A preliminary investigation of the dynamic characteristics of dried soil layers on the Loess Plateau of China

Serious soil desiccation, resulting from climatic conditions and poor land management, may lead to the formation of a dried soil layer (DSL), which can negatively affect ecological and hydrological processes. To mitigate these effects through management, it is necessary to understand property interactions within DSLs, compared with those in the whole soil profile, and DSL formation processes under different land uses. We investigated the relationships between soil water content (SWC) and plant root indices, and other soil properties, under various land uses in the Liudaogou watershed on the Loess Plateau, China. We also studied the development of DSLs as a function of the growth age of two vegetation types. Rate of formation and thickness of DSLs were dependent on vegetation type: DSLs formed after 2 years of alfalfa (Medicago sativa) growth and 3 years of Caragana korshinskii growth; after 4 years of growth, DSLs under alfalfa were thicker than those under C korshinskii, but after 31 years the DSL thickness under C korshinskii (4.4 m) exceeded that formed under alfalfa (3 m). The more persistent DSLs occurred below a 100 cm thick upper soil layer that was seasonally dried and replenished by rainfall under both vegetation types. The degree of soil desiccation under natural vegetation was generally less than that under non-indigenous plant species, and was similarly less over a period of about 30 years for a natural plant succession sequence than for an artificial one. Thus, the use of natural vegetation succession management principles would possibly reduce soil desiccation during vegetative restoration. Densities of root length, weight, and surface area, and the average root diameter of soybean (Glycine max), alfalfa, Stipa bubgeana, and C korshinskii all decreased with increases in soil depths below 20 cm. Correlations between SWC and root indices, and various soil physical and chemical properties, were generally weaker within the DSL layers than within the whole soil profile. The only significant correlation was between soil organic carbon and SWC under alfalfa (r = 0.627, P < 0.05). Soil desiccation may thus interfere with these typical interrelationships occurring within the whole soil profile. Our findings may provide a helpful base reference for the control and restoration of DSLs occurring on the Loess Plateau and in similar and and semi-arid regions. (C) 2009 Elsevier B.V. All rights reserved.