Soil Structural Stability At near Saturation As Affected by Soil Properties and Condition.

Characteristics of soil-structure form portray the stability and resistance to changes imposed by external forces of the soil aggregates, and controls many processes vital to agricultural practices and the environment. The study presents and discusses results of water retention curves at near saturation (matric potential, ψ , 0 to -5 J kg^-1) obtained by the High Energy Moisture Characteristic (HEMC) method for soil samples from mostly semi-arid zones. Quantifying the differences in the water retention curves obtained by the HEMC method was achieved using the modified van Genuchten (1980) model that yielded soil structure indices (volume of drainable pores, modal suction, and model parameters, α and n that represent the location and the steepness of the S-shaped water retention curve). The structure indices and model parameters were then used to elucidate in quantitative terms possible interactions among soil properties and conditions or management practices. Evaluation of the behavior of the α and n parameters produced a clearer picture of the contribution of aggregate size to the pore size distribution and hence to soil structure stability. It is suggested that the use of the ratio of α/n could be applied for characterizing the effects of spatio-temporal variation on soil structural condition in soil-crop models. The presented detailed analyses of the contribution of soil inherent properties and extrinsic conditions to inter- and intra-aggregate porosity, structural index and model parameters at near saturation, sheds additional light on the processes that are involved in stabilizing soil structure, and may assist in developing more efficient soil and environment management practices to achieve and maintain stable soils.