M. Amjadi - Department of Soil Science, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Islamic Republic of Iran.
H. Emami - Department of Soil Science, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Islamic Republic of Iran.
E. Farahani - Department of Soil Science, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Islamic Republic of Iran.
A. Gholoubi - University of Texas at Austin, Bureau of Economic Geology, Austin, TX, USA.

The aim of this research was to study soil structural stability indices of clay loam soil treated with organic amendments, using High Energy Moisture Characteristic (HEMC). For this purpose, three sizes of soil aggregates (۰.۵-۱, ۱-۲, and ۲-۴ mm) were treated with three rates (۰, ۱.۵, and ۳ %) of vermicompost and urban waste compost. After three months of incubation, water retention of the slow (۲ mm hˉˡ) and fast (۱۰۰ mm hˉ ˡ) wetted soil aggregates were measured at six pressure heads from ۰ to ۵۰ hPa, and HEMC stability indices such as Volume of Drainable Pores (VDP), Stability Index (SI), and Stability Ratio (SR) were determined. The results showed that only the stability of ۰.۵-۱ mm aggregates was significantly (P< ۰.۰۱) affected by organic treatments. The stability indices were significantly influenced by the rates of amendments, and increased with increasing their rates. However, the type of organic amendments had no significant effect on stability of aggregates. The mean ​​of VDP, SI, and SR decreased by increasing diameter of the aggregates and decreasing the rate of the organic amendments, due to breakdown of macro-aggregates and decrease of macropore fraction. In general, to increase structure stability of clay loam soil in arid regions of Iran, application of at least ۳% organic amendments is recommended.

Drainable pores, Soil amendments, Soil structure, Stability index, Stability ratio.