Relationship between plant community succession and fertility variation of mountain yellow soil in east Chongqing Variations of soil fertility level in red soil region under long-term fertilization. Soil fertility in tea plantations in different slope positions and elevation regions Features of soil enzyme activity under different land uses in Ningnan Mountain area Characteristics and evolution of soil nutrients in apple orchards at the gully region of Loess Plateau Assessment of forest soil fertility using an integrated index based on the Nemerow meth