Effects of Different Improving Patterns for Degraded Robinia Pseucdoacacia Plantation on Soil Enzyme Activity and Physicochemical Properties in Yellow River Delta

In order to understand the effects of different improving patterns for badly degraded Robinia pseucdoacacia plantation in the Yellow River Delta area,soil enzyme activity,soil density,porosity,saline-alkali content and soil nutrients under the plantation improved for five years were determined.Four improving measures,including cotton field,pure forest of Fraxinus chinensis,agro-forestry of F.chinensis + cotton and mixed forest of F.chinensis + R.pseucdoacacia,were selected,with the badly degraded R.pseucdoacacia plantation serving as the control(CK).Results are as follows:(1) The improving patterns clearly affected soil phosphatase,urease and polyphenol oxidase,but not soil peroxidase.Soil phosphatase and urease activity increased,but soil polyphenol oxidase decreased.The activities of polyphenol oxidase and urease showed such an order of mixed forestpure forestagro-forestrycotton field.Phosphatase activities in mixed forest,agro-forestry,pure forest and cotton field were 3.5,3.2,1.7 and 1.6 times of that of CK,respectively.(2) Soil density and soil salt content decreased after adopting the four improving patterns,and these indexes were in the order of mixed forest agro-forestry pure forest cotton field.Compared with CK,soil density decreased by 14.5%,12.3%,9.0% and 7.7%;and soil salt content decreased by 35.3%,27.9%,13.2% and 7.4%,respectively.However,soil total porosity increased.(3) Soil nutrient content,such as soil organic matter,available N,P and K increased after adopting the four improving measures.These indexes were the highest in mixed forest,those in agro-forestry were higher than pure forest,and the data for cotton field were unstable.Soil enzyme activities and physicochemical properties for mixed forest and agro-forestry were better than pure forest and cotton filed.Accordingly,we propose that mixed forest and agro-forestry should be fostered and managed firstly in the future.