She Dongli

Profile characteristics of temporal stability of soil water storage in two land uses

Information on soil water storage (SWS) within soil profiles is essential in order to characterize hydrological and biological processes. One of the challenges is to develop low cost and efficient sampling strategies for area estimation of profile SWS. To test the existence of certain sample locations which consistently represent mean behavior irrespective of soil profile wetness, temporal stability of SWS in ten soil layers from 0 to 400xa0cm was analyzed in two land uses (grassland and shrub land), on the Chinese Loess Plateau. Temporal stability analyses were conducted using two methods viz. Spearman rank correlation coefficient (rs) and mean relative differences. The results showed that both spatial variability and time stability of SWS increased with increasing soil depth, and this trend was mainly observed at above 200xa0cm depth. High rs (pu2009<u20090.01) indicated a strong temporal stability of spatial patterns for all soil layers. Temporal stability increased with increasing soil depth, based on either rs or standard deviation of relative difference index. The boundary between the temporal unstable and stable layer of SWS for shrub land and grassland uses was 280 and 160xa0cm depth, respectively. No single location could represent the mean SWS for all ten soil layers. For temporal stable layers, however, some sampling locations could represent the mean SWS at different layers. With increasing soil depth, more locations were able to estimate the mean SWS of the area, and the accuracy of prediction for the representative locations also increased.

Comparison of soil hydraulic properties with different levels of soil salinity and sodicity

Increases in soil salinity and/or sodicity are degrading soils worldwide. To address the problem, more information is needed about the effects of salinity and sodicity on soil hydraulic properties, as well as on the relative effects of other interacting soil properties. In this study, tests were conducted using an infiltrometer with negative hydraulic heads (0, −3, −6, and −9xa0cm) to compare the soil hydraulic properties of two kinds of soils (soil 1: a sullage-puddle silt soil collected from a coastal reclamation region in China; soil 2: a yellow brown soil collected from a water-saving area) with different soil salt contents. The results showed that with increasing soil salt content, the parameters including the steady infiltration rate, sorptivity, and the unsaturated hydraulic conductivity decreased with decreasing negative heads for soil 2. As the soil salt contents decreased for soil 2, the contribution of fine pores (<0.1xa0mm) to water flow increased, while that of macropores (>0.5xa0mm) decreased. Soil salt content had no significant effects on the hydraulic conductivity of soil 1 due to its very poor soil structure that the salt could not make significantly worse. Soil texture played a major role in determining whether soil salt contents would significantly affect hydraulic properties.