lume to allow net downward movement of salts; (b) the adjustment of soil fertility programs to correct nutritional deficiencies, imbalances, or toxicities; and (c) to select turf grasses that can tolerate.
The salinity levels expected when saline irrigation water is used on a regular schedule.
During dry periods, the background soil salinity will not be any lower than what the salinity level in the irrigation water is, and usually accumulated soil salinity is higher. Some common management considerations on saline soils are as follows (D.A. Horneck et al 2007)
• Irrigation system distribution uniformity and efficiency become very important since the non-uniformity of irrigation water will affect spatial distribution on not just the water but also soluble salts. Design issues (spacing between sprinklers and wind issues) will become more pronounced, and salinity leaching more difficult.
• Irrigation scheduling, to avoid normal and physiological drought stress and for salt leaching, is critical.
• Factors to enhance water infiltration (into soil surface), percolation (through the root zone), and drainage past the root zone “Cultivation, Topdressing, and Soil Modification.
• Traffic control programs to avoid total salt-induced wear injury must be carefully designed.
• Fertilization must be adjusted not just to meet plant growth requirements but also to maximize salt tolerance mechanisms and to correct imbalances. As irrigation water salinity increases, so do the nutritional interaction issues and these can become dominant management challenges under high salinity?
• Proactive soil and water quality testing should be performed, as well as tissue testing if needed, to monitor salinity impacts.
• Drought and high-temperature stresses are more common on saline sites since high-soluble salts cause physiological drought and may injure roots, and plant tolerance to these stresses is reduced by high salinity.
• High soil salinity depresses cytokinin synthesis in roots, and this “biostimulant” may be necessary to promote adequate growth.
2.9.2 Managing Sodic Soils
Similar to saline sites, numerous secondary problems or challenges arise from the primary effects of Na-induced deterioration of soil physical conditions, most of the extensive publication on sodic and saline-sodic soil management has been focused on agriculture situations (Levy, 2000; Suarez, 2001; Rengasamy, 2002; Qadir and Oster, 2004; Qadir, Noble, et al., 2006; Qadir, Oster, et al., 2006, 2007). While soil permeability problems are present in all sodic soils, except for very sandy soils with single-grain structure, soil pH affects other problems, including nutrient availability.
• Leaching of soluble salts by application of sufficient infiltrated water volume to allow net downward movement of salts. Even without adding gypsum, leaching can remove Na carbonates and bicarbonates that may be precipitated in the soil since these are soluble salts, but these may cause sodic conditions deeper in the profile. Leaching is also essential to remove the Na displaced from the CEC sites; otherwise, the Na simply goes back on the CEC sites without changing the negative soil physical conditions.
• Application of sufficient quantities of granular Ca is necessary for displacement of Na on the CEC sites so that flocculation of clay and organic colloids can occur.
• Routine and vigorous surface and subsurface (deep) cultivation programs are essential to improve water and air permeability. Soils with high clay content of 2:1 clays require the most systematic cultivation to create temporary macropores for water and air movement. The depth during cultivation must penetrate below any salt accumulation or compaction It should be stressed that while sodic soils do not have a high concentration of total soluble salts compared to saline soils, irrigation water with only moderate salinity can result in a build-up of high total soluble salts in the surface zone of sodic soils due to their inherent low infiltration and percolation rates where water can accumulate and then evaporate, leaving the salts to layer or migrate upward and deposit at the surface. Thus, salts may not be high in concentration throughout the whole root zone and therefore not result in high soil ECe; but within the top few centimetres, salts may accumulate at much higher concentrations. This can be an issue especially with new seedlings or newly established sites with vegetative planted materials and when irrigating with short-duration, frequent irrigation cycles. Cultivation and leaching programs must be developed with this aspect in mind.
• Irrigation system distribution uniformity and efficiency become very important ecosystem infrastructure components since non-uniformity of irrigation water will affect spatial distribution on not just the water applications but also the potential accumulation of total soluble salts. Design issues will become more pronounced and salinity leaching more difficult if not properly designed for salt management.
