Moisture adsorption capacity and surface area as deduced from vapour pressure isotherms in relation to hygroscopic water of soils

Abstract

Six calcareous and alluvial soil profiles differing in their texture, CaCO3 and salinity were chosen from west and middle Nile Delta for the present study. The 1 st and 2 nd profiles from Borg El-Arab area were sandy loam in texture and > 30% CaCO3, while the 3 rd and 4 th profiles (from Nubaria area) were sandy clay loam and < 30% CaCO3. The 2 nd and 4 th profiles were taken from cultivated area with maize. The 5 th profile from Epshan area was non-saline clay alluvial soil and the 6 th from El-Khamsen was saline clay alluvial soil. The relation between soil moisture content (W%) and water vapour pressure (P/Po) was established for the mentioned soils. Data showed that the specific surface area (S) values were 34-53 and 44-60 m 2 /g for calcareous soils of Borg El-Arab and Nubaria areas, 206-219 and 206-249 m 2 /g for non-saline and saline clay alluvial soils of Epshan and El-Khamsen areas, respectively. The corresponding values of the external specific surface area (Se) were 16-21, 14-22, 72-86 and 92-112 m 2 /g. Submitting Wm + Wme as an adsorption boundary of moisture films (Wc) (where Wm is mono-adsorbed layer of water vapour on soil particles and Wme is the external mono-adsorbed layer), the maximum water adsorption capacity (Wa) was found to be Wc + Wme or Wm + 2Wme. It was ranged from 1.88 to 2.70%, 1.97 to 2.95%, 9.70-10.70% and 10.80 to 13.12% while the maximum hygroscopic water (MH) values were 2.43-3.78%, 2.91-4.65%, 16-17% and 18.30-21.9% for the studied soil profiles respectively. The residual moisture content (θr) at pF 7 and P/Po = 0 was ranged from 0.0005-0.0010%, 0.0007-0.0019% and 0.0043-0.0048% in Borg El-Arab, Nubaria and Epshan soil profiles, respectively. The inter-relations between the surface area and the hygroscopic moisture parameters of the soils under investigation were as follows: Calcareous soils; Wm = 0.40 MH, Wc = 0.55 MH, Wa = 0.70MH, S = 14 MH Non-saline soil; Wm = 0.35 MH, Wc = 0.49 MH, Wa = 0.63 MH, S = 13 MH Saline soil; Wm = 031 MH, Wc = 0.45 MH, Wa = 0.59 MH, S = 12 MH These relations give possibility to deduce the soil moisture adsorption capacities and specific surface area via maximum hygroscopic water, which can be obtained through the experimental determination of water vapor adsorption isotherms.

Water flow and conductivity into capillary and non-capillary pores of soils

“…As given in Amer (1993Amer ( , 2009), we used the water vapour adsorption isotherm method, with applying the BET theory to estimate the moisture adsorption capacity (Wa), which is considered to be immobile water content in a soil. Wa is equal to three layers of adsorbed water (films); Wa = Wm + 2Wme where, Wm is the mono-adsorbed layer of water vapor on soil particles, and Wme is the external mono-adsorbed layer of water vapor.…”

Effects of erosion and deposition on particle size distribution of deposited farmland soils on the chinese loess plateau

“…Studies on this topic improve our understanding on what kind of particle size was retained in the DFs as a result of human interventions against soil loss. This information may be required for the establishment of sediment budgets, implementing precision agriculture and estimating the potential of sediment for absorbing and transporting chemicals (Young, 1980;Ampontuah et al, 2006;Amer, 2009). In the case of the Yellow River in China, the main deposition materials raising the river streambed were particles > 0.05 mm, reducing the channel capacity and causing periodic flooding (Tang et al, 1993).…”

Water vapour adsorption on water repellent sandy soils

“…The adsorption isotherms measured on our materials exhibited typical sigmoidal shape (Fig. 2) that suggests occurrence of adsorption in multi-molecular layers rather than a monomolecular one (Amer, 2009). Figure 3 shows the main physicochemical characteristics estimated from the vapour adsorption isotherms by BET model.…”