horizons with different chemical and physical properties (including magnetic properties) were selected with the aim of determining their dielectric constant-volumetric water content relationship as calibration functions for TDR soil moisture measurements. These samples were supplemented by other, soil-like, capillary-porous reference materials (montmorillonite, glass beads, washed sand and a sand from a C horizon). The study showed that a unique calibration function for mineral soils and another distinct calibration function for organic soils can be established.

Journal ArticleDOI
TL;DR: In this paper, three methods to estimate soil microbial biomass, namely, CHC13 fumigation-incubation (CFI), CFE and SIR, were compared with each other and with arginine ammonification and basal respiration using soils over a wide range of textural classes and organic matter content.
Abstract: Three methods to estimate soil microbial biomass, CHC13 fumigation-incubation (CFI), CHC13 fumigation-extraction (CFE), and substrate-induced respiration (SIR), were compared with each other and with arginine ammonification and basal respiration using soils over a wide range of textural classes and organic matter content. Biomass and activity of the soil microflora were significantly related to clay, soil organic C and especially to total N content. Values for microbial biomass C as estimated by CFI, CFE and SIR were highly correlated and not affected by soil texture. Only the estimation of biomass C by CFE was slightly influenced by soil organic matter including the two peat soils into the regression analysis. While the absolute values for biomass C deviated considerably when estimated by CFI, CFE and SIR, the ranking of the soils was the same for all these methods. These differences were usually not caused by the abiotic soil conditions we examined. The factors to convert the additional amount of organic C extracted after CHC13 fumigation or the substrate-induced respiration to microbial biomass C are discussed.

Journal ArticleDOI
TL;DR: Both microbial counts and microbial biomass were higher in early spring than other seasons, and annual cropping significantly reduced declines in soil organic matter and soil microbial biomass.
Abstract: Understanding microbial dynamics is important in the development of new management strategies to reverse declining organic-matter content and fertility of agricultural soils. To determine the effects of crop rotation, crop residue management, and N fertilization, we measured changes in microbial biomass C and N and populations of several soil microbial groups in long-term (58-yr) plots under different winter wheat (Triticum aestivum L.) crop rotations. Wheat-fallow treatments included: wheat straw incorporated (5 Mg ha), no N fertilization; wheat straw incorporated, 90 kg N ha , wheat straw fall burned, no N fertilization; and wheat straw incorporated, 11 Mg barnyard manure ha. Annual-crop treatments were: continuous wheat, straw incorporated, 90 kg N ha, wheat-pea (Pisum sativum L.) rotation (25 yr), wheat and pea straw incorporated, 90 kg N ha 1 applied to wheat; and continuous grass pasture. Total soil and microbial biomass C and N contents were significantly greater in annualcrop than wheat-fallow rotations, except when manure was applied. Microbial biomass C in annual-crop and wheat-fallow rotations averaged 50 and 25%, respectively, of that in grass pasture. Residue management significantly influenced the level of microbial biomass C; for example, burning residues reduced microbial biomass to 57% of that in plots receiving barnyard manure. Microbial C represented 4.3, 2.8, and 2.2% and microbial N 5.3, 4.9, and 3.3% of total soil C and N under grass pasture, annual cropping, and wheat-fallow, respectively. Both microbial counts and microbial biomass were higher in early spring than other seasons. Annual cropping significantly reduced declines in soil organic matter and soil microbial biomass. View complete article To view this complete article, insert Disc 5 then click button8

Book
01 Aug 1992
TL;DR: In this paper, a mathematical model of Soil Organic Matter Transformation is presented, based on Lignin, Humic and Fulvic Acids, Formation and Decomposition.
Abstract: Organic Matter: A Dynamic Soil Component. Organic Matter Transformations: Ecosystem Examples. Biological Mediators of Soil Organic Matter Transformations. Soil Enzymes and Organic Matter Transformations. Source and Transformations of Readily Metabolized Organic Matter. Humification and Organic Matter Stability. Lignin: Decomposition and Humification. Humic and Fulvic Acids: Formation and Decomposition. Soil Organic Matter as a Plant Nutrient Reservoir. Mineral Availability and Soil Organic Matter. Organic Matter and Soil Physical Structure. Mathematical Modeling of Soil Organic Matter Transformation. Ecostytem Management and Soil Organic Matter Levels. Soil Organic Matter: A Current and Future Concern. Index.

