How Soil Salinity Affects Agriculture and the Environment

 

Soil salinity is a serious problem that affects millions of hectares of land worldwide, especially in arid and semi-arid regions. It reduces plant growth and crop productivity, affects soil biological activity, contributes to desertification and damages infrastructure. In this post, we will explore what causes soil salinity, how it affects plants and the environment, and what can be done to prevent or reverse it.

A field with white salt crusts on the soil

What is soil salinity and what causes it?

Soil salinity refers to the presence of excess salts in the soil, such as sodium, chloride, potassium, calcium, magnesium, sulfate and carbonate. These salts can come from natural sources, such as weathering of rocks, seawater intrusion or evaporation of groundwater. They can also come from human activities, such as irrigation, fertilization, industrial waste or mining.

Irrigation is one of the main causes of soil salinization, especially in drylands where rainfall is scarce and evaporation is high. When irrigation water is applied to the soil, some of it is taken up by plants or percolates into the groundwater. The rest remains on the surface or in the root zone and evaporates, leaving behind the dissolved salts. Over time, these salts accumulate in the soil and reach levels that are harmful to plants and soil organisms.

How does soil salinity affect plants and the environment?

Soil salinity affects plants in two ways: by creating osmotic stress and by causing toxicity. Osmotic stress occurs when the salt concentration in the soil solution is higher than that in the plant cells. This reduces the ability of plants to absorb water and nutrients from the soil, leading to wilting, stunted growth and reduced yield. Toxicity occurs when certain salts, such as sodium and chloride, accumulate in plant tissues and interfere with their metabolic functions, causing leaf burn, necrosis and death.

a maize crop with yellow and brown leaves and stunted growth in a saline soil

Soil salinity also affects the environment in various ways:

• It reduces soil fertility by leaching essential nutrients and organic matter from the soil.
• It decreases soil biological activity by inhibiting or killing beneficial microorganisms and earthworms.
• It increases soil erosion by reducing vegetative cover and soil aggregation.
• It contaminates groundwater by increasing its salinity and dissolving metals such as copper, cadmium, manganese and zinc.
• It damages infrastructure by corroding pipes, cables, roads and buildings.
• It fragments ecosystems by reducing biodiversity and habitat quality.

How can soil salinity be prevented or reversed?

Soil salinity can be prevented or reversed by adopting various strategies that aim to reduce salt input, increase salt output or improve salt tolerance. Some of these strategies are:

• Prevention: This involves avoiding or minimizing irrigation practices that contribute to salinization, such as using poor quality water, overwatering or applying water unevenly. It also involves improving drainage systems to prevent waterlogging and salt accumulation. Additionally, it involves adopting sustainable land use practices that prevent soil degradation and desertification.
• Stabilization: This involves maintaining or restoring the existing level of soil salinity without further deterioration. It can be achieved by applying amendments such as gypsum or organic matter to improve soil structure and permeability. It can also be achieved by planting salt-tolerant crops or trees that can cope with saline conditions and reduce evaporation.
• Active management: This involves reducing or removing the existing salts from the soil through leaching or flushing. This requires applying large amounts of good quality water to dissolve and wash away the salts from the root zone. This can be done periodically or continuously depending on the severity of salinization and the availability of water.
• Land retirement or abandonment: This involves giving up on agricultural production on severely salinized lands that are beyond recovery or too costly to restore. This can be done by converting them into non-agricultural uses such as wildlife reserves or solar farms. Alternatively, they can be left fallow to allow natural processes of recovery.

According to a research ¹, “A crucial consideration is whether the desired end point is stabilizing the soils against further change, or reversing the process and restoring soils to another state.” The choice of strategy depends on various factors such as the extent and severity of salinization, the economic viability of restoration, the environmental impacts of intervention and the social acceptability of change. New agricultural strategies have been developed to help farmers grow crops in places where land has been degraded by salinization. An example is the use of soil moisture neutron probes to monitor soil moisture levels, and the nitrogen-15 isotopic technique which allows farmers to know the appropriate type and amount of fertilizer and water required based on both the soil properties and the crop types. We will discuss these techniques in detail in our future blog posts.

Conclusion

Soil salinity is a major threat to agriculture and the environment that requires urgent attention and action. By understanding its causes, effects and solutions, we can make informed decisions and adopt best practices to prevent or reverse it. We can also raise awareness and advocate for policies that support sustainable management of land and water resources.

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