SWAE4412 Management of Salt Affected Soils PDF

SWAE4412 Management of Salt Affected S Sultan Qaboos University SWAE4412 Management of Salt Affected Soils The Problem Dr. Afrah Al-Shukaili [email protected] 1 What do you observe?...

SWAE4412 Management of Salt Affected S Sultan Qaboos University SWAE4412 Management of Salt Affected Soils The Problem Dr. Afrah Al-Shukaili [email protected] 1 What do you observe? 2 Remember !!!! “Salts usually become a problem when too much water is supplied, not too little.” 3  SWAE4412 Management of Salt Affected Soils What is soil salinization? Process by which water soluble salts accumulate in the soil. Salinization is a resource concern because excess salts hinder the growth of crops by limiting their ability to take up water. Since 4th Century BC. 4  SWAE4412 Management of Salt Affected Soils What is soil salinization? What is a salt? Compound consisting of ionic bounded molecules Cations: Calcium Ca2+, potassium K+, sodium Na+, Ammonium NH4+ ,iron Fe2+ and Fe3+ Magnesium Mg2+, Copper Cu2+ Anions: Carbonate CO32−, Chloride Cl−, Fluoride F−, Nitrate NO3−, Phosphate H2PO4−, Sulfate SO42− 5  SWAE4412 Management of Salt Affected Soils What is soil salinization? What is a salt? Compound consisting of ionic bounded molecules 6  SWAE4412 Management of Salt Affected Soils What is a salt affected soil? Salt-affected soils are soils that contain excessive amounts of soluble salts. These salts can adversely affect plant growth and crop yields. Classified into three categories based on their salinity levels: saline, sodic, and saline-sodic. Salt crystals 7  SWAE4412 Management of Salt Affected Soils Soil salinity Salt affected soils are caused by excess accumulation of salts, typically most pronounced at the soil surface. Salts are transported to the soil surface by capillary transport from a salt laden water table and accumulates due to evaporation. 8  SWAE4412 Management of Salt Affected Soils Soil salinity As soil salinity increases, salt effects can result in degradation of soils and vegetation. Salt is a natural element of soils and water. The ions responsible for salinization are: Na+, K+, Ca2+, Mg2+ and Cl-, SO42-, and HCO3-. Small quantities of NH4+, NO3-, and CO32- also occur. As the Na+ (sodium) predominates, a salt affected soil is often also a sodic soil. 9  SWAE4412 Management of Salt Affected Soils Main Types and Sources of Salts There are 2 main types of soil salinity: Primary salinity due to natural causes (certain types of relief, geomorphological, hydrogeological conditions, high groundwater table, impeded drainage or even an absence of drainage). Secondary salinity due to irrational land use and inappropriate agricultural practices (excessive water inputs via irrigation, absence of appropriate drainage systems, which causes a rapid raising of the groundwater table). 10  SWAE4412 Management of Salt Affected Soils Soil Salinity: Natural Great Salt Lake and Desert in US Salar de Uyuni in Bolivia (Source: www.destination360.com) (Source: www.legendsofamerica.com) 11 (Source: Fotos de Bolivie, http://tunari.tripod.com)  SWAE4412 Management of Salt Affected Soils Soil Salinity: man-made Human Activities a) Salts from areas of over-irrigation accumulate in poorly drained areas. b) Relatively saline irrigation water are used. c) Oil-field development, waste- spreading operation, and crop fertilization d) Urban areas poor drainage and aquifer recharge e) Construction of dams f) Sea water intrusion due to over pumping 12  SWAE4412 Management of Salt Affected Soils Soil Salinity: man-made In some areas (for example the Middle East, Australia) enormous amounts of salts are stored in the soils. Human practices have increased the salinity of top soils by bringing salt to the surface through disrupting natural water cycles (irrigation, land clearing, draining etc.). One of the best examples of excess salinization was Aswan Dam observed in Egypt in 1970 when the Aswan High Dam was built: Change in the level of ground water before the construction enabled soil erosion Led to high concentration of salts in the water table. High level of the water table after construction led to the salinization of the arable land 13  SWAE4412 Management of Salt Affected Soils Soil Salinity: Urban areas Salinity in urban areas often results from the combination of irrigation and groundwater processes. Cities are often located on drylands, leaving the rich soils for agriculture. Irrigation is also now common in cities (gardens and recreation areas). Can cause yield damage to infrastructure (roads, bricks, corrosion of pipes and cables) 14  SWAE4412 Management of Salt Affected Soils Salinity is a global problem Salt-affected soils cover approximately 7% of the Earth’s total land area, about 23% of its cultivated agricultural land, and almost 50% of its irrigated land. 15  SWAE4412 Management of Salt Affected Soils Salinity is a global problem Salt is turning farmland into wasteland around the world Salinization affects about 70 million ha of irrigated lands, about one-third of the world irrigated area. The World Map of the status of Human- Induced Soil Degradation indicates that about 77 million ha are affected by human-induced salinization, comprising 45 million ha of irrigated and 32 million ha of rainfed agricultural land. Distribution of salt-affected soils in the world. The percentage of salt-affected soils Based on the FAO/UNESCO Soil Map of on the total land surface is reported for each region of the world the World, the total area of saline soils is about 394 million hectare and that of sodic soil is about 434 million hectare (ha). 