Showing papers on "Soil organic matter published in 2004"

Soil carbon sequestration impacts on global climate change and food security.

Abstract: :The carbon sink capacity of the world’s agricultural and degraded soils is 50 to 66% of the historic carbon loss of 42 to 78 gigatons of carbon. The rate of soil organic carbon sequestration with adoption of recommended technologies depends on soil texture and structure, rainfall, temperature, farming system, and soil management. Strategies to increase the soil carbon pool include soil restoration and woodland regeneration, no-till farming, cover crops, nutrient management, manuring and sludge application, improved grazing, water conservation and harvesting, efficient irrigation, agroforestry practices, and growing energy crops on spare lands. An increase of 1 ton of soil carbon pool of degraded cropland soils may increase crop yield by 20 to 40 kilograms per hectare (kg/ha) for wheat, 10 to 20 kg/ha for maize, and 0.5 to 1 kg/ha for cowpeas. As well as enhancing food security, carbon sequestration has the potential to offset fossilfuel emissions by 0.4 to 1.2 gigatons of carbon per year, or 5 to 15% of the global fossil-fuel emissions.

A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics

Abstract: Since the 1900s, the link between soil biotic activity, soil organic matter (SOM) decomposition and stabilization, and soil aggregate dynamics has been recognized and intensively been studied. By 1950, many studies had, mostly qualitatively, investigated the influence of the five major factors (i.e. soil fauna, microorganisms, roots, inorganics and physical processes) on this link. After 1950, four theoretical mile-stones related to this subject were realized. The first one was when Emerson [Nature 183 (1959) 538] proposed a model of a soil crumb consisting of domains of oriented clay and quartz particles. Next, Edwards and Bremner [J. Soil Sci. 18 (1967) 64] formulated a theory in which the solid-phase reaction between clay minerals, polyvalent cations and SOM is the main process leading to microaggregate formation. Based on this concept, Tisdall and Oades [J. Soil Sci. 62 (1982) 141] coined the aggregate hierarchy concept describing a spatial scale dependence of mechanisms involved in micro- and macroaggregate formation. Oades [Plant Soil 76 (1984) 319] suggested a small, but very important, modification to the aggregate hierarchy concept by theorizing the formation of microaggregates within macroaggregates. Recent research on aggregate formation and SOM stabilization extensively corroborate this modification and use it as the base for furthering the understanding of SOM dynamics. The major outcomes of adopting this modification are: (1) microaggregates, rather than macroaggregates protect SOM in the long term; and (2) macroaggregate turnover is a crucial process influencing the stabilization of SOM. Reviewing the progress made over the last 50 years in this area of research reveals that still very few studies are quantitative and/or consider interactive effects between the five factors. The quantification of these relationships is clearly needed to improve our ability to predict changes in soil ecosystems due to management and global change. This quantification can greatly benefit from viewing aggregates as dynamic rather than static entities and relating aggregate measurements with 2D and 3D quantitative spatial information.

Adsorption of heavy metal ions on soils and soils constituents

Abstract: The article focuses on adsorption of heavy metal ions on soils and soils constituents such as clay minerals, metal (hydr)oxides, and soil organic matter. Empirical and mechanistic model approaches for heavy metal adsorption and parameter determination in such models have been reviewed. Sorption mechanisms in soils, the influence of surface functional groups and surface complexation as well as parameters influencing adsorption are discussed. The individual adsorption behavior of Cd, Cr, Pb, Cu, Mn, Zn and Co on soils and soil constituents is reviewed.

Microbial diversity in soil: Selection of microbial populations by plant and soil type and implications for disease suppressiveness

Abstract: An increasing interest has emerged with respect to the importance of microbial diversity in soil habitats The extent of the diversity of microorganisms in soil is seen to be critical to the maintenance of soil health and quality, as a wide range of microorganisms is involved in important soil functions This review focuses on recent data relating how plant type, soil type, and soil management regime affect the microbial diversity of soil and the implication for the soil's disease suppressiveness The two main drivers of soil microbial community structure, ie, plant type and soil type, are thought to exert their function in a complex manner We propose that the fact that in some situations the soil and in others the plant type is the key factor determining soil microbial diversity is related to the complexity of the microbial interactions in soil, including interactions between microorganisms and soil and microorganisms and plants A conceptual framework, based on the relative strengths of the shaping forces exerted by plant and soil versus the ecological behavior of microorganisms, is proposed

