Soil moisture distribution in deep layers and its response to different land use patterns on Loess Tableland

The characteristics of soil moisture distribution in 0～20 m loess profiles under different land use patterns and its relations with soil texture on the Changwu Loess Tableland were investigated for the optimal allocation of land use patterns and the study of regional hydrology and water resources. Results showed that physical clay in soil layers of red-brown paleosol was 2%-6% higher than in loess layers. Field capacity and wilting point were (21.39±0.13)% and (8.06±0.45)%, respectively. The characteristics of soil moisture distribution in deep layers were related to the loess- paleosol sequences. Generally, one paleosol layer and one loess layer constituteda up-down humidity level and there was an increasing trend in soil moisture with increased depth. The average soil moisture contents in the loess profiles in grassland was measured, 18-yr apple orchard, and 8-yr and 23-yr planted alfalfa grasslands were 18.89%, 15.45%, 14.77%, and 10.59%, respectively. The average soil moisture content at 0-13 m layer in high-yield wheat field was 18.74%. There was no soil desiccation below the depth of 3 m in high-yield wheat field and grassland. In 18-yr apple orchard, soil desiccation occured in the upper 10 m of the profile, being mainly moderate desiccation and light desiccation. In 8-yr planted alfalfa grassland, soil desiccation occured above 10 m of the profile, being severe desiccation, moderate desiccation, and light desiccation, and the severe desiccation occured above 4 m of the profile. In 23-yr planted alfalfa grassland, soil desiccation occured in the whole loess profile and the severe desiccation occured in the upper 17 m of the profile. The soil desiccation caused by negative water balance can gradually develop to deep soil layers with age in planted woodland and grassland and it is more prominent in alfalfa grassland.