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Showing papers on "Soil organic matter published in 2005"


Journal ArticleDOI
TL;DR: Several approaches have been suggested to address the soil compaction problem, which should be applied according to the soil, environment and farming system as discussed by the authors, which can help the soil/crop system to resist harmful external stresses.
Abstract: Soil compaction is one of the major problems facing modern agriculture. Overuse of machinery, intensive cropping, short crop rotations, intensive grazing and inappropriate soil management leads to compaction. Soil compaction occurs in a wide range of soils and climates. It is exacerbated by low soil organic matter content and use of tillage or grazing at high soil moisture content. Soil compaction increases soil strength and decreases soil physical fertility through decreasing storage and supply of water and nutrients, which leads to additional fertiliser requirement and increasing production cost. A detrimental sequence then occurs of reduced plant growth leading to lower inputs of fresh organic matter to the soil, reduced nutrient recycling and mineralisation, reduced activities of micro-organisms, and increased wear and tear on cultivation machinery. This paper reviews the work related to soil compaction, concentrating on research that has been published in the last 15 years. We discuss the nature and causes of soil compaction and the possible solutions suggested in the literature. Several approaches have been suggested to address the soil compaction problem, which should be applied according to the soil, environment and farming system. The following practical techniques have emerged on how to avoid, delay or prevent soil compaction: (a) reducing pressure on soil either by decreasing axle load and/or increasing the contact area of wheels with the soil; (b) working soil and allowing grazing at optimal soil moisture; (c) reducing the number of passes by farm machinery and the intensity and frequency of grazing; (d) confining traffic to certain areas of the field (controlled traffic); (e) increasing soil organic matter through retention of crop and pasture residues; (f) removing soil compaction by deep ripping in the presence of an aggregating agent; (g) crop rotations that include plants with deep, strong taproots; (h) maintenance of an appropriate base saturation ratio and complete nutrition to meet crop requirements to help the soil/crop system to resist harmful external stresses.

1,499 citations


Journal ArticleDOI
TL;DR: In this article, the authors discuss the main SOM stabilisation mechanisms with respect to their ability to specifically protect root-derived organic matter (SOM) and show that rootC has a longer residence time in soil than shootC.
Abstract: Understanding the origin of the carbon (C) stabilised in soils is crucial in order to device management practices that will foster Caccumulation in soils. The relative contributions to soilC pools of roots vs. shoots is one aspect that has been mostly overlooked, although it appears a key factor that drives the fate of plant tissueC either as mineralized CO2 or as stabilized soil organic matter (SOM). Available studies on the subject consistently indicate that rootC has a longer residence time in soil than shootC. From the few studies with complete datasets, we estimated that the mean residence time in soils of root-derived C is 2.4times that of shoot-derived C. Our analyses indicate that this value is biased neither by an underestimation of root contributions, as exudation was considered in the analysis, nor by a priming effect of shoot litter on SOM. Here, we discuss the main SOM stabilisation mechanisms with respect to their ability to specifically protect root-derived SOM. Comparing in situ and incubation experiments suggests that the higher chemical recalcitrance of root tissues as compared to that of shoots is responsible for only a small portion, i.e. about one fourth, of the difference in mean residence time in soils of root-derived vs. shoot-derivedC. This suggests that SOM protection mechanisms other than chemical recalcitrance are also enhanced by root activities: (1)physico-chemical protection, especially in deeper horizons, (2)micrometer-scale physical protection through myccorhiza and root-hair activities, and (3)chemical interactions with metal ions. The impact of environmental conditions within deeper soil layers on rootC stabilisation appear difficult to assess, but is likely, if anything, to further increase the ratio between the mean residence time of root vs. shootC in soils. Future advances are expected from isotopic studies conducted at the molecular level, which will help unravel the fate of individual shoot and root compounds, such as cutins and suberins, throughout soil profiles.

1,491 citations


Journal ArticleDOI
TL;DR: The benefits of organic technologies are higher soil organic matter and nitrogen, lower fossil energy inputs, yields similar to those of conventional systems, and conservation of soil moisture and water resources as discussed by the authors.
Abstract: Various organic technologies have been utilized for about 6000 years to make agriculture sustainable while conserving soil, water, energy, and biological resources. Among the benefits of organic technologies are higher soil organic matter and nitrogen, lower fossil energy inputs, yields similar to those of conventional systems, and conservation of soil moisture and water resources (especially advantageous under drought conditions). Conventional agriculture can be made more sustainable and ecologically sound by adopting some traditional organic farming technologies.

1,241 citations


Journal ArticleDOI
Rattan Lal1
TL;DR: In this article, the authors proposed a method to improve the soil organic carbon (SOC) stock through afforestation of agricultural soils and management of forest plantations through C sequestration, and the rate of SOC sequestration and the magnitude and quality of soil C stock depend on the complex interaction between climate, soils, tree species and management.

