Soil structure

Structureless No observable aggregation or no orderly arrangement of natural lines of weakness. 

Moderate Well-formed distinct peds, moderately durable and evident, but not distinct in undisturbed soil. 

Strong Durable peds that are quite evident in undisplaced soil, adhere weakly to one another, 

Angular blocky Block-like peds bounded by other peds whose sharp angular faces form the cast for the 

Mirrerol soil mixed with humus, dorker thon lower horizons 

A1 oxides etc, often lighter coloured than other horizons Tronsition to B, more like A than B Tronsition to A, more like B than A 

Al oxides, more strongly coloured Transition to C, more like B than C 

Mg corbonotes, cementotion, high bulK density sometimes differentiate if from B 

A soil profile, illustrating the traditional O, A, B, and C horizons and some further subdivisions of them. From D. J. Greenland and M. H. B. Hayes, Eds., The Chemistry of Soil Constituents, John Wiley Sons, 1978. Reprinted by permission. 

The basic soil structure is that shown in Hgure 7.1a the A horizon is the top layer containing a high proportion of organic matter, the B horizon is the mid laya composed mainly of partially weathered (modified by climatic action) material and the C horizon contains relatively undisturbed material. Thae are seven otha horizon types a basic classification was given by McDonald et al. (1990) as follows (from top to bottom)  

O horizons are dominated by organic matta that has accumulated on the surface of the soil. O horizons are subdivided according to the degree of organic material decomposition. These horizais are not common and are mostly restricted to moist or cool environments (e.g., alpine areas, swamps, and rainfijrests). 

A horizons consist of one or more surface mineral horizons with some accumulation of organic materials (less than that of O horizons). A horizons are usually darker than those undalying, but they may also be horizons that 

P horizons are dominated by organic materials in various stages of decomposition that have accumulated either under water or in very wet areas. They are often referred to as peat layers. 

C horizons are layers below the A and B horizons, which are composed of consolidated or unconsolidated materials. These materials are usually partially weathered, and geological features are often evident. C horizons can be dug by hand when they are moist. 

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Agricultural Advisory Council on Soil Structure and Soil Fertility, HMSO, London, 1970. 

Consider a lake with a smaU watershed in a forest ecosystem. The forest and vegetation can be considered as an acid concentrator. SO2, NO2, and acid aerosol are deposited on vegetation surfaces during dry periods and rainfalls they are washed to the soil floor by low-pH rainwater. Much of the acidity is neutralized by dissolving and mobilizing minerals in the soil. Aluminum, calcium, magnesium, sodium, and potassium are leached from the soil into surface waters. The ability of soils to tolerate acidic deposition is very dependent on the alkalinity of the soil. The soil structure in the... 

The Seismic Safety Margins Research Program developed a computer code called SMACS (Seismic Methodology Analysis Chain with Statistics) for calculating the seismic responses of structures, systems, and components. This code links the seismic input as ensembles of acceleration time histories with the calculations of the soil-structure interactions, the responses of major structures, and the responses of subsystems. Since uses a multi-support approach to perform the time-history response calculations for piping subsystems, the correlations between component responses can be handled explicitly. SMACS is an example of the codes that are available for calculating seismic response for PSA purposes. 

Petroleum Enhancing oil recovery, regulation of filterability and rheological properties of drilling muds, thickening of water, soil structure formation, oil flotation... 

Acrylamide polymers are used as multipurpose additives in the oil-producing industry. Introduction of polymers into drilling fluids-drilling muds improves the rheological properties of the fluids in question, positively affects the size of suspended particles, and adds to filterability of well preparation to operation. Another important function is soil structure formation, which imparts additional strength to the well walls. A positive effect is also observed in secondary oil production, where acrylamide polymers additives improve the mobility of aqueous brines injections, which contribute to... 

Soil structure and land drainage within the reclaimed ground. 

Soil physical properties most likely to be altered by biomass burning are soil structure, soil wettability, and clay mineralogy (Table HI) (43). The destruction of organic matter results in losses of soil structure, increases in bulk density, diminished aggregate stability and decreases in macropore space (44). 

Bridge, B.J., Mott, J.J., Winter, W.H. Hartigan, R.J. (1983). Improvement in soil structure resulting from sown pastures on degraded areas in the dry savanna woodlands of northern Australia. Australian Journal of Soil Research, 21, 83-90. Cionco, R.M. (1972). A wind profile index for canopy flow. Boundary Layer Meteorology, 3, 255-63. 

