Study On Soil Physical And Chemical Properties And Soil Enzyme Dynamics Of Four De-farming And Reafforestation Patterns In High Precipitation Area Of Western China

Long-term research of the effect of de-farming and reafforestation on soil fertility was an important assurance that the engineering could go on wheels.Present studies only indirectly understood effects of plant restoration on soil ecological process by using spatial the method of spatial sequence instead of time temporal sequence,however long-term located studies(especially in preliminary stage) still were reported scarcely.In order to evaluate the effect of de-farming and reafforestation on the soil fertility,establish scientific and effective vegetation restoration approach and provide the theory basis for sustainable management, the soil nutrients and enzyme activity of four de-fanning and reafforestation patterns in Hongya were studied in this thesis.The results were mainly as follows:1 The forest and grass ecosystems both had ecological and economic benefits.Under the influence of satisfying the economic output,serious human disturbance,Hemarthria compressa's death and stopping fertilization,the annual changes of soil physical and chemical properties fluctuated heavily.The improvement of soil physical properties was not obvious.Because crown density had become larger during 2005-2007,Hemarthria compressa disappeared gradually under each model and soil bulk density and soil porosity were improved gradually.Soil total nutrients increased firstly and decreased then.Available nutrients changed heavily.The contents of NH4~+-N,available-P and available-K increased after stopping fertilization in 2004.Because of different land utilization and management,the soil organic matter accumulated indistinctively and all pattems changed differently.Increasing of soil total nutrients became more stable from 2005 to 2007.2 Soil nutrients had an obvious dynamics.The seasonal or monthly changes of soil nutrients of every pattern were different.Soil total nutrients of all patterns changed little compared to cultivated land.The soil organic matter contents of Betula luminfera were highest in autumn and lowest in spring,while the other patterns were highest in autumn and lowest in summer.The soil hydrolysable-N contents of all patterns changed about same.The soil hydrolysable-N contents of all patterns were lowest in July,highest in Oct. The soil available-P contents of Sinocalamus affinis were abundant in available-P.The soil available-P contents of Sinocalamus affinis and Pleioblastus amarus changed about same, highest in April and lowest in July.The soil available-P contents of Betula luminfera changed little,lowest in April and highest in Jan.Compared to other patterns,the soil available-P contents of Bambusa pervariabilis×Dendrocala mopsis were short,which changed little.The soil available-P contents of Bambusa pervariabilis×Dendrocala mopsis were lowest in Jan and highest in October.The soil available-K contents of Bambusa pervariabilis×Dendrocala mopsis were lack and lower from October to next Jan,but other pattems were high in this time and got down from April to July.3 Soil urease activity of all patterns was lowest in winter.Soil urease activity of Bambusa pervariabilis×Dendrocala mopsis and Betula luminfera was highest in summer, while Sinocalamus affinis and Pleioblastus amarus was highest in spring.Soil invertase activity of all patterns was highest in autumn.Soil invertase activity of Sinocalamus affinis and Betula luminfera was lowest in winter,while Bambusa pervariabilis×Dendrocala mopsis and Pleioblastus amarus was lower in spring and summer.Soil catalase activity of Sinocalamus affinis was highest in summer and lowest in spring,but the other patterns changed in sinasoid and highest in winter and lowest in spring.Soil acid phophatase activity of Pleioblastus amarus was lowest in autumn and highest in summer,while Bambusa pervariabilis×Dendrocala mopsis was lowest in winter and highest in spring. Besides,soil acid phophatase activity of Sinocalamus affinis and Betula luminfera was both highest in winter.Soil acid phophatase activity of Sinocalamus affinis was lowest in summer,while Betula luminfera was lowest in spring.Soil neutral phophatase activities of all patterns were highest in summer.Soil neutral phophatase activity of Sinocalamus affinis and Pleioblastus amarus was lowest in winter,while Bambusa pervariabilis×Dendrocala mopsis and Betula luminfera was lowest in autumn and spring.4 In the text,the vertical distributions of total-K of four patterns were different.Soil total-K contents in subsoil of Bambusa pervariabilis×Dendrocala mopsis,Sinocalamus affinis and Pleioblastus amarus were higher than in topsoil,while Betula luminfera was opposite.All soil nutrients and enzyme activity in topsoil were higher than in subsoil. Obvious surface assemble effect were showed in four patterns.5 Evaluating indexes of the effects of different de-farming and reafforestation patterns on soil fertility were based on applying factor analysis showed that the indexes of total-N, hydrolysable-N,organic matter,acid phophatase and physical properties were very important;the indexes of total-P,total-K,available-P and enzyme activity were also important in evaluating soil fertility;but the index of available-K had a less effect on soil fertility evaluation.According to the IFI of four patterns and farmland,the sequence is as follows:the topsoil of Sinocalamus affinis＞the topsoil of Betula luminfera＞the topsoil of Pleioblastus amarus＞the subsoil of Sinocalamus affinis＞the subsoil of Betula luminfera＞the subsoil of Pleioblastus amarus＞the topsoil of farmland＞the topsoil of Bambusa pervariabilis×Dendrocala mopsis＞the subsoil of Bambusa pervariabilis×Dendrocala mopsis＞the subsoil of farmland.Soil fertility in each models changed with time.Soil fertility on above layer in Sinocalamus affinis,Pleioblastus amarus and Betula luminfera was higher than that in farmland.It shows that economic benefits of de-farming and reafforestation patterns have appeared.6 Based on the ecological and economic benefits,according to soil fertility integrated evaluation index and the dynamics of soil available nutrients,the patterns of Betula luminfera+ Sinocalamus affinis+ Hemarthria compressa should be generalized in this area. And the management measures of four patterns were studied out in order to obtain an relative balance between ecological and economic benefits.As long as complementing with scientific management,this pattern would have a sustainable development.