Soil organic carbon rate constant

Figures 15.4, 15.5 and 15.6 show the simulated changes in the soil-plant system during 4.1-million-year soil development. The model results are compared with observed data from the LSAG sites with a focus on plant production, inorganic phosphorus fractions, soil organic carbon, nitrogen and phosphorus, nutrient mineralization rates, soil respiration, nitrogen and phosphorus losses, and live leaf nutrient ratios. A key assumption in the model run is that climate remained constant during the 4.1-million-year simulation in fact the...

The Rothamsted Carbon Model (RothC) uses a five pool structure, decomposable plant material (DPM), resistant plant materials (RPM), microbial biomass, humified organic matter, and inert organic matter to assess carbon turnover (Coleman and Jenkinson 1996 Guo et al. 2007). The first four pools decompose by first-order kinetics. The decay rate constants are modified by temperature, soil moisture, and indirectly by clay content. RothC does not include a plant growth sub-module, and therefore NHC inputs must be known, estimated, or calculated by inverse modeling. Skjemstad et al. (2004) tested an approach for populating the different pools based on measured values. 

Pentachlorophenol, a widely used wood preservative, is considered to be moderately biorefractory with a biodegradation rate constant of 3 x 1012 L/ cell/hr, a log of 5.01, and a vapor pressure of 1.1 x 10-4 mmHg at 20°C. Watts et al. (1990) carried out completely mixed batch tests by treating penta-chlorophenol-contaminated soils with Fenton s reagent. Mineralization of pentachlorophenol (PCP) was studied in commercially available silica sand and two natural soils by removal of parent compound and total organic carbon with corresponding stoichiometric recovery of chloride. The soluble iron concentration decreased over the first 3 hr of treatment, and the concentration remained relatively constant thereafter. A possible mechanism for iron precipitation was proposed as follows ... 

FIGURE 10.21 First-order Fe(III) reduction rate constants and initial cumulative carbon dioxide and methane production in a wetland soil amended with different amounts of labile organic matter. (Redrawn from Roden and Wetzel, 2002.)... 

In CPT, a rod-shaped, 35.7 mm diameter (10 cm cross section) cone with 60° apex is either mechanically, or hydraulically pushed into the soil at a constant penetration rate, usually 2 cm/sec. The penetration resistance of the cone (cone bearing), as well as the shaft friction resistance along a 150 cm friction sleeve, placed just behind the cone, are continuously measured by a load cell and a strain gauge, respectively, and the results are processed and plotted automatically. An inclinometer incorporated into the cone tip assembly continuously monitors the deviations of the CPT tip from the vertical. Details of the test is described in detail in Chapter 4. The penetration resistance is affected by the particle size, relative density, gradation, compressibility, degree of saturation, and organic/ carbonate content of the soil, as well as the shape and the compressive strength of the soil particles (Broms and Foldin, 1988). 

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