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 Because of the highly variable nature of salt-affected soils and the expense of reclamation, field mapping is prerequisite to effective reclamation. Visual observation mapping of plant growth and soil appearance is the quickest and least expensive method for mapping low-, medium-, and high-salinity impacted areas of the landscape. Native plant species and stunted growth or leaf burn in cultivated crops are effective identifiers of saline and sodic areas. Saline soil areas will also have white salt crusts, while sodic areas will be barren with dark-to-black, oily-looking slick shining surfaces bordered by water-stressed plants. Remote-sensing procedures, such as aerial photography, videography, infrared thermometry and imaging, multispectrial scanners, microwave sensors, and time domain reflectometry, also are used for salinity mapping. Once the productive and problem areas are defined, deep sample holes can be bored to determine if a high water table is the salt source. Water samples from high water tables should be analyzed for salt concentration and type. Soil samples should also be analyzed to determine salt type and concentration. Exchangeable cation concentrations are also needed to determine the degree of the sodium problem. Irrigation-water salt concentration and cation ratios are also important factors in salinity management. Once the salt sources, concentrations, and cation ratios are determined, a reclamation plan can be developed; or if reclamation is not practical, crops tolerant to the conditions can be selected. Reclamation Four conditions must be satisfied in order to reclaim salt-affected soils by removing soluble salts and excess sodium: (1) less salt must be added to the soil than is removed; (2) salts must be leached downward through the soil; (3) water moving upward from shallow water tables must be removed or intercepted to prevent additional salts from moving back to the soil surface; and (4) in sodic and saline-sodic soils the exchangeable sodium must be replaced with another cation, preferably calcium, and the sodium leached out. Applications of soil amendments (gypsum, iron sulfate, sulfur, or sulfuric acid) are beneficial only on sodic soils when leaching also occurs and on leaching of saline-sodic soils that do not contain natural gypsum. Adding chemical amendments such as gypsum to saline soils only adds more salts and is not needed unless the water has a sodium adsorption ratio of 10 or greater. Effects on plants  Many ions are essential to plant growth as major or minor nutrients. However, when ion concentrations become too high, plant growth is adversely affected by either the toxic effect of a specific ion or the general effects of high ion concentrations. Salinity decreases plant growth through a combination of nonspecific ionic effects and by causing a decrease in the water potential of the soil, which is principally an osmotic effect. The point at which salinity limits plant growth varies because plants have adapted to a wide range of salinity environments. The ocean, which has salt concentrations in excess of 35 parts per thousand (ppt), is abundant in plant life and contains over half of the Earth's plant biomass. Concentrations at which specific ions become harmful to plant growth also vary over several orders of magnitude. For example, boron is toxic to some plants at soil-water concentrations as low as 0.05 mol/m3, whereas some plants can tolerate chloride concentrations as high as 20 mol/m3. Sodium and chloride are the most abundant salinity-inducing ions in soils and water; however, significant amounts of calcium, magnesium, sulfate, carbonate, and bicarbonate ions are also found in nature. The proportions of these ions vary with respect to soil types and local geology. Terrestrial plants that are tolerant of high concentrations of soluble salts in their root zones (the area around the root from which a plant extracts water) are known as halophytes. Halophytes can survive and complete their life cycles at optimum salt concentrations of 1.2–30 ppt in their root zone. Most terrestrial plant species are not adapted to high salt concentrations and may be considered glycophytes. In agriculture, salt is a serious hazard in irrigated areas if growers do not leach their soils properly during irrigation, fail to provide adequate drainage for their crops, or allow their water tables to rise too near the surface. High concentrations of salts in the water used for irrigation may also damage crops or reduce yields. High-salinity waters may include ground and surface water and water recycled from municipal and industrial uses. Salinity acts as an environmental plant stress that may cause leaf damage of reduced growth or, at high concentrations, may be lethal. Plant responses to excess salts in their root zones or on leaf surfaces (from ocean sprays or irrigation) are quantitatively dependent on salt concentration, composition, and time of exposure. Plant sensitivity to salt also varies according to growth stage. Generally, plants are salt-tolerant during germination, are most sensitive during the seedling stage, and become more tolerant with maturity. Plants also may show increased salt sensitivity during their reproductive stage, as seen by decreased pollen viability and seed setting ability.  