Journal ArticleDOI
TL;DR: In this article, the authors suggest that ecosystem level approaches offer the best possibilities for rapidly assessing changes in soil quality, and they suggest that the ecosystem level approach offers the best possibility for rapid assessment of soil quality.
Abstract: Diverse soil microbiological studies have attempted to assess deterioration or improvement in soil quality. These studies have been done on three levels: population level studies of the dynamics of species that are presumed to be important or sensitive; community level studies of microbial community structure, such as species diversity and frequency of occurence of species; and ecosystem level studies of a range of soil processes. We suggest that ecosystem level approaches offer the best possibilities for rapidly assessing changes in soil quality. Data from such studies will allow researchers to decide whether to proceed with population or community level studies.

Journal ArticleDOI
TL;DR: In this paper, the sorption at room temperature of benzene and carbon tetrachloride from water on three high-organic-content soils (muck, peat, and extracted peat) and on cellulose was determined in order to evaluate the effect of sorbent polarity on the solute partition coefficients.
Abstract: The sorption at room temperature of benzene and carbon tetrachloride from water on three high-organic-content soils (muck, peat, and extracted peat) and on cellulose was determined in order to evaluate the effect of sorbent polarity on the solute partition coefficients. The isotherms are highly linear for both solutes on all the organic matter samples, which is consistent with a partition model. For both solutes, the extracted peat shows the greatest sorption capacity while the cellulose shows the lowest capacity; the difference correlates with the polar-to-nonpolar group ratio [(O+N)/C] of the sorbent samples

Journal ArticleDOI
TL;DR: If the objective is to store carbon rapidly in the short term and achieve high carbon storage in the long term, Populus plantations growing on fertile land were the best option examined and plantations of conifers of any species with above-average Yield Classes would suffice.
Abstract: A carbon-flow model for managed forest plantations was used to estimate carbon storage in UK plantations differing in Yield Class (growth rate), thinning regime and species characteristics. Time-averaged, total carbon storage (at equilibrium) was generally in the range 40-80 Mg C ha(-1) in trees, 15-25 Mg C ha(-1) in above- and belowground litter, 70-90 Mg C ha(-1) in soil organic matter and 20-40 Mg C ha(-1) in wood products (assuming product lifetime equalled rotation length). The rate of carbon storage during the first rotation in most plantations was in the range 2-5 Mg C ha(-1) year(-1).A sensitivity analysis revealed the following processes to be both uncertain and critical: the fraction of total woody biomass in branches and roots; litter and soil organic matter decomposition rates; and rates of fine root turnover. Other variables, including the time to canopy closure and the possibility of accelerated decomposition after harvest, were less critical. The lifetime of wood products was not critical to total carbon storage because wood products formed only a modest fraction of the total.The average increase in total carbon storage in the tree-soil-product system per unit increase in Yield Class (m(3) ha(-1) year(-1)) for unthinned Picea sitchensis (Bong.) Carr. plantations was 5.6 Mg C ha(-1). Increasing the Yield Class from 6 to 24 m(3) ha(-1) year(-1) increased the rate of carbon storage in the first rotation from 2.5 to 5.6 Mg C ha(-1) year(-1) in unthinned plantations. Thinning reduced total carbon storage in P. sitchensis plantations by about 15%, and is likely to reduce carbon storage in all plantation types.If the objective is to store carbon rapidly in the short term and achieve high carbon storage in the long term, Populus plantations growing on fertile land (2.7 m spacing, 26-year rotations, Yield Class 12) were the best option examined. If the objective is to achieve high carbon storage in the medium term (50 years) without regard to the initial rate of storage, then plantations of conifers of any species with above-average Yield Classes would suffice. In the long term (100 years), broadleaved plantations of oak and beech store as much carbon as conifer plantations. Mini-rotations (10 years) do not achieve a high carbon storage.

