Identifying development degree of some soils calcareous in nature at the eastern desertic rim of Beni Suef governorate, Egypt

الملخص EN

This work aimed at identifying the profile maturity of some calcareous soils developed on different geomorphic units of Wadi Sannur, i.e., Wadi Terraces, Wadi bottom and Wadi fan under different intensive geochemical weathering conditions at the eastern desert rim of Beni Suef Governorate, Egypt.

The morphological description indicate that the investigated soils have soil profiles vary in soil depth and texture, beside they represent different development stages (recent, moderate and more developed).

These variations are clarified by the genetic sequences of carbonate accumulation and modification of the soil structure from massive to well defined subangular blocky, which is more related to the combinations of calcic horizons to gross shifts in landscape position and soil truncation or sediment deposition.

The more developed profile is characterized by surface lime-crust, which is considered as a function of soil physico-chemical management, in addition to subsoil calcic and gleyic horizons.

These conditions reflecting the more arid and humid conditions at the top and bottom of soil profile, respectively.

Also, soil physical properties showed that soil texture tended towards the finest in mid-profile with increasing the intensity of chemical weathering due to the migration or accumulation of secondary CaCO3 particles in situ.

The previous process is associated with decreasing the values of soil bulk density and permeability versus increasing soil strength and available water.

Data obtained showed an increase in the inherited salts, soil pH and CEC associated with the intensive weathering, the reverse was true for the exchangeable sodium percent.

Soluble salts content exhibited an alternative pattern or a regular increase towards soil surface due the upward movement for the moderate or more developed profile, respectively.

The specific soluble ions pattern reveal that Na+ and Cl- dominated in the recent soil profile, however, Ca2+, Mg2+, SO42- and HCO3- dominated in soil solutions of the more developed one as a result of carbonation process.

Mineralogical data indicate that, there was an apparently uniform for the soil parent materials due to the similarity of resistant heavy mineral ratios within profile layers, except for the more developed one that exhibited multi-deposition environment.

Soil development degree could be also detected by the pedogenic criteria of low weathering values.

The intensive weathering media are characterized by high content of alkaline earth cations such as Ca2+ and Mg2+, which enhanced the formation of magnesium bearing clays (palygorskite, sepiolite and vermiculite), beside calcite and dolomite as authogenic minerals.The intensive chemical weathering enhance release of plant nutrients from nutrient-bearