Drainage and salinity problems on the Valley’s West side were exacerbated by the construction of the San Luis Unit.The San Luis Unit authorized by the Luis Act of 1960 is part of both the federal Central Valley Project and the State Water Project.The primary purpose of the San Luis Unit was to supply irrigation water for over 400,000 ha of prime farmland.The Luis Act of 1960 as part of a comprehensive basin salinity management plan required that drainage be constructed either as a master drain constructed by the state of California to serve the entire valley or an interceptor drain constructed by the federal government to serve the San Luis Unit service area.The idea was that either of these two drainage systems would convey brackish water northward in a concrete canal into the Sacramento-San Joaquin delta.In mid-1960s the federal and state governments started planning for a master drain that would drain and transport salts out of the entire valley from Bakersfield on the southern end of the valley to the delta.However,plant benches in the early stages of the project the state of California withdrew after failing to get assurances from irrigators that they would pay state expenditures for the project.
In 1968 the federal government through the Bureau of reclamation started construction of a drain system to collect and transport subsurface drainage water from the San Luis Unit service area to the Sacramento-San Joaquin Bay-Delta.However, of the planned 302 km of drain, only 140 km were completed from Kettleman City, near Fresno County, to Kesterson Reservoir in Merced County.Construction was halted in 1975 because of mounting costs and water quality concerns.The main water quality issue was selenium in the Kesterson National Wildlife Refuge which caused various ecological concerns including wildlife birth defects and other toxicities.These instances had a major impact on irrigated agriculture in California.To date the project has stalled due in part to ecological and environmental concerns.In terms of salinity management, the failure to complete the drainage system resulted in reduced agricultural productivity on many farmlands particularly in the Western San Joaquin due to shallow water tables and evapo-concentration of salts in the root zone.Lack of a system to export drainage water and salts out of the valley has stimulated innovative management practices to reduce drainage waters and to find “in valley” solutions for disposal.The threat that salinity poses to California’s economy is widely acknowledged by both public and private stakeholders.For example, a study by Howitt et al.reported that Central Valley salinity accumulations would cause an estimated loss of $2.167 billion in California’s value of goods and services produced by 2030, if they remain unmanaged.
Incomes would decline by $941 million while employment would reduce by 29,270 jobs.Potential benefits of implementing salinity management strategies in the Central Valley were estimated at over $10 billion.It is reasonable to assume that improved salinity management could bring economic benefits to other regions of California that experience salt problems including the Imperial Valley and the Central Coast, while neglecting this problem would bring dire consequences.In California current efforts to address salinity management have included both traditional and contemporary strategies.Traditional salinity management strategies have included source control , dilution, and displacement.While contemporary strategies have included salinity management such as treatment , storage, export, real-time management, and recycling as described in a 2016 inter-agency report by the California Department of Water Resources.The following sections describe recent salinity management case studies in California ranging from on-farm to basin-wide efforts.On-farm salinity management—In California providing environmentally and politically acceptable disposal of drainage water from irrigated agricultural lands is a major challenge for growers.Ayars and Soppe reported to have successfully used a technique called Integrated On-Farm Drainage Management to significantly reduce drainage water to 0.7% of field-applied irrigation water, eliminating the need for evaporating ponds.
IFDM was demonstrated on four 65-ha fields located at Red Rock Ranch on the West side of the San Joaquin Valley of California, by sequentially using saline drainage water for supplemental irrigation.In this study three of the 65 ha blocks were used to grow salt sensitive crops and drainage from these blocks was used to irrigate a salt-tolerant crop.IFDM has been successfully used on other farms in the San Joaquin Valley, e.g., Andrews Ag farm, located in Kern County where IFDM was implemented on 486 ha.At Andrews Ag, salt-sensitive crops were irrigated using drip and sprinkler irrigation.A subsurface drainage system collected the drainage water that was subsequently used to irrigate salt-tolerant crops such as cotton.The salt grass volatilizes selenium as it grows, removing it from the drainage water and rendering it harmless.By 2005 the farm reported that it was able to reduce drainage by 90% and selenium by 80%.Eliminating the need for an evaporating basin provides several benefits, including minimizing the size of land taken out of production and need to mitigate environmental impacts associated with evaporating basins such as leaching of salts to groundwater.However, it is worth noting that management practices such as IFDM only provide short term solutions, and that long-term sustainable irrigation requires exporting salts out of the basin to maintain a salt balance, for example through a brine line.Regional salinity management—A major regional initiative to address the salinity problem in California is the Central Valley Salinity Alternatives for Long-term Sustainability.CV-SALTS is focused on sustainable salinity management.CV-SALTS is a collaborative effort that was initiated in 2006 to find solutions to the salt problem in the Central Valley.It includes several stakeholders such as the State Water Resources Control Board, the Central Valley Regional Water Quality Control Board, agricultural coalitions, cities and municipalities, growers, academics, and environmental justice groups.The goals of CV-SALTS are multifaceted and include sustaining the Central Valley’s lifestyle, support regional economic growth, sustain agricultural economy, maintain a reliable and high-quality urban water supply, and protect and enhance the environment.Because of the seriousness of salt and nitrate issues in the Central Valley, the California State Water Resources Control Board voted in 2019 to approve a Central Valley-wide Salt and Nitrate Control Program that was submitted by CV-SALTS.Subsequently, the Regional Central Valley Water Board started sending out Notices to Comply for the Nitrate Control Programin late May 2020.The Salt and Nitrate Control Program includes both short- and long-term strategies to address salt issues in the central valley.Dischargers can participate in the program as individuals or as a part of a group of dischargers organized in form of a management zone.This is significant because the Salt and Nitrate Control Program provides a framework for the Central Valley Water Board to regulate salt and nitrate discharges for an area covering 46,619 km2.