Journal ArticleDOI
TL;DR: In this paper, the authors examined factors controlling aerobic and anaerobic soil respiration in three contrasting types of freshwater North Carolina peatland communities (short pocosins, tall poccosins and gum swamps) which occur along a natural soil nutrient availability gradient.
Abstract: Production of soil gases is important in nutrient and carbon cycling, particularly in peatlands due to their large atmospheric emissions of several greenhouse gases. We examined factors controlling aerobic and anaerobic soil respiration in three contrasting types of freshwater North Carolina peatland communities (short pocosins, tall pocosins and gum swamps) which occur along a natural soil nutrient availability gradient. Short pocosins occur in the ombrotrophic center of the bog complexes and are extremely nutrient-deficient; tall pocosins are slightly less nutrient-deficient; and gum swamps are relatively nutrient-rich. Short pocosin had the lowest soil CO 2 production rates under both aerobic and anaerobic conditions in laboratory experiments, while rates in tall pocosin were similar to or somewhat less than in the gum swamp. Methanogenesis rates were extremely low in laboratory experiments, and indicate that CH 4 production is not a significant pathway of carbon flow in these peatlands. Methane production is also low in relation to other peatlands. Amendment experiments indicate that the poor substrate quality of the highly decomposed, humified peat limits both CO 2 and CH 4 production rates, even though the peat is 95% organic matter. Low soil nutrient concentrations and low pH do not directly limit soil respiration in these peatlands, although there is a positive feedback of nutrients with organic matter inputs and litter quality, causing greater soil respiration in nutrient-rich sites. In situ CO 2 emissions similarly differed between the communities, with highest rates in the gum swamp and lowest rates in the pocosins. Emissions were highly seasonal with soil temperature explaining the majority of the temporal variability. Maximum potential CH 4 emission estimates derived from laboratory temperature relationships and in situ soil temperature data indicate that pocosins make an insignificant contribution to the global atmospheric CH 4 flux. The continued existence of peatlands in warm climates may to a large extent depend on the low substrate quality of their soil organic matter, which maintains low decomposition rates under both aerobic and anaerobic conditions.


Journal ArticleDOI
TL;DR: The effects of endogeic earthworms on the soil organic matter (SOM) dynamics of moist tropical soils are: (i) a sharp increase of mineralization during digestion; (ii) the presence in fresh casts of large amounts of mineral nutrients which are reorganized in microbial biomass at the scale of days to weeks depending on soil properties; and (iii) a subsequent blocking of mineralisation at a scale of months to years in the compact structure of ageing casts (i.e. older than 1-2 weeks) as discussed by the authors.
Abstract: The effects of endogeic earthworms on the soil organic matter (SOM) dynamics of moist tropical soils are: (i) a sharp increase of mineralization during digestion; (ii) the presence in fresh casts of large amounts of mineral nutrients which are reorganized in microbial biomass at the scale of days to weeks depending on soil properties; (iii) a subsequent blocking of mineralization at the scale of months to years in the compact structure of ageing casts (i.e. older than 1–2 weeks). It is hypothesized that, at the larger scale of soil profile and years, activities of earthworms will result in an acceleration of SOM turnover and the accumulation of labile rather than passive organic matter.

Journal ArticleDOI
TL;DR: In this paper, the effects of organic matter content and composition on narrowband soil reflectance across the visible and reflective infrared spectral ranges were evaluated in four Indiana agricultural soils, ranging in organic C content from 0.99 to 1.72 percent.
Abstract: Recent breakthroughs in remote-sensing technology have led to the development of high spectral resolution imaging sensors for observation of earth surface features. This research was conducted to evaluate the effects of organic matter content and composition on narrowband soil reflectance across the visible and reflective infrared spectral ranges. Organic matter from four Indiana agricultural soils, ranging in organic C content from 0.99 to 1.72 percent, was extracted, fractionated, and purified. Six components of each soil were isolated and prepared for spectral analysis. Reflectance was measured in 210 narrow bands in the 400- to 2500-nm wavelength range. Statistical analysis of reflectance values indicated the potential of high dimensional reflectance data in specific visible, near-infrared, and middle-infrared bands to provide information about soil organic C content, but not organic matter composition. These bands also responded significantly to Fe- and Mn-oxide content.