1,188 citations


Journal ArticleDOI
TL;DR: In this paper, soil characteristics and gross rates from 100 studies conducted in forest, shrubland, grassland, and agricultural systems to answer the following questions: What factors appear to be the major drivers for production and consumption of inorganic N as measured by isotope dilution studies? Do rates or the relationships between drivers and rates differ among ecosystem types?
Abstract: Isotope pool dilution studies are increasingly reported in the soils and ecology literature as a means of measuring gross rates of nitrogen (N) mineralization, nitrification, and inorganic N assimilation in soils. We assembled data on soil characteristics and gross rates from 100 studies conducted in forest, shrubland, grassland, and agricultural systems to answer the following questions: What factors appear to be the major drivers for production and consumption of inorganic N as measured by isotope dilution studies? Do rates or the relationships between drivers and rates differ among ecosystem types? Across a wide range of ecosystems, gross N mineralization is positively correlated with microbial biomass and soil C and N concentrations, while soil C:N ratio exerts a negative effect on N mineralization only after adjusting for differences in soil C. Nitrification is a log-linear function of N mineralization, increasing rapidly at low mineralization rates but changing only slightly at high mineralization rates. In contrast, NH 4 1 assimilation by soil microbes increases nearly linearly over the full range of mineralization rates. As a result, nitrification is proportionately more important as a fate for NH4 1 at low mineralization rates than at high mineralization rates. Gross nitrification rates show no relationship to soil pH, with some of the fastest nitrification rates occurring below pH 5 in soils with high N mineralization rates. Differences in soil organic matter (SOM) composition and concentration among ecosystem types in- fluence the production and fate of mineralized N. Soil organic matter from grasslands appears to be inherently more productive of ammonium than SOM from wooded sites, and SOM from deciduous forests is more so than SOM in coniferous forests, but differences appear to result primarily from differing C:N ratios of organic matter. Because of the central importance of SOM characteristics and concentrations in regulating rates, soil organic matter depletion in agricultural systems appears to be an important determinant of gross process rates and the proportion of NH4 1 that is nitrified. Addition of 15 N appears to stimulate NH4 1 consumption more than NO3 2 consumption processes; however, the magnitude of the stim- ulation may provide useful information regarding the factors limiting microbial N trans- formations.

908 citations


Book ChapterDOI
TL;DR: In this paper, the authors considered the sensitivity of individual organic matter fractions to changes in soil management and have specific effects on soil properties and processes, and concluded that individual organics are sensitive to changes and have a specific effect on soil function.
Abstract: Total soil organic matter content is a key attribute of soil quality since it has far-reaching effects on soil physical, chemical, and biological properties. However, changes in contents of organic carbon (C) and total nitrogen (N) occur only slowly and do not provide an adequate indication of important short-term changes in soil organic matter quality that may be occurring. Labile organic matter pools can be considered as fine indicators of soil quality that influence soil function in specific ways and that are much more sensitive to changes in soil management practice. Particulate organic matter consists of partially decomposed plant litter, and it acts as a substrate and center for soil microbial activity, a short-term reservoir of nutrients, a food source for soil fauna and loci for formation of water stable macroaggregates. Dissolved (soluble) organic matter consists of organic compounds present in soil solution. This pool acts as a substrate for microbial activity, a primary source of mineralizable N, sulfur (S), and phosphorus (P), and its leaching greatly influences the nutrient and organic matter content and pH of groundwater. Various extractable organic matter fractions have also been suggested to be important, including hot water-extractable and dilute acid-extractable carbohydrates, which are involved in stabilization of soil aggregates, and permanganate-oxidizable C. Measurement of potentially mineralizable C and N represents a bioassay of labile organic matter using the indigenous microbial community to release labile organic fractions of C and N. Mineralizable N is also an important indicator of the capacity of the soil to supply N for crops. It is concluded that individual labile organic matter fractions are sensitive to changes in soil management and have specific effects on soil function. Together they reflect the diverse but central effects that organic matter has on soil properties and processes. (c) 2005 Elsevier Inc.

826 citations


Journal ArticleDOI
TL;DR: In this article, the authors reviewed the literature along with Michigan farmer experience to evaluate promising cover crop species for four niches: Northern winter (USDA Hardiness Zones 5-6), Northern summer (Zones 5 -6), Southern winter (Zone 7-8), and Southern summer (Zone 6 -8).
Abstract: The integration of cover crops into cropping systems brings costs and benefits, both internal and external to the farm. Benefits include promoting pest-suppression, soil and water quality, nutrient cycling efficiency, and cash crop productivity. Costs of adopting cover crops include increased direct costs, potentially reduced income if cover crops interfere with other attractive crops, slow soil warming, difficulties in predicting N mineralization, and production expenses. Cover crop benefits tend to be higher in irrigated systems. The literature is reviewed here along with Michigan farmer experience to evaluate promising cover crop species for four niches: Northern winter (USDA Hardiness Zones 5-6), Northern summer (Zones 5-6), Southern winter (Zones 7-8), and Southern summer (Zones 7-8). Warm season C 4 grasses are outstanding performers for summer niches (6-9 Mg ha -1 ), and rye (Secale cereale L.) is the most promising for winter niches (0.8-6 Mg ha -1 ) across all hardiness zones reviewed. Legume-cereal mixtures such as sudangrass (Sorghum sudanese L.)-cowpea (Vigna unguiculata L.) and wheat (Triticum aestivum L.)-red clover (Trifolium pretense L.) are the most effective means to produce substantial amounts (28 Mg ha -1 ) of mixed quality residues. Legume covers are slow growers and expensive to establish. At the same time, legumes fix N, produce high quality but limited amounts (0.5-4 Mg ha -1 ) of residues, and enhance beneficial insect habitat. Brassica species produce glucosinolate-containing residues (2-6 Mg ha -1 ) and suppress plant-parasitic nematodes and soil-borne disease. Legume cover crops are the most reliable means to enhance cash crop yields compared with fallows or other cover crop species. However, farmer goals and circumstances must be considered. If soil pests are a major yield limiting factor in cash crop production, then use of brassica cover crops should be considered. Cereal cover crops produce the largest amount of biomass and should be considered when the goal is to rapidly build soil organic matter. Legume-cereal or brassica-cereal mixtures show promise over a wide range of niches.