Crop salt tolerance  Salt tolerance is the capacity of a plant to endure excess salt in its environment. This characteristic is quantitative and influenced by many soil, climate, and cultural factors. Tolerance assessment may be based on the ability of the plant to survive, to produce high yields, or to withstand adverse growth reductions. In nature, the measure of tolerance may be the ability to survive, reproduce, and compete with other species; whereas in sustenance agriculture, tolerance may be related to both survival and productive yield. In commercial agriculture, the ability of the crop to withstand salt effects without reducing yields below the profit margin is the most important consideration. Thus crop salt tolerance is usefully described by two parameters: the threshold salinity (T) at which yield reduction is significantly measurable, and the rate (R) at which yield decreases with increasing salinity beyond the threshold (Fig. 26). The rate of yield decrease for most crops can be described simply as the slope of a straight line. Salinity concentrations are described as an index of the electrical conductivity of a soil-saturated paste in units of dS/m. Salt tolerance parameters are useful for predicting how one crop may compare with another under similar conditions. However, such assessments are general and relate to crop growth after germination and seedling establishment.    Fig. 26  Typical classifications for salt tolerance of crops based on their relative yields under nonsaline conditions in contrast to yields under increasing saline conditions.   Climate and agricultural management practices may reduce or increase the effects of salinity upon plants. Irrigation and management practices that leach salts away from, or maintain lower concentrations of salt in, the root zone during growth will reduce salt effects. Seed beds should be sloped or maintained in a manner that allows the irrigation water to move salts past the root zone. If excess salts in the seed bed are not kept low, the resulting reduction in plant stand will decrease yields far more than is predicted by salt tolerance parameters. Flood, furrow, drip, and sprinkler irrigations should also be applied at times and in ways that reduce salt accumulation on plant parts and within root zones. Climate factors such as high temperature, low humidity, and high wind speed will increase salt damage, whereas factors that reduce transpiration demand will reduce salt damage. Soil type is also an important factor. Sandy soils will not accumulate salts as readily and are easier to leach than clay soils.  See also: Irrigation (agriculture)  Genetic variability  Many crops, such as sugarbeet, asparagus, date palm, cotton, and barley, are salt-tolerant and are standard crops in saline areas. Different types of beans and berries, as well as avocado and many fruit trees, are very sensitive to salt. In salt-sensitive species, sensitivity is often associated with the accumulation of a specific ion in leaves, usually chloride or sodium. Saline soil environments with high proportions of sulfate compared to chloride may have less severe salinity effects on chloride-sensitive plants. The ability to exclude specific ions at the level of the root or shoot is one of the major causes for genetic variability among plant varieties and ecotypes. Rice, although salt-sensitive, is grown on saline lands for reclamation because it has a shallow root zone and can be grown on flooded fields if water of good quality is available. Salt tolerance also varies less between cultivars and ecotypes of the same species. Conventional breeding efforts to improve salt tolerance of crops include selection for more tolerant cultivars through hybridization among varieties of a species; hybridization of a cultivated species with related, wild salt-tolerant species to increase genetic variability prior to selection; and exploitation of the useful agronomic potential of wild halophytes. The ability of the grower to control the effects of salt in the field is of more greater consequence than the variability in salt tolerance among cultivars.  