16  SWAE4412 Management of Salt Affected Soils Salinity problem is increasing day by day The UN report estimates that 2,000 hectares of farmland (nearly 8 square miles) of farmland is ruined daily by salt degradation. So far, nearly 20 percent of the world’s farmland has been degraded, an area approximately the size of France. the global annual cost of salt-induced land degradation in irrigated areas could be US $27.3 billion because of lost crop Economic cost of salt- production.” induced land degradation in irrigated areas of the world 17  SWAE4412 Management of Salt Affected Soils Impacts of soil salinity Salinization has negative impacts on agricultural production, the living conditions of farmers, the economy at different levels, the balance of ecosystems including the quality of natural resources. The impacts are often felt not only at the farm, but also at landscape levels. In many countries they can pose serious problems to sustainable development. 18  SWAE4412 Management of Salt Affected Soils 1- Impacts on crop production Decline in soil productivity and crop yields Increased requirement and use of inputs including seeds, water and fertilizers Low crop yield per unit of input used Less choice in cropping systems, as farmers are forced to cultivate salt-tolerant crops which might not always be high income cash crops Reduced water use efficiency In cases of severe salinization and sodicity land cannot be used anymore for production 19  SWAE4412 Management of Salt Affected Soils 2- Impacts on living conditions of farmers & the economy The reduction of yields results in less income and less food supply, especially in subsistence farming Working with salt-affected soils requires more labour to reclaim soils The use of more inputs and the reduction of yields result in less returns Lowered income and loss of land are often factors for the migration of farmers to cities Soil reclamation programmes are costly Rehabilitation programmes to improve the living conditions of those affected require high investments 20  SWAE4412 Management of Salt Affected Soils 3- Impacts on ecosystems Reducing the diversity of organisms Reducing the efficiency of nutrient cycling Reducing population sizes of previously dominant species Increasing the populations of salt tolerant organisms Changing disease patterns and prevalence in different species of plants, terrestrial and aquatic animals Salt-affected areas result in sparse vegetation that in turn leads to wind-blown dust storms. Health effects associated with dust may be a problem in salt-affected area 21  SWAE4412 Management of Salt Affected Soils 4- Impacts on the quality of natural resources Salt-affected soils are fragile and more prone to other forms of degradation, e.g. wind and water erosion Wind-born salts can reach and damage vegetation, soils and water in nearby areas Water draining out of agricultural fields can increase the salt contents in groundwater and other surface water Wastewater from reclamation of salt-affected soils, if not disposed off safely, can contaminate other soils and water bodies 22  SWAE4412 Management of Salt Affected Soils 5- Impacts on the quality of natural resources In the case of sodic soils, the loss of organic matter weakens the strength of soil aggregates, increase the loss of nutrients in run-off, and increase carbon dioxide emitted to the atmosphere. Extreme conditions in sodic soils (pH and sodium salts) decrease water infiltration due to surface sealing and promote runoff and erosion during storm events Land is a Nonrenewable Resource! 23  SWAE4412 Management of Salt Affected Soils Identifying the Problem Early signs: Increased soil wetness in semiarid and arid areas The growth of salt-tolerant weeds Irregular patterns of crop growth and lack of plant vigour 24  SWAE4412 Management of Salt Affected Soils Identifying the Problem Advanced signs: White crusting on the surface A broken ring pattern of salts adjacent to a body of water White spots and streaks in the soil The presence of naturally growing, salt-tolerant vegetation Soil salinity can be estimated by measuring the electrical conductivity of the soil solution. Electrical conductivity increases in a solution in direct proportion to the total concentration of dissolved salts. 25  SWAE4412 Management of Salt Affected Soils Summary Soil salinity is a serious problem in many parts of the world and is becoming worse with growing dryland agriculture and irrigation practice. Better solutions need to be sought to invert soil moisture and salinity simultaneously and to directly derive the standard measure of soil salinity. 26