Progressive Nitrogen Limitation of Ecosystem Responses to Rising Atmospheric Carbon Dioxide

Abstract: A highly controversial issue in global biogeochemistry is the regulation of terrestrial carbon (C) sequestration by soil nitrogen (N) availability. This controversy translates into great uncertainty in predicting future global terrestrial C sequestration. We propose a new framework that centers on the concept of progressive N limitation (PNL) for studying the interactions between C and N in terrestrial ecosystems. In PNL, available soil N becomes increasingly limiting as C and N are sequestered in long-lived plant biomass and soil organic matter. Our analysis focuses on the role of PNL in regulating ecosystem responses to rising atmospheric carbon dioxide concentration, but the concept applies to any perturbation that initially causes C and N to accumulate in organic forms. This article examines conditions under which PNL may or may not constrain net primary production and C sequestration in terrestrial ecosystems. While the PNL-centered framework has the potential to explain diverse experimental...

Carbon input to soil may decrease soil carbon content

Abstract: It is commonly predicted that the intensity of primary production and soil carbon (C) content are positively linked. Paradoxically, many long-term field observations show that although plant litter is incorporated to soil in large quantities, soil C content does not necessarily increase. These results suggest that a negative relationship between C input and soil C conservation exists. Here, we demonstrate in controlled conditions that the supply of fresh C may accelerate the decomposition of soil C and induce a negative C balance. We show that soil C losses increase when soil microbes are nutrient limited. Results highlight the need for a better understanding of microbial mechanisms involved in the complex relationship between C input and soil C sequestration. We conclude that energy available to soil microbes and microbial competition are important determinants of soil C decomposition.

Crop and Soil Productivity Response to Corn Residue Removal: A Literature Review

Abstract: Society is facing three related issues: overreliance on imported fuel, increasing levels of greenhouse gases in the atmosphere, and producing sufficient food for a growing world population. The U.S. Department of Energy and private enterprise are developing technology necessary to use high-cellulose feedstock, such as crop residues, for ethanol production. Corn (Zea mays L.) residue can provide about 1.7 times more C than barley (Hordeum vulgare L.), oat (Avena saliva L.), sorghum [Sorghum bicolor (L.) Moench], soybean [Glycine max (L.) Merr.], sunflower (Helianthus annuus L.), and wheat (Triticum aestivum L.) residues based on production levels. Removal of crop residue from the field must be balanced against impacting the environment (soil erosion), maintaining soil organic matter levels, and preserving or enhancing productivity. Our objective is to summarize published works for potential impacts of wide-scale, corn stover collection on corn production capacity in Corn Belt soils. We address the issue of crop yield (sustainability) and related soil processes directly. However, scarcity of data requires us to deal with the issue of greenhouse gases indirectly and by inference. All ramifications of new management practices and crop uses must be explored and evaluated fully before an industry is established. Our conclusion is that within limits, corn stover can be harvested for ethanol production to provide a renewable, domestic source of energy that reduces greenhouse gases. Recommendation for removal rates will vary based on regional yield, climatic conditions, and cultural practices. Agronomists are challenged to develop a procedure (tool) for recommending maximum permissible removal rates that ensure sustained soil productivity.

