Root penetration

In this figure one can clearly see an image of a weld defective area with a superimposed groove defectometer Fe2 4 mm thick. The depth of a minimum groove was 0,5 mm. One can clearly see a groove 0,2 mm deep, which corresponds to sensitivity less than 2% Both incomplete root penetration and metal weld beads can be clearly seen in the image. 

The second degree of freedom is to design-out crevices where possible, although it must be remembered that crevice corrosion can go on underneath deposits. Crevice corrosion at a butt weld with incomplete root penetration is a common case (Fig. 9.7a). Where internal inspection is not possible and crevice corrosion is recognised as likely, A"-radiography of each weld can be specified. 

Fig. 9.8 Erosion/corrosion downstream of a butt weld with too much root penetration...

Capillary barrier ET cover systems may also eliminate the need for a separate biointrusion and/ or gas collection layer. The coarser-grained layer can act as a biointrusion layer to resist root penetration and animal intrusion, due to its particle size and low water content. The coarser-grained layer can also act as a gas collection layer, because the soil properties and location within the cover system are comparable with a typical gas collection layer in a conventional cover system.3944... 

Thus the root occupies the total length of the element for those elements less than the total root length. When the root penetrates only part way into the soil element, as shown in Fig. 1,... 

Soil often occurs as a series of horizontal layers called soil horizons, shown in Figure 15.7. The deepest horizon, which lies just above solid rock, is the substratum, which is rock just beginning to disintegrate into soil by the action of water that has seeped down to this level. No growing plant material is found in the substratum. Above the substratum is the subsoil, which consists mostly of clay. Only the deepest roots penetrate into the subsoil, which may be up to 1 meter thick. Above the subsoil is the topsoil, which lies on the surface and varies in thickness from a few centimeters to up to 2 meters. The topsoil usually contains sand, silt, and clay in about equal amounts. This is the horizon where the roots of plants absorb most of their nutrients. 

The size, shape, and nature of soil aggregates, peds, or slickensides play a major role in determining profile hydrology and the ease of root penetration. 

Soils are loessial sandy loams in most areas, with some alluvial deposits. It is not uncommon to find hard calcarious layers at depths of ten to forty inches. These require fracturing before planting for both water and root penetration. In many places, the soil is underlaid with basalt. Many areas show basaltic outcroppings. Yet, because of the nature of the weather, these are not degraded sufficiently to produce volcanic soils in any significant amount. Soil depths vary from less than twenty inches in some vineyards to more than ten feet in others. 

In crumbly soil there is abundant, uniform and deep root penetration the individual roots are extended (crumb <10 mm). 

In friable soil (Ist-degree compaction) there is less root penetration the root hairs are undulated and grow around the aggregates (aggregates >10 mm). 

In soil which breaks into clods (2nd-degree compaction) there is little root penetration. The roots are usually found only on the fracture surfaces of the clods (clods >50 mm). 

In soil which breaks into plates (3rd-degree compaction) there is hardly any root penetration in a vertical direction. The roots are found predominantly in the horizontal fracture surfaces. 

Mechanisms of Rapid Root Penetration into Deep Soil ... 

However, even in such areas tree roots can penetrate great distances (25-30 ft (lft = 0.3048 m)) below the surface (Nepstad et al., 1994) and reach bedrock (see also Figure 2). If there is a change in the plant cover due to drought, flood, disease, storms, or forest fires, so that the depth of root penetration changes, rate of weathering in low relief areas can change. Also, there... 

In the tropics thick layers of weathered soil make access to fresh rock more difficult, but tree roots can penetrate very deeply. Nepstad et al. (1994) found root penetration up to 10 m in the Amazon Basin, and deep penetration is also evident in Hawaii (see Figure 2). 

Impermeable top covers in terms of plastic liners or clay membranes can be installed in order to prevent water infiltration into the waste and hence cease leachate generation for waste landfilled above the seasonal water table. Top covers are relatively expensive to install and maintenance must be expected in perpetuity. Adequate surface water removal is important to limit the infiltration through cracks, fracmres, or pinholes in the liners. Vegetation is often introduced to improve landscape value but requires special measures to avoid root penetration of the membranes. 

The postmining land-use objective must be selected with the characteristics of the topsoil in mind. Chemical soil properties are more easily amended than physical properties such as texture. Thus, when adequate topsoil is not available, the substitute material must be selected with special attention to texture, coarse-fragment content, and mineral content. Bulk density and soil strength must be considered during soil handling. Methods and equipment used for redistribution of topsoil must be selected to minimize compaction, which can inhibit root penetration and movement of air and water. 

Gossypol and its methyl ethers (Fig. 1) also are formed in the epidermis and root hairs of the developing seedling root (9) and later are infused throughout the periderm of the root bark of older plants. Terpenoids also are exuded by roots, and exudation is increased by microbial infections (10, 11). Only the root tip is devoid of terpenoids, which may explain wRy this is the only area of the root penetrated by root-knot nematode or fungal wilt pathogens. 

Some chloroacnegens, such as 3.4, are so potent that drug companies hesitate to work with them.46 The widespread use of triclosan (3.5) as a bactericide in personal care products needs to be reduced now that several strains of bacteria resistant to it have been isolated.47 Soap and water alone will suffice in many of these applications. The use of dichlobenil (3.6) to kill roots penetrating underground pipes might be eliminated by designing tighter pipe joints.48... 

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