| The problem of rocky desertification in karst areas is becoming more and serious in south-west China, of which is characterized by a vicious cycle:water loss and soil erosion→rocky desertification→karst hydrological and geological disaster→karst ecosystem degeneration. Rocky desertification increases annually by 2%, which leads to soil erosion, non-zone drought and loss of lives and properties to mankind. It not only aggravates the poverty situation in karst regions, but threatens the ecological security of lower-middle of Yangtze River and Zhujiang River.In the past half century, the scientists of karst have made a lot of achievments both in theories and practice of rocky desertification rehabilitation. But the importance of herbaceous plants against on the rocky desertification were not gotten attention, also it is difficult to transplant the modles of rock desertification.Based on the principles and methods of geogrophy, restoration ecology and system theory, supported by project of the eleventh five-year plan, contrastive studies on the the physioecological characteristics, soil and water conservation benefits and the differences about soil physical and chemical properties in Phyla Nodiflora land, abandoned land and tillage were done through digital modeling of Grey Theory and evaluating of comprehensive ecological benefits of grey association analysis method. Some preliminary conclusions are obtained as follows:First, biological effects about Phyla Nodiflora:(1) The coverage rate of the Phyla Nodiflora land is 100% after transplanting 90 days. The coverage rate of the abandoned land is about 60%. The coverage rate about tillage is limited to less than 50%, because of little vegtation coverage. We discussed the relationaship between the coverage rate of Phyla Nodiflora and the surface runoff, of which that the effect of reduction of the surface runoff is not very effective when the coverage rate is less than 30%, while the effect of reduction of the surface runoff will increase when coverage is 30%-40%, and surface runoff decrease rapidly when coverage rate is 80%-100%. (2)Phyla Nodiflora is rich root, and growing rapidly. The average root length is 22.3cm, and average root density is 2100 per meter quare, and root biomass is 780 kilogram per meter quare.The second, influence of Phyla Nodiflora on physical properties of soils:(1)The soil temperature decreased in summer and increased in winnter,when soil were covered by Phyla Nodiflora.In summer, the soil temperature covered by 2 years Phyla Nodiflora is lower than the temperature of tillage at Ocm,10cm and 20cm of which is 1.2℃,3.2℃and 3℃respectively. The daily of variation of soil temperature covered by 2 years of Phyla Nodiflora decreased 2.8℃,1.8℃and 1.2℃than the daily of variation of soil temperature of tillage at Ocm,10cm and 20cm. In winter, the soil temperature covered by 2 years Phyla Nodiflora is higher than the temperature of tillage at Ocm,10cm and 20cm of which is 1.2℃,2.4℃and 2.1℃respectively. The Phyla Nodiflora land has a good warm-keeping effect. (2)There are different in the soil moisture of Phyla Nodiflora land, abandoned land and tillage, Which followed the order:2 years of Phyla Nodiflora land> 1 year Phyla Nodiflora land>abandoned land> tillage. In summer, the soil moisture of 2 years of Phyla Nodiflora land is higher than the soil moisture of tillage at Ocm and 20cm. The growth rate is 12.6% and 17.9%, respectivly. In winter The growth rate is 13.7% and 14.1%, respectivly.(3) Phyla Nodiflora can reduce soil bulk density and increase soil porosity and enhance soil permeability.The third, influence of Phyla Nodiflora on chemical properties of soils:Phyla Nodiflora can improve soil fertility, increase soil organic matter, total nitrogen and total potassium.The forth, influence of Phyla Nodiflora on water-soil conservation effect:(1) Phyla Nodiflora can reduce funoff. The runoff coefficient of 2 years of Phyla Nodiflora land decreased by 47.5%, 60.4% and 55.6% than that of tillage under different precipitation. The runoff coefficient of 1 year Phyla Nodiflora land decreased by 37.3%,52.1% and 50% than that of tillage. There is a relationship between the variation of runoff coefficient and precipitation. The runoff coefficient of soil covered different plant increased when rainfall and rainfall intensity become higher. But the growth average of runoff coefficient of Phyla Nodiflora land is smallest. (2) The soil erosion amount of Phyla Nodiflora land is smallest in the same condition. The amount of soil erosion of 2 years of Phyla Nodiflora land account for 4.89%,5.21% and 5.55% of tillage, respectively. The difference is remarkble for the F=100.0192>Fcrit=7.708647 of soil erosion amount between Phyla Nodiflora land and tillage.At the same time, the runoff coefficient of 2 years of Phyla Nodiflora land account for 52.5%,39.6% and 44.4% of tillage, respectively. It indicated that conservation of soil of Phyla Nodiflora is better than control of water.The fifth, according to gravy theory, simplified gray association analysis method, the similarity correlation degree of 2 years of Phyla Nodiflora land and tillage is r3=0.886, and the similarity correlation degree of 1 year of Phyla Nodiflora land and tillage is r2=0.90, the similarity correlation degree of abandoned land and tillage is r1=0.944, which indicated that the ecological effect of 2 years of Phyla Nodiflora is the best.The sixth, we find out the ecological indicators of abandoned land are better than whose of tillage. Because it reduces of human interence by abandoning land and there are good temperature and rainfall conditions in Chongqing karst area, it is suited for the succession from grass to shrub to small tree, and recoverying of soil function, and improving karst ecosystem.
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