Tillage and Manure Effects on Soil and Aggregate-Associated Carbon and Nitrogen

Abstract: In agricultural systems, maintenance of soil organic matter (SOM) has long been recognized as a strategy to reduce soil degradation. No-tillage and manure amendments are management practices that can increase SOM content and improve soil aggregation. We investigated the effects of 10-yr of different tillage systems and N sources on soil aggregate-size distribution and aggregate-associated C and N. The study was a split-plot design replicated four times. The main plot treatment was tillage (no-tillage, NT; conventional tillage, CT) and the subplot treatment was N source (manure, M; NH 4 NO 3 fertilizer, F). The experiment was established in 1990 on a moderately welldrained Kennebec silt loam (Fine-silty, mixed, superactive mesic Cumulic Hapludll) with continuous corn (Zea mays L.). In 1999, soil samples were collected (0- to 5-cm depth) from the field treatments and separated into four aggregate-size classes (>2000, 250-2000, 53-250, and 20-53 μm) by wet sieving. Labile C and N content of all aggregate-size fractions were measured using 28-d laboratory incubations of intact and crushed aggregates. No-tillage and M treatments significantly increased total C and N and the formation of macroaggregates. Conventional tillage in comparison with NT significantly reduced macroaggregates with a significant redistribution of aggregates into microaggregates. Aggregate protected labile C and N were significantly greater for macroaggregates, (>2000 and 250-2000 μm) than microaggregates (53-250 and 20-53 μm). and greater for M than F indicating physical protection of labile C within macroaggregates. Notillage and M a lone each significantly increased soil aggregation and aggregate-associated C and N; however, NT and M together further improved soil aggregation and aggregate-protected C and N.

Mechanisms of Carbon Sequestration in Soil Aggregates

Abstract: Soil and crop management practices have a profound impact on carbon (C) sequestration, but the mechanisms of interaction between soil structure and soil organic C (SOC) dynamics are not well understood. Understanding how an aggregate stores and protects SOC is essential to developing proper management practices to enhance SOC sequestration. The objectives of this article are to: (1) describe the importance of plants and soil functions on SOC sequestration, (2) review the mechanisms of SOC sequestration within aggregates under different vegetation and soil management practices, (3) explain methods of assessing distribution of SOC within aggregates, and (4) identify knowledge gaps with regards to SOC and soil structural dynamics. The quality and quantity of plant residues define the amount of organic matter and thus the SOC pool in aggregates. The nature of plant debris (C:N ratio, lignin content, and phenolic compound content) affects the rate of SOC sequestration. Mechanisms of interaction of aggregate dy...

Effects of compost, mycorrhiza, manure and fertilizer on some physical properties of a Chromoxerert soil

Abstract: Addition of organic materials of various origins to soil has been one of the most common rehabilitation practices to improve soil physical properties. Mycorrhiza has been known to play a significant role in forming stable soil aggregates. In this study, a 5-year field experiment was conducted to explore the role of mycorrhizal inoculation and organic fertilizers on the alteration of physical properties of a semi-arid Mediterranean soil (Entic Chromoxerert, Arik clay-loam soil). From 1995 to 1999, wheat ( Triticum aestivum L.), pepper ( Capsicum annuum L.), maize ( Zea mays L.) and wheat were sequentially planted with one of five fertilizers: (1) control, (2) inorganic (160–26–83 kg N–P–K ha −1 ), (3) compost at 25 t ha −1 , (4) farm manure at 25 t ha −1 and (5) mycorrhiza-inoculated compost at 10 t ha −1 . Soil physical properties were significantly affected by organic fertilizers. For soil depths of 0–15 and 15–30 cm, mean weight diameter (MWD) was highest under the manure treatment while total porosity and saturated hydraulic conductivity were highest under the compost treatment. For a soil depth of 0–15 cm, the compost and manure-treated plots significantly decreased soil bulk density and increased soil organic matter concentration compared with other treatments. Compost and manure treatments increased available water content (AWC) of soils by 86 and 56%, respectively. The effect of inorganic fertilizer treatment on most soil physical properties was insignificant ( P >0.05) compared with the control. Mycorrhizal inoculation+compost was more effective in improving soil physical properties than the inorganic treatment. Organic fertilizer sources were shown to have major positive effects on soil physical properties.

Soil Water Content and Organic Carbon Availability Are Major Determinants of Soil Microbial Community Composition

