The plain hosts shallow water tables, which, combined with negative climatic water balances, makes it prone to salt accumulation both in its deep sediments and in the surface of its low landscape sectors.Grasslands dominate in the South of the sedimentary plain, showing some areas with salt affected soils.Besides those areas also few coastal and swampy areas with saline-acid soils are found as well as large internal salt marshes elsewhere, among them the Pantanal in southern Brazil, one of the larger wetlands of the world.Overview of anthropic salinity problems—In general terms, no country in Latin America is completely free from salinization, and we will focus our analysis on human-induced salinization, mainly caused by irrigation, though not exclusively.Most of the secondary salinization occurs in irrigated areasin arid and semi-arid zones, where intensive agriculture is practiced.This process is mainly due to non-efficient water management, poor drainage conditions, and low irrigation water quality.Irrigation mode and extension as well as type of crops vary considerably within the region.Fruit and vegetable production are mostly irrigated.In some area’s extensive crops such as sugarcane, rice, cotton, maize, and wheat are partially grown under irrigation, using modern technologies.In others, irrigated areas are populated by small holder farmers who generate most of the locally consumed food.The ratio between these two ways of production varies among countries and regions within them but does not to appear to be related to soil salinization processes.Arid and semi-arid areas under full irrigation are common in Mexico, Peru, Chile, and Argentina.While irrigated production value exceeds that of rainfed agriculture in Mexico, Chile and Peru, the reverse occurs in Argentina.In most cases furrow and flooding irrigation systems are used, but sprinkler, micro-sprinkler or drip irrigation systems are being increasingly adopted.
Waters from various origins are used,vertical farming tower for sale from surface to ground waters, and quality ranges from good to bad.Irrigation in non-graded and uneven lands has led to low water use efficiencies and rising groundwater levels.Low efficiencies are additionally caused by non-lined water distribution ditches and poor drainage conditions.Besides the typical effects of salts , boron is an additional problem in several irrigation districts.The Brazilian semiarid region in the northeast of the country is one of the largest semiarid regions of the world.It features tropical climate conditions with variable rainfall associated with high temperatures during much of the year.The region is also characterized by shallow soils, low quality irrigation waters, lack of drainage and often shallow groundwater.Irrigation has improved the economy of the region through diversified cropping practices, stimulation of agroindustry and export of products, but has also led to large areas being degraded by salinization because of poor water quality and deficient or absent drainage schemes.In general, those degraded areas are left fallow so that agricultural production is moved to other areas.The return of vegetation of these deserted areas would initiate a slow reclamation process.In semiarid/subhumid zones, as in Colombia, Venezuela, Cuba, the Dominican Republic and in some of the other countries in the region, similar salinization processes have occurred where sugarcane, rice and othertropical crops are irrigated with waters of varied quality and drainage is poor or nonexistent.Further south, in the temperate area of Pampas region of Argentina, field crops are usually grown under rainfed conditions but are exposed to occasional drought events.Supplementary sprinkler irrigation allows farmers to increase and stabilize grain yields.Exchangeable sodium has increased sharply but no consistent impacts on soil physical degradation have been detected.Human-induced salinization has also developed in the above-mentioned Chaco-Pampas plain, mainly promoted by land use and land cover changes, by cropping or overgrazing.In the Chaco and Espinal regions in the North of this plain, deforestation and cultivation have altered the hydrologic balance, mainly because cropped areas present lower evapotranspiration rates.
The resultant water excess infiltrates and slowly causes the rise of deep groundwater tables that bring salts to the surface, thereby damaging crops and soils.This process of salinization is somewhat like the “dryland salinization” in Australia.The Southern part of this Chaco-Pampas is mostly devoted to field crops, but alkaline and to a lesser extent saline soils predominate in an area known as the “Flooding Pampa,” where livestock production activities prevail.There, intensive cattle grazing removes vegetation and high evapotranspiration causes salts from the water table to reach the soil surface in the summer.Subsequent rains leach the salts, but this man-made process affects the composition of the plant communities.A similar process has been observed in grazed salt wetlands.Research on salt affected soils was very active in the 1960–1980 period, when several countries experienced large agricultural development through investments in large irrigation schemes.Research on soil salinity research at that time was mainly applied and based on results published by the US Laboratory Staff.One consequence of such effort was the organization of regional and international conferences, such as those that took place in 1971 in Colombia and in Venezuela in 1983.However, advances in research and evaluation of salt-affected soils subsequently faded.In most irrigated areas attention was focused on the engineering aspects of irrigation infra-structures rather than on the installation of effective drainage systems and adequate preparation of irrigation fields at the farm-scale.This has led to problems of drainage, water logging,and salinization.More recently, the development of large and expensive irrigation schemes has diminished, whereas new irrigation developments have been for small local irrigation units, using nearby surface and groundwater resources but most often done without consideration of regional impacts.In some extreme cases, due to competition for alternative uses of scarcely available good-quality water resources, non-treated residual waters of urban and industrial origin are used for irrigation.This is valid for small irrigation units, mainly dedicated to production for local markets, but not for larger irrigation units.Research on soil, water, and crop management in saline areas in Brazil is concentrated in universities and research organisms in NE Brazil.
