World Soil Day | Why is our soil turning white?

December 5

World Soil Day

This year's theme is

"Prevent soil salinization and improve soil productivity"

Aims to

Meeting the growing challenges in soil management

Preventing soil salinization and raising soil awareness

Encouraging society to improve soil health

To raise awareness of maintaining healthy ecosystems

and the importance of human well-being

Source: Food and Agriculture Organization of the United Nations

Globally, soil salinization and sodicity are among the most important issues threatening agricultural production, food security and sustainability in arid and semi-arid regions.

Image credit: International Rice Research Institute

December 2013

UN General Assembly adopts resolution

December 5th is designated as World Soil Day

Aims to promote the importance of healthy soil

Advocate for sustainable management of soil resources

Food and Agriculture Organization of the United Nations (FAO)

World Soil Day commemorations held

Highlighting the threat of soil salinization to global food security

And pointed out

Many countries still do not have

Full soil analysis capabilities

FAO Director-General Qu Dongyu said

Soil is the foundation of agriculture

95% of the world’s food comes from soil

He emphasized that

“However, our soils are at risk.”

FAO holds World Soil Day commemoration event. ©FAO

Key questions include:

Unsustainable agricultural practices, overexploitation of natural resources and a growing population are putting increasing pressure on soils and causing them to be degraded at an alarming rate across the world.

The global saline-alkali soil distribution map released by FAO in October shows that more than 833 million hectares of soil in the world have been affected by salinization.

FAO has recently published a map of the world's saline soils. Most of these soils are located in naturally arid or semi-arid regions of Africa, Asia and Latin America. The map allows experts to identify where sustainable soil management measures should be taken to prevent salinization.

©FAO

According to estimates, more than 10% of farmland has become salinized, posing a major threat to global food security.

Central Asia, the Middle East, South America, North Africa and the Pacific region are the hardest hit areas.

Managing salinized soils requires an integrated approach involving sustainable soil, irrigation and drainage management practices and the selection of salt-tolerant crops and plants, including halophytes that grow well in saline environments.

"We must prevent soil salinization, properly manage natural saline-alkali land, and repair soil degraded by salinization," Qu said.

FAO Director-General Qu Dongyu calls for strengthening soil laboratory capacity. ©FAO

"The saline-alkali land is covered with white flowers. If you plant one crop a year, the seedlings will not survive and you will have nothing to harvest in autumn."

Speaking of saline land, many farmers probably start to have a headache again.

But you may not know that saline soil is actually a very important resource. In October, when General Secretary Xi Jinping visited Shandong, he specifically inspected the comprehensive utilization of saline-alkali land and the development of modern agriculture in the Yellow River Delta, which shows the special significance of saline soil.

Today let’s talk about soil salinization.

Photos of saline-alkali landforms. Image source: Xie Wenping, Wang Xiangping, Sun Ruijuan

Why did the soil turn white?

Salinization is the process by which salt accumulates in the soil, causing a deterioration in its basic properties and quality.

Salinization can be caused by natural factors, such as arid climate (scarce precipitation, strong evaporation), salty soil parent material and strata, flat and low-lying terrain, slow groundwater flow, etc. In areas with little precipitation but strong evaporation, salt easily accumulates on the surface; in low-lying depressions, salt easily accumulates and is difficult to remove; when the parent material contains a lot of salt, the salt content will remain high during the soil formation process; in areas with shallow groundwater depth (Editor's note: refers to the distance from the groundwater surface to the surface) and high groundwater mineralization, the salt in the groundwater easily migrates with the soil moisture and accumulates on the surface.

Salinization may also be caused by human activities. Improper production activities will change the original movement of water and salt in the soil, causing the accumulation of soluble salts in the soil, resulting in secondary salinization of the soil, which will also seriously affect the production capacity and ecological function of the soil. For example, inadequate facilities and improper management during the development of irrigation, the use of salt water and alkaline water for irrigation, inadequate management during the development of facility cultivation production, and the lack of attention to salinization prevention and control in the construction of large and medium-sized water conservancy projects, and large-scale water surface aquaculture, etc., may all lead to secondary salinization of the soil.