Abstract: Exploration of environmental factors governing soil microbial community composition is long overdue and now possible with improved methods for characterizing microbial communities. Previously, we observed that rice soil microbial communities were distinctly different from tomato soil microbial communities, despite management and seasonal variations within soil type. Potential contributing factors included types and amounts of organic inputs, organic carbon content, and timing and amounts of water inputs. Of these, both soil water content and organic carbon availability were highly correlated with observed differences in composition. We examined how organic carbon amendment (compost, vetch, or no amendment) and water additions (from air dry to flooded) affect microbial community composition. Using canonical correspondence analysis of phospholipid fatty acid data, we determined flooded, carbon-amended (+C) microcosm samples were distinctly different from other +C samples and unamended (-C) samples. Although flooding without organic carbon addition influenced composition some, organic carbon addition was necessary to substantially alter community composition. Organic carbon availability had the same general effects on microbial communities regardless of whether it was compost or vetch in origin. In addition, flooded samples, regardless of organic carbon inputs, had significantly lower ratios of fungal to bacterial biomarkers, whereas under drier conditions and increased organic carbon availability the microbial communities had higher proportions of fungal biomass. When comparing field and microcosm soil, flooded +C microcosm samples were most similar to field-collected rice soil, whereas all other treatments were more similar to field-collected tomato soil. Overall, manipulating water and carbon content selected for microbial communities similar to those observed when the same factors were manipulated at the field scale.

Carbon sequestration in temperate grassland ecosystems and the influence of management, climate and elevated CO2

Abstract: Contents I. Introduction 2 II. Carbon in temperate grasslands 2 III. The process of carbon sequestration in soils 4 IV. Tracking carbon movement 9 V. Models of soil carbon dynamics 10 VI. Management effects on carbon sequestration 11 VII. Climate-change effects on carbon sequestration 12 VIII. Response to elevated CO2 13 IX. Conclusions 14 References 14 Summary The substantial stocks of carbon sequestered in temperate grassland ecosystems are located largely below ground in roots and soil. Organic C in the soil is located in discrete pools, but the characteristics of these pools are still uncertain. Carbon sequestration can be determined directly by measuring changes in C pools, indirectly by using 13C as a tracer, or by simulation modelling. All these methods have their limitations, but long-term estimates rely almost exclusively on modelling. Measured and modelled rates of C sequestration range from 0 to > 8 Mg C ha−1 yr−1. Management practices, climate and elevated CO2 strongly influence C sequestration rates and their influence on future C stocks in grassland soils is considered. Currently there is significant potential to increase C sequestration in temperate grassland systems by changes in management, but climate change and increasing CO2 concentrations in future will also have significant impacts. Global warming may negate any storage stimulated by changed management and elevated CO2, although there is increasing evidence that the reverse could be the case.

Nitrogen cycling in a northern hardwood forest: Do species matter?

Abstract: To investigate the influence of individual tree species on nitrogen (N) cycling in forests, we measured key characteristics of the N cycle in small single-species plots of five dominant tree species in the Catskill Mountains of New York State. The species studied were sugar maple (Acer saccharum), American beech (Fagus grandifolia), yellow birch (Betula alleghaniensis), eastern hemlock (Tsuga ca- nadensis), and red oak (Quercus rubra). The five species varied markedly in N cycling characteristics. For example, hemlock plots consistently showed characteristics associated with slow N cycling, in- cluding low foliar and litter N, high soil C:N, low extractable N pools, low rates of potential net N mineralization and nitrification and low NO3 amounts trapped in ion-exchange resin bags buried in the mineral soil. Sugar maple plots had the lowest soil C:N, and the highest levels of soil characteristics associated with NO3 production and loss (nitrification, extractable NO3 , and resin bag NO3 ). In con- trast, red oak plots had near-average net mineralization rates and soil C:N ratios, but very low values of the variables associated with NO3 production and loss. Correlations between soil N transformations and litter concentrations of N, lignin, lignin:N ratio, or phenolic constituents were generally weak. The in- verse correlation between net nitrification rate and soil C:N that has been reported in the literature was present in this data set only if red oak plots were excluded from the analysis. This study indicates that tree species can exert a strong control on N cycling in forest ecosystems that appears to be mediated through the quality of soil organic matter, but that standard measures of litter quality cannot explain the mechanism of control.

