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Organic C Content (organic + c_content)
Selected AbstractsThe role of mineral and organic components in phenanthrene and dibenzofuran sorption by soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2006R. Celis Summary Improved predictions of sorption of hydrophobic organic compounds (HOCs) in soil require a better knowledge of the relative contribution of inorganic and organic soil constituents to the sorption process. In this paper, sorption of a three-ring polycyclic aromatic hydrocarbon (phenanthrene) and a three-ring heterocyclic,aromatic compound (dibenzofuran) by six agricultural soils, their clay-size fractions, and a series of single, binary, and ternary model sorbents was evaluated to elucidate the relative role of soil mineral and organic components in the retention of these two model HOCs. The sorption coefficients for phenanthrene and dibenzofuran on purified soil organic materials (Kd = 821,9080 litre kg,1) were two orders of magnitude greater than those measured on mineral model sorbents (Kd = 0,114 litre kg,1). This, along with the strong correlation between sorption and the organic C content of the soil clay fractions (r = 0.99, P < 0.01), indicated a primary role of soil organic matter in the retention of both compounds. However, weak relationships between phenanthrene and dibenzofuran sorption coefficients and the organic C content of the bulk soils and variability of Koc values among soils, clay fractions, and model sorbents (1340,21020 litre kg,1 C for phenanthrene and 1685,7620 litre kg,1 C for dibenzofuran) showed that sorption was not predictable exclusively from the organic C content of the materials. Organic matter heterogeneity and domain blockage arising from organic matter,clay interactions and associated pH shifts were identified as the most likely causes of the different organic C-normalized sorption capacities of the soils. A direct contribution from minerals to the sorption of phenanthrene and dibenzofuran by the soils studied was likely to be small. Our results suggested that suitable descriptors for the extent of organic matter,mineral interactions would help to improve current Koc -based sorption predictions and subsequently the assessment of risk associated with the presence of HOCs in soil. [source] The dynamics of organic matter in rock fragments in soil investigated by 14C dating and measurements of 13CEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2002A. Agnelli Summary Rock fragments in soil can contain significant amounts of organic carbon. We investigated the nature and dynamics of organic matter in rock fragments in the upper horizons of a forest soil derived from sandstone and compared them with the fine earth fraction (<2 mm). The organic C content and its distribution among humic, humin and non-humic fractions, as well as the isotopic signatures (,14C and ,13C) of organic carbon and of CO2 produced during incubation of samples, all show that altered rock fragments contain a dynamic component of the carbon cycle. Rock fragments, especially the highly altered ones, contributed 4.5% to the total organic C content in the soil. The bulk organic matter in both fine earth and highly altered rock fragments in the A1 horizon contained significant amounts of recent C (bomb 14C), indicating that most of this C is cycled quickly in both fractions. In the A horizons, the mean residence times of humic substances from highly altered rock fragments were shorter than those of the humic substances isolated in the fine earth. Values of ,14C of the CO2 produced during basal respiration confirmed the heterogeneity, complexity and dynamic nature of the organic matter of these rock fragments. The weak 14C signatures of humic substances from the slightly altered rock fragments confirmed the importance of weathering in establishing and improving the interactions between rock fragments and surrounding soil. The progressive enrichment in 13C from components with high- 14C (more recent) to low- 14C (older) indicated that biological activity occurred in both the fine and the coarse fractions. Hence the microflora utilizes energy sources contained in all the soil compartments, and rock fragments are chemically and biologically active in soil, where they form a continuum with the fine earth. [source] Soil organic matter composition and soil lightnessJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 5 2004Sandra Spielvogel Abstract Relationships between soil lightness, soil organic matter (SOM) composition, content of organic C, CaCO3, and texture were studied using 42 top-soil horizons from different soil types located in southern Germany. SOM composition was determined by CPMAS 13C NMR spectroscopy, soil color was measured by diffuse-reflectance spectrophotometry and given in the CIE L*a*b* color coordination system (Commission Internationale de l'Eclairage, 1978). Multiple-regression analysis showed, that soil lightness of top-soil horizons is principally determined by OC concentration, but CaCO3 and soil texture are also major variables. Soil lightness decreased with increasing OC content. Carbonate content had an important effect on soil lightness even at low concentrations due to its lightening property. Regressions between soil lightness and organic C content were strongly linear, when the soils were differentiated according to texture and CaCO3 content. The aryl-C content was the only SOM component which correlated significantly with soil lightness (rS = ,0.87). In the linear regressions carried out on the different soil groups, soil aryl-C content was a more significant predictor for soil lightness than total OC content. Zusammensetzung der organischen Bodensubstanz und Bodenhelligkeit Der Zusammenhang zwischen Bodenhelligkeit, Zusammensetzung der organischen Substanz und Gehalt an Corg., CaCO3 und Textur wurde in 42 Oberböden aus verschiedenen Bodentypen Süddeutschlands untersucht. Die Zusammensetzung der organischen Substanz wurde mittels CPMAS- 13C-NMR-Spektroskopie bestimmt, die Bodenfarbe mittels Spektralphotometer und als Bodenhelligkeitswert im CIE L*a*b*-Farbkoordinatensystem (Commission Internationale de l'Eclairage, 