Mapping ground reality

It takes nature about 200 to 400 years to build about 1 centimeter of black soil, a key element in China's food security. In many parts of Northeast China, that soil is thinning. But the key to saving it, a geologist argues, lies not only in the soil itself, but also in the ground beneath it.

A ground substrate survey team from the Langfang Natural Resources Comprehensive Survey Center of the China Geological Survey has completed a survey across 83 key black soil counties on more than 410,000 square kilometers of land. Their job was not to look at the soil, but to drill through it, down to dozens of meters, to see what lies underneath.

"On the surface, the black soil looks uniform. Drill into it, and the profile changes completely," said Chen Peng, a member of the center's ground substrate survey team.

Some fields sit on a thick layer of clay. Water and nutrients stay put. Others sit on sand and gravel. Water and fertilizer drain straight through. In some places, bedrock is just below the black soil. And once the top layer thins, recovery is painfully slow, he added.

"Underneath, one field can be completely different from another. We cannot protect them in the same way," the 44-year-old said.