Morphological and physiological effects  Salinity reduces plant growth through both osmotic and ionic influences. The osmotic effects are a result of increased solute concentrations at the root-soil water interface, which create lower water potentials. Growth suppression is the result of total electrolyte concentration, soil water content, and matrix effects, and is manifested in reduced cell enlargement and metabolism. The plant suffers water stress for a short period until it can make some type of osmotic adjustment. Plants make this adjustment by accumulating more salt within their tissues (a halophytic response) or by the synthesis of organic solutes, which increases the osmotic potential of the cytoplasm so that water will flow into the root and plant tissues. Ionic effects may be both general and specific. General ionic effects are the result of the increased ionic strength of the soil water. Ionic effects may interfere with the normal processes by which plants take up nutrients by changing the surface chemistry at the cell wall and plasma membrane. Specific ions may disrupt normal metabolic processes or upset nutrient balances. For instance, high sodium concentrations relative to other salts can disrupt root permeability to ions by displacing calcium in the plasma membrane. Upsetting calcium metabolism and nutrition within the cell may cause additional effects. At higher sodium-to-calcium ratios, soil structure, tilth, and permeability of the soil to water may be reduced (sodicity). The specific physiological cause of growth reduction due to salt stress is undoubtedly complex in both the metabolic and genetic sense. Salt stress reduces plant growth primarily because it increases the metabolic energy needed to acquire water from the root zone and to make the biochemical and morphological adjustments necessary to maintain growth in a higher ionic environment.  See also: Plant-water relations; Plants of saline environments; Soil fertility  Erosion  Soil erosion results from the detachment and transport of soil materials by water. Geologic erosion and erosion from human activities are the principal types. Long-term geologic erosion creates topographic features such as canyons, stream channels, and valleys. Removal of natural vegetation by human activities, such as farming, ranching, forestry, and construction, may also cause erosion. Excessive erosion could threaten the world supply of agricultural and forest products. The efficiency of water conveyance and storage structures may be significantly impacted by sedimentation resulting from soil erosion. Excessive amounts of sediment in streams and rivers can reduce their suitability as a biological habitat and create water supply difficulties. Understanding the various types of erosion and the factors affecting erosion is necessary in identifying appropriate control practices. Types  Erosion by water occurs when soil particles are detached from the soil surface and then transported by runoff. As runoff rate increases, small channels, called rills, begin to form. The region between rills is defined as the interrill area. When concentrated runoff is sufficiently large to cut deep channels, gully erosion occurs. Stream channel erosion may develop within a water course that has nearly continuous flow. Interrill erosion, rill erosion, gully erosion, and stream channel erosion each have distinct characteristics. Interrill erosion On interrill areas, raindrops impacting the soil surface serve to detach soil particles. Some of the soil particles are transported by thin interrill flow into rills. Residue materials from the previous crop that are left as a surface mulch are very effective in reducing interrill erosion. Raindrop energy is absorbed and dissipated by the residue mulch, thus protecting the soil surface.  Rill erosion  Soil materials removed by raindrop impact on interrill areas may eventually be delivered to rills where they are transported down a hillslope by rill flow. Rills are small enough to be removed by normal tillage operations. Substantial erosion may occur once rills have formed. If conservation measures are not employed to reduce rill erosion, rapid loss of soil productivity may result. Rill erosion can usually be controlled by contouring, strip cropping, and conservation tillage.  Gully erosion  Gullies are deep channels larger than rills that cannot be removed by tillage. Gully erosion generally occurs near the upper end of intermittent streams. Once they are formed, gullies become a permanent part of the landscape, and they may expand rapidly. Gully formation often develops where there is a water overfall causing the gully to move upslope. Water moving through the gully may cause the channel to deepen. In addition, sections of the exposed banks may be undercut and slide into the gully, where they are later removed during large runoff events. Control measures, such as terraces or vegetated waterways, may be required to prevent gully erosion.  