824 citations


Journal ArticleDOI
06 Jan 2005-Nature
TL;DR: It is found that SOM decomposition or soil basal respiration rate was significantly affected by changes in SOM components associated with soil depth, sampling method and incubation time, suggesting that the temperature sensitivity for resistant organic matter pools does not differ significantly from that of labile pools, and that both types of SOM will respond similarly to global warming.
Abstract: Our understanding of the relationship between the decomposition of soil organic matter (SOM) and soil temperature affects our predictions of the impact of climate change on soil-stored carbon. One current opinion is that the decomposition of soil labile carbon is sensitive to temperature variation whereas resistant components are insensitive. The resistant carbon or organic matter in mineral soil is then assumed to be unresponsive to global warming. But the global pattern and magnitude of the predicted future soil carbon stock will mainly rely on the temperature sensitivity of these resistant carbon pools. To investigate this sensitivity, we have incubated soils under changing temperature. Here we report that SOM decomposition or soil basal respiration rate was significantly affected by changes in SOM components associated with soil depth, sampling method and incubation time. We find, however, that the temperature sensitivity for SOM decomposition was not affected, suggesting that the temperature sensitivity for resistant organic matter pools does not differ significantly from that of labile pools, and that both types of SOM will therefore respond similarly to global warming.

689 citations


Journal ArticleDOI
TL;DR: Differences in litter calcium concentrations among tree species resulted in profound changes in soil acidity and fertility that were similar within and among tree groups, and were associated with increased native earthworm abundance and diversity.
Abstract: Tree species can influence biogeochemistry through variation in the quantity and chemistry of their litter, and associated impacts on the soil heterotrophic community. However, the role that different plant traits play in these processes is not well understood, nor is it clear whether species effects on soils largely reflect a gymnosperm vs. angiosperm contrast. Using a replicated, long-term monoculture plot experiment, we examined variation in soils among 14 gymnosperm and angiosperm tree species 30 years after plot establishment, and assessed the role of litter chemistry vis-a`-vis such variation. Differences in litter calcium concentrations among tree species resulted in profound changes in soil acidity and fertility that were similar within and among tree groups. Tree species rich in calcium were associated with increased native earthworm abundance and diversity, as well as increased soil pH, exchangeable calcium, per cent base saturation and forest floor turnover rate.

624 citations


Journal ArticleDOI
TL;DR: This paper conducted a meta-analysis to quantify the impact of changing agricultural land use and management on soil organic carbon (SOC) storage under moist and dry climatic conditions of temperate and tropical regions.
Abstract: We conducted a meta-analysis to quantify the impact of changing agricultural land use and management on soil organic carbon (SOC) storage under moist and dry climatic conditions of temperate and tropical regions. We derived estimates of management impacts for a carbon accounting approach developed by the Intergovernmental Panel on Climate Change, addressing the impact of long-term cultivation, setting-aside land from crop production, changing tillage management, and modifying C input to the soil by varying cropping practices. We found 126 articles that met our criteria and analyzed the data in linear mixed-effect models. In general, management impacts were sensitive to climate in the following order from largest to smallest changes in SOC: tropical moist>tropical dry>temperate moist>temperate dry. For example, long-term cultivation caused the greatest loss of SOC in tropical moist climates, with cultivated soils having 0.58 ± 0.12, or 58% of the amount found under native vegetation, followed by tropical dry climates with 0.69 ± 0.13, temperate moist with 0.71 ± 0.04, and temperate dry with 0.82 ± 0.04. Similarly, converting from conventional tillage to no-till increased SOC storage over 20 years by a factor of 1.23 ± 0.05 in tropical moist climates, which is a 23% increase in SOC, while the corresponding change in tropical dry climates was 1.17 ± 0.05, temperate moist was 1.16 ± 0.02, and temperate dry was 1.10 ± 0.03. These results demonstrate that agricultural management impacts on SOC storage will vary depending on climatic conditions that influence the plant and soil processes driving soil organic matter dynamics.

