Abstract:Based on a long-term experiment, the effects of different fertilization on labile organic matter (LOM) and carbon management index (CMI) in different soil layers were explored. Four typical fertilization treatments were selected as:(1) No fertilizer (CK); (2) mineral nitrogen, phosphorus, and potassium (NPK); (3) NPK plus manure (NPKM); (4) NPK plus straw (NPKS). The highly, moderately and lowly LOM and CMI were measured and analyzed. The results showed that the soil organic matter (SOM) content and its difference among treatments were decreased with increment of soil depth. Compared with CK, the SOM content under the treatments with fertilizer was significantly higher, and the highest one was under NPKM with 13.91~33.55 g/kg. The Non-LOM and lowly LOM accounted for the major part of the total SOM, and the proportion increased with depth. CK showed the highest proportion with 35.6%~56.6% and 17.7%~50.7%, respectively. The CMI increased under the fertilization treatments, and varied among soil layers. At 0-40 cm, the CMI of highly and moderately LOM under NPKS was obviously higher than that under the other treatments as 149.54, 147.01, 237.65, respectively. The CMI under NPKM was the highest at 40-60 cm as 237.65, 537.67, respectively. In sum, the SOM and LOM content and their difference among treatments decreased with increment of soil depth. The fertilization improved SOM and LOM content, and the optimum one was NPKM. The CMI of highly and moderately LOM was higher under NPKS at upper layer (0 - 40 cm), and which was higher under NPKM at below layer (40 - 60 cm). Generally, the soil fertility was improved under NPKM, and followed by NPKS.