Nitrogen deposition modifies soil carbon storage through changes in microbial enzymatic activity

Abstract: Atmospheric nitrogen (N) deposition derived from fossil-fuel combustion, land clearing, and biomass burning is occurring over large geographical regions on nearly every continent. Greater ecosystem N availability can result in greater aboveground carbon (C) sequestration, but little is understood as to how soil C storage could be altered by N deposition. High concentrations of inorganic N accelerate the degradation of easily decom- posable litter and slow the decomposition of recalcitrant litter containing large amounts of lignin. This pattern has been attributed to stimulation or repression of different sets of microbial extracellular enzymes. We hypothesized that soil C cycling in forest ecosystems with markedly different litter chemistry and decomposition rates would respond to anthro- pogenic N deposition in a manner consistent with the biochemical composition of the dominant vegetation. Specifically, oak-dominated ecosystems with low litter quality should gain soil C, and sugar maple ecosystems with high litter quality should lose soil C in response to high levels of N deposition (80 kg N-ha-1-yr-1). Consistent with this hypothesis, we observed over a three-year period a significant loss of soil C (20%) from a sugar maple- dominated ecosystem and a significant gain (10%) in soil C in an oak-dominated ecosystem, a result that appears to be mediated by the regulation of the microbial extracellular enzyme phenol oxidase. Elevated N deposition resulted in changes in soil carbon that were ecosystem specific and resulted from the divergent regulatory control of microbial extracellular en- zymes by soil N availability.

Sorption of Sulfonamide Pharmaceutical Antibiotics on Whole Soils and Particle-Size Fractions

Abstract: Residues of pharmaceutical antibiotics are found in the environment, whose fate and effects are governed by sorption. Thus, the extent and mechanisms of the soil sorption of p-aminobenzoic acid and five sulfonamide antibiotics (sulfanilamide, sulfadimidine, sulfadiazine, sulfadimethoxine, and sulfapyridine) were investigated using topsoils of fertilized and unfertilized Chernozem and their organic-mineral particle-size fractions. Freundlich adsorption coefficients (K(f)) ranged from 0.5 to 6.5. Adsorption increased with aromaticity and electronegativity of functional groups attached to the sulfonyl-phenylamine core. Adsorption to soil and particle-size fractions increased in the sequence: coarse silt < whole soil < medium silt < sand < clay < fine silt and was influenced by pH. Sorption nonlinearity (1/n

Microbial and biochemical soil quality indicators and their potential for differentiating areas under contrasting agricultural management regimes

Abstract: The aim of this study was to examine interrelationships between functional biochemical and microbial indicators of soil quality, and their suitability to differentiate areas under contrasting agricultural management regimes. The study included five 0.8 ha areas on a sandy-loam soil which had received contrasting fertility and cropping regimes over a 5 year period. These were organically managed vegetable, vegetable–cereal and arable rotations, an organically managed grass clover ley, and a conventional cereal rotation. The organic areas had been converted from conventional cereal production 5 years prior to the start of the study. All of the biochemical analyses, including light fraction organic matter (LFOM) C and N, labile organic N (LON), dissolved organic N and water-soluble carbohydrates showed significant differences between the areas, although the nature of the relationships between the areas varied between the different parameters, and were not related to differences in total soil organic matter content. The clearest differences were seen in LFOM C and N and LON, which were higher in the organic arable area relative to the other areas. In the case of the biological parameters, there were differences between the areas for biomass-N, ATP, chitin content, and the ratios of ATP: biomass and basal respiration: biomass. For these parameters, the precise relationships between the areas varied. However, relative to the conventionally managed area, areas under organic management generally had lower biomass-N and higher ATP contents. Arbuscular mycorrhizal fungus colonization potential was extremely low in the conventional area relative to the organic areas. Further, metabolic diversity and microbial community level physiological profiles, determined by analysis of microbial community metabolism using Biolog GN plates and the activities of eight key nutrient cycling enzymes, grouped the organic areas together, but separated them from the conventional area. We conclude that microbial parameters are more effective and consistent indicators of management induced changes to soil quality than biochemical parameters, and that a variety of biochemical and microbial analyses should be used when considering the impact of management on soil quality.