Issues of salinity in California have tremendous consequences, as there is a lot at stake in terms of economic losses,rolling bench environment degradation and livelihood disruptions.Therefore, to not proactively address salinity is not an option.In California salt moves statewide through the interconnected waterways across different basins.Salinity management should carefully integrate water flows and salt loadings.Sustainable salinity management decisions in any basin involves a wide range of stakeholders such as water managers, regulators, facility operators, policy makers, landowners, growers, agricultural coalitions, environmental justice groups and others.To successful manage salinity in California these entities must strive to coordinate their efforts to use resources efficiently, develop solutions to local and regional problems, optimize funding opportunities, and seek to achieve a salt balance in any given basin.Sustainable salinity management in California will require collaborative efforts to build consensus on scientifically proven solutions that meet multiple objectives for its diverse regions.Both short and long strategies will need to be considered, for example, to achieve a salt balance in a closed basin such as the Tulare Lake basin, discussions must include options for exporting salts out of the basin using a brine line.Water conservation in the Salton Sea basin should be integrated with salinity management.Integrated approaches should be pursued to mitigate sea saltwater intrusion including substituting groundwater pumping in agricultural regions along the central coast with recycled water.Salt-affected soils have a broad distribution and a rich variety of types in China, totally accounting for approximately 100 Mha, or about 1/10th of the entire land area of the country.Climatic conditions, landform and geomorphology, and agricultural practices are key factors influencing soil salinization in this country.The ratio of evaporation to precipitation is often more than one in most regions of Northern China.According to the formation characteristics and geological distribution, salt-affected soils are clarified into seven major zones.In Northwest China, the closed inflow basins , provide the physical base for the development of soil salinization, which associated with the localized arid and hot climate conditions eventually result in the formation of salt-affected soils.In Northeast China and North China Plain, controlled by the monsoon climate, 60–70% of the precipitation occurs in summer, resulting in a cycle of summer water logging and spring drought.Therefore, salt is frequently exchanged between the soil and groundwater.China also has a large area of coastal low plains distributed with salt-affected soils that are mainly due to the seawater encroachment.
Modern integrated investigations on land resources at large-scales in China were started in the 1950s, which have provided an important foundation for improved understanding of the geographical and genetic classifications of salt-affected soils.From then on, research and management practices have been focusing on the reclamation, improvement and sustainable utilization of salt-affected soils regionally, typically located in Xinjiang, Ningxia, Inner Mongolia, and the Songnen plain.Key measures to control soil salinity included artificial salt leaching, paddy rice sowing, fodder rotation, and application of drainage and irrigation systems.Relying on these measures, China has promoted agricultural development in some of its salt-affected soil zones, especially in Northwest China.However, the inadequate irrigation and drainage systems resulted in a dramatic rising of the groundwater table across these regions, and eventually led to secondary soil salinization.Nevertheless, agricultural development led to research and use of water-conserving agricultural technologies, including those that control groundwater depth, prevent water losses of irrigation canals, and building of open ditch and subsurface drainage systems.Additional engineering and agronomic practices developed during this period, including land leveling, flooding sedimentation, green manure planting, organic manure application, and salt-tolerant crop selection.After mid-1970s, key state research projects were launched aiming for integrated management of drought, water logging, and soil salinization.Typically, a national project was initiated in Huang-Huai-Hai Plain in 1978.To systematically study the interrelation and regularities of drought, water logging and soil salinization, a system for monitoring and predicting the regional water and salt was developed.The focus of soil management in this region was on shallow groundwater exploitation.The shallow groundwater water was extracted from tube wells and used for irrigation, which simultaneously lowered the groundwater table.In addition, the low-pressure water transport technique, deep ditches, optimized fertilizer, and shelter belt were used to improve the basic conditions of agricultural production.By 1995, the agricultural total output value in this region was raised by 20–56%.Meanwhile, important progresses were made in the other regions, such as drainage-based rice sowing in Xinjiang and Ningxia, soda-saline soil improvement in Jilin Province , coastal salt marsh development, and improved agricultural drainage systems in Inner Mongolia.Food security is a long-lasting challenge for China because it needs to feed 20% of the world’s population, relying on only 7% of the world’s arable land.The implementation of the integrated salt-affected soil management projects has improved nearly 1.67 Mha of saline-alkali land and has increased nearly 4 million tons of grain production since 2000.Since 2000, China has prioritized the application of water-saving irrigation techniques, especially in arid and semi-arid regions, including the use of pressurized irrigation such as drip and sprinkler irrigation, as well as subsurface irrigation.By the end of 2015, the total area of water-saving irrigated cropland was about 31 Mha in China, including 9 Mha with sprinkler and drip irrigation.In addition, China has initialized multiple policies to facilitate intensive implementations of WSI technologies, e.g.to mobilize local governments by providing additional funds for WSI investment, and to promote the Water Users Associations to take on the irrigation management responsibilities in rural areas.Furthermore, China has launched a comprehensive water management plan in 2006 to improve agricultural water use efficiency.By the end of 2015, it was reported that the average agricultural water-use efficiency increased from 0.53 to 0.58.On the other hand, the agricultural water consumption estimated in 2017 accounted for more than 62% of China’s total annual water consumption, announcing limited potential for continued application of high-quality irrigation water to meet food demand.