Is “Turning Stone into Gold” a delusion? It works in the desert!

Produced by: Science Popularization China

Author: What's more

Producer: China Science Expo

The barren desert covers a huge area. If you stand there and the wind blows, your mouth will be full of sand. Not only can it not be used for farming, but it also often becomes more and more aggressive, greedily "eating up" countless fertile fields and green land.

On the world-famous ancient Silk Road, there was a country called Loulan. It was once extremely prosperous, with envoys and merchants coming and going all the time. But around 400 AD, Loulan gradually disappeared from history books. One of the theories about the disappearance of Loulan is that it was buried in the vast yellow sand.

The current appearance of Loulan Ancient City

(Image source: Wikipedia)

Why is the seemingly harmless sand so cruel that it can quietly wipe out a once prosperous country? Faced with the vast desert, can humans only retreat step by step?

The Mystery of the Lost Ancient Country

The disappearance of Loulan was not like the ancient city of Pompeii in Italy, which was sealed by volcanic ash overnight. Instead, it gradually declined after many years of desert invasion and was eventually abandoned by people. This process is mainly related to the geographical location, topography and human activities of the ancient city of Loulan.

The ancient city of Loulan is located in the Tarim Basin in Xinjiang, surrounded by towering mountains. The Qinghai-Tibet Plateau in the south is like a giant wall, blocking the water vapor from the Indian Ocean, making the precipitation here scarce. At the same time, the activities of ancient humans have destroyed the local vegetation and waters, causing lakes and rivers to disappear and desertification to intensify. Under the influence of various factors, the ancient city of Loulan was eventually buried under the yellow sand.

The ancient city of Loulan is located on the edge of the Tarim Basin, far away from the oceans, with little rainfall.

(Image source: Screenshot from Google Earth)

Three tricks to prevent desertification

Once a desert is formed, it is difficult to recover. At the same time, it will expand outward, constantly swallowing up the surrounding land that has not yet been desertified. The disappearance of the ancient city of Loulan is a famous example. In ancient society, people were helpless against desertification. Even in modern times, how to prevent desertification is still a difficult problem.

China is one of the countries with the most serious desertification in the world, with desertified areas accounting for 18% of the country's land area, which is larger than the entire Iran. In the past, we said that China is vast and rich in resources, but behind the vast land are a large number of plateaus, mountains and desertified land. Mountains cannot be flattened and deserts cannot be restored to oases, but at least we cannot continue to allow the desert to expand. We must try to fight a defensive battle and then wait for an opportunity to counterattack.

(Photo source: veer)

There are three main methods of traditional desert transformation, which can be simply described as engineering method, chemical method and plant method.

Among these three methods, the plant method is the easiest to understand, which is to delay desertification by planting drought-resistant plants and providing appropriate water. The chemical method is to use a special "glue" to spray on the surface of the desert to fix the sand.

The most famous engineering method is the "straw grid sand barrier", which uses square straw walls to fix sand and prevent sand from flowing. It looks like a large waffle from a distance. This method is used to fix sand near the famous Mogao Grottoes in Dunhuang. Professionals use straw to tie the soil to form a 1-meter square grid, which is high around and low in the middle, just like a big bird's nest, to prevent the desert from swallowing up this great world heritage.

Grass grid sand barrier

(Photo source: Xinhuanet)

Generally speaking, there is only one idea to prevent desertification: fix the easily flowing sand and prevent it from running around, so that it will not harm fertile farmland.

But these methods also have their own problems. For example, the plant method is expensive, and the engineering and chemical methods cannot change the microclimate. Moreover, none of these three methods change the properties of sand. Is there a way to reduce costs and really make sand quickly become like soil, with a certain viscosity and water retention?

Add some adhesive and turn stone into gold!

Everyone must have heard the story of turning stone into gold, which is nothing more than wishful thinking. However, in the scientific exploration of desertification control, learning to be wishful thinking can often open up new scientific ideas.

The best defense is offense. Professor Yi Zhijian's team from Chongqing Jiaotong University changed their perspective. If they did not think about how to fix sand and adapt to the desert, but how to change the characteristics of sand and make the desert work for them, could they achieve a surprising victory?

They extracted adhesives from plants, mixed them into sand, and then added water to stir them. In this way, the "loose sand" underwent an amazing change: it could store water, be squeezed into a ball like soil when wet, and become solid when dry. More importantly, it could switch between the two states.

Of course, experiments are experiments. If you want to transform nature, you have to go to nature and accept the "beating". They brought this idea to the Ulan Buh Desert, one of the "Eight Great King Kongs" in China's desert world.

In the Ulan Buh Desert ecoregion, drought-tolerant plants grow in a natural environment (without artificial irrigation), forming an ecological barrier that contrasts sharply with the desert in the distance.

(Photo source: Chongqing Jiaotong University)

First, make a small modification to the experimental site: mix an adhesive into the upper 20-30 cm of sand and stir evenly. In this way, the land becomes two layers, the upper part is the desert soil layer that can retain water, and the lower part is still sand . Then you can start planting on this land. In the desert soil layer containing water, plants are of course relatively easy to survive, and the sand that can "hold together" will not be easily blown away by the wind and become quicksand.

After the plants grow up, their roots in turn hold onto the desert soil layer and the sand underneath. As time goes by, some rotten roots and fallen leaves become tools to further lock the desert soil layer. In this cycle, the land that was originally desertified has "come back to life". By adjusting the proportion of the adhesive, it is also possible to form a mud-like soil with anti-seepage capabilities, so that aquatic plants can be grown in the desert.

The sunflowers planted swayed in the wind, corn and sweet potatoes became the meals of the staff, and the underground, which looked more and more like soil, had earthworms and ants, frogs in the sand date trees and grass, and even little foxes wandering around, making people feel as if they were seeing the vibrant Ulan Buhe. But this time, it was not a mirage.

The Ulan Buh Desert Soil Reclamation Base is lush and full of vitality.

(Photo source: Chongqing Jiaotong University)

A useless desert can be transformed into soil that can grow vegetables and fruits. Isn’t this the real-life version of turning stone into gold?

Conclusion

Loulan has long disappeared in the desert, and generations of scientists have worked hard on the edge of the sand sea to control desertification. The black technology brought by "Yi Zhijian" is not invincible, and there are still issues such as cost, large-scale application and adaptability in different environments that need to be further studied, but at least they have sounded the clarion call, and it may not be far away to recreate an oasis in the desert and reproduce the scene of merchants traveling on the Silk Road in the Western Regions.

References:

1. Desert “Soilization”: An Eco-Mechanical Solution to Desertification[J]. Zhijian Yi, Chaohua Zhao. Engineering. 2016, 2(3): 270–273

2. Theory and practice of desert “soilization” ecological restoration[J]. Yi Zhijian. Journal of Chongqing Jiaotong University (Natural Science). 2016.11(35):27-32

3. On the impact of the uplift of the Qinghai-Tibet Plateau on the formation and evolution of deserts in China [J]. Wang Yue, Li Sen, Wang Jianhua, Yan Mancun. Arid Zone Research. 1996.6 (13): 20-24

4. Research progress and prospects of plant sand fixation technology[J]. Zhang Yujia, Zhang Kehai, Fang Qiao. Green Technology. 2020.3: 123-127

5. Yi Zhijian: The Promise of Sand[J]. Guo Ling. China Xiaokang Network. 2022.3