The Characteristics Of "Fertile Island" On Shrubs At An Oasis-desert Ecotone And Its Significant On Arid Region In The North Of Xinjiang

Agriculture soil Desertification is most serious ecological problem which threatens land quality and caused soil degradation in arid and semi-arid region. There have variety of possible reasons involved in soil desertification. However, the key factors influence the severity of desertification including the percentage of existent vegetative cover, and the amount of drifting sand. It is said different shrub species growing at desert could exhibit fertile island effect which play a significant function in prevent agriculture soil form desertification. The objective of the present study is to investigate the shrubs of"Fertile Island"characteristics and its effects on agriculture soil desertification at Oasis–desert Ecotone in the North of Xinjiang. Tamarix spp., Haloxylon ammodendron, Calligonum spp. and Nitraria spp. shrubs were used to the research abject at Oasis–desert Ecotone in the North of Xinjiang. Through two-year field investigation and laboratory analysis, the changes of soil properties in different extent degradation and different using patterns of shrubs land, it showed that the protective effects and efficient using mechanism of the shrubs to the soil nutrient in the system and studied the formation mechanism and variation characteristics of'fertile island', which provided some basis for the reasonable application of soil in our district.The results of the characteristics of'fertile island'indicated that:1)Soil small particle and nutrition was accumulated under the shrub cover by the shrub vegetation, therefore the soil fertility and structure under the shrubs are significantly different from the shrub-unaffected soils, particularly on the top-soil. Tamarix spp., H. ammodendron, Calligonum spp. and Nitraria spp. shrubs exhibit a strong'fertile island'effect, and the soil properties differences between under shrubs and interspaces decreased with the soil depth added; 2)The soil chemical properties such as soil total N content, Olsen-P content, as well as soil total potassium content decreased with the increasing distance from the centre of the shrub to interspaces. The degree of'fertile island'is decreased with the distance increasing from the centre of the shrub to out space of shrub cover and decreased with the soil depth profile; 3)Different variety of desert shrubs have obvious distinctive distribution model of soil nutritional chemical elements under the shrubs. There are gradients in biologically-limiting nutrients from'islands'toward interspaces, whereas the biologically-unlimited elements are more or less or equally distributed in'islands'relative to interspaces. Its structure depends on the shrub with the wind, water and other climatic factors complex interaction; 4)The'fertile island'of Haloxylon ammodendron is significantly more strong than Nitraria spp.shrubs which showed that different shrubs species have different'fertile island'.The changes of soil chemical and physical properties in different soil degradation degree as well as different land utility patterns shrubs land showed that:1)Soil nutrition and soil fractal dimension of soil particle were declining following the orient direction from the oasis to desert hinterland and soil structure is deteriorating. However, the shrubs "island" effect which is formed by physical, biological and climatic factors complex interactive process and the growth of shrubs are conducive to the improvement of soil fertility and the protection and improve the micro-climate and soil conditions under the shrubs; 2)The enrichment ratio of the soil nutrient in desert hinterland is much higher than in the edge of the desert,'fertile island'is stronger and deeper in desert hinterland than in the edge of the desert, which showed the development degree of'fertile island'is increased with the degree of drought in arid and semiarid regions; 3)Land utility model has significantly impact on soil physical properties, soil total nutrients and total salt content, namely, soil nutrition content of enclosed shrubs land > those of sand barrier shrubs land > free grazing shrubs land, the available nutrients in enclosed shrubs land is substantial larger than sand barrier shrubs land, and free grazing shrubs land, and soil particles as well. Fractal dimension of soil particle have the similar trend; 4) Intensive desert land utility accelerated erosion of the top layer of agriculture soil, caused soil quality decreased and land degradation in North Xinjiang. Desert shrub play an important role to prevent soil desertification and land degradation, consequently, shrub plant exhibit an significant ecological role in arid region, desert vegetation should be conservation and restoration from destroy.