Mechanism of formation of physical soil crust in desert soils treated with straw checkerboards

Abstract

An experiment was conducted in early March 2003 on 0.5, 1 and 1.5 m 2 straw checkerboard plots on the windward slope and leeward slope of a sand dune on the southeastern edge of Tengger desert, China, to study the mechanism of formation of physical soil crust in desert soils. The samples collected after 1 year were analyzed by sedimentation method, results demonstrated that in the 0.5, 1 and 1.5 m 2 straw checkerboards, the contents of the finer particulate matter sorted by wind are 1.5, 34.75, and 13.92 times of that of the blown sand, and the contents of the finer particulate matter on the windward slope are 1.77, 1.17 and 1.34 times of the counterparts on the leeward slope, respectively. The stable concave curved surfaces is most easily formed in the 1.0 m 2 straw checkerboards among the three sizes of straw checkerboards but not formed in 0.5 m 2 straw checkerboards. The sorted finer particulate matter, that cannot be buried by extrinsic sand under the protection of the stable concave curved surfaces developed in suitable size of straw checkerboards, provide material base of physical soil crust formation. Dustfall collected in this region was analyzed including its size distribution by sedimentation, chemical elements by X-ray fluorescence and mineral components by X-ray diffraction. The contents of the finer particulate matter of dustflall are more than 412 times of that of the blown sand. The enrichment factors of Zn, Pb, Ca, Mg and K in the aeolian dustfall are 2.14 ± 0.279 (mean ± S.E.), 4.00 ± 0.670, 2.61 ± 0.336, 1.21 ± 0.131 and 1.21 ± 0.076, respectively. The mineral contents of chloride, illinite, calcite, dolomite and gypsum in the dustfall are significantly higher than those in the blown sand. Dustfall accelerates the formation and evolution of physical soil crust. Precipitation is an important dynamic factor to physical soil crust formation in the sand-stabilized desert soils.