Photos of salinization landscape and cross-section salt distribution. Image credit: Xie Wenping, Wang Xiangping, Sun Ruijuan

What are the characteristics of saline soil?

After soil salinization, what we "harvest" is white saline soil with mottled vegetation. Saline soil includes soils of different types and degrees affected by saline and alkali components. Among them, the vast saline soil on the coastal beaches and the white saline and alkali beaches in the northwest inland may be our first impression of saline soil. In fact, in addition to these, my country's saline soil also includes tidal saline soil in the Huanghuaihai Plain, soda alkaline soil in the northeast and many other types.

Saline soil in coastal areas

Saline soils in Northeast and Northwest China

The reason why saline soil is a headache for many people is that it contains a large amount of salt and alkali components, which can cause the soil to become compacted, the soil to have poor water permeability, and salt to be difficult to infiltrate and discharge; higher salt concentrations will also increase the osmotic pressure of the soil solution, weakening the ability of plant roots to absorb water and nutrients; some salt ions (sodium ions and chloride ions) can cause damage to plant cells and poison plants; plant growth on saline soil is restricted, and the number of soil organisms is small and their activity is weak.

In general, saline soil and alkaline soil are basically barren land. Halophytic and salt-tolerant plants mainly grow on severely salinized soils, while on slightly to moderately salinized soils, the growth of general plants will be significantly inhibited.

Severely salinized landscape photos

Image source: Xie Wenping, Wang Xiangping, Sun Ruijuan

Where is the saline soil?

The distribution of saline soil involves more than 100 countries and regions in the world, covering an area of ​​about 16.5 billion mu.

Distribution map of saline soil in the world (Source: Wicke et al., 2011)

The total area of ​​saline soil in my country is nearly 1.5 billion mu, and about 550 million mu of saline soil resources are available, concentrated in the coastal areas, the northwest inland, the Songnen Plain in the northeast, the upper and middle reaches of the Yellow River and the North China region. A considerable part of these areas are important grain production bases in my country.

At present, the area of ​​saline soil with potential for agricultural improvement and utilization in my country is about 100 million mu, mainly distributed in 18 provinces, municipalities and autonomous regions such as Jilin, Ningxia, Inner Mongolia, Hebei, Xinjiang and Jiangsu. In general, the distribution of saline soil in my country is characterized by more in the north and less in the south.

White soil, great use

The area of ​​saline soil is vast, and there is also a large amount of salinized soil distributed in cultivated land. Although the saline soil mentioned in the previous article is basically "barren land", it actually has huge potential for utilization. Specifically, saline soil is an important reserve land resource. At the same time, the management and utilization of saline soil can also enhance the regional ecological function and play an important role in addressing global climate change issues.

1. Important reserve arable land resources

A considerable part of the area where saline soil is distributed is the main grain production area, but the productivity of salinized land is low and the agricultural development situation is grim. Most crops have weak salt tolerance. Mild to moderate soil salinization will cause a 10% to 50% drop in crop yields, and severe salinization will cause a more than 75% reduction in grain production, and sometimes even a total crop failure. Therefore, improving saline soil is an important way to increase land productivity in saline areas and expand reserve arable land resources.

So far, domestic scholars have proposed targeted technical models for the classification and management of saline soil based on the occurrence and development characteristics of soil salinization in different regions, such as the northwest inland, the upper and middle reaches of the Yellow River, the Songnen Plain in the northeast, and the eastern coastal areas.

The management and utilization of saline soil are mainly carried out from the aspects of reducing soil surface evaporation, controlling groundwater level, improving soil structure, enhancing soil fertility, and improving soil environment. It integrates the application of ecological integrated technology models such as concealed pipe and open ditch drainage, water, salt and fertilizer regulation, biological improvement, and drip irrigation to transform saline soil from barren land into high-yield fertile farmland, which becomes a golden reserve resource to ensure the safety of cultivated land and provides important guarantee for national food security.

2. Vegetation construction improves the ecological function of saline areas

Salinization inhibits plant growth, making ecological landscape and ecological protection issues more prominent. For example, in the saline-alkali desert areas in inland areas, normal plants cannot grow, the degree of desertification is serious, and the ecological environment needs to be improved urgently.