623 citations


Journal ArticleDOI
TL;DR: In this paper, the role of low molecular weight (LMW) DOM compounds in the C dynamics of temperate and boreal forest soils focussing in particular on organic acids, amino acids and sugars was assessed.
Abstract: Dissolved organic matter (DOM), typically quantified as dissolved organic carbon (DOC), has been hypothesized to play many roles in pedogenesis and soil biogeochemical cycles, however, most research to date concerning forest soils has focussed on the high molecular weight (HMW) components of this DOM. This review aims to assess the role of low molecular weight (LMW) DOM compounds in the C dynamics of temperate and boreal forest soils focussing in particular on organic acids, amino acids and sugars. The current knowledge of concentrations, mineralization kinetics and production rates and sources in soil are summarised. We conclude that although these LMW compounds are typically maintained at very low concentrations in the soil solution (

Journal ArticleDOI
TL;DR: This review examines selected papers containing soil enzyme data that could be used to distinguish enzyme sources and substrate specificity, at scales within and between major nutrient cycles.

Journal ArticleDOI
01 Sep 2005-Geoderma
TL;DR: In this paper, the authors quantified the soil organic carbon (SOC) and nitrogen (N) storage in silty soils under wheat, maize, grassland and spruce, and determined the SOC and N storage in water-stable aggregates of different size and in density fractions.

Journal ArticleDOI
TL;DR: In this paper, the authors hypothesize that DON uptake from the soil may not contribute largely to N acquisition by plants but may instead be primarily involved in the recapture of DON previously lost during root exudation.
Abstract: The direct uptake of dissolved organic nitrogen (DON) by plants has the potential to be a primary Factor in ecosystem functioning and vegetation succession particularly in N-limiting environments. Clear experimental evidence to support this view, however, is still lacking. Further, many of the experimental approaches used to assess whether DON is important may be compromised due to the use of inappropriate methods for comparing and quantifying plant available inorganic and organic soil N pools. In addition, experiments aimed at quantifying plant DON capture using dual-labelled (15N, 13C) organic N tracers often do not consider important aspects such as isotope pool dilution, differences in organic and inorganic N pool turnover times, bi-directional DON flows at the soil–root interface, and the differential fate of the 15N and 13C in the tracer compounds. Based upon experimental evidence, we hypothesize that DON uptake from the soil may not contribute largely to N acquisition by plants but may instead be primarily involved in the recapture of DON previously lost during root exudation. We conclude that while root uptake of amino acids in intact form has been shown, evidence demonstrating this as a major plant N acquisition pathway is still lacking.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the reported decreases in P sorption are not related to competition from the decomposition products of organic matter breakdown, but are the result of P release from the OM that was not accounted for when calculating the reduction in P-sorption.
Abstract: The incorporation of organic matter ( OM) in soils that are able to rapidly sorb applied phosphorus ( P) fertiliser reportedly increases P availability to plants. This effect has commonly been ascribed to competition between the decomposition products of OM and P for soil sorption sites resulting in increased soil solution P concentrations. The evidence for competitive inhibition of P sorption by dissolved organic carbon compounds, derived from the breakdown of OM, includes studies on the competition between P and (i) low molecular weight organic acids (LOAs), (ii) humic and fulvic acids, and (iii) OM leachates in soils with a high P sorption capacity. These studies, however, have often used LOAs at 1 - 100 mM, concentrations much higher than those in soils ( generally < 0.05 mM). The transience of LOAs in biologically active soils further suggests that neither their concentration nor their persistence would have a practical benefit in increasing P phytoavailability. Higher molecular weight compounds such as humic and fulvic acids also competitively inhibit P sorption; however, little consideration has been given to the potential of these compounds to increase the amount of P sorbed through metal - chelate linkages. We suggest that the magnitude of the inhibition of P sorption by the decomposition products of OM leachate is negligible at rates equivalent to those of OM applied in the field. Incubation of OM in soil has also commonly been reported as reducing P sorption in soil. However, we consider that the reported decreases in P sorption ( as measured by P in the soil solution) are not related to competition from the decomposition products of OM breakdown, but are the result of P release from the OM that was not accounted for when calculating the reduction in P sorption.

Journal ArticleDOI
TL;DR: In this article, a life cycle assessment of different cropping systems emphasizing corn and soybean production was performed, assuming that biomass from the cropping system is utilized for producing biofuels (i.e., ethanol and biodiesel).
Abstract: A life cycle assessment of different cropping systems emphasizing corn and soybean production was performed, assuming that biomass from the cropping systems is utilized for producing biofuels (i.e., ethanol and biodiesel). The functional unit is defined as 1 ha of arable land producing biomass for biofuels to compare the environmental performance of the different cropping systems. The external functions are allocated by introducing alternative product systems (the system expansion allocation approach). Nonrenewable energy consumption, global warming impact, acidification and eutrophication are considered as potential environmental impacts and estimated by characterization factors given by the United States Environmental Protection Agency (EPA-TRACI). The benefits of corn stover removal are (1) lower nitrogen related environmental burdens from the soil, (2) higher ethanol production rate per unit arable land, and (3) energy recovery from lignin-rich fermentation residues, while the disadvantages of corn stover removal are a lower accumulation rate of soil organic carbon and higher fuel consumption in harvesting corn stover. Planting winter cover crops can compensate for some disadvantages (i.e., soil organic carbon levels and soil erosion) of removing corn stover. Cover crops also permit more corn stover to be harvested. Thus, utilization of corn stover and winter cover crops can improve the eco-efficiency of the cropping systems. When biomass from the cropping systems is utilized for biofuel production, all the cropping systems studied here offer environmental benefits in terms of nonrenewable energy consumption and global warming impact. Therefore utilizing biomass for biofuels would save nonrenewable energy, and reduce greenhouse gases. However, unless additional measures such as planting cover crops were taken, utilization of biomass for biofuels would also tend to increase acidification and eutrophication, primarily because large nitrogen (and phosphorus)-related environmental burdens are released from the soil during cultivation.

