Roots porosity

These findings broadly agree with experimental observations. Measured rates of CH4 oxidation in the rice rhizosphere range widely from 5 to 90% of the CH4 transported (Holzapfel-Pschom et al 1985 Epp and Chanton, 1993 van der Gon and Neue, 1996). This agrees with the model. Rates of O2 flow through rice roots to the rhizosphere are of the order of a few mmol 02m (soil surface) h (Section 6.4), which is sufficient to account for the rates of oxidation calculated with the model. Measured differences in emissions between rice cultivars are largely due to differences in root biomass (Lu et al., 1999) the effects of differences in root porosity are smaller (Aulakh et al., 2001a,b). 

Relationship of Reduction Intensity with Root Porosity and Radial Oxygen Loss... 

In Taxodium distichum, a significant increase in root porosity and ROL was noted at Eh intensity of -240 to -260 mV in root medinm (Kludze et al., 1994a, 1994b). ROL increased from 12.7 in control treatments to 42.3 mmol O2 day Similarly, root airspace increased from 13.3 to 41.4% in response to the intensity of rednction. In 0. saliva (rice), ROL increased in response to a drop... 

FIGURE 7.35 Root porosity and radial oxygen loss in Spartina patens gvov/n under various soil redox intensity for 50 days. (Modified from Kludze and DeLaune, 1994.)... 

Intensity of soil reduction promotes increase in root porosity and ROL from root to rhizosphere. There is an increasingly higher rate of oxygen loss as soil redox potential becomes more reduced. 

What is the relationship of soil reduction intensity to the root porosity and radial oxygen loss (ROL) ... 

Eor pesticides to leach to groundwater, it may be necessary for preferential flow through macropores to dominate the sorption processes that control pesticide leaching to groundwater. Several studies have demonstrated that large continuous macropores exist in soil and provide pathways for rapid movement of water solutes. Increased permeabiUty, percolation, and solute transport can result from increased porosity, especially in no-tiUage systems where pore stmcture is stiU intact at the soil surface (70). Plant roots are important in creation and stabilization of soil macropores (71). 

Plate thickness is an important factor in electroplating, in terms of both performance and economics. Corrosion resistance, porosity, wear, appearance, and several other properties are proportional to plate thickness. Minimum plate thicknesses are, or should be, specified as should the location, or check-point, where the thickness is to be measured. In some appHcations, such as threaded fasteners, maximum thicknesses should be specified. Root diameters of finer machine threads can be adversely affected by as Htde as 10 p.m of plating. 

Long-term grasslands provide plenty of organic matter for humus formation. If the soil is not acidic or waterlogged, the soil fauna and flora create humus and the subsequent useful development of a porous crumb and granular structure. Porosity encourages root growth and the uptake of soil nutrients. 

The porosity of the cortex, permeability of the root wall and the coverage of the root with laterals vary along the root length, with a much smaller porosity. 

Figure 6.5 defines for the purposes of the model the distances at which the porosity and coverage with laterals change. It is assumed that, because of the changes in wall permeability along the root, nutrients are only absorbed by the primary root in the zones beyond the laterals (riat < r < rmax) and by the laterals. This is also the surface across which O2 leaks. 

Figure 6.6 Effect of cortical porosity of primary root and fraction of root covered with laterals on (a) maximum primary root length, (b) absorbing root surface per unit root mass, and (c) absorbing root surface per primary root as a function of net O2 consumption, and (d) O2 consumed in root respiration and loss to the soil. Numbers on curves are porosities other parameters have standard values (Kirk, 2003). Reproduced by permission of Blackwell Publishing...

Kirk GJD, Le van Du. 1997. Changes in rice root architecture, porosity, and oxygen and proton release under phosphorus deficiency. New Phytologist 135 191-200. 

The pore volume j)er unit mass, Vg, (a measure of the catalyst pellet porosity) is also a parameter which is important and is implicitly contained in eqn. (14). Since the product of the particle density, Pp, and specific pore volume, V, represents the porosity, then Pp is inversely proportional to Fg. Therefore, when the rate is controlled by bulk diffusion, it is proportional not simply to the square root of the specific surface area, but to the product of Sg and Vg. If Knudsen diffusion controls the reaction rate, then the overall rate is directly proportional to Vg, since the effective Knudsen diffusivity is proportional to the ratio of the porosity and the particle density. 

Periodontal disease is characterized by a sequence of chronic oral inflammation and excessive alveolar bone resorption (i.e., receding alveolar bone) that results in root surface exposure of teeth, increased sensitivity, eventual detachment of the periodontal ligament, and subsequent tooth loss. Alveolar ridge bone exhibits intrinsic porosity, a structural fragility, and a proximity to vasculature that in effect virtually ensures it has the potential to be a vulnerable site in times of rapid bone resorption, much like the trabecular-rich regions in the hip and spine. Subsequent retention of the quantity and quality of bone in edentulous jaws also becomes critically important in terms of being able to provide surface support for dental implants and dentures that are desirable for both functional and cosmetic purposes (Bodic et al., 2005) (Figure 6.4). 

The speed of carbonation into the depth of the concrete depends strongly on the consistency and porosity of the material and follows a square root relation 403... 

Indicates the pore space available for water and roots influenced by soil composition (mineral content, mineral type, and organic matter) and soil texture Affects adsorption of the chemical Affects the surface area where adsorption can take place Influences partitioning and availability of chemicals Affects ability of a soil to transmit water or air Dictates the porosity of the soil Affects the form, reactivity, solubility, availability, and toxicity of some contaminants Affects the toxicity of some substances (mainly heavy metals) with binding or antagonistic mechanisms, for example, by alkaline-earth metals and aluminum Organic matter content, type, and % carbon Influences soil sorption properties for heavy metals and... 

---