Mapping ground reality

The team developed a comprehensive model for evaluating black soil stability. The model categorizes the land into four types: stable, relatively stable, vulnerable and degraded. They also built the nation's first database of ground substrate samples for black soil.

In early spring in Northeast China, the ground was still frozen solid. A pickaxe could leave only a white mark. The backpack drills shook hard, and the members' hands often cracked. They just wrapped tape around them and kept going. When the ground thawed and the rains came, they carried heavy gear through the mud. If someone slipped, they wiped off the mud and moved on to the next spot.

In 2023, on the Songnen Plain, they drilled over a hundred boreholes. But what they actually measured differed greatly from the model's predictions about the black soil layer.

The model was supposed to predict black soil conditions across the larger area around the borehole, but the reality on the ground was too complex to fit the model's simulation results.

One night in Qiqihar, Heilongjiang province, someone suggested shrinking the survey area to avoid the difficulty. Shrinking the scope would have meant sidestepping the trickiest unknown, but that would leave a gap in the report.

"We refused to give up. We then realized our old way was to just drill to a set depth of 5 meters no matter what the ground was like. That turned out to be inefficient because it ignored the regional background. So later, we made the depth depend on the actual geological conditions," he said.

For example, in weathered rock areas, soil is often only 1 to 2 meters deep. In river floodplains, where sediments run deep, investigation depth went down 20 to 50 meters.

"Our new survey system was developed through trial and error — and it is now logically self-consistent."

The survey is part of a shift in how China reads its land.

In 2020, the Ministry of Natural Resources proposed the survey. The Langfang center ran a pilot in Baoding, Hebei province, then expanded to areas including the northeast's black soil region, the northwest's loess region and the coastal zone in Zhejiang province's Ningbo city.

In 2024, the team published China's first working methodology for ground substrate surveys, and developed the technical requirements for surveying the ground substrate in the black soil region of Northeast China, closing a critical technical gap that had existed in the country.

In the same year, they also tackled the problem of surface salt loss after rain and deep-layer salt resurgence after clear days, offering long-term solutions for saline-alkaline land improvement in places like Cangzhou, Hebei province and Lianyungang, Jiangsu province.

In the future, the team will extend efforts to key farming regions, such as the North China Plain, the middle and lower Yangtze River Plain, the hills along the southeastern coast, and Hainan Island.

"As long as there is land beneath our feet that needs guarding, we geologists will be the first to rush to the front line — to uncover the secrets of the earth and to take stock of all it holds," Chen said.

lihongyang@chinadaily.com.cn