Book ChapterDOI
TL;DR: In this paper, the subsoil carbon (C) sequestration may be achieved by higher inputs of fairly stable organic matter to deeper soil horizons, which can be achieved directly by selecting plants/cultivars with deeper and thicker root systems that are high in chemical recalcitrant compounds like suberin.
Abstract: Routine soil surveys for estimating the soil organic carbon (SOC) pool account for a soil depth of about 1 m Deeper soil horizons, however, may have a high capacity to sequester significant amounts of SOC as the turnover time and chemical recalcitrance of soil organic matter (SOM) increases with depth The subsoil carbon (C) sequestration may be achieved by higher inputs of fairly stable organic matter to deeper soil horizons This can be achieved directly by selecting plants/cultivars with deeper and thicker root systems that are high in chemical recalcitrant compounds like suberin Furthermore, recalcitrant compounds could be a target for plant breeding/biotechnology to promote C sequestration A high surface input of organic matter favors the production of dissolved organic carbon that can be transported to deeper soil horizons and thus contribute to the subsoil C storage By promoting the activity of the soil fauna, organic matter can be transferred to deeper soil layers and stabilized (eg, in earthworm casts) Manipulating the subsoil microorganisms may result in higher amounts of fairly stable aliphatic compounds The subsoil below 1‐m depth may have the potential to sequester between 760 and 1520 Pg C These estimates are, however, highly uncertain and more studies on C storage in subsoil horizons and the assessment of the chemical nature of subsoil organic C are needed

Journal ArticleDOI
TL;DR: It is hypothesized that belowground changes to the soil microbial community provide a mechanistic link between exotic plant invasion and changes to ecosystem nutrient cycling.
Abstract: Plant invasions have dramatic aboveground effects on plant community composition, but their belowground effects remain largely uncharacterized. Soil microorganisms directly interact with plants and mediate many nutrient transformations in soil. We hypothesized that belowground changes to the soil microbial community provide a mechanistic link between exotic plant invasion and changes to ecosystem nutrient cycling. To examine this possible link, monocultures and mixtures of exotic and native species were maintained for 4 years in a California grassland. Gross rates of nitrogen (N) mineralization and nitrification were quantified with 15N pool dilution and soil microbial communities were characterized with DNA-based methods. Exotic grasses doubled gross nitrification rates, in part by increasing the abundance and changing the composition of ammonia-oxidizing bacteria in soil. These changes may translate into altered ecosystem N budgets after invasion. Altered soil microbial communities and their resulting effects on ecosystem processes may be an invisible legacy of exotic plant invasions.

Journal ArticleDOI
TL;DR: In this paper, the effects of changes in land-use type on some soil properties in a Mediterranean plateau were investigated, and the results showed that the cultivation of the pastures degraded the soil physical properties, leaving soils more susceptible to the erosion.
Abstract: Forest and grassland soils in highlands of southern Mediterranean Turkey are being seriously degraded and destructed due to extensive agricultural activities. This study investigated the effects of changes in land-use type on some soil properties in a Mediterranean plateau. Three adjacent land-use types included the cultivated lands, which have been converted from pastures for 12 years, fragmented forests, and unaltered pastures lands. Disturbed and undisturbed soil samples were collected from four sites at each of the three different land-use types from depths of 0–10 cm and 10–20 cm in Typic Haploxeroll soils with an elevation of about 1400 m. When the pasture was converted into cultivation, soil organic matter (SOM) pool of cultivated lands for a depth of 0–20 cm were significantly reduced by, on average 49% relative to SOM content of the pasture lands. There was no significant difference in SOM between the depths in each land-use type, and SOM values of the forest and pasture lands were almost similar. There was also a significant change in soil bulk density (BD) among cultivation (1.33 Mg m−3), pasture (1.19 Mg m−3), and forest (1.25 Mg m−3) soils at depth of 0–20 cm. Only for the pasture, BD of the depth of 0–10 cm was significantly different from that of 10–20 cm. Depending upon the increases in BD and disruption of pores by cultivation, total porosity decreased accordingly. Cultivation of the unaltered pasture obviously increased the soil erodibility measured by USLE-K factor for each soil depth, and USLE-K factor was approximately two times greater in the cultivated land than in the pasture indicating the vulnerability of the cultivated land to water erosion. The mean weight diameter (MWD) and water-stable aggregation (WSA) were greater in the pasture and forest soils compared to the cultivated soils, and didn’t change with the depth for each land-use type. Aggregates of >4.0 mm size were dominant in the pasture and forest soils, whereas the cultivated soils comprised aggregates of the size ≤0.5 mm. I found that samples collected from cultivated land gave the lowest saturated hydraulic conductivity values regardless of soil depths, whereas the highest values were measured on samples from forest soils. In conclusion, the results showed that the cultivation of the pastures degraded the soil physical properties, leaving soils more susceptible to the erosion. This suggests that land disturbances should be strictly avoided in the pastures with the limited soil depth in the southern Mediterranean highlands.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the potential role of microbial community composition in soil carbon and nitrogen cycling, and found that microbial community characteristics correlated with N2O production, nitrification potential, gross Nmineralization, and soil NO3− concentration, independent of environmentalcontrollers.
Abstract: To investigate the potential role of microbial community composition in soil carbon and nitrogen cycling, we transplanted soil cores between a grassland and a conifer ecosystem in the Sierra Nevada California and measured soil process rates (N-mineralization, nitrous oxide and carbondioxide flux, nitrification potential), soil water and temperature, and microbial community parameters (PLFA and substrate utilization profiles) over a 2 year period. Our goal was to assess whether microbial community composition could be related to soil process rates independent of soil temperature and water content. We performed multiple regression analyses using microbial community parameters and soil water and temperature as X-variables and soil process rates and inorganic N concentrations as Y-variables. We found that field soil temperature had the strongest relationship with CO2 production and soil NH4+ concentration, while microbial community characteristics correlated with N2O production, nitrification potential, gross N-mineralization, and soil NO3− concentration, independent of environmentalcontrollers. We observed a relationship between specific components of the microbial community (as determined by PLFA) and soil processes,particularly processes tightly linked to microbial phylogeny (e.g. nitrification). The most apparent change in microbial community composition in response to the 2 year transplant was a change in relative abundance of fungi (there was only one significant change in PLFA biomarkers for bacteria during 2 years). The relationship between microbial community composition and soil processes suggests that prediction of ecosystem response to environmental change may be improved by recognizing and accounting for changes in microbial community composition and physiological ecology.

