| Based on lots of the outdoor investigations, the physicochemical characteristics of physical soil crust and biological soil crust, including colour,thickness, bulk density, particle composition, microstructure, nutrient content and pH, had been analyzed.This thesis discusses topics about soil crusts (SCs) in Yanchi county of Ningxia province. It include types and the distribution features of SCs, the physicochemical characteristics of the SCs,the microstructure of the SCs, the influnces of SCs on soil water conservation and precipitation penetration, and the relationship between the coverage of the SCs and and the coverage and the species numbers of vascular plants. The physicochemical characteristics of soil crusts,which are sampled in different types,under different communities, and in different location, were discussed,So were the the influences of the soil crusts on the soil water and vascular plants.The research will provide the evidence of theory for revegetation and management of degraded ecosystem in YanChi sandy land. The major conclusions are as follows:(1) For dunes stabilized for over 5 years, the BSCs have been developed. The distribution of of different types of BSCs vary significantlyaccording to their micro-topography characteristics. depends on the location of the dune. Microbe crust occurs mainly on the top of the dune and spreads along the ridge of the sand field. The weak algae crusts appear at first, and then better developed algae crust exists at the bottom of the dune. Well developed moss crusts appear in large scale of the shrubs. Physical soil crusts (PSCs) are developed under nitraria tangutorums, meahwhile BSCs are developed under salix cheilophyla, Artemisia sphaerocepha and caragana korshinskii shrubs.(2) When PSCs grows into algae crusts (ACs), lichen crusts (LCs) and moss crusts (MCs), the crusts will turn thicker, the bulk density will decrease and the moisture capacity of the capillary will increase. Meanwhile, SCs will enhance clay content and accumulate nutrients of the soil. The micro structures of different types of SCs are different. The grains in the PSCs are the skeleton of the structure. The minor grains surrounded by the gels have the function of gluing the skeleton grains together. Filaments of Algae and desert granules are closely netted and interweaved in AC layer, because of which AC layer has made a steady whole. The grains in LC layer are surrounded tightly by gels and form stable soild structures. Meanwhile, the rhizoids of the moss are the sewer of the MCs.(3) The increase of clay content of the crust can help increasing hygroscopicity and water holding capacity of the soil. It makes the soil having significantly higher water retention compared to flowing sands. Generally, water holding capacity of the crust is increased by 28.6%～211.1%, among which ACs behaves the best by 63%. Through the analysis of soil water infiltration with or without MCs, the existence of MCs only has limited effect of water infiltration. It only increases the water infiltration in the initial phases for a short period of time. The range of precipitation which could infiltrate the curst is 3.15～5.50mm, much higher than drifting sand 1.52mm. But ACs and MCs require higher than 5mm to be infiltrated.(4) The relationship between SCs and vascular plants show beta distriubution feature. As the coverage of the SCs grow, the coverage and species number of the vascular plants will first increase then decrease.SCs can effectly occupies the spare spaces among the vascular plants. They change the characteristic features of the soil surface and resist soil erosion. Together with shrubs and herbs, they will compose a multiple layer protection system, which have significant value for resist wind erosion in the sandy areas.And also the SCs play an inportant roal in improving desert soil, Therefore, SCs can be an effective option to stabilize drifting sands in sandy areas.
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