Enzymatic activity and nutrient availability in the rhizosphere of poplar plantations treated with fresh grass mulch

Poplar plantations have been established in upland areas of southwestern China in recent years. However, poor site conditions limit the growth and ecological function of poplar plantations. In this experiment, poplar plantations were established in 2004 and circular areas were mulched around each tree at four rates: 0, 10,000, 20,000 and 30,000 kg ha−1 fresh grass (Imperata cylindrical var. major). The effects of varying amounts of fresh grass mulch on urease and acid phosphatase activities and nutrient availability (N, P and K) in the rhizosphere and bulk soil were assessed under field conditions. Additions of fresh grass mulch greatly improved urease and acid phosphatase activities as well as the concentrations of N, P and K in the rhizosphere and bulk soils, and all measured variables were enhanced as the mulching quantity increased, highlighting the importance of conducting effective residue management in poplar plantations growing on degraded agricultural soil. Enzymatic activity and nutrient availability were always higher in the rhizosphere than in the bulk soil, and rhizosphere effects were more pronounced in the mulch treatment. The results from the present study assume that reactions of enzymatic activity and available nutrients in rhizosphere soils are very sensitive to management practices and that the rhizosphere is an important indicator that reflects conditions and changes in soil fertility.