[Objective] The soil physical and chemical properties under different types of cultivation for a fixed number of years were studied to provide a scientific basis for the improvement of regional ecosystem services and ecological civilization construction.[Methods] Soil samples of forest land with different vegetation restoration periods (20

25

35

and 50 years) were collected by a spatiotemporal method. Unfertilized farmland and natural forest were taken as the control area.[Results] ① The soil particle composition did not change significantly in the early stage of returning farmland and was similar to that of the natural forestland at 50 years

while the content of large aggregates in 20

25

35

and 50-year abandoned plots increased by different degrees compared with the cultivated land (17.70%

53.23%

52.50%

and 70.30%

respectively). ② With the increase in the number of years of vegetation restoration

the soil bulk density showed a downward trend and finally tended to natural vegetation. The soil bulk density of the 50-year plot was close to that of natural woodland. All the soil moisture characteristic curve fitted well with the Gardner model. The order of the soil water-holding capacity was as follows: natural vegetation > 25 years > 35 years > 20 years > farmland > 50 years. ③ With the increasing number of years of vegetation restoration

both soil organic matter and total nitrogen content obviously increased (p<0.05). The content in the upper layer of soil was higher than that in the subsoil

and there was a significant phenomenon of surface layer accumulation. The contents of organic matter and total nitrogen in the upper layer of soil increased by 27%

134%

71%

and 343%

and by 20%

76%

64%

and 246%

respectively

while those in subsoil increased by 7%

88%

53%

and 422%

and by 12%

59%

35%

and 201%

respectively. However

the content of total phosphorus was between 0.55 and 0.36 g/kg; thus

it was less affected by the fixed number of years of the returning farmland.[Conclusion] The grain for green project can obviously improve the soil bulk density

increase soil particle size aggregates

improve the content of organic matter and total nitrogen

and further improve soil physical and chemical properties. The physical and chemical properties of the soil abandoned in 50 years were close to that of natural forestland.