How to go from "white soil" to "oasis"? Let's see the "salty confession" of the earth

In ancient my country, people have already realized the importance of soil in nurturing all things. "Shuowen Jiezi" mentions: "'Soil' is the earth that produces all things." "Guan Zi Di Yuan" mentions "The chief of all soils is the five grains. The five grains are red, green, white, black, or yellow." The "five grains" mentioned here are the "five-color soils" that were widely used for sacrifices later. In order to let everyone have a deeper understanding and cherish this important resource on which we depend for survival, next, I will lead you to explore the wonderful world of China's "five-color soils", focusing on one of them, white soil.

Dongying, Shandong: Sweet potatoes grow in saline-alkali land (Photo by Zhou Guangxue of Guangming Photo)

As one of the "five colored soils", white soil plays an important role in soil science and ecology. In ancient China, white soil symbolized Shaohao of the West (son of the emperor, god of the West in ancient Chinese mythology), who was assisted by the golden god holding a square ruler and in charge of autumn. As we all know, autumn is the season of harvest, but white soil in real life is not as "beautiful" as the ancients thought, because white soil is not suitable for growing most crops. Why is that?

In fact, white soil is what we often call saline-alkali land. Saline-alkali land refers to land with too high salt or too strong alkalinity in the soil. These lands are usually difficult to use for agricultural production due to the lack of suitable vegetation and soil quality. my country is the third largest country in the world in terms of saline-alkali land distribution, with more than 99 million hectares of saline-alkali land, accounting for about 10% of the global total area.

The soil in saline-alkali land is called saline-alkali soil, which includes two types: saline soil and alkaline soil. Saline soil mainly refers to salinized soil with high chloride or sulfate content. These salts will have an adverse effect on plant growth at high concentrations. Alkaline soil refers to soil containing carbonate or heavy phosphate, with a high pH value and alkaline soil. This alkalinity may lead to a compact soil structure, making it difficult to penetrate and retain water.

Saline-alkali soils are mainly distributed in arid, semi-arid or semi-humid areas such as Northwest my country, Xinjiang, Gansu, Qinghai, Inner Mongolia, Ningxia Plain and eastern coastal areas. All kinds of saline-alkali soils are formed under certain natural conditions. The essence of their formation is mainly the horizontal and vertical redistribution of various soluble salts on the ground, so that salt gradually accumulates on the soil surface in the salt-collecting area.

The formation of saline-alkali soil is affected by natural and human factors. Natural factors include climate, geology, geomorphology, hydrology and hydrogeology. For example, in the arid and semi-arid areas of Northeast, Northwest and North my country, due to low precipitation and high evaporation, the salt dissolved in the water easily accumulates on the soil surface, thus forming saline-alkali land.

Image source: Jingxin Geography Public Account

The main human cause is due to unreasonable irrigation. For example, flooding is used when watering, or irrigation is done without drainage in low-lying areas, which causes the groundwater level to rise rapidly and salt to accumulate, thus turning the original good land into saline-alkali land. In addition, the long-term excessive use of pesticides and fertilizers will also aggravate the salinization of the soil to a certain extent.

The general characteristics of saline-alkali land are: soil is prone to water retention, poor ventilation and water permeability, slow land temperature rise, low enzyme activity in the soil, slow organic matter conversion, poor soil fertility, easy to compact, low permeability coefficient, etc. Saline-alkali land not only hinders engineering construction, but also damages the ecological environment, affects agricultural and forestry production, and causes a certain degree of loss to the environment, economy and society.

Therefore, it is imperative to improve saline-alkali land. Specific measures include:

1. Physical improvement measures

Physical improvement refers to the use of some physical methods to transform saline-alkali soil, such as covering with sand and soil, micro-area soil improvement, deep plowing and deep turning, and ground covering to achieve the purpose of improvement and utilization.

2. Chemical treatment measures

Chemical improvement measures for saline-alkali land can be achieved by adding exogenous additives (phosphogypsum, humic acid, superphosphate, peat, slag, vinegar residue, etc.) to saline-alkali soil. In this process, base exchange, i.e. ion exchange, occurs in the soil, which reduces the adsorption of Na+ by the soil, lowers the soil pH, changes the acidity, and ultimately reduces the degree of soil salinization.

3. Biological remediation measures

Biological improvement is one of the most effective methods for improving saline-alkali land. Its principle is to absorb, transform and transport soil salt through the growth and metabolism of plants or microorganisms, thereby improving soil quality.

4. Engineering improvements

Engineering improvement is the main method of improving saline-alkali land. By building anti-seepage canals, drainage ditches, and water diversion canals, the evaporation and loss of soil moisture during irrigation can be reduced to lower the groundwater level and soil salt content and improve soil fertility. In addition, water conservancy facilities such as water retaining ridges, drainage ditches, and branch ditches can be built to remove water from the fields and lower the groundwater level, thereby achieving the purpose of improving saline-alkali land.

Although saline-alkali soil is a very challenging type of land, the fate of this land can be changed through scientific management and improvement methods. Protecting and improving the land is an important part of maintaining ecological balance and ensuring sustainable agricultural development. On World Soil Day, let us work together to find the most suitable "growth code" for every inch of soil on the earth, so that this land can regain its vitality.

References

[1] Wang Shiping, Chen Yue, Pan Dawei, Xue Wenduo, Zhou Lei, Zhao Na, Gong Zongqiang, Zhang Xiaorong. A review of saline-alkali land management research: current status, problems and countermeasures [J]. Chemical Minerals and Processing, 1-11.

[2] Zang Chao, Hu Yanjun. Comprehensive transformation and utilization of saline-alkali land, how to transform? How to use? [N]. Study Times, 2023-10-04 (007).

[3] Yan Maolu, Wang Xiaopeng, Zheng Yunzhu, Chen Zhihong, Tang Longxiang. Effects of organic fertilizer on soil improvement and crop growth in saline-alkali land in my country[J]. Agricultural Engineering, 2023, 13(08): 56-62.

Scientific review: Kuang Zongren (Associate Professor, College of Humanities and Development, China Agricultural University)

Author: Gao Jinyu (Undergraduate student of College of Humanities and Development, China Agricultural University)

Planning: Zhan Zhao, Wu Yuetong