Characteristics of salt crust layers in the forests irrigated with saline water in mobile desert.

Salt crust is a special layer on soil surface after irrigation in arid zone.But now the research work on its forming conditions and temcporal and spatial rules isn't systematically carried out yet.The experiments carried out in 2004 and 2005 on the forestland irrigated with saline water in the Taklimakan Desert indicated that a significant salt crust layer formed in the topsoil of forestland affer being irrigated.Through surveying the thickness and electrical conductivity(EC) of salt crust layers in all experimental plots,some conclusions are drawn as the followings: 1) the degree of minalization of irrigating water,irrigation method,irrigation program(irrigation water quota,irrigation interval) and texture of soil have great effects on the features of salt crust;2) the features of salt crust have a clear spatial distribution.The two irrigation ways,ie ridge irrigation and drip irrigation,have great effects on the micro-spatial distribution of characteristics of salt crust layers in the forestland.Slope aspects and soil texture and structure also have great effects on the distribution of salt crust;3) the temporal changes of salt crust are very significant.In an irrigation period,the EC of surface soil increases firstly,then decreases and levels off,salt crust generally forms since five days after irrigation.The EC of salt crust changes monthly with the variation of air temperature.Because of the dust deposition and litter accumulation on ground surface year by year,which leading to the great changes of topsoil structure, so with the development of forestland,the thickness of salt crust in the ground surface of forestland tends to be stable gradually,while the EC of it increases firstly and then decreases.