Stream channel erosion  Stream channel erosion results from the removal of soil from stream banks or beds. Runoff flowing over the side of the stream bank or scouring below the water surface can cause stream channels to erode, especially during severe floods. The major cause of erosion along stream banks is meandering. Stream channel erosion may increase when sediment delivery from upland areas is reduced through control practices or when upstream sediments are caught in water storage facilities.   Factors affecting erosion  The principal elements affecting soil erosion are rainfall characteristics, soil factors, topography, climate, and land use. Rainfall characteristics  Runoff is rainfall that is neither absorbed by the soil nor accumulated on the surface but moves downslope. Rainfall rate and duration are important variables influencing runoff and erosion. Runoff occurs only when rainfall intensity exceeds soil infiltration rate, which decreases with time. Thus, no runoff may occur from a storm of short duration, while substantial runoff may result from a storm of the same intensity but of longer duration. Both the rate and volume of runoff are influenced by rainfall intensity. Infiltration capacity is exceeded by a greater margin during a high-intensity storm than a less intense rainfall event. As a result, the high-intensity storm may produce a greater volume of runoff even though total precipitation was similar for the two events. The infiltration rate may also be substantially reduced by the destructive action of the storm on the soil surface. Irrigation is used on some agricultural areas. Runoff may result from both irrigation and natural precipitation events. The runoff potential may be compounded on irrigated areas because of the increased quantities of water introduced through irrigation.  Soil factors  The physical, chemical and mineralogical characteristics of soils vary greatly, as does their susceptibility to erosion. Soil erodibility is influenced significantly by the size of primary soil particles, organic matter content, soil structure, and permeability. These soil characteristics affect the susceptibility of soil particles and aggregates to detachment. For erosion to occur, runoff must be present. In general, as runoff rates become greater, erosion also increases. One of the most effective means of reducing erosion is to maintain high infiltration rates. Keeping crop residue materials on the soil surface to reduce sealing caused by raindrop impact helps to preserve high infiltration rates.  Topography  The degree and length of slope, and the size and shape of the watershed influence erosion. As slope gradient increases, the velocity of flowing water becomes greater. The ability of moving water to detach and transport soil particles increases substantially with larger flow velocity. Rill erosion becomes greater on longer slopes because of an increased accumulation of overland flow. Concave slopes, with a smaller slope gradient at the bottom of the hillslope, are less erosive than convex slopes. Deposition frequently occurs at the bottom of concave slopes because of reduced transport capacity of flow.  Climate  The quantity of erosion that occurs from a given region is influenced by the total amount and intensity of rainfall. The dense vegetation found on areas that receive substantial rainfall reduces erosion potential. Regions with low rainfall and limited vegetation are often susceptible to erosion during high-intensity rain storms. Runoff from melted snow and ice can cause serious erosion problems in colder climates. During several months of the year, frozen soil is not subject to erosion. However, if the snow cover melts rapidly and infiltration does not take place, substantial runoff may result. The rapid melting that may occur when rain falls upon a snow-covered surface can also produce significant runoff. Substantial erosion may occur as water moves over a thin layer of freshly thawed soil. In many colder climates, more erosion results from snowmelt than from rainfall.  