Book ChapterDOI
TL;DR: In this paper, the intelligent management and utilization of crop residues is essential for the improvement of soil quality and crop productivity under rice-based cropping systems of the tropics, where the major issue is adapting drills to sow into loose residues.
Abstract: Publisher Summary Crop residues, usually considered a problem, when managed correctly can improve soil organic matter dynamics and nutrient cycling, thereby creating a rather favorable environment for plant growth. The intelligent management and utilization of crop residues is essential for the improvement of soil quality and crop productivity under rice-based cropping systems of the tropics. Viable option is to retain residue in the field; burning should be avoided. The major issue is adapting drills to sow into loose residues. Strategies include chopping and spreading of straw during or after combining or the use of disc-type trash drills. Residues rich in lignin and polyphenol contents experience the lowest decay. Decomposition of crop residues occurs at a rapid rate—about 80% of crop residue C is lost in the first year—under the warm and humid conditions of the tropics. Factors that control C decomposition also affect the N mineralization from the crop residues. Decomposition of poor-quality residues with low N contents, high C:N ratios, and high lignin and polyphenol contents generally results in microbial immobilization of soil and fertilizer N. Nutrient cycling in the soil–plant ecosystem is an essential component of sustainable productive agricultural enterprise. Although during the last three decades, fertilization practices have played a dominant role in the rice-based cropping systems, crop residues—the harvest remnants of the previous crop still play an essential role in the cycling of nutrients. Incorporation of crop residues alters the soil environment that in turn influences the microbial population and activity in the soil and subsequent nutrient transformations.

Journal ArticleDOI
TL;DR: In this paper, the amount of hydroxyl ions released after exposure to NaF solution was used to establish a reactivity gradient spanning 12 subsoil horizons collected from 10 different locations.
Abstract: Summary Soil minerals are known to influence the biological stability of soil organic matter (SOM). Our study aimed to relate properties of the mineral matrix to its ability to protect organic C against decomposition in acid soils. We used the amount of hydroxyl ions released after exposure to NaF solution to establish a reactivity gradient spanning 12 subsoil horizons collected from 10 different locations. The subsoil horizons represent six soil orders and diverse geological parent materials. Phyllosilicates were characterized by X-ray diffraction and pedogenic oxides by selective dissolution procedures. The organic carbon (C) remaining after chemical removal of an oxidizable fraction of SOM with NaOCl solution was taken to represent a stable organic carbon pool. Stable organic carbon was confirmed as older than bulk organic carbon by a smaller radiocarbon (14C) content after oxidation in all 12 soils. The amount of stable organic C did not depend on clay content or the content of dithionite–citrate-extractable Fe. The combination of oxalate-extractable Fe and Al explained the greatest amount of variation in stable organic C (R2 = 0.78). Our results suggest that in acid soils, organic matter is preferentially protected by interaction with poorly crystalline minerals represented by the oxalate-soluble Fe and Al fraction. This evidence suggests that ligand exchange between mineral surface hydroxyl groups and negatively charged organic functional groups is a quantitatively important mechanism in the stabilization of SOM in acid soils. The results imply a finite stabilization capacity of soil minerals for organic matter, limited by the area density of reactive surface sites.

