Abstract: Taking the Cuninghamia lanceolata and Pinus elliottii plantations at different development stages in the midsubtropics of China as test objects, and with the secondary evergreen broadleaved forest as the control, their soil organic matter, total nitrogen and phosphorus, and available nitrogen, phosphorus,and potassium contents were analyzed. Comparing with secondary evergreen broadl eaved forest, the C. lanceolata and P. elliottii plantations had lower contents of soil organic matter and total nitrogen and phosphorus. These contents increased with increasing age of C. lanceolata but decreased with increasing age of P. elliottii, and the changes in soil total phosphorus content were more smoothly than those in soil organic matter and total nitrogen contents. Soil available nutrient contents showed the same variation trends, but the soil available nitrogen and potassium contents were lower in 10 and 20 year-old than in 30 year-old C. lanceolata while in adverse for P. elliottii. From the viewpoint of the eco-environmental effects of soil quality evolvement, to properly prolong the rotation period of C. lanceolata and shorten the rotation period of P. elliottii  would be of practical significance in maintaining soil fertility and soil organic carbon sink.

Key words: Northwest plateau of Hebei Province, Vegetation, Actual productivity, Converting farmland to forest and pasture land, Strategy