1978) angegeben. Die Auswertung über multiple Regression zeigte, dass die Bodenhelligkeit hauptsächlich vom OC-Gehalt bestimmt wird; CaCO3 -Gehalt und Textur erwiesen sich als weitere relevante Variablen. Die Bodenhelligkeit nimmt mit zunehmendem OC-Gehalt ab. Aufgrund seiner stark aufhellenden Wirkung hat der Carbonatgehalt auch bei niedrigen Konzentrationen einen deutlichen Einfluss auf die Bodenhelligkeit. Bei Berücksichtigung der Textur und des Carbonatgehalts ergaben sich lineare Beziehungen zwischen Bodenhelligkeit und OC-Gehalt. Der Aryl-C-Gehalt des Bodens war als einzige Humuskomponente signifikant mit der Bodenhelligkeit korreliert (rS = ,0.87). Der Aryl-C-Gehalt des Bodens bestimmt die Bodenhelligkeit schärfer als der OC-Gehalt. [source] Effect of water and nitrogen management on aggregate size and carbon enrichment of soil in rice-wheat cropping system,JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2004Rojalin Tripathy Abstract A study was carried out on a silty clay loam soil (Typic Haplustept) to evaluate the effect of farmyard manure (FYM) vis-à-vis fertilizer and irrigation application on the soil organic C content and soil structure. The fertilizer treatments comprised of eight different combinations of N and FYM and three water regimes. The results indicated that the application of FYM and increasing N rate increased soil organic carbon (SOC) content. Addition of FYM also increased the percentage of large sized water stable aggregates (> 5,mm) and reduced the percentage of smaller size aggregates. This was reflected in an increase in the mean weight diameter (MWD) and improved soil structure. The organic carbon content in macroaggregates (> 1,mm) was greater compared to microaggregates, and it declined with decrease in size of microaggregates. This difference in organic C content between macro- and microaggregates was more with higher N dose and FYM treated plots. The effect of residual FYM on MWD and organic C content of the soil after wheat harvest was not significant. The effect was less in deeper layers compared to surface layers of the soil. MWD was significantly correlated with the SOC content for the top two layers. [source] Managing precipitation use in sustainable dryland agroecosystemsANNALS OF APPLIED BIOLOGY, Issue 2 2004GARY A PETERSON Summary In the Great Plains of North America potential evaporation exceeds precipitation during most months of the year. About 75% of the annual precipitation is received from April through September, and is accompanied by high temperatures and low relative humidity. Dryland agriculture in the Great Plains has depended on wheat production in a wheat-fallow agroecosystem (one crop year followed by a fallow year). Historically this system has used mechanical weed control practices during the fallow period, which leaves essentially no crop residue cover for protection against soil erosion and greatly accelerates soil organic carbon oxidation. This paper reviews the progress made in precipitation management in the North American Great Plains and synthesises data from an existing long-term experiment to demonstrate the management principles involved. The long-term experiment was established in 1985 to identify dryland crop and soil management systems that would maximize precipitation use efficiency (maximization of biomass production per unit of precipitation received), improve soil productivity, and increase economic return to the farmers in the West Central portion of the Great Plains. Embedded within the primary objective are sub-objectives that focus on reducing the amount of summer fallow time and reversing the soil degradation that has occurred in the wheat-fallow cropping system. The experiment consists of four variables: 1) Climate regime; 2) Soils; 3) Management systems; and 4) Time. The climate variable is based on three levels of potential evapotranspiration (ET), which are represented by three sites in eastern Colorado. All sites have annual long-term precipitation averages of approximately 400,450 mm, but vary in growing season open pan evaporation from 1600 mm in the north to 1975 mm in the south. The soil variable is represented by a catenary sequence of soils at each site. Management systems, the third variable, differ in the amount of summer fallow time and emphasize increased crop diversity. All systems are managed with no-till techniques. The fourth variable is time, and the results presented in this paper are for the first 12 yr (3 cycles of the 4-yr system). Comparing yields of cropping systems that differ in cycle length and systems that contain fallow periods, when no crop is produced, is done with a technique called "annualisation". Yields are "annualised" by summing yields for all crops in the system and dividing by the total number of years in the system cycle. For example in a wheat-fallow system the wheat yield is divided by two because it takes 2 yr to produce one crop. Cropping system intensification increased annualised grain and crop residue yields by 75 to 100% compared to wheat-fallow. Net return to farmers increased by 25% to 45% compared to wheat-fallow. Intensified cropping systems increased soil organic C content by 875 and 1400 kg ha,1, respectively, after 12 yr compared to the wheat-fallow system. All cropping system effects were independent of climate and soil gradients, meaning that the potential for C sequestration exists in all combinations of climates and soils. Soil C gains were directly correlated to the amount of crop residue C returned to the soil. Improved macroaggregation was also associated with increases in the C content of the aggregates. Soil bulk density was reduced by 0.01g cm,3 for each 1000 kg ha,1 of residue addition over the 12-yr period, and each 1000 kg ha,1 of residue addition increased effective porosity by 0.3%. No-till practices have made it possible to increase cropping intensification beyond the traditional wheat-fallow system and in turn water-use efficiency has increased by 30% in West Central Great Plains agroecosystems. Cropping intensification has also provided positive feedbacks to soil productivity via the increased amounts of crop residue being returned to the soil. [source] | ||||||||||