Journal ArticleDOI
TL;DR: It is shown that the SOM pool does not necessarily reach equilibrium and may increase continuously, which explains how SOM can accumulate over thousands of years.
Abstract: Soil organic matter (SOM) models are based on the equation dC/dt = −kC which states that the decomposition rate of a particular carbon (C) pool is proportional to the size of the pool and the decomposition constant k. However, this equation does not adequately describe the decomposition of recalcitrant SOM compounds. We present an alternative theory of SOM dynamics in which SOM decay rate is controlled by the size and the diversity of microbe populations and by the supply of energy-rich litter compounds. We show that the SOM pool does not necessarily reach equilibrium and may increase continuously, which explains how SOM can accumulate over thousands of years. However, the simulated SOM accumulation involves the sequestration of available nutrients. How can plants persist? This question is explored with two models that couple the C cycle with a limiting nutrient. The first model considers a single type of microbe whereas the second includes two functional types in competition for energy and nutrient acquisition. The condition for plant persistence is the presence of these two competing microbial types.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the source of the C and N flush that occurs upon rewetting of dry soil, and whether it is from microbial death and/or aggregate destruction.
Abstract: Drying and rewetting of soil is an important process in soil aggregation, soil organic matter (SOM) decomposition, and nutrient cycling. We investigated the source of the C and N flush that occurs upon rewetting of dry soil, and whether it is from microbial death and/or aggregate destruction. A moderately well drained Kennebec silt loam (Fine-silty, mixed, superactive, mesic Cumulic Hapludoll) was sampled to a 10 cm depth. Soil under constant water content (CWC) was compared with soil subjected to a series of four dry‐wet (DW) cycles during the experimental period (96 d) and incubated at 25 8C. Mineralized C and N were measured during the drying and rewetting periods. Aggregate size distributions were studied by separating the soil into four aggregate size classes (O2000, 250‐2000, 53‐250, and 20‐ 53 mm) by wet sieving. Repeated DW cycles significantly reduced cumulative N mineralization compared with CWC. The reduction in cumulative mineralized C resulting from DW compared with CWC increased as the DW treatments were subjected to additional cycles. The flush of mineralized C significantly decreased with repeated DW cycles. There was no significant effect on aggregate size distributions resulting from to the DW cycles compared with CWC treatment. Therefore, the flush of mineralized C and N seemed to be mostly microbial in origin in as much as aggregate distribution was unaffected by DW cycles. Published by Elsevier Ltd.

Journal ArticleDOI
TL;DR: In this paper, the potential activity of several extracellular enzymes involved in SOM degradation at nine experimental sites located in northern Michigan were measured and compared to the ambient plots, with three treatment plots (ambient, +30 kg N ha 1 y 1 ).
Abstract: Anthropogenic nitrogen enrichment alters decomposition processes that control the flux of carbon (C) and nitrogen (N) from soil organic matter (SOM) pools. To link N-driven changes in SOM to microbial responses, we measured the potential activity of several extracellular enzymes involved in SOM degradation at nine experimental sites located in northern Michigan. Each site has three treatment plots (ambient, +30 and +80 kg N ha 1 y 1 ). Litter and soil samples were collected on five dates over the third growing season of N treatment. Phenol oxidase, peroxidase and cellobiohydrolase activities showed significant responses to N additions. In the Acer saccha- rum-Tilia americana ecosystem, oxidative activity was 38% higher in the litter horizon of high N treatment plots, relative to ambient plots, while oxidative activity in mineral soil showed little change. In the A. saccharum-Quercus rubra and Q. velutina-Q. alba ecosystems, oxidative activities declined in both litter (15 and 23%, respectively) and soil (29 and 38%, respectively) in response to high N treatment while cellobiohydrolase activity increased (6 and 39% for litter, 29 and 18% for soil, respectively). Over 3 years, SOM content in the high N plots has decreased in the Acer-Tilia ecosystem and increased in the two Quercus ecosystems, relative to ambient plots. For all three ecosystems, differences in SOM content in relation to N treatment were directly related (r 2 = 0.92) to an enzyme activity factor that included both oxidative and hydrolytic enzyme responses.

Journal ArticleDOI
01 Jan 2005-Geoderma
TL;DR: In this article, a combination of physical fractionation (size and density separation) and chemical characterisation (C-to-N ratios, CuO lignin signature, 13C NMR spectroscopy) was used to identify sensitive organic matter fractions in an agricultural system with sandy dystric cambisols in Bavaria, Germany, 7 years after a land-use change.

