Fig. 4

Linear relationships between SOM fractions (soil organic C, SOC; total nitrogen, TN), MAOM and oPOM at 0–15 cm depth and soybean grain yields. (a) SOC stock of oPOM-C, (b) TN stock of oPOM-N, (c) SOC stock of MAOM-C, and (d) TN stock of MAOM-N. *, P < 0.05; **, P < 0.01; ***, P < 0.001.