Soil organic carbon pool changes following land-use conversions

Abstract: Carbon (C) can be sequestered in the mineral soil after the conversion of intensively cropped agricultural fields to more extensive land uses such as afforested and natural succession ecosystems Three land-use treatments from the long-term ecological research site at Kellogg biological station in Michigan were compared with a nearby deciduous forest Treatments included a conventionally tilled cropland, a former cropland afforested with poplar for 10 years and an old field (10 years) succession We used soil aggregate and soil organic matter fractionation techniques to isolate C pools that (1) have a high potential for C storage and (2) accumulate C at a fast rate during afforestation or succession These fractions could serve as sensitive indicators for the total change in C content due to land-use changes At the mineral soil surface (0‐7cm), afforesting significantly increased soil aggregation to levels similar to native forest However, surface soil (0‐7cm) C did not follow this trend: soil C of the native forest site (229tCha � 1 ) was still significantly greater than the afforested (126tCha � 1 ) and succession (154tCha � 1 ) treatments However, when the 0‐50cm soil layer was considered, no differences in total soil C were observed between the cropland and the poplar afforested system, while the successional system increased total soil C (0‐50cm) at a rate of 0786tCha � 1 yr � 1 Afforested soils sequestered C mainly in the fine intraaggregate particulate organic matter (POM) (53‐250lm), whereas the successional soils sequestered C preferentially in the mineral-associated organic matter and fine intraaggregate POM C pools Nomenclature

Ecosystem Level Impacts of Invasive Acacia saligna in the South African Fynbos

Abstract: Recent efforts to clear invasive plants from the fynbos of South Africa forces managers to think about how N2-fixing invasives have altered ecosystem processes and the implications of these changes for community development. This study investigated the changes in nitrogen (N) cycling regimes in fynbos with the invasion of Acacia saligna, the effects of clear-cutting acacia stands on soil microclimate and N cycling, and how altered N resources affected the growth of a weedy grass species. Litterfall, litter quality, soil nutrient pools, and ion exchange resin (IER)-available soil N were measured in uninvaded fynbos, intact acacia, and cleared acacia stands. In addition, a bioassay experiment was used to ascertain whether the changes in soil nutrient availability associated with acacia would enhance the success of a weedy grass species. Acacia plots had greater amounts of litterfall, which had higher concentrations of N. This led to larger quantities of organic matter, total N, and IER-available N in the soil. Clearing acacia stands caused changes in soil moisture and temperature, but did not result in differences in IER-available N. The alteration of N availability by acacias was shown to increase growth rates of the weedy grass Ehrharta calycina, suggesting that secondary invasions by nitrophilous weedy species may occur after clearing N2-fixing alien species in the fynbos. It is suggested that managers use controlled burns, the addition of mulch, and the addition of fynbos seed after clearing to lower the levels of available N in the soil and initiate the return of native vegetation.

3 Soil Organic Matter Fractions and Their Relevance to Soil Function

Abstract: History and Purpose of Organic Matter Measurement 68 Importance of SOM and Its Relationship to Management 68 Approaches to Organic Matter Fractionation 71 Types of Organic Matter in Mineral Soils and Their Probable Functions 72 Relationship between Dynamics and Measured Fractions 72 Commonly Described SOM Pools and Related Fractions 73 Fractions Equated with the Biologically Active Pool 73 Fractions Associated with Physically Active and Slow Pools 76 Fractions Associated with Recalcitrant Pools 77 Measures of POM and Their Interpretation 78 POM as an Index 78 Approaches to POM Fractionation and Interpretation of Results 80 Methods Yielding a Single POM Fraction 83 Methods Separating Fresh POM from Resident POM 87 Methods Separating Protected from Nonprotected POM 87 Summary 90 References 90

Calibration of the Rothamsted organic carbon turnover model (RothC ver. 26.3), using measurable soil organic carbon pools

