Farmers in salt-affected coastal soils have two workable options for building soil carbon, and new research shows they work differently. In a two-year field trial in China's Yellow River Delta, adding straw or biochar alongside manure raised soil organic carbon by about 19 percent compared with manure alone. Straw worked through biology, feeding microbes that leave behind stable residues called necromass. Biochar worked through physics, increasing large soil aggregates by 40.9 percent and aggregate stability by 31.9 percent, which physically shields carbon from decomposition. The choice matters for soil health and for carbon accounting. Straw suits farms that want faster nutrient cycling and fertility. Biochar suits degraded land that needs better structure and long-term protection. Carbon credit programs should look at how carbon is stabilized, not just how much total organic carbon shows up in a soil test. Longer field trials are still needed to see how these gains hold under continued salinity.
