Researchers at Tsinghua University incubated soil from a six meter deep agricultural profile in Beijing to test how moisture and carbon affect nitrate in deep subsurface layers. At 100 percent water-filled pore space, nitrate concentrations fell by 39 to 54 percent over 45 days. Adding glucose as a labile carbon source cut nitrate by 85 percent, with most of the loss happening in the first 15 days. These results matter because groundwater recovery in northern China is rewetting vadose zones that hold decades of fertilizer nitrate. The key question is whether that nitrate gets flushed into drinking water or broken down in place. The study suggests saturated, carbon-rich conditions favor the latter, but the lab setup used static moisture and sieved soil, so field hydrology and real carbon availability still need to be tested.
