Recent United Nations (UN) population projections predict that the
world population population of 7.3 billion inhabitants is expected to reach 8.5 billion in 2030 and 9.7 billion in 2050.
Therefore, delivering enough calories and nutrients to a larger and increasingly urban population will require increasing global food production by some 70% between 2005 and 2050, much of which is expected to come from intensified cultivation of land, conversion of forests, grasslands and other ecosystems to arable land, which will affect biodiversity and multiple ecosystem services.
Soils are one of the most complex and diverse ecosystems in the world. In addition to providing humanity 98.8% of its food, they are at the heart of many societal issues such as access to drinking water, carbon storage, climate regulation, climate change mitigation and biodiversity preservation.
Access to drinking water in 2005 © Fanny Schertzer / Wikimedia CC BY-SA 2.5
However, the intensification of agricultural production, various anthropogenic pressures and climate change are modifying the capacity of soils to provide its many ecosystem services.
The main forms of this degradation are erosion, loss of organic carbon, pollution, waterproofing,
compaction, salinization, waterlogging, acidification, nutrient imbalance and loss of biodiversity.
Among these threats, soil salinization-sodication is becoming a major agricultural problem worldwide, mainly in arid and semi-arid regions.
7% of the Earth’s surface
Salinization problems in soils can refer to an excess of soluble salts (saline soils), to an excess of exchangeable sodium in the soil solution (sodic soils), or to a mixture of the two cases (saline-sodium soils). . The term salt affected soil is more commonly used to refer to saline soils, sodic soils, and saline-sodium soils.
Soil salinity-sodicity is one of the biggest global challenges in arid and semi-arid regions, which severely affects agricultural production. 20% of total cultivated land and 33% of irrigated agricultural land in the world is affected. About 1 billion hectares of the world’s land surface are affected by salinization, which represents around 7% of the planet’s land surface. Globally, the economic losses due to this phenomenon are estimated at US $ 27.3 billion.
A phenomenon older than Mesopotamia
It should be remembered that this is not a recent phenomenon, a well-known historical example is that of Mesopotamia (present-day Iraq), where the first civilizations first prospered and then failed due to salinization induced by human.
A publication titled Salt and silt in ancient Mesopotamian agriculture traces the history of salinization in Mesopotamia, where three episodes have been identified (the oldest and most severe affected southern Iraq from at least 2400 to 1700 BC; a lighter s (produced in central Iraq between 1200 and 900 BC, and eastern Baghdad after 1200 AD).
Map of the agricultural regions of Ancient Mesopotamia © Joel Bellviure / Wikimedia CC BY-SA 4.0
At the roots of soil salinization
There are two major factors of soil salinization, namely primary salinization due to natural causes (weathering of rocks containing soluble salts, volcanic activity, atmospheric deposition of sea salts by wind, etc.) and secondary salinization linked to anthropogenic actions, mainly due to inappropriate irrigation methods, often associated with poor drainage conditions.
With a climate marked by low precipitation and soil characteristics that limit the subsequent elimination of salts (leaching), arid irrigated lands are “hot spots” of salinization.
In addition, climate change could accelerate the intrusion of salt water due to sea level rise, temperature rise, increased evaporation and overuse of groundwater in the areas. dry regions of the world. It is estimated that around 600 million people living in coastal areas around the world could be affected by salinization.
Globally, the area of global agricultural land destroyed each year by salt accumulation is estimated at 10 million hectares. This rate may be accelerated by climate change, overuse of groundwater and the increasing use of poor quality water for irrigation.
Impact of salinity on plants
The increase in the level of salinity and sodicity leads to negative impacts on soil properties and plant physiology.
Indeed, numerous scientific works show that salinity and sodicity affect almost all aspects of plant development, including germination, vegetative growth and reproductive development. The salinity-sodicity of the soil imposes on the plants an ionic toxicity, an osmotic and oxidative stress, a nutrient deficiency and thus limits the absorption of water from the soil.
The increasing use of poor quality water for irrigation is damaging agricultural land (here, manual irrigation in Ghana) © Joe Ronzio-IWMI / Flickr CC BY-NC-ND 2.0
The salinity-sodicity of the soil leads to an increase in electrical conductivity, a degradation of the soil structure and a low water potential of the soil. The development of salt stress in plants can be described in two ways: osmotic phase and ionic phase.
Management of soils affected by salts
Faced with this saline stress, many strategies such as plant breeding, genetic engineering of plants and a whole series of agricultural techniques, including the application of rhizobacteria, have been developed in order to improve the defense system of plants.
Among these strategies, organic amendments such as biochar, compost and inorganic amendments rich in calcium for example, fly ash, gypsum and phosphogypsum have been used to rehabilitate sodic soils.
Other techniques have been used to reduce the salinity-sodicity of the soil: agroforestry, biodrainage (the use of vegetation to manage water flows by evapotranspiration), halophyte plants (plants adapted to salty environments) and sustainable soil management.
However, none of these techniques can guarantee long-term sustainability. They depend on the type of soil, topography, geohydrology, climate and other local factors varying from one environment to another.
In addition, careful selection of sites for establishing crops can decrease the risk of soil salinization and sodication.
Monitor soil salinity
Updated maps are needed to quantify rates of soil salinization and to inform national and international policies and strategies to protect soils from increased salinization.
Indeed, monitoring of soil salinity in agricultural regions is necessary to inventory soil resources, to identify trends and factors of salinization and to judge the effectiveness of restoration and conservation programs.
Therefore, remote sensing tools and advanced data analysis methods such as machine learning techniques are the best means to achieve this in a timely manner.
In fine, given the inherent complexity of salinity problems, it is essential to adopt a holistic, multidisciplinary approach, ensuring the participation of several actors when making decisions on the development and implementation of technologies, thereby accelerating the rate of restoration of
saline-sodium soils.
This analysis was written by Sougueh Cheik, doctor in soil sciences – environmental sciences at the Institute for Research for Development (IRD).
The original article was published on the website of The Conversation.