Land use Areas having complete ground cover throughout the year are least susceptible to erosion. Erosion from undisturbed forests is usually minimal, because a constant vegetative cover is maintained on the soil surface. On croplands, the amount of surface cover is influenced by the cropping and management conditions employed. One of the most critical periods exists after planting when residue cover is at a minimum and high-intensity rains frequently occur. A study conducted in the southeastern United States demonstrated the effects of selected land use on runoff and soil loss (Table 2). The results showed that cultivated land left fallow with no vegetative cover is particularly vulnerable to erosion. Row crops such as corn and cotton grown continually on areas with steep slopes may also result in significant erosion. Planting row crops in rotation with grasses and legumes that maintain a dense surface cover substantially reduces erosion. Interseeding row crops with a legume can also be an effective conservation measure on areas that receive sufficient precipitation. The legume provides a protective surface cover during the critical planting period and also serves as a supplemental nitrogen source for the following cropping season. A herbicide is usually applied to kill the legume before the row crop is planted. The dense sod found in pastures grown in humid areas is very effective in reducing erosion. Erosion is also minimal on natural rangelands where adequate surface cover is maintained. In regions with limited rainfall where bunch grasses are found, severe erosion may occur during intense storms from the exposed soil located between the bunches of grass. Reduction of vegetative cover through excessive grazing may also result in serious erosion. On some rangeland areas, gravel and cobble materials are found throughout the soil profile. Since they are not easily transported by overland flow, gravel and cobble materials remain on the surface of eroded soils. This creates an armoring process in which the gravel and cobble materials reduce further erosion from rangeland soils. Erosion is greatly diminished on forest lands because of the overhead canopy of trees and the surface layer of decaying organic matter. In an undisturbed forest, almost all erosion occurs from channel banks or adjacent steep slopes. Erosion rates may increase substantially on forest areas that are disturbed by timber harvesting, road construction, or fires.  Control  Contouring, strip cropping, conservation tillage, terraces, buffer strips, and stream channel erosion control measures have been used effectively to reduce the damage caused by soil erosion. Contouring Planting crops and performing tillage along the contours of the land can be an effective conservation measure. Surface runoff is confined in small depressions, thus reducing rill development. Ridge tillage systems are used to significantly increase the storage capacity of furrows. To maintain furrow storage capacity, row crops are planted on the top of the same furrow each year. As the slope gradient increases, the effectiveness of ridges in trapping runoff and reducing soil loss decreases.  Strip cropping  Strip cropping occurs when alternate strips of different crops are grown in the same field. The strips with the greatest vegetative cover reduce runoff velocity and capture soil eroded from upslope areas. The strip widths selected allow for the convenient use of farm equipment. For erosion control, the strips are usually planted on the contour in a rotation that shifts crops annually from one strip to the next.  Conservation tillage  Leaving a residue mulch from the previous crop on the soil surface greatly reduces erosion (Fig. 27). The reduction is related to the percent of residue cover left on the soil surface. Even small amounts of residue cover can cause substantial reductions in erosion. The amount of erosion protection provided with a given percent of surface cover is influenced by the type of residue material.    Fig. 27  Ratio of soil loss for given residue covers to soil loss with no cover. The vertical broken line indicates the residue cover necessary to be defined as conservation tillage. (After T. S. Colvin and J. E. Gilley, Crop residue: Soil erosion combatant, Crops and Soils, 39(7):7–9, 1987)    Conservation tillage has been defined as any tillage or planting system that leaves at least 30% of the soil surface covered with residue after planting (Fig. 27). When tillage is performed, implements are used that cause only minimal disturbance to the soil surface, thus maintaining existing crop residues. For some row crops, such as soybeans, no tillage is used before planting to leave sufficient residue cover to control erosion.  Terraces  Terraces are broad channels built perpendicular to the slope of steep land. The gentle grades used in terraces allow runoff to be carried around a hill at relatively low velocities, causing sediment to settle from the runoff water. Terraces usually empty onto grassed waterways or into underground pipes, thus preventing the formation of gullies. Crops are usually planted parallel to the terrace channel, requiring the use of contour farming. Conservation tillage is also frequently used in conjunction with terracing. A significant investment is required to construct terraces, and farming operations are more difficult on terraced hillslopes. As a result, terraces are used only when other control measures cannot provide adequate erosion protection.  