Abstract: A fractionation scheme that provided the measurement of a labile pool (particulate organic carbon), a charcoal-carbon pool, and a humic pool by difference was tested as a means of initialising the Rothamsted organic carbon turnover model version 26.3. Equating these 3 fractions with the resistant plant material, inert organic matter, and humic pools of the model, respectively, gave good agreement between measured and modelled data for 2 long-term rotation trials in Australia using a soil depth of 30 cm. At one location, Brigalow Research Station in Queensland, there were 3 distinct soil types, two clays and a duplex soil, in a semi-arid, subtropical climate. At this site, continuous wheat with some sorghum was established after clearing land under brigalow (Acacia harpophylla) and continued for 18 years. The second location was near Tarlee, South Australia, and was established on existing agricultural land. One soil type (red brown earth) with 2 rotations (continuous wheat and wheat–fallow) were available over a period of 8 years. The modelled and measured data were in good agreement for both locations but the level of agreement was substantially improved when the resistant plant material decomposition rate was reduced from 0.3 to 0.15/year. No other modifications were required and the resulting values provided excellent agreement between the modelled and measured data not only for the total soil organic carbon but also for the individual pools. Using this fractionation scheme therefore provides an excellent means of initialising and testing the Rothamsted model, not only in Australia, but also in countries with similar soil types and climate. For the first time, the work reported here demonstrates a methodology linking measured soil carbon pools with a conceptual soil carbon turnover model. This approach has the advantage of allowing the model to be initialised at any point in the landscape without the necessity for historical data or for using the model itself to generate an initial equilibrium pool structure. The correct prediction of the changing total soil organic carbon levels, as well as the pool structure over time, acts as an internal verification and gives confidence that the model is performing as intended.

Agricultural activities and the global carbon cycle

Abstract: The observed and projected increase in emission of greenhouse gases, with attendant effects on global warming and sea level rise, have raised interests in identifying mitigation options. Terrestrial C sequestration involves capture of atmospheric C through photosynthesis and storage in biota, soil and wetlands. Land use, vegetation and soil management have a strong impact on the biotic processes of C sequestration. Losses of C from the terrestrial ecosystems are exacerbated by deforestation, biomass burning, plowing, resource-based and subsistence agriculture, and practices that mine soil fertility and deplete the soil organic C (SOC) pool. Biomass burning may also produce charcoal, which is an inert carbon with long residence time. Practices that enhance C sequestration include afforestation and reforestation, conservation tillage and mulch farming, integrated nutrient management and adopting systems with high biodiversity. Net C sequestration within an ecosystem can be assessed by taking into account the hidden C costs of fertilizers, pesticides, tillage, irrigation and other input. Restoration of degraded soils and ecosystems has a vast potential of C sequestration. The Kyoto Protocol provides for C sequestration in terrestrial sinks and C trading through Clean Development Mechanisms. Terrestrial C sequestration, besides being a win–win strategy, offers a window of opportunity for the first few decades of the 21st century. It is a natural process of reducing the rates of gaseous emissions while alternatives to fossil fuel take effect.

Microbial community utilization of recalcitrant and simple carbon compounds: impact of oak-woodland plant communities

Abstract: Little is known about how the structure of microbial communities impacts carbon cycling or how soil microbial community composition mediates plant effects on C-decomposition processes. We examined the degradation of four 13C-labeled compounds (starch, xylose, vanillin, and pine litter), quantified rates of associated enzyme activities, and identified microbial groups utilizing the 13C-labeled substrates in soils under oaks and in adjacent open grasslands. By quantifying increases in non-13C-labeled carbon in microbial biomarkers, we were also able to identify functional groups responsible for the metabolism of indigenous soil organic matter. Although microbial community composition differed between oak and grassland soils, the microbial groups responsible for starch, xylose, and vanillin degradation, as defined by 13C-PLFA, did not differ significantly between oak and grassland soils. Microbial groups responsible for pine litter and SOM-C degradation did differ between the two soils. Enhanced degradation of SOM resulting from substrate addition (priming) was greater in grassland soils, particularly in response to pine litter addition; under these conditions, fungal and Gram + biomarkers showed more incorporation of SOM-C than did Gram – biomarkers. In contrast, the oak soil microbial community primarily incorporated C from the added substrates. More 13C (from both simple and recalcitrant sources) was incorporated into the Gram – biomarkers than Gram + biomarkers despite the fact that the Gram + group generally comprised a greater portion of the bacterial biomass than did markers for the Gram – group. These experiments begin to identify components of the soil microbial community responsible for decomposition of different types of C-substrates. The results demonstrate that the presence of distinctly different plant communities did not alter the microbial community profile responsible for decomposition of relatively labile C-substrates but did alter the profiles of microbial communities responsible for decomposition of the more recalcitrant substrates, pine litter and indigenous soil organic matter.

Significance of soil organic matter to soil quality and health.

