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 ofarid 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. Thevapour pressure and isothermal adsorption of water vapour is used to predict soil moistureadsorption capacity (Wa) and the specific surface area. To achieve these objectives, four soilprofiles at different depths were investigated to indicate the status of hydro-physicalproperties of the studied area. The 1st & 2nd profiles are sandy loam (Felix Farm) and clayloam soils (Shebin El-Kom Farm), and 3rd & 4th are clay soils (INIAP Farm). Data of soilwater adsorption (W%) at different relative vapor pressures P/Po are obtained for thestudied soil profiles, where the W% values increased with increasing P/Po from 1.87% to10.01% in the 1st and 2nd sandy loam and clay loam soil profiles, and reached 27.44% in the4th clay soil profile. The highest values of water adsorption capacity (Wa) were observed inthe clay depths of 60 – 90 cm and 90 – 120 cm (INIAP-soil profiles) while the lowest valueswere in the subsurface depth (30 – 60 cm) of soil profiles 1st and 2nd. The other hygrophysical properties such as adsorbed layers and maximum hygroscopic water wereobtained. The specific surface area (S) in sandy loam 1st&2nd soil profiles is ranged from113m2/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 to98m2/g and 74 m2/g to 252 m2/g respectively. Two equations were assumed (1) to predictP/Po at water adsorption capacity (Wa), and (2) to apply Wa in prediction of soil moistureretention i.e., ѱ(W) function at pF < 4.5.