Abstract
Soil salt crusts are special layers at soil surface which are widely distributed in the Trim Desert Highway Shelterbelt under drip-irrigation with high salinity groundwater. In order to reveal annual variation of their chemical characteristics, soil salt crusts in shelterbelt of different ages in hinterland of the Taklimakan Desert were sampled. SOM, total salt, inions and pH were analyzed. Following results were obtained. SOM of salt crusts increased with the shelterbelt ages, but increasing trend became lower gradually. Total salt, ions, and pH of salt crusts reduced gradually with the shelterbelt ages. Total salt of salt crusts in shelterbelt of different ages was much higher than shifting sandy land. Ions were higher than shifting sandy land, Cl-, Na+, and SO42- increased more obvious, then Mg2+, K+, Ca2+ and HCO3-, CO32- was little and nearly had no change. pH was all alkaline, pH of salt crusts in shelterbelt of 11 years was even lower than shifting sandy land. We can include that the quality of shallow soil (0~30 cm) in the Trim Desert Highway Shelterbelt becomes better gradually.
Highlights
Soil crusts are widely distributed in land surface, especially prevalent in arid and semiarid regions [1], and are mainly divided into physical crusts and biological crusts [2]
Physical soil crusts are a thin compacted layers formed at the soil surface by the combined action of raindrop impacting, splashing and physicochemical dispersion of the finer particulate matter blocking the soil porosities, or by the sedimentation action of finer particles carried by water current or still water on the soil surfaces [3]
Soil salt crusts are different from physical crusts or biological crusts; some scholar thought that it should be classified as chemical crusts individually in the soil crusts classification system [7]
Summary
Soil crusts are widely distributed in land surface, especially prevalent in arid and semiarid regions [1], and are mainly divided into physical crusts and biological crusts [2]. Biological soil crusts commonly result from the development of communities of micro-organisms on soil surface [4,5,6]. Soil salt crusts are special layers at the soil surface which are mainly formed by soluble salt crystallizing soil particles. As a result of drip-irrigation with local high salinity groundwater (2.8~29.7 g/L), soil salt crusts develop extensively in the shelterbelt [7,10]. Under salinity water drip-irrigation, salt accumulates at soil surface, and salt content of distribution layers of trees roots is lower, so salt-injuries don’t happen. Unexpected precipitations can leach salt of soil salt crusts downwards, if soil salt contents of distribution layers of roots exceeds trees’ salt-tolerance threshold, plants physiological drought might happen, even results in plants death. Unexpected strong precipitations happened in the summer of 2003 & 2005, which caused a lot Calligonum L. died and caused certain bad influence on protection of the shelterbelt
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