Buffer strips Buffer strips are areas of land maintained with permanent vegetation, designed to intercept runoff. They are most effective when used in combination with other erosion control practices. Buffer strips are located at various positions along the landscape as part of a planned conservation system. The types of vegetation used in buffer strips is influenced by local conditions. Periodic maintenance may be required for sustained buffer strip performance. The types of buffer strips frequently used are contour buffer strips, filter strips, and grassed waterways. Contour buffer strips containing perennial grasses are planted along steep slopes. The grass strips remove sediment from overland flow. The species of perennial grasses used and the spacing of the grass strips are tailored to local conditions. A narrow terrace may eventually form along the grass strip as a result of sedimentation. The expense of establishing contour buffer strips is substantially less than the cost for constructing terraces. Filter strips can also be used to remove sediment from overland flow and provide increased infiltration. They are usually located on the edge of fields or adjacent to streams, ponds, or wetlands, and thus do not interfere significantly with normal farming operations. Filter strips are best suited for areas with gentle slopes where rilling is not a problem. Grassed waterways can be used to convey runoff from terraces or other concentrated flow areas, and prevent channel erosion and gully formation. Sediment transported by overland flow is deposited in grassed waterways, thus reducing costly downstream sedimentation. A stable outlet below the grassed waterway is provided to reduce runoff velocity and disperse the flow before it enters a vegetated filter.  Stream channel erosion control measures  Vegetative, mechanical, or combined vegetative-mechanical means have been developed to reduce stream channel erosion. Depending on the size of the upstream drainage area, grading of the stream bank to a less severe slope may be necessary. Grass, shrubs, and trees have been successfully used to stabilize stream channels. Dikes made of loose stone or rock piles are placed within the stream channel to divert the faster-flowing water away from the bank. Mechanical covers of stones, rocks, or other protective material may also be placed over the erodible bank. Areas with the greatest erosion hazard, such as the bottom of a stream bank, may be protected with a mechanical cover, while the upper portion of the stream banks is usually stabilized with vegetation. Wind erosion  Soil erosion by wind is a dynamic process. The results of wind erosion are evident when soil particles are dislodged from the soil surface, injected into the wind stream, and in some cases transported around the world as “dust” before being deposited. In the process of being dislodged by wind, soil particles are sorted according to size, like the winnowing of grain. Wind erosion is the geomorphological process responsible for the tremendous loess (wind-borne) deposits of highly fertile soil around the world. While wind erosion has always been an active process, human activities tend to accelerate it. As humans disturb large areas, loose soil particles may result. Large, coarse particles may move a few feet or be deposited in fence rows or road ditches at the edge of a field. When carried by strong winds, these coarse particles damage plants, abrade paint, break down soil crusts, and accelerate the wind erosion process. The loss of fine soil particles from a field reduces the capacity of the soil to produce crops; moreover, these particles reduce visibility and degrade air quality.  See also: Dust storm; Loess When susceptible soils are exposed to erosive winds, ominous dust clouds occur. To effectively control the wind erosion that produces these dust clouds, all available resources, including the climate, soil, crop, and management systems, must be utilized. No single erosion control system will be equally effective for all wind erosion problem areas. For example, in regions that normally produce high-residue (vegetation) crops, the most effective wind erosion control systems maintain those residues either erect or on the soil surface. For semiarid regions growing crops that produce little residue, the most effective wind erosion control systems include a rough and cloddy soil surface and vegetative wind barriers. Options for humid or subhumid regions should include cover crops and residue management. For all regions, if the erosive winds blow from the same direction, the benefits of residue management, soil roughness, or cover crops could be supplemented with strip cropping, annual or perennial crop wind barriers, and