Journal ArticleDOI
TL;DR: In this paper, the authors used the current Rothamsted model for the turnover of organic C in soil to calculate how the organic C content of the topsoils from the four sites would change with time for a range of annual inputs.
Abstract: Soil samples collected from four of the Rothamsted long-term field experiments over the last 100 yr were used to follow the effects of management on soil organic matter content. The experimental sites were:Broadbalk and Geescroft Wildernesses, both on old arable land that had been fenced off in the early 1880s and allowed to revert naturally to deciduous woodland; the unmanured plot in the Rothamsted Park Grass Continuous Hay Experiment, started in 1856; the unmanured and one of the NPK plots in the Broadbalk Continuous Wheat Experiment started in 1843. Total C, radiocarbon and (in some cases) soil microbial biomass C were measured in stored and contemporary soil samples. The current Rothamsted model for the turnover of organic C in soil was then used to calculate how the organic C content of the topsoils from the four sites would change with time for a range of annual inputs. The inputs that generated the best fit to the measured values were: Broadbalk Wilderness 3.5 t C ha−1 yr−1; Geescroft Wilderness 2.5 t C ha−1 yr−1;unmanured plot on Park Grass 3.01 t C ha−1 yr−1; unmanured plot on Broadbalk Wheat 1.3 t C ha−1 yr−1; NPK plot on Broadbalk Wheat 1.71 t C ha−1 yr−1. The model also generated the radiocarbon content of soil organic C for these inputs of C, knowing the 14C content of the atmosphere over the period 1840–1985. The marked increase in the 14C content of soil organic C brought about by thermonuclear testing during the 1960's was accurately represented by the model. The quantities of soil microbial biomass (measured by fumigation-incubation) in the top 23 cm of soil from the four sites were: Broadbalk Wilderness,1.571 t C ha−1; Geescroft Wilderness, 0.58 t C ha−1; unmanured plot on Park Grass,1.621C ha−1; unmanured plot on Broadbalk Wheat, 0.47 t C ha−1; NPK plot on Broadbalk Wheat, 0.76 t C−1.The values for soil microbial biomass C generated by the model for the above annual inputs agreed closely (with one exception) with the measured values. For a site under steady-state conditions, the annual input of organic matter to the soil plus the annual removal of organic matter from the site (if any) gives the Net Primary Production (NPP). NPP thus calculated was 4.0 t C ha−1 yr−1 for the unmanured plot on Park Grass, 2.2 for the unmanured plot on Broadbalk and 5.2 for the NPK plot on Broadbalk. The two Wilderness sites are still accumulating C in both soil and vegetation and here NPP is given by annual input to the soil, plus the annual increment of C in the trees. NPP calculated in this way was 4.8 t C ha−1 yr−1 for Broadbalk Wilderness and 3.3 for Geescroft Wilderness. This new way of estimating NPP, from measurements made on soil organic matter, needs to be tested on a wider range of soils, climates and vegetation types before it can be generally recommended. However, it has many potential advantages, not least that it can give a value for NPP that is integrated over many years from a single sampling. For sites under steady-state conditions it is not essential to have stored soil samples—the necessary measurements can be made on contemporary samples alone.

Journal ArticleDOI
TL;DR: Phosphorus fractionation indicated that the decline in P fertility was not a result of net export of P in the crop, but arises from the mineralisation of organic P and subsequent transformation of the surplus inorganic P to unavailable forms.

Journal ArticleDOI
TL;DR: The hypotheses that disruption of soil structure increases mineralization rates in loams and clays more than in sandy soils and that this increase can be used to estimate the fraction of physically protected organic matter were tested were tested.
Abstract: The hypotheses that disruption of soil structure increases mineralization rates in loams and clays more than in sandy soils and that this increase can be used to estimate the fraction of physically protected organic matter were tested. C and N mineralization was measured in undisturbed, and in finely and coarsely sieved moist or dried/remoistened soil. Fine sieving caused a temporary increase in mineralization. The relative increase in mineralization was much larger in loams and clays than in sandy soils and much larger for N than for C. The combination of remoistening and sieving of the soil gave a further increase in the mineralization flush after the disturbance. Again, the extra flush was larger in loams and clays than in sandy soils, and larger for N than for C. In loams and clays, small pores constituted a higher percentage of the total pore space than in sandy soils. The fraction of small pores explained more than 50% of the variation in the N mineralization rate between soils. There was also a good correlation between the small-pore fraction and the relative increase in N mineralization with fine sieving. For C, these relations were not clear. It is suggested that a large part of the organic matter that was present in the small pores could not be reached by microorganisms, and was therefore physically protected against decomposition. Fine sieving exposed part of this fraction to decomposition. This physically protected organic matter had a lower C: N ratio than the rest of the soil organic matter. The increase in N mineralization after fine sieving can be regarded as a measure of physically protected organic matter.