Vegetation construction in saline-alkali land can effectively beautify the ecological landscape, and at the same time play the role of windbreak, sand fixation, forage production and soil and water conservation, improve the stability of the ecosystem and enhance the environmental carrying capacity. At the same time, in the process of vegetation restoration, saline-alkali land can effectively improve the physical and chemical properties of the soil, increase biodiversity, and lay the foundation for the further development and utilization of saline-alkali land.

Vegetation construction in saline areas. Image source: Xie Wenping, Wang Xiangping, Sun Ruijuan

3. Significant carbon sequestration potential

The soil organic carbon pool is the largest and most active carbon pool in terrestrial ecosystems. Soil organic carbon has an important impact on soil productivity, and its changes and regulation are also part of the global carbon cycle. Saline soil has a low organic carbon content. Plant growth on saline soil under natural conditions is inhibited, microbial activity is low, the mineralization rate of organic carbon is slow, and the exogenous carbon input to the soil is small. Therefore, its potential carbon fixation capacity is higher than that of other terrestrial ecosystems.

The soil carbon density of saline soil in my country is generally low. In the process of saline soil management and improvement, the accumulation of soil organic carbon and continuous improvement of soil fertility are important processes for the soil to exert its carbon sink function. The increase in soil carbon inventory is of great significance to achieving the increase of my country's total soil carbon sink and realizing carbon fixation and emission reduction.

The management and utilization of saline soil is an important way to ensure the red line of cultivated land, protect the ecological environment, and achieve carbon fixation and emission reduction. More ecological management methods should be used in its management and utilization process, such as strengthening the application of biotechnology, ecological salt drainage and salt control technology, salt-alkali barrier reduction and nutrient efficiency enhancement technology, and the introduction of smart agriculture precision management methods.

Saline-alkali land is a complex ecosystem. Its management and utilization should take into account comprehensive principles such as improving quality, protecting the environment and increasing carbon sinks, so that the managed saline soil can become the primary reserve arable land resource, while contributing to ecological protection and carbon sequestration and emission reduction in my country and the world.

“Food is the people’s heaven, and soil is their root.”

Soil safety is related to

Food security

Water safety and ecological environment safety

It is the key to maintaining the sustainable development of the country's social economy.

Even today when science is advanced, crops grown on farmland are still the most important direct and indirect source of human food. Therefore, soil has always been and will always be the foundation for human survival.

World Soil Day

We have a responsibility to protect the land

Reference Links:

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Wang Zunqin. Saline soil in China[M]. Beijing: Science Press, 1993: 130-161.

[2] Yang Jinsong, Yao Rongjiang, Wang Xiangping, et al. Research on saline soil in China: history, current situation and prospects [J/OL]. Acta Pedologica Sinica, 2021. https://kns.cnki.net/kcms/detail/32.1119.P.20211112.0951.002.html

[3] Yang Jinsong, Yao Rongjiang, Wang Xiangping, et al. Ecological governance of saline-alkali land and development model of ecological industry in Hetao Plain[J]. Acta Ecologica Sinica, 2016.

[4] Yang Jinsong, Yao Rongjiang. Control of saline-alkali land and efficient agricultural utilization in my country. Bulletin of the Chinese Academy of Sciences. 2015(30): 162-170

[5]Rozema J , Flowers T . Crops for a Salinized World[J]. Science, 2008, 322(5907):1478-1480

[6]Wicke B, Smeets E, Dornburg V, et al. The global technical and economic potential of bioenergy from salt-affected soils[J]. Energy & Environmental Science, 2011, 4(8):2669-2681.

[7]Olsen MW, Frye RJ, Glenn E P. Effect of salinity and plant species on CO2 flux and leaching of dissolved organic carbon during decomposition of plant residue[J]. Plant and Soil, 1996, 179(2): 183－188.

[8]Yao RJ, Yang JS, Wang XP, et al. Response of soil characteristics and bacterial communities to nitrogen fertilization gradients in a coastal salt-affected agroecosystem, Land Degradation & Development, 2021, 32: 338-353

[9] United Nations official website. https://www.un.org

Comprehensive sources: United Nations official website, Food and Agriculture Organization of the United Nations, Xinhuanet, Earth Institute, etc.