Objective To explore the effects of different forest types and ages on soil nutrients in the loess area of western Shanxi province, so as to provide reference for sustainable forest management and enrich the ecological service assessment data.

Method  Forest investigation, soil sampling and laboratory analysis were used to analyze the contents of organic carbon, total nitrogen and total phosphorus in different soil layers at three plantations with different ages (mid-aged Populus davidiana, Young Pinus tabulaeformis and mid-aged Platycladus orientalis), and studied the C, N, and P stoichiometry in different soil layers in July and August of 2011 and 2016.

Result The soil nutrients of different forest lands were accumulated in surface:the content of organic carbon, total nitrogen and total phosphorus in 0~30 cm soil layer accounted for more than 70% of the total in 0~100 cm soil layer, the soil nutrients decreased with soil depth. After 5 years, the average soil total nitrogen content of 0~50 cm in Populus davidiana, Pinus tabulaeformis and Platycladus orientalis forests increased by 0.26, 0.20, 0.17 g·kg^-1, the total phosphorus content increased by 0.05, 0.06, 0.09 g·kg^-1; the carbon storage of 0~100 cm layer increased by 21.17, 23.74, 2.21 t·hm^-2 respectively. The C:N of soil in different forest lands decreased gradually with the depth of soil layer, while the N:P and C:P in different soil layers changed irregularly; the N:P and C:P of soil surface layer (0~10 cm) decreased significantly with forest age, while the change of C:N was not obvious.

Conclusion According to the national soil nutrients classification standards, the carbon and nitrogen in the experimental forests are relatively rich. The total phosphorus content was 0.36~0.46 g·kg^-1, which is at level 4 or 5. Pinus tabulaeformis, Platycladus orientalis and Populus davidiana perform better in improving soil organic carbon storage, total nitrogen and total phosphorus in the experimental forests.