Diffusion, in soil

The development of the theory of solute diffusion in soils was largely due to the work of Nye and his coworkers in the late sixties and early seventies, culminating in their essential reference work (5). They adapted the Fickian diffusion equations to describe diffusion in a heterogeneous porous medium. Pick s law describes the relationship between the flux of a solute (mass per unit surface area per unit time, Ji) and the concentration gradient driving the flux. In vector terms. 

Kirk GJD, Solivas JL, Alberto MC. 2003. The effects of redox conditions on solute diffusion in soil. European Journal of Soil Science 54 617-624. 

Radon moves upwards in soil partly by molecular diffusion in soil gas and partly by bulk flow caused by changes in air pressure at the surface. The diffusion flux can be calculated, if it is assumed that the radioactivity, porosity and density of the soil are independent of depth and that lateral movement of radon can be neglected. 

Chelation by LMMO substances is a major factor in the transport of micronutrient cations such as Cu, Zn, Ni, Fe, and Mn to root surface by mass flow and diffusion. In soil solutions of calcareous soils 40 to 75% of tlie zinc and 98% of copper have been found in organic complexes (Hodgson et al., 1966 Sanders, 1982, 1983 McGrath et al., 1988). For plants the importance of complexed micronutrients in the soil solution is particularly evident in calcareous soils. This is also indicated by the fact that soil extractions with synthetic chelators such as EDTA and DTPA provide suitable soil tests for estimation of available micronutrieiits (Sims and Johnson, 1991) (summarized in detail in Section 11.3). 

Anderson et al. (1996) used Eq. [14], in conjunction with digitized images of thin sections, to investigate the influence of pore space geometry on diffusion in soil systems. Giona et al. (1996) applied renormalization analysis to study diffusion and convection on fractal media. Coppens (1997), Santra et al. (1997), and Levitz (1998) have studied the effects of geometrical confinement on diffusion in the Knudsen regime, in which particle collisions with a fractal internal surface dominate over particle-particle collisions. 

The productivity of many ecosystems is determined by the chemical stability of phosphate, its relative immobility in soil, and its low concentration in the soil solution (approximately 1 xM). Phosphorus uptake by plant roots occurs mainly as phosphate ions (H2P0 and HPO ) from the soil solution, which depends on the solubilization of mineral phosphates and the degradation or mineralization of organic phosphorus. During phosphate uptake, a phosphorus-depleted area is formed close to the root, since phosphate uptake is faster than its diffusion in soil (Bhat and Nye, 1973). Having... 

Lewis, D.G., Quirk, J.P., 1967. Phosphate diffusion in soil and uptake by plants. III. P -movement and uptake by plants as indicated by P -autoradiography. Plant Soil 27, 445 53. 

Claassen, N., 1990. Fundamentals of sod-plant interactions as derived from nutrient diffusion in soil, uptake kinetics and morphology of roots. Proceedings of the Fourteenth International Congress of Soil Science, Kyoto, Japan, vol. 11, pp. 118-123. 

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