Carbon (C) occluded in phytolith (PhytOC) is highly stable at millennium scale and its accumulation in soils can help increase long-term C sequestration. Here, we report that soil PhytOC storage significantly increased with increasing duration under intensive management (mulching and fertilization) in Lei bamboo (Phyllostachys praecox) plantations. The PhytOC storage in 0-40[emsp14]cm soil layer in bamboo plantations increased by 217[emsp14]Mg C ha-1, 20 years after being converted from paddy fields. The PhytOC accumulated at 79[emsp14]kg C ha-1 yr-1, a rate far exceeding the global mean long-term soil C accumulation rate of 24[emsp14]kg C ha-1 yr-1 reported in the literature. Approximately 86% of the increased PhytOC came from the large amount of mulch applied. Our data clearly demonstrate the decadal scale management effect on PhytOC accumulation, suggesting that heavy mulching is a potential method for increasing long-term organic C storage in soils for mitigating global climate change.