Soil moisture adsorption capacity and specific surface area in relation to water vapor pressure in arid and tropical soils

Abstract

This study is devoted to predict water vapour adsorption and hydro-physical properties of arid soils in middle Nile Delta (Farm of the Faculty of Agriculture, Shebin El-Kom, Egypt) and of tropical soils (Felix and INIAP Farms) in Quevedo zone, Los Rios, Ecuador. The vapour pressure and isothermal adsorption of water vapour is used to predict soil moisture adsorption capacity (Wa) and the specific surface area. To achieve these objectives, four soil profiles at different depths were investigated to indicate the status of hydro-physical properties of the studied area. The 1st & 2nd profiles are sandy loam (Felix Farm) and clay loam soils (Shebin El-Kom Farm), and 3rd & 4th are clay soils (INIAP Farm). Data of soil-water adsorption (W%) at different relative vapor pressures P/Po are obtained for the studied soil profiles, where the W% values increased with increasing P/Po from 1.87% to 10.01% in the 1st and 2nd sandy loam and clay loam soil profiles, and reached 27.44% in the 4th clay soil profile. The highest values of water adsorption capacity (Wa) were observed in the clay depths of 60 – 90 cm and 90 – 120 cm (INIAP-soil profiles) while the lowest values were in the subsurface depth (30 – 60 cm) of soil profiles 1st and 2nd. The other hygro-physical properties such as adsorbed layers and maximum hygroscopic water were obtained. The specific surface area (S) in sandy loam 1st&2nd soil profiles is ranged from 113m2/g to 187m2/g and raised to 385m2/g and 553m2/g in the 3rd & 4th clay soil profiles. The corresponded values of the external specific surface area (Se) ranged from 42m2/g to 98m2/g and 74 m2/g to 252 m2/g respectively. Two equations were assumed (1) to predict P/Po at water adsorption capacity (Wa), and (2) to apply Wa in prediction of soil moisture retention i.e., ѱ(W) function at pF < 4.5.