tree shelter belts. Farmers should be aware of all the wind erosion control practices that are available and then use whatever combination will be most effective for their conditions. It is possible to estimate soil erosion with computer modes. Wind erosion models utilize weather, soil, crop, and management information in the calculation of predicted soil erosion losses. The losses can be estimated daily or for the entire crop-growing period. Each erosion control strategy must consider the potential for rainwater to degrade soil surface roughness, temperature and rainfall requirements for growing cover crops, and the rate at which crop residues decompose. Wind erosion damage can never be completely eliminated, but with careful planning and wise use of available resources (climate, soil, crop, and management) the impact of wind erosion on plants, soils, the atmosphere, and humans can be minimized.  See also: Erosion; Soil conservation Bibliography   P. W. Birkeland, Soils and Geomorphology, 1984 Ali Fazeli = egeology.blogfa.com A. Blum, Plant Breeding for Stress Environments, 1988 Ali Fazeli = egeology.blogfa.com N. C. Brady and R. R. Weil, The Nature and Properties of Soils, 11th ed., 1995 Ali Fazeli = egeology.blogfa.com E. Bresler, B. L. McNeal, and D. L. Carter, Saline and Sodic Soils, 1982 Ali Fazeli = egeology.blogfa.com H. D. Foth, Fundamentals of Soil Science, 8th ed., 1990 Ali Fazeli = egeology.blogfa.com H. D. Foth, Soil Fertility, 1988 Ali Fazeli = egeology.blogfa.com W. H. Gardner and J. C. Hsieh, Water Movement in Soil, 1960 (27-min time-lapsed video cassette, available in Soil Conservation Service and university audio-visual libraries, from Crop and Soil Sciences Club, Washington State University, P.O. Box 646420, Pullman, WA 99164-6420) Ali Fazeli = egeology.blogfa.com C. T. Haan et al., Design Hydrology and Sedimentology for Small Catchments, Academic Press, San Diego, 1994 Ali Fazeli = egeology.blogfa.com C. T. Haan, H. P. Johnson, and D. L. Brakensiek (eds.), Hydrologic Modeling of Small Watersheds, Amer. Soc. Agr. Eng. Monogr. 5, 1982 Ali Fazeli = egeology.blogfa.com D. Hillel, Environmental Soil Physics, Academic Press, San Diego, 1998 Ali Fazeli = egeology.blogfa.com N. Hudson, Soil Conservation, 3d ed., Iowa State University Press, Ames, 1995 Ali Fazeli = egeology.blogfa.com E. H. Isaaks, An Introduction to Applied Geostatistics, 1990 Ali Fazeli = egeology.blogfa.com H. Jenny, The Soil Resource: Origin and Behavior, Ecological Studies, vol. 37, 1980 Ali Fazeli = egeology.blogfa.com W. A. Jury, W. R. Gardner, and W. H. Gardner, Soil Physics, 5th ed., 1991 Ali Fazeli = egeology.blogfa.com A. Klute (ed.), Methods of Soil Analysis, pt. 1: Physical and Mineralogical Methods, 2d ed., 1986 Ali Fazeli = egeology.blogfa.com R. Lal, Soil Erosion and Its Control, 1988 Ali Fazeli = egeology.blogfa.com A. Lieth and A. M. Massoun, Towards Rational Use of High Salinity Tolerant Plants: Agriculture and Forestry under Marginal Soil Water Conditions, 1993 Ali Fazeli = egeology.blogfa.com L. Lyles, L. J. Hagan, and E. L. Skidmore, Soil Conservation: Principles of Erosion by Wind, Amer. Soc. Agron. Monogr. 23, 1983 Ali Fazeli = egeology.blogfa.com National Academy of Sciences, Soils of the Humid Tropics, 1972 Ali Fazeli = egeology.blogfa.com National Association of Review Appraisers Staff, Land Classification for Land Uses Management and Valuation, 1983 Ali Fazeli = egeology.blogfa.com M. A. Nearing et al., A process-based soil erosion model for USDA: Water erosion prediction project technology, Trans. Amer. Soc. Agr. Eng., 32(5):587–1593, 1989 Ali Fazeli = egeology.blogfa.com F. J. Pierce and W. W. Frye (eds.), Advances in Soil and Water Conservation, Sleeping Bear Press, Chelsea, MI, 1998 Ali Fazeli = egeology.blogfa.com K. G. Renard and G. R. Foster, Soil Conservation: Principles of Erosion by Water, Amer. Soc. Agron. Monogr. 23, 1983 Ali Fazeli = egeology.blogfa.com G. Richardson and P. Mueller-Beilschmidt, Winning with Water: Soil Moisture Monitoring for Efficient Irrigation, 1988 Ali Fazeli = egeology.blogfa.com G. O. 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Troeh et al., Soil and Water Conservation: Productivity and Environmental Protection, 3d ed., Prentice Hall, Upper Saddle River, NJ, 1999 Ali Fazeli = egeology.blogfa.com U.S. Department of Agriculture, Soil: Yearbook of Agriculture, 1957 Ali Fazeli = egeology.blogfa.com U.S. Department of Agriculture Soil Conservation Service, Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys, 1988 Ali Fazeli = egeology.blogfa.com W. H. Wischmeier and D. D. Smith, Predicting Rainfall Erosion Losses: A Guide to Conservation Planning, USDA Agr. Handb. 537, 1978 Ali Fazeli = egeology.blogfa.com نوشته شده در تاريخ ۸۸/۰۴/۲۲ توسط مهندس مهرداد فرهنگی GetBC(4668);