Cool Footnote: Sandbar Fixation
This morning while reading Tigers, Rice, Silk, and Silt: Environment and Economy in Late Imperial South China, by Robert Marks, I stumbled on a fascinating description on how the Pearl River Delta in southern China – one of the great centers of agricultural production in the late imperial area – came to be formed by a confluence of natural circumstances and human activity (both wittingly and unwittingly).
The delta was historically created by silt carried by the West, North, and East rivers, although until relatively recently, by geological standards, the accumulation of silt was slow. In comparison to the Yellow and Yangzi rivers, these southern Chinese rivers carried relatively low amounts of silt prior to the rise of human civilization.
Those silt levels started to surge as the indigenous inhabitants of the region perfected a style of slash-and-burn agriculture that contributed to serious erosion of the upland hills where the West, North, and East Rivers originated. Later, starting around the 11th century, the introduction of wet rice agriculture by Chinese immigrants was accompanied by flood control projects that directly channeled the growing flow of silt into the delta.
Then came the Mongol conquest of China in the early 13th century. Many of the wealthiest lineages of those recently arrived Chinese immigrants scrambled as far south as they could go, some of them all the way to islands in what was then known as the Nan Hai, or South Sea. Upon arrival, they turned their attention to the task of extending their island territories by creating “shatan” sand flats.
Marks:
The method of creating shatan was relatively simple, but did require years until the land was usable. When a sandbar arose by natural means close to the water level, rocks were thrown around its perimeter not merely to fix the existing sand in place, but also to capture more sediment. After a more substantial enclosure was built, the sediment was “transformed by planting legumes” (which fix nitrogen in the soil). After three to five years, the shatan would be ready for rice.
The jolt that went through me upon reading those words will, I’m sure, be understandable by readers who know how much time I’ve spent thinking about nitrogen fixation in recent months. Now, I can’t say for sure that these legumes were soybeans; the Chinese agricultural arsenal included multiple members of the legume family. But even if these legumes were some kind of other, lesser, bean, the whole process stills strikes me as yet another terrifically vivid tribute to the ingenuity, determination, and patience of Chinese farmers. There’s something magical to me about the notion of morphing a barely emergent sandbar at the membrane between the saltwater sea and the freshwater delta into a rice paddy while leveraging the symbiotic relationship between nitrogen-fixing bacteria and legumes.
As Zhuangzi never tires of saying: All is transformation!