Abstract: Soil Quality, Soil Health, and Ecosystem Functions 1 Soil Quality Indicators, Perceptions, and Indices 2 Nature and Composition of SOM 3 Levels of SOC Accumulation in Relation to Global Greenhouse Effects 5 Influences on SOM Accumulation 6 Environmental Influences 6 Soil Management Practices That Influence the Balance between C Gains and Losses 9 SOM Influences on SQ Indicator Properties and Functions 10 Physical Properties Influenced by SOM 10 Soil Aggregation 11 Soil Water Availability 15 Chemical Soil Properties Influenced by Organic Matter 18 Nutrient Storage and Release 18 Microbial Enhancement of Nutrient Availability 20 Cation Exchange Capacity 20 Sorption of Organic Compounds 21 Anion Sorption 22 Metal Mobility 22 Soil pH Buffering and Amelioration 23 Growth-Regulating Substances 23 Biological Properties 24 Influence of Organic Residues and SOM Management on Crop Pests 28 Pools of Soil Organic Carbon 28 Relationship of SOM with Soil Productivity and Crop Yields 33 Conclusions 34 References 36

Carbon Sequestration in Microaggregates of No-Tillage Soils with Different Clay Mineralogy

Abstract: Identification of diagnostic soil organic matter (SOM) fractions and the mechanisms controlling their formation and turnover is critical for better understanding of C dynamics in soils Enhanced microaggregate formation and stabilization of C due to reduced macroaggregate turnover has been proposed as a mechanism promoting C sequestration in no-tillage (NT) compared with conventional tillage (CT) systems in temperate soils dominated by 2:1 clay mineralogy We evaluated the contribution of macroaggregate-protected microaggregates to total soil organic carbon (SOC) sequestration in NT relative to CT in three soils differing in clay mineralogy: a 2:1 clay-dominated soil (2:1), a soil with mixed clay mineralogy [2:1 and 1:11 and oxides (mixed), and a soil dominated by (1:1) clay minerals and oxides (1:1) Microaggregates (mM) were isolated from macroaggregates from 0- to 5- and 5- to 20-cm soil layers Particulate organic matter (POM) located within the microaggregates (intra-mM-POM) was separated from POM outside of the microaggregates (inter-mM-POM) and the mineral fraction of the microaggregates (mineral-mM) In all three soils, total SOC as well as microaggregate-associated C (mM-C) was greater with NT compared with CT Although less than half of the total SOC under NT was associated with the microaggregate fraction, more than 90% of the total difference in SOC between NT and CT was explained by the difference in mM-C in all three soils Thus, we identified and isolated a fraction that explains almost the entire difference in total SOC between NT and CT across soils characterized by drastically different clay mineralogy

Decomposition rate of organic substrates in relation to the species diversity of soil saprophytic fungi

Abstract: Despite the great interest concerning the relationship between species diversity and ecosystem functioning, there is virtually no knowledge as to how the diversity of decomposer microbes influences the decomposition rate of soil organic matter. We established a microcosm study in which the number of soil fungi was investigated in relation to the system's ability to (i) degrade raw coniferous forest humus, and (ii) use resources that were either added to the systems or released into the soils after a disturbance (drought). With the exception of the most diverse treatment, in each of the six replicates of each of the six diversity treatments (1, 3, 6, 12, 24 or 43 taxa), fungal taxa were randomly chosen from a pool of 43 commonly isolated fungal species of raw humus. Two months after initiation of the study CO2 production increased as fungal diversity increased, but in the species-poor end of the diversity gradient only. Addition of various energy resources to the microcosms generally increased the level of soil respiration but did not affect the shape of the diversity-CO2-production curve. Rewetting the soil after severe drought resulted in a rapid flush of CO2, particularly in the most diverse communities. The biomass of the fungi in the non-disturbed soils, and soil NH4-N concentration and soil pH in both disturbed and non-disturbed systems were slightly but significantly higher in the diverse than in the simple systems. Fungal species richness had no influence on the organic matter content of the humus at the end of the experiment. The results suggest that the functional efficiency of fungal communities can increase with the number of fungal taxa. This diversity effect was, however, significant at the species-poor end of the diversity gradient only, which implies considerable functional equivalency (redundancy) among the decomposer fungi.