| Caliche nodule is a product from soil genesis process,soil erosion and human activities especially in the wind-water erosion crisscross region of the Loess Plateau the caliche nodules often gather in surface soil.Due to the size and hydraulic properties of caliche nodule different from soil particle,it can affect soil evaporation,infiltration and surface runoff and sediment yield.As being a medium with high water absorption,caliche nodule can also affect the estimation of soil water storage.In this study,we took the caliche nodule presenting in Liudaogou small catchment in the wind-water erosion crisscross region of the Loess Plateau as an object and investigated spatial distribution of caliche nodule and its influencing factors through field sampling,effects of caliche nodule content on soil water distribution in soil column profile and soil water storage,and the variation characteristics of soil temperature and soil water in the plots with caliche nodules mulching by field in-situ observation.We draw following conclusions:(1)Caliche nodule content in topsoil indicated intensity of soil erosion on hillslopes.Soil clay particle decreased gradually along the hillslopes.Caliche nodule content showed a distribution pattern of single peak along the hillslopes and it achieved peak value(10-15 %)at the position of 1/4-1/3 hillslopes(about 20-30 m distance from the top of the hillslopes).Caliche nodule content was positively correlated with slope gradient.It had a single peak curve relationship between caliche nodule content and vegetation above-ground biomass.This peak value was the threshold point of vegetation affecting caliche nodule content and the vegetation coverage at the threshold point was among 11-16 %.Slope gradient and vegetation were two most important factors to control caliche nodule distribution on the hillslopes.Small size caliche nodules spread more widely on the hillslopes and meanwhile their numbers were the most.The dominant size of caliche nodule was 5-15 mm.(2)Field in-situ observation showed that caliche nodule affected soil temperature and soil water.The average soil temperature in bare soil land was the highest and in the land with vegetation and caliche nodule mulching was the lowest.The difference in soil temperature for different months was significant(P < 0.05)under four land uses: bare soil,vegetation cover,caliche nodule cover and both vegetation and caliche nodule cover.In addition,the variability coefficient of soil temperature in 0-5 cm soil layer were moderate in September.The variability coefficient increased with increasing soil depth.In top 50 cm soil layer,the changes of soil water content under different vegetation-caliche nodule coverage conditions were different.Variation range of soil water in bare soil land was the smallest.Caliche nodule affected measurement result of soil water,especially in the positions of 60 cm and 80 cm soil layers.(3)Caliche nodule can affect soil water distribution in soil column.The distribution pattern of caliche nodule water content(CWC)along the profile for different treatments were different from that of soil water content(SWC).Soil water storage(SWS)between top soil layer and bottom soil layer had no significant difference when soil contained relatively high caliche nodule content(CNC= 0.2,0.3 and 0.4)(P > 0.05).When CNC ? 0.1,the difference in SWS for top soil layer and bottom soil layer were significant(P < 0.05).Both caliche nodule water storage and its available water storage increased with increasing caliche nodule content.The SWS could be underestimated by 3.02%,7.96%,10.49% and 16.88%,respectively for the soils with CNCs of 0.1,0.2,0.3 and 0.4,respectively.Available water storage in caliche nodules accounted for almost half of total caliche nodule water storage. |
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