Low-rainfall areas

The pH of Soils. The pH of soils (see Textbox 48) varies widely with location and climate the local climate of a region usually provides a clue as to the pH of the soil. In high-rainfall regions, for example, soils are generally acid. Alkaline soils, in contrast, typically occur in low-rainfall areas the actual value of the pH varies over a wide range, from below 5 in very acid... 

The alkali and alkaline earth metals are examples of relatively simple cations that occur in only one oxidation state and are surrounded by water (see Figure 6.1). The most common of these ions in soil, in order of decreasing abundance, are calcium (Ca2+), magnesium (Mg2+), potassium (K+), and sodium (Na+). Sodium is typically present in very small amounts in high-rainfall areas, whereas it may have a relatively high concentration in low-rainfall areas. 

One place where soil solution from saturated soils is routinely used is in the determination of salts in soil. Salts can build up in soil in low-rainfall areas. A measure of the salt content is essential for these soils. Typically, a saturated paste of soil is made and the water filtered by vacuum filtration. The filtrate can then be analyzed for electrical conductivity and this measurement, together with calcium, magnesium, and sodium content, can be used to calculate various measures of salt content and potential detrimental effects of salts on crops and water quality. 

Chernozemic and Sierozemic Medium to heavy textured soils of low rainfall area 88 7.20 T = 4.12 -1- 0.82xi -1- 5.12x2... 

Solid phase water-soluble sulfates, especially gypsum (CaS04-2H20), are likely to occur in low rainfall areas with a prior marine influence. For example, it is found in many soils of inland Australia (Rayment etal. 1983). 

In addition to compounds of sulphur and nitrogen oxides, acid precipitation is known to contain a variety of heavy metals, particularly in the vicinity of metal smelters. The metals such as lead, cadmium, zinc and vanadium are obviously soluble, and in areas experiencing high rainfall are washed out, giving rise to rather higher levels of deposition than in low rainfall areas. 

Low rainfall areas 500-600mm annual rainfall, up to 150 mm excess winter rainfall Light sands or shallow soils over sandstone... 

With cereals, irrigation can only be jrrstilied on very light soils in low rainfall areas and only if higher value crops have had their water need satisfied. The most critical time is about GS 37 when the flag leaf is showing and the ear is developing rapidly. An application of 25 rrun should be adeqirate. 

Because of the low rainfall and high evaporation rate, other water sources which might carry contamination Into the ground water were Investigated. The Company was required to check the Industrial water settling basin and all existing storm and sanitary sewers In the potllner area for leaks. 

The formation of mineral coal is not an instantaneous process, but is an extremely lengthy one, spread over an extended period. Millions of years ago, when the temperature was moderate and rainfall was heavy, vegetation was quite thick, especially in the low-lying areas of the Earth. Coal-forming plants probably grew in swamps, and as the plants died, their debris gradually formed a thick layer of matter on the swamp floor. Over a prolonged period, this matter hardened into a substance called peat. The peat deposits became buried under sand or other mineral matter. As the mineral matter accumulated, some of it turned... 

Because an assessment of this detail can be very difficult and costly to perform, however, (especially if it requires the use of complex fate models), exposure estimates may be limited to average seasonal conditions (e.g., summer — low flow — low rainfall, etc.) and to specific "worst case" meteorological or hydrological conditions for that area (e.g., inversion conditions, 7 day-10 year low flow). 

Seed quality depends heavily on the climatic characteristics of site locations. Thus, in order to limit seedbome disease inocula, seed production should be in areas characterized by low rainfall during flowering and ripening stages and by soils with low soil-nitrogen levels. 

Horizon Development in Areas between High- and Low-Rainfall... 

In areas between high and low rainfalls, horizonation may be well or poorly developed, soil pH may be either acidic or basic, and there may or may not be... 

The feasibility of an evaporation pond is determined by the volume of concentrate, the cost of land and the ambient evaporation rate. They are most cost-effective in areas with low rainfall, high evaporation rates, and where large expanses of land are available at low cost (Mickley 2009). This best suits inland desalination plants in regional and remote areas where these conditions can be met. 

High rates of water influx remove SiO at low solution concentrations. Normal ground water and streams carry about 17 ppm SiO and less in high rainfall areas (Davis, 1964). In some weathering profiles silicification or deposition of silica has been observed. Most often the form of the phase deposited is crypto-crystalline, either opal or chalcedony. In these cases quartz grains do not show overgrowths (Elouard and Millot,... 

Sediment phosphorus extraction analyses show that hydrous iron oxides (extracted by (NH4)2C204) play a major role in the transport of sediment phosphorus. In northern areas of the Genesee River watershed calcium carbonate formation also appears to be Involved in phosphorus fixation. Ion activity product calculations for water column samples from the Genesee River consistently exhibit subsaturation with respect to the stable calcium phosphate phase, hydroxyapatite. Calcium carbonate, which can serve as a substrate for phosphate mineralization, shows an ion activity product below the solubility product in the Genesee River except during the summer low-rainfall season. 

The leaching and precipitation of copper at Rio Tinto in Spain this century is described by Taylor and Whelan (Tl) and an extensive report on the present-day technology of copper leaching practices in the western United States is discussed by Sheffer and Evans (SIO). Modified practices have been successfully used throughout the world both in low- (SlO) and high-rainfall areas (B7). 

But that means that finding sodium compounds on land is somewhat unusual. They tend to be more common in desert areas because deserts experience low rainfall. So sodium compounds are less likely to be washed away. Huge beds of salt and sodium carbonate are sometimes found in desert areas. 

Outdoor recovery of sodium chloride by evaporation of sea water or natural brines is carried out in areas, which have a high evaporation rate and low rainfall. Slow-evaporation rate in temperate countries restricts the use of natural evaporation to only a small fraction of the production in these... 

Water use requirements are an important issue for consideration, particularly for areas with low rainfall or limited water resources. In-situ gasification and the use of air cooling in place of water cooling for the major processes can substantially reduce water requirements. 

Low rainfall in the area is preferable, as is a low ground water table. Ground water and surface water hydrology must be carefully studied. Such a study would probably result in a well-survey system, which could also be used to monitor the burial grounds. 

In 1993 cropped land accounted for 19 per cent of the total land area of developing countries of the region. This indicates that significant inroads have already been made into land with low production potential, which include unirrigated areas with arid and semi-arid climates, or unreliable rainfall, areas with steep slopes or poor soil drainage or a combination of these features. Such areas tend to be ones where environmental degradation is most severe. 

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