Fixation in soil

Several authors have applied in situ pulse labeling of plants (grasses and crops) with C-CO2 under field conditions with the objective of quantifying the gross annual fluxes of carbon (net assimilation, shoot and root turnover, and decomposition) in production grasslands and so assess the net input of carbon (total input minus root respiration minus microbial respiration on the basis of rhizodeposition and soil organic matter) and carbon fixation in soil under ambient climatic conditions in the field. 

Martinez-Toledo, M.V., T.D.L. Rubia, J. Moreno, and J. Gonzalez-Lopez. 1988. Effect of diflubenzuron on Azotobacter nitrogen fixation in soil. Chemosphere 17 829-834. 

Metal complexation (and fixation) in soils and sedimentary basins Deposition of ore metals (reducing agents)... 

Fluoride is a natural component of most types of soil, in which it is mainly bound in complexes and not readily leached. The major source of free fluoride ion in soil is the weathering and dissolution of fluoride rich rock that depends on the natural solubility of the fluoride compound in question, pH, and the presence of other minerals and compounds and of water. The major parameters that control fluoride fixation in soil through adsorption, anion exchange, precipitation, formation of mixed solids and complexes are aluminium, calcium, iron, pH, organic matter and clay [19,20]. 

One of the factors which has confused mechanism analysis has been the failure to make a distinction between studies involving micro- and macro-concentrations of the heavy metals. Whereas, with micro-concentrations, sorption reactions may predominate, precipitation frequently occurs with macro-concentrations (68). Exchange of copper and zinc with hydrogen on clay mineral surfaces was proposed as a cause of zinc and copper fixation in soils by DeMumbrum and Jackson (59) who noted... 

There is some slight evidence that Clostridia can fix nitrogen when growing in association with aerobic cellulose decomposers but such an association would not be expected, except possibly where there are anaerobic pockets in an otherwise aerobic soil, or where alterations of aerobic and anaerobic conditions occur. Such fixation in soils is probably negligible. 

Surface emissions include technological sources (industry, transportation and other fossil fuel combustion processes), biomass burning, nitrogen fixation in soils and oceanic activity and totals 39 Tg yr"F The photochemical production (31 Tg yr ) from HCHO photolysis accounts for about 45% of the total source of H2. 

Schuffelen, A. C.,andH. W. vanderMarel, 1955. Potassium fixation in soils. 157-201. 

Potassium fixation in soils. Potassium Symposium, International Potash Institute,... 

Domenach, A.M., Kurdali, F. and Bardin, R. 1989 Estimation of symbiotic dinitrogen fixation in alder forest by the method based on natural N-abundance. Plant and Soil 118 51-59. 

Apart from its use in studies of nitrogen fixation, N-labeled substrates have been used to assess the association of contaminants with organic matter in soil, and in metabolism. 

Nevertheless, cereal plants can interact with endosymbionts, capable of nitrogen fixation in other species, and be stimulated in their productivity. The odds of soil life are balanced for some bacteria by their interactivity at rhizosphere level, and a realm of exchanged signals dictates entry into hormonally reprogrammed root sites. Specificity for partner plant species is part of a fine speciation process that actively involves the bacterial nodulation genes, and continues to drive their variation dynamics. 

The ammonium dynamics showed that the initial concentrations of N were reduced after the first 3 days, and after that, a release of the mineral occurred from day 3 up to day 14. Later still, the concentration of ammonium decreased by up to < 14 mg N kg 1 dry soil for all the treatments in both the Otumba and Texcoco soils, and the ammonium concentration decreased by up to < 2 mg N kg 1 dry soil for all treatments, except for the soil treated with sterilized sludge, < 31 mg N kg 1 dry soil. The contour of the ammonium dynamics was similar in both the Otumba and Texcoco soils. Many abiotic and biotic processes might affect the concentration of NH4+ in soil, such as NH4+ fixation in the soil matrix, volatilisation of NH3, and immobilization or oxidation of NH4+. Some soil processes were occurring at too low a level to be detectable, such as NH4+ fixation and the volatilisation of NH3. The nitrate dynamics were similar in both soils. The concentration of N03 was 120 mg N kg 1 dry soil in the control treatment in both soils. The ammonium concentration was similar in both soils, > 200 mg N kg 1 dry soil, treatments with sludge reached > 255 mg N kg 1 dry soil and > 300 mg N kg 1 dry soil in the Texcoco and Otumba soils respectively, and soils treated with sterilized sludge increased the concentration... 

Molybdate, although present in small amounts in soil, is an essential nutrient for nitrogen fixation, specifically in the enzyme nitrogenase. It does not move readily through soil and is therefore considered to be of limited mobility. 

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