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TL;DR: In this article, a computer simulation model to analyse risks of soil erosion to long-term crop production is described, called PERFECT, which simulates interactions between soil type, climate, fallow management strategy and crop sequence.
Abstract: A computer simulation model to analyse risks of soil erosion to long-term crop production is described. The model, called PERFECT, simulates interactions between soil type, climate, fallow management strategy and crop sequence. It contains six main modules; data input, water balance, crop growth, crop residue, erosion and model output. Modules are arranged in a framework that allows alternative modules to be used as required for the potential range of applications. The model contains dynamic crop growth models for wheat, sorghum and sunflower. Validation of PERFECT against small catchment and contour bay data collected throughout Queensland showed that PERFECT explained up to 84% of the variation in total available soil water, 89% of the variation in daily runoff, and up to 75% of the variation in grain yield. Average annual soil erosion was accurately predicted but daily erosion totals were less accurate due to the exclusion of rainfall intensity in erosion prediction. Variability in climate dominates agricultural production in the subtropical region of Australia. The validated model can be coupled with long-term climate and soils databases to simulate probabilities of production and erosion risks due to climatic variability. It provides a method to determine the impact of soil erosion on long-term productivity.

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TL;DR: Soil respiration responded to management like microbial biomass-C but varied significantly over the season with the smallest respiration found in the driest month (October) and the largest respiration at end of the rains in May.
Abstract: The effects of clearfelling a tropical rainforest and establishing pasture on soil microbial biomass and nitrogen transformations were assayed monthly over 1 yr in three adjacent systems in the central Amazon region: (1) virgin rainforest; (2) slashed-and-burnt forest; and (3) recently established pasture. The amounts of soil organic matter (SOM) and soil microbial biomass-carbon (biomass-C) were substantial in all systems. Total soil-C ranged between 1.9 and 5.2% depending on management and soil layer, whereas biomass-C ranged between 3.5 and 5.3% of total soil-C. The soil biomass-C decreased upon slashing-and-burning to 64% of its original value (1287 μg g −1 ) in the forest (0–5 cm soil layer) and increased after establishment of pasture to 1290 μg g −1 , but remained unchanged in the deeper 5–20 cm soil layer. No significant seasonal variation was measured in any system or soil layer. Soil respiration responded to management like microbial biomass-C but varied significantly over the season with the smallest respiration found in the driest month (October) and the largest respiration at end of the rains in May. Pools of mineral N varied considerably in all systems and soil layers and displayed identical seasonal variations. The forest topsoil contained the highest amounts (on average 47 μg N g −1 ) and the pasture soil the smallest amounts (on average 24 μg N g −1 ). The transition of the forest ecosystem to a pasture resulted in increased NO 3 − concentrations. Net N-mineralization and net NO 3 − production monitored during short-term laboratory incubations were used as indices of N mineralization and nitrification. No significant differences in N-mineralization indices were measured between systems, but substantial within season variations were recorded in all systems and soil layers. The variations were synchronized in time with extreme net N-mineralization in September and net N-mineralization in October. Significant nitrification indices were measured in all systems. They were identical in the systems, except for small indices found in topsoil of the slashed and burnt area, where, on the other hand, certain localized areas with extreme nitrification rates were detected.


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TL;DR: In this article, the authors evaluate the hypothesis that soil DOC constitutes a readily available microbial resource, and that DOC concentrations are related to rates of biological decomposition and associated nutrient release from soil organic matter.
Abstract: Dissolved organic carbon (DOC) and C and N mineralization were measured during a 210 day regulated in vitro incubation of soils from an old field successional sequence at Cedar Creek Natural History Area. The objective of the study was to evaluate the hypothesis that soil DOC constitutes a readily-available microbial resource, and that DOC concentrations are related to rates of biological decomposition and associated nutrient release from soil organic matter. Soils from five previously cultivated old fields undergoing secondary succession and an oak savanna were selected because they had demonstrated different patterns of C and N cycling. Although amounts of total C differed dramatically (496–1371 μmol g−1), DOC concentrations of all soils at the time of collection were between 0.70 and 1.30 μmol g−1. During the incubation, total and relative DOC concentrations generally remained constant or increased while mineralization rates decreased. When all soils and incubation intervals were considered, there was no obvious relationship between DOC and instantaneous rates of mineralization. Asymptotic exponential response curves did describe positive associations between DOC and CO2-C mineralization rates at early incubation times (R2 = 0.98 for 14 and 35 days), but not later. Similar models did not show a strong relationship between DOC and net-N mineralization rates. By the end of the incubation, the DOC pool could potentially supply 1.5–3.4 days of total C mineralization, but the instantaneous C mineralization rate at any given DOC concentration was 3–10 times lower than at 14 days. These results reflect decreased DOC utilization relative to supply, and could be caused by the accumulation of recalcitrant DOC.