Abstract:

In this paper, the effects of Robinia pseudoacacia plantation at different ages on soil enzyme activity was studied in loess hilly region using a method of time-space mutual substitution, slope cropland and Platycladus orientalis forest were selected as references. The results showed that urease, phosphatases, saccharase and catalase activities in the soil were increased significantly with increase of years, however cellulase fluctuated dramatically. In 50 years, activities of the enzymes increased by 160.2%,281.8%,162.2%,92.6%,73.8% respectively, compared to the slope cropland, but still lower than that in P. orientalis forest. Soil polyphenol oxidase was decreased by 39.11% and amylase was increased in the early years and then declined with time. The significant relationships were observed between soil urease, phosphatases, sucrase, cellulase, catalase, polyphenol oxidase activity and nutrient factors, therefore the enzymes could be used as biological indicators for assessing soil quality. SEI (soil enzyme index) increased at the early stage, followed by a relatively stable stage for 10 to 25 years, after then it continued to increase and reached to the maximum in the 50 years. But it was still lower than that of P. orientalis forest. It is concluded that low soil enzyme activity of slope cropland under erosive environment, owing to human cultivation activities, was improved greatly after planting the R. pseudoacacia forests, but it needs a longer time to reach to the level of P. orientalis forest, the climax community in this region.

Key words: Robinia pseudoacacia plantation, soil enzyme activity, soil enzyme index, loess hilly region