• Irrigation scheduling to avoid normal drought and physiological drought stress problems and for effective salt leaching is critical. The most effective leaching program for removal of Na from the CEC sites is by application of sufficient water volume with each irrigation event to cause slow downward movement of any total soluble salts and activation of Na displacement from the CEC sites by available Ca. Since sodic soils have less than desirable soil physical properties, pulse irrigation cycling is the most effective leaching strategy, and site-specific irrigation is critical-that is, adjusting each zone (single-head zones are best) to achieve adequate irrigation volume to facilitate salt movement.
• Proactive soil and water quality testing as well as tissue testing, if needed, to monitor salinity impacts on plant.
• Drought, high temperature, and wear stresses are more common on sodic sites since grasses often cannot develop Inherent low oxygen stress on sodic soils depresses cytokinin synthesis in roots just as inherent highly salinity does on saline soils. Thus, this “biostimulant” may be necessary to promote adequate growth and to sustain root regeneration.
• Secondary biotic problems usually increase on the turfgrass or landscape plants.
2.9.3 Managing Saline-Sodic Soils
Loch et al. (2003, 2006) conducted studies of treatment options on coastal parks with soil dredged from the adjacent ocean tidal lands, which then became an upon oxidation and were saline-sodic in nature. They evaluated an array of treatments such as grass selection, liming, fertilization, cultivation, sand capping, and leaching. Important factors to consider before reclamation are the quantity of pyrite present; location of pyrite in the soil profile; potential for leaching toxic concentrations of Al from the profile; degree of saline and sodic stresses; and potential for control of the water table. Some ripe acid-sulfate soils that have been exposed to considerable weathering and leaching may be reclaimed using as little as 150 lb. CaCO3 per 1000 sq. ft. (7300 kg/ha), while others may require many years of weathering remediation and much higher lime rates (Dear et al., 2002). When applying lime and gypsum prior to establishment, these amendments should be incorporated into the root zone or surface foot of soil. If application is delayed until after plant establishment, deep injection can be applied with a device such as the Water Wick Turf Drainage System. Other management factors to consider are the influence of soil mixing and contouring of the landscape on movement of pyrite during reclamation; location of the water table; leaching ability; need for gypsum in the surface zone for establishment and improvement of soil physical conditions; cultivation needs; fate of leachates; and non-uniformity of pyrite within the soil. Organic matter additions can help reduce soluble Al, but should not be added until later in the reclamation program if it hinders initial leaching of toxic levels of Al. Plant nutritional adjustments will also require calcium amendments when Al, Na, and S are all potentially toxic. Any irrigation water pHs 5.5 should also be adjusted to higher ranges prior to application on turf grass or landscape plants as well as to protect pumping equipment and any metal in or exposed to the irrigation system.
2.10 Salt-affected soils in Iran
With a total area of 1648 million km2 (land: 1636 million km2 and water: 0012 million km2), the Islamic Republic of Iran-later referred to as Iran-is located in West Asia. About 90 per cent of the Country is arid and semi-arid with summer temperatures in the interior reaching as high as 558 oC. In winter, temperatures in the minus range are common in many places, reaching as low as 308 oC in the north-west. The average annual rainfall ranges from less than 50mm in the Central Plateau to more than 1600mm on the Caspian Coastal Plain, with a 250mm national average. Owing to extremely hot summer, the average annual potential evaporation is very high, ranging from less than 700mm along the Caspian Sea shore to over 4000mm in the deserts and the southwestern part of the Khuzestan.
The arable soils of Iran have a long history of human interventions. The recent estimates for cultivated area reveal a figure 18.2 million ha, including both arable land (16.1 million ha) and area under permanent crops (2.1 million ha). There has been an increase of about 6 per cent in the total cultivated area since late 1990s. The total cultivated land constitutes about 11 per cent of the land area of Iran. Of the total
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