Saline agriculture improves food security, with minimal impact on already scarce fresh water supplies.
(From Saline Agriculture Worldwide - Knowledge Centre)
Saline Agriculture: The practical solution
People have long believed that salt-affected land was unusable. But as a result of in-depth research and years of testing, a practical solution was found: Saline agriculture.
It is quite feasible to grow crops on salt-affected land, as long as the right (salt tolerant) crops are being used, combined with alternative techniques in irrigation, fertilization and water management.
With saline agriculture, food is produced on salt-affected soils and salt or brackish water is used for irrigation.
Less demand on an already scarce fresh water supply
Freshwater is a (very) limited resource in the world. Most of the water available for irrigation comes from groundwater (aquifers) and lakes.
The total amount of fresh water from these two resources only accounts for less than 1% of the total water supply.
Traditional farming techniques use fresh water for irrigation, putting a heavy demand on the world's already scarce fresh water supplies. In fact, of all the water in the world, only 1% is fresh water, of which 70% is used for agriculture!
The amount of saline water is almost equal to the amount of fresh water in both lakes as well as aquifers. Of all water on Earth, 0.76% is fresh groundwater while 0.9% is saline groundwater, the remainder being found in the sea.
So, if saline water can be used as a resource, this can greatly reduce the amount of fresh water used by agriculture and decrease water stress in many areas.
Improve & re-use salt-affected soil
Saline agriculture can make use of the world's saline resources. If all of the world's saline water would be used for irrigation, it could double the amount of available water for agriculture. At the same time, saline agriculture limits the damage caused by salinization by employing sustainable practices for agriculture and water management, and by making use of salt-tolerant crop varieties. If salt-affected soils are put (back) into production, 70-120 million hectares of new arable land can be saved, along with their natural ecosystems and the associated biodiversity.The Four Pillars of Saline Agriculture
With saline agriculture food is produced on salt-affected soils and/or using salt or brackish water for irrigation water. The latter strategy also saves fresh water, which is a scarce resource on this planet, and even more so in those areas generally affected by salinization.
To make saline agriculture possible, conventional farming techniques would need to be adapted. We have identified four pillars of agriculture, all of which would need to be adapted to make saline agriculture possible:Crop and cultivar choice
Different crop species differ in their tolerance to salinity. There are very sensitive species, such as some beans, that may die at salinity levels equivalent to one tenth seawater (~5 dS/m), up to very tolerant species that can survive and reproduce at seawater salinity levels. The very tolerant species are called halophytes (which translates to salt plants). They are species that usually have a succulent (swollen) appearance. Even though in most diets of people around the world halophytes are not very common, most people have tasted or at least know about glassworts, species in the Salicornia genus or relatives thereof. From the sensitive to the tolerant there is a whole range of different levels of tolerance to salinity, which means that for most salinity levels, a suitable crop can be identified.
Just as there is variation between crops species, there is also variation within one crops species, between different varieties or cultivars. These differences can be quite large which means that for saline agriculture, a smart choice of cultivar is the first thing to do.
The salinity tolerance of a (cultivar of a) crop is often expressed according to the model suggested by Maas and Hoffman (1977). They suggested expressing salinity tolerance of any plant species based on two parameters: the threshold and the slope. The threshold is the salinity level at which yields start to become negatively affected. The slope is the degree with which yields are further decreasing as salinity increases. (Technically, a third parameter needs to be estimated, which is the yield under fresh water conditions).
Irrigation
Irrigation is very important in saline agriculture. Irrigation can be done using fresh water or brackish water. In both cases it is important to irrigate regularly because salts concentrate in the soil when the amount of water decreases through evapotranspiration (i.e. the sum of evaporation and transpiration through the plant leaves). For this reason, it is important to keep the soil moisture as constant as possible. When irrigating with brackish water it is also important to irrigate enough so that salts don't accumulate in the top layers but are drained to deeper soil layers or, preferably, a drainage system.
When irrigation is done using brackish water, only sandy soils or loamy sandy soils are suitable. Irrigating with brackish water on clay soils will lead to structural problems with the soil. This in turn affects the permeability to water and the aeration of the soil which also negatively affects crop performance.
Some combinations are easier than others and some are not recommended but if all the aspects of the four pillars of saline agriculture are considered, more is possible than is currently recognized by many.
Irrigation is best done using drip irrigation because this is the most efficient way in terms of water use. When using flood irrigation, it is important to take into account the drying out of the soil. Crops should be planted on those areas where the drying out is slowest.
Fertilization
The effect of fertilizers on the Electrical Conductivity of the soil can be problematic in saline agriculture since the EC of the soil is already high in saline agriculture. In this way, the addition of fertilizers can increase the osmotic stress of crops associated with salinity. It important to take this into account and foliar fertilizers may be a solution to this issue. Additionally, salinity may lead to specific deficits in crops, or higher demands for certain minerals and consequently these may require higher doses of application than in conventional agriculture.
Soil Management
Soil management is a broad umbrella under which we count things such as the management of organic matter in the soil, practices such as soil tillage, bed or ridge shape and size, the application of soil additives etc. Salinized soil may require certain additives at the start of the growing season, such as gypsum, to alleviate salt stress.
In saline agriculture it is very important that the soil is rich in organic matter. So, manure and compost should be applied regularly if available. Bed shape can be important depending on irrigation method as we have seen in the case of flood irrigation. A rich and healthy soil life is important for good crop performance, especially under saline conditions so the use of microbial-based soil additives may help boost yields.