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TL;DR: Research on factors controlling net N mineralization from organic residues as well as research on laboratory and field modeling efforts are reviewed, with the objective of highlighting areas with opportunities for additional research.
Abstract: Research on nitrogen (N) mineralization from organic residues is important to understand N cycling in soils. Here we review research on factors controlling net N mineralization as well as research on laboratory and field modeling efforts, with the objective of highlighting areas with opportunities for additional research. Among the factors controlling net N mineralization are organic composition of the residue, soil temperature and water content, drying and rewetting events, and soil characteristics. Because C to N ratio of the residue cannot explain all the variability observed in N mineralization among residues, considerable effort has been dedicated to the identification of specific compounds that play critical roles in N mineralization. Spectroscopic techniques are promising tools to further identify these compounds. Many studies have evaluated the effect of temperature and soil water content on N mineralization, but most have concentrated on mineralization from soil organic matter, not from organic residues. Additional work should be conducted with different organic residues, paying particular attention to the interaction between soil temperature and water content. One- and two-pool exponential models have been used to model N mineralization under laboratory conditions, but some drawbacks make it difficult to identify definite pools of mineralizable N. Fixing rate constants has been used as a way to eliminate some of these drawbacks when modeling N mineralization from soil organic matter, and may be useful for modeling N mineralization from organic residues. Additional work with more complex simulation models is needed to simulate both gross N mineralization and immobilization to better estimate net N mineralized from organic residues.

BookDOI
01 Jan 2005
TL;DR: In this paper, the separation, preconcentration and speciation of organic phosphorus in natural waters by mass spectrometry was discussed, as well as its interactions with nutrient cycles.
Abstract: Separation, preconcentration and speciation Organic phosphorus speciation in natural waters by mass spectrometry Abiotic degradation of organic phosphorus compounds in the environment Enzymatic hydrolysis of organic phosphorus Abiotic stabilization of organic phosphorus Microbial tumover of phosphorus in soil Organic phosphorus dynamics in tropical agroecosystems Organic phosphorus transfer from terrestrial to aquatic environments Interactions in terrestrial ecosystems Organic phosphorus in the aquatic environment: speciation, transformations and interactions with nutrient cycles

Journal ArticleDOI
TL;DR: In this paper, a large-scale girdling experiment was performed in a long-term nutrient optimization experiment in a 40-year-old stand of Norway spruce in northern Sweden.
Abstract: The boreal forest is expected to experience the greatest warming of all forest biomes, raising concerns that some of the large quantities of soil carbon in these systems may be added to the atmosphere as CO2. However, nitrogen deposition or fertilization has the potential to increase boreal forest production and retard the decomposition of soil organic matter, hence increasing both tree stand and soil C storage. The major contributors to soil-surface CO2 effluxes are autotrophic and heterotrophic respiration. To evaluate the effect of nutrient additions on the relative contributions from autotrophic and heterotrophic respiration, a large-scale girdling experiment was performed in a long-term nutrient optimization experiment in a 40-year-old stand of Norway spruce in northern Sweden. Trees on three nonfertilized plots and three fertilized plots were girdled in early summer 2002, and three nonfertilized and three fertilized plots were used as control plots. Each plot was 0.1 ha and contained around 230 trees. Soil-surface CO2 fluxes, soil moisture, and soil temperature were monitored in both girdled and nongirdled plots. In late July, the time of the seasonal maximum in soil-surface CO2 efflux, the total soil-CO2 efflux in nongirdled plots was 40% lower in the fertilized than in the nonfertilized plots, while the efflux in girdled fertilized and nonfertilized plots was 50% and 60% lower, respectively, than in the corresponding nongirdled controls. We attribute these reductions to losses of the autotrophic component of the total soil-surface CO2 efflux. The estimates of autotrophic respiration are conservative as root starch reserves were depleted more rapidly in roots of girdled than in nongirdled trees. Thus, heterotrophic activity was overestimated. Calculated on a unit area basis, both the heterotrophic and autotrophic soil respiration was significantly lower in fertilized plots, which is especially noteworthy given that aboveground production was around three times higher in fertilized than in nonfertilized plots.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed relations of SOM composition to soil wettability by considering functional group compositions of different soluble fractions in forest soil samples from two loamy sand Cambisol profiles and from a Podzol (Waldstein) profile.
Abstract: Soil organic matter (SOM) as a solid or as a film at mineral surfaces affects wetting properties in unsaturated soil Soil organic matter mostly consists of a heterogeneous mixture of components with hydrophilic and hydrophobic functional groups This paper analyzes relations of SOM to soil wettability by considering functional group compositions of different soluble fractions Forest soil samples from two loamy sand Cambisol profiles (locations Chorin and Steigerwald) and from a Podzol (Waldstein) were used to obtain water [SOM(W)] and sodium pyrophosphate [SOM(PY)] soluble SOM fractions The hydrophobic (A) and hydrophilic (B) functional groups of bulk soil SOM and of the soluble fractions were evaluated using transmission Fourier-transform infrared (FT-IR) spectroscopy Advancing liquid-solid contact angles (CA) were determined by using the capillary rise method For soil organic carbon (SOC) contents 10 g kg -1 Although hydrophilic groups in FT-IR spectra of SOM(W), SOM(PY), and bulk soil dominated (ie, A/B ratios between 008 and 05), soil wettability was reduced (ie, CA between 88 and 52°) Soil specific relations between CA and A/B ratios could be obtained after introducing relatively soil type independent factors, G As exponential functions of the SOC/clay relation, the G-factors imitate the effectiveness of functional groups with respect to wettability The results suggest that in addition to SOC content, the SOM composition may improve explanations of soil wettability if the spatial orientation of SOM functional groups at the SOM-mineral surface in the presence of sorption sites and polyvalent cations is considered