Macropore soil waters

Fig. 7. Size scale associated with soil mineral particles, organic components, pores and aggregations of mineral and organic components (Baldock 2002). The definitions of pore size have used those developed by IUPAC (micropores < 2 nm, mesopores 2-50 nm and macropores > 50 nm). Alternatively, the pore sizes corresponding to the lower ( /m = - 1500 kPa) and upper ( /m = - 100 kPa) limits of water availability to plants may be used to define the boundaries between the different classes of pore size. /m is soil water metric potential.

Beven, K. Germann, P. (1982) Macropores and water flow in soils. Water Resources Research 18, 1311-1325. 

Jarvis NJ, Jansson PE, Dik PE, Messing I. Modelling water and solute transport in macroporous soil I. Model description and sensitivity analysis. I Soil Sci 1991 42 59-70. 

Larsbo M, Jarvis N. MACRO 5.0. A model of water flow and solute transport in macroporous soil Technical description. Emergo 2003 6. Swedish University of Agricultural Sciences, Department of Soil Sciences, Uppsala, 2003. 

While phosphorus export from agricultural systems is usually dominated by surface runoff, important exceptions occur in sandy, acid organic, or peaty soils that have low phosphorus adsorption capacities and in soils where the preferential flow of water can occur rapidly through macropores. Soils that allow substantial subsurface exports of dissolved phosphorus are common on parts of the Atlantic coastal plain and Florida, and are thus important to consider in the management of coastal eutrophication in these regions. 

Bevin, K., and P. Germann (1982) Macropores and Water Flow in Soils, Water Resources Res. 18, 1131-1325. 

Larsbo, M. and Jarvis, N. MACRO5.0 a model of water flow and solute transport in macroporous soil. Technical description. 2003. Uppsala, Sweden, SLU, Department of soil sciences. 

Fig. 10. Representation of micro-macropore interaction in the unsaturated mode in terms of components of soil-water potential.

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). 

Macroporous diatomaceous column (e.g.. Chem Elut column). The combined soil extract is concentrated to dryness under vacuum, the residue is dissolved in 15 mL of water and the solution is applied to a Chem Elut column. After charging for 20 min, acetamiprid is eluted with 100 mL of dichloromethane. The eluate is evaporated to... 

Figure 3. Water fluxes in soil with micropores. The following processes are relevant (1) infiltration into soil matrix, (2) lateral infiltration from macropores, and (3) exchange between aggregates (Richter 1999).

Although the above studies conducted with packed columns are important from a fundamental standpoint as they relate to the mechanisms of cell sorption to solid surfaces, in situ remediation of contaminants in subsoils requires microbial transport in well-structured soils. The presence of soil macropores that facilitate preferential water flow is well appreciated (Thomas Phillips, 1979). Sorption phenomena are less important when bacterial transport occurs through structured soils in which cells pass unimpeded through relatively large conduits (Smith et al., 1985). 

Angley et al., 1992) and the retarded rate of desorption and diffusion from the soil micropore surfaces to the macropore water. In the case of PCBs, the retarded rate of desorption can affect both lower- and higher-chlorinated PCB congeners however, the effect is likely to be more severe with higher chlorinated congeners. 

Downward movement of triazines may occur from percolating water carrying them to lower soil depths. Within well-structured soils with abundant macropores, triazines have been reported to move to deeper depths than in nonstructured soils with fewer pores. Increased permeability, percolation, and solute movement can result from increased porosity -especially in no-tillage systems where there is pore connectivity at the soil surface. Triazines can move to shallow ground-water by macropore flow in sandy soil if sufficient rainfall occurs shortly after they are applied (Ritter et al, 1994a, b). 

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