Soil structure. High salt concentrations, and high sodium adsorption ratios in particular, adversely affect the physical properties of the soil (Davidson Quirk, 1961), altering such parameters as particle size and hydraulic conductance. 

The growth of roots through soil is perceived often as improving soil structure for plant growth. In the context of this review, the question is one of whether a plant s root products directly improve the soil structure for the growth of that plant. However, it is a difficult question to answer because, in addition to the... 

J. N. Ladd, Foster, P. Nannipieri, and J. M. Oades, Soil structure and biological activity Soil Biochemistry Volume 9 (G. Stotzky and J. M. Bollag, eds.), Marcel Dekker. New York, 1996, pp. 23-78. 

The importance of including soil-based parameters in rhizosphere simulations has been emphasized (56). Scott et al. u.sed a time-dependent exudation boundary condition and a layer model to predict how introduced bacteria would colonize the root environment from a seed-based inoculum. They explicitly included pore size distribution and matric potential as determinants of microbial growth rate and diffusion potential. Their simulations showed that the total number of bacteria in the rhizosphere and their vertical colonization were sensitive to the matric potential of the soil. Soil structure and pore size distribution was also predicted to be a key determinant of the competitive success of a genetically modified microorganism introduced into soil (57). The Scott (56) model also demonstrated that the diffusive movement of root exudates was an important factor in determining microbial abundance. Results from models that ignore the spatial nature of the rhizosphere and treat exudate concentration as a spatially averaged parameter (14) should therefore be treated with some caution. 

N. van der Hoeven, J. D. van Elsas and C. E. Heijnen, A model based on. soil structural aspects describing the fate of genetically modified baeteria in. soil. Ecol. Model ins S9 161 (1996). 

As far as grass growth is concerned, the most important source of water is that available to the roots, and this is known as the available water capacity (AWC). The remainder is unavailable and while this is highest in heavy clays and clay loams, these soils also have the highest AWC. The AWC of soils is improved by an increase in their organic matter content, which improves the soil s capacity to absorb and hold water and also benefits soil structure. 

Grass roots can grow and absorb water down to 1 m, or deeper if soil structure is good, although subsoil water is usually poorer in nutrients than topsoil water (Frame, 1992). Transpiration is highest... 

Some assets are difficult to cost accurately for example, the notional financial value of providing a haven for wildlife, or of keeping your part of the river free from excess nitrates. Another example would be the value of keeping beef cattle indoors and then using the farmyard manure to improve soil structure and maintain wheat yield. 

The TSDF standards also establish requirements to ensure that hazardous waste management units are closed in a manner that protects human health and the environment. The closure provisions require the facility to stop accepting waste remove all waste from management units and decontaminate all soils, structures, and equipment. Some units (i.e., land treatment units, landfills, and surface impoundments) serve as places for the final disposal of hazardous waste. These land disposal units must comply with additional postclosure requirements to ensure proper long-term unit maintenance. 

Hydraulic conductivity is one of the characteristic properties of a soil relating to water flow. The movement of water in soil depends on the soil structure, in particular its porosity and pore size distribution. A soil containing more void space usually has a higher permeability. Most consolidated bedrocks are low in permeability. However, rock fractures could create a path for water movement. 

The trench method is applicable only when the water table is relatively shallow, less than 10 to 15 ft below the ground surface. For a deeper water table, the cost of the trench method becomes more expensive than other methods such as pump systems. Another limitation of the trench method is the soil structure. The soil above the water table has to be firm and well aggregated to allow for the trench to be self-supporting. Otherwise, embankment enforcement or screening would be needed. A third limitation is that continuous pumping and skimming is required to maintain a flow gradient towards the trench. Otherwise, the free product will move back and reenter the soil. 

The environmental conditions that lead to the formation of a vertic soil structure are also conducive to the formation of suitable parent materials ... 

Figure 1.8. Cracks, surface mulch and soil structure in a Vertisol during the dry season (from FAO, 2001. Reprinted from World Soil Resources Reports 94, P. Driessen, J. Deckers, O. Spaargaren, F. Nachtergaele, eds., p80, Copyright (2001), with permission from FAO)...

Mineral Colloid-Organic Substance-Microorganism Interactions in Relation to Soil Structural Stability... 

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