Approaches include the development of soil and water management strategies, appropriate cropping systems, the sustainable use of brackish waters, cultivation of halophytes and salt-tolerant crops, application of mineral and organic amendments, phytoremediation and plant/microorganism interactions.A specific concern is the mitigation of socio-economic impacts of soil salinity in agricultural lands, which translate into loss or reduction of crop yields, profit margins, increased unemployment, and reduction of commercial land value.Technologies are being developed to provide a source of income for impacted smallholder farmers to provide for water and food security.This include the desalination of brackish water and its use in an integrated production system involving reject brine for farm-raised fish and the use of fish-pond water to grow organic salt-tolerant vegetables and forage crops for small ruminants.Argentina has active research on soil, water and crop management and salt tolerance mechanisms.Technologies on salt affected soils of humid/ sub-humid areas are aimed mainly at increasing biomass productivity without altering soil properties.They include grazing management, afforestation, agro-hydrological management, plant introduction, among others.Salinization in semiarid deforested areas has been studied in the great Chaco area and is focusing on ways to mitigate soil and water quality degradation , such as by changing cropping systems.The use and management of native woody species for degraded and salinized areas is considered.The characterization, collection and multiplication of both native and introduced species, and their incorporation into breeding program are prominent activities.Traditional breeding efforts have produced new salt-tolerant forage plant cultivars, such as Epica INTA Peman ,hydroponic vertical farming and new breeding alternatives have been explored to increase salt tolerance in Melilotus albus.Research on Lotus species for alkaline and sodic soils has contributed to their expansion in the Flooding Pampa.Molecular components of signaling chains and salt tolerance mechanisms have been successfully incorporated into commercial crops, soybean for example.Research interest in the region on salinity-related agricultural aspects has gained new momentum in this century, mainly in Brazil, Mexico, Argentina and Chile.In addition to many publications, this is also reflected by recent national salinity conferences in Argentina and in Brazil.The First Latin American Salinity Symposium was held in Fortaleza, Brazil, in 2019.Books on regional salinity issues have been published in Spanish and in Portuguese , including a recent comprehensive book.The subcontinent is re-awakening to its saline perspective.Social impacts of this problem are being addressed, particularly because of food security issues.The process of salinization in irrigated areas is continuing, although in some cases drainage and improved irrigation technologies improved the situation noticeably.However, in many Latin-American regions soil salinization is still expanding.Deforestation has been extensive, and the consequences of these land use changes will further cause land degradation and affect the sustainability of its land and water resources.It is expected that the coming decade will provide more certain quantification of its increasing spatial extent, as FAO and various organizations from Latin American countries are on the way to develop a contemporary soil salinization map, following unified protocols.
Problems with salinity in the Netherlands mainly occur in the North Sea coastal regions.Fig.31 shows in blue colors areas either above or below sea level protected by dikes and in orange color areas below sea level not protected by dikes.The white areas along the coast, including islands in the north and southwest, are dunes in which fresh water floats on sea water.Throughout history, various aspects of salinity were recognized and dealt with, specifically causes of salinization and sodification leading to soil structure deterioration, desalinization and rehabilitation by de-sodification, and crop salt tolerance/intolerance.Originally, experience of water managers and farmers formed the basis in their decision-making.From 1850 onwards, traditional opinions gradually evolved into scientific understanding.First, these were mainly based on chemical analysis of soils, later combined with physico-chemical concepts, and more recently through inclusion of analyses of flow and transport processes and plant physiology.In the first half of the 20th century, salinization and sodification arose from both natural floods and wartime strategic inundations.In the aftermath of the large 1916 flood, plans were made for the Zuiderzee Works, resulting in completion of the Afsluitdijkin 1932, changing the former tidal and saline Zuiderzee in a freshwater environment.Behind this dam are now the freshwater Lakes IJssel and Marken, surrounded by a series of new polders with a total area of 165.000 ha.In other words, where formerly was the Zuiderzee are now two lakes and the Wieringer meer and Flevo polders.The two lakes serve as fresh water reservoirs for the northern provinces, including replenishment of water pumped for domestic use in the coastal dunes.The early salinity research in the Netherlands was linked to consequences of the major floods and the Zuiderzee Works.Much of this specific research was presented in Raats and includes pioneering studies by Dutch scientists through the later 1800s and into the first half of the 20th century.Specifically, attention was paid to acid sulfate soils, application of gypsum to remedy soil structural degradation, analysis of plant salt tolerance, planting of salt tolerant vegetation to reclaim lands below sea-level , and understanding seepage from saline open water into lower lying land.Immediately following the devastating February 1953 Storm flood, the Delta Plan was launched, aimed at preventing recurrence of damage from such rare, huge storms in the future.The plan included upgrading all dikes along the entire coastline and build a series of barriers in the Southwest to close off all tidal inlets , except the Western Scheldt.The original main aims were protection of life and property and reduction of costs of maintenance of dikes.A reduction of saline seepage into many polders on the islands in the Southwest would also have resulted.During the execution of the Delta Plan, pressure from environmentalists and fisherman ultimately led to drastic changes in the plans.While construction of a dam in the Eastern Scheldt had started already in 1960, it was not until 1979 that parliament approved a novel type of storm surge barrier, with gates that can be closed when necessary.This barrier was completed in 1986.Earlier, in 1974 it was decided to keep the planned fresh water Grevelingen Lake saline by means of a sluice in the dam, which was completed in 1978.Density stratified flows—Already in the 1950s W.H.Van der Molen noted the occurrence of high salinities in the North-East Flevo Polder at depths of 10–15 m in places where a highly permeable Pleistocene deposit reached the land surface.He speculated that these high salinities were probably due to convection currents caused by the small difference in density between the freshwater present in the soil and the supernatant seawater of the former Zuiderzee between 1600 and 1931 AD.