Physical And Chemical Properties Of Soil And Related Enzymes Activity After Returning Farmland To Lake In Dongting Lake Region

Heterogeneity of soil characteristics was existed between temporal and spatial scale and human activities has a profound impact on the temporal and spatial variation of soil quality. The project of "Returning Farmland to Lake" is an important measurement to improving the ecological environment artificially, and it has a profound influence on physical-chemical properties and biological characteristics of soil. Long-term dynamic supervision and research on the change of soil quality is an important part to make sure whether the project carried on smoothly after the implementation of the project. This paper focus on the three different "Returning Farmland to Lake" models (natural state, planting reeds, planting poplar) in "double returning" regions (qingshanyuan, guanyuan,xiaojicheng) in Dongting lake were selected to compare the distribution patterns of the physical-chemical properties and biological characteristics of soil in ag-ecosystem, marsh regions and regions after "Returning Farmland to Lake". The results are as follows:1. Distribution pattern of soil particle composition after "Returning Farmland to Lake"In the three models of "Returning Farmland to Lake", the different depth profiles particle analysis showed that soil depth had no significant effect on the soil particle composition. The soil particles in three "Returning Farmland to Lake" models are closer to cropland ecosystem, but a significant difference was also exists with the different patterns of returning farmland to lake.Our study showed that planting poplar, a model for wetland restoration was benefit for the formation of clay and silt; in the "guanyuan" plots, where planting reeds was considered as an another model for wetland restoration, the physical characteristics was acclimated to the natural ecosystem due to the influence of incessant flooding; however in "qingshanyuan" plots, which was the model of restoring the natural lake, the soil physical properties had no significant change.2. Distribution pattern of soil chemical property after "Returning Farmland to Lake" An clear table effect exists in the three models indicating that the highest nutrients content appeared in the upper layer .However, potassium had an opposite tendency, in the "xiaojicheng" plot, the soil could accumulate the organic matter, total phosphorus and total potassium quickly; in the "guanyuan", the organic matter content declined seriously, while an opposite tendency was found in total phosphorus content ; in the "qingshanyuan", compared with the paddy field and glebe, no significant change was found in the nutrients.3. Distribution characteristics of soil enzyme activity after "Returning Farmland toLake"The soil enzymes activity decreased significantly according to the soil depth except the catalase, which was not influenced by the soil profiles. However, the responses of soil enzyme activity to land use were not exactly the same as the soil profile, suggesting that differences in the intensity of soil decomposition and synthesis of organic residue existed among soil use methods in different soil layers.The performances of soil enzyme activity in three "Returning Farmland to Lake" models are as follows: the catalase activity in "xiaojicheng" plot increased significantly, while no significant change was found in other enzymes; in "guanyuan", the sucrlase and the phosphates all decreased significantly; in the "qingshanyuan", compared with the paddy field and glebe, no significant change was found in all of the soil enzymes activities.4. Relationship between soil characteristics in Dong-ting lake regions Correlation analysis between the different "Returning Farmland to Lake" modelswhich suggested that soil organic matter could be considered as the ties to linking with the soil ph-chemical properties and biological characteristics.From the above results, we could know that "xiaojicheng" plot could improve the soil quality effectively, mainly through the accumulation of soil nutrients and the enhancement of soil enzyme activities; when compared with paddy field and glebe, the soil quality was decreased in different degree in the "guanyuan" and no significant change was found in the "qingshanyuan". Compared with the natural forest, the Planted forest in the "guanyuan" plot was not steady due to the disturbance of human activities; meanwhile, planting poplar had already caused lots of environment problems due to the emergence of large numbers of paper mills.In generally, the restores rate of eight years "Returning Farmland to Lake" was slower than our expect, the soil ecological process can't be restored in a short time suggesting that the restoration of damaged ecosystem was an slowly process. Our result showed that soil organic matter could be considered as the band of the soil physics-chemistry property and the soil enzyme activities. The organic matter content was correlated with the soil productivity significantly, so in the process of "Returning Farmland to Lake" project, enhancement productivity and biological output maybe the feasible ways to improving the soil ecological environment promptly.