Variation of Soil Physical Properties and Moisture Content Along Toposequences in the Arid to Semiarid Area

Accurate prediction and characterization of the spatial distribution and temporal
variation of soil water is indispensable to optimize the use and management of land
within dry areas, which suffer from limited arable land and water resources. The objective of this research is to examine the effect of hillslope position and characteristics on soil properties and variation of soil moisture in an arid to semiarid region.
Five transects representing toposequences in the transitional Arid to Semiarid Mediterranean region of Jordan were selected to study the effect of hillslope position on soil properties and variation of soil moisture. Four sites representing different hillslope positions were chosen within each transect from the summit down to the toeslope. Soil profile, at each position, was described and sampled for laboratory analyses. Moisture content at different depths was monitored during the rainy season. The results indicated a systematic relationship between topographic characteristics (hillslope position, slope steepness, and curvature) and the particle size distribution. Soil erodibility was found to be indirectly related to topographic position as extrapolated from the consistent relationship with clay content. Soil moisture content was related to the topographic position, the variation in clay content, and vegetation condition. The topographic position was found to govern the flow of water from upper to lower positions, resulting in higher moisture availability at lower positions. The variations of other parameters were not only related to the topographic position of particular soil, but also to the characteristics of the soil at the upper positions, and to the sequence in which that soil is positioned in the toposequence. Understanding the distribution of soil properties and their relationship along the soil-landscape continuum, which is unique to this environment, should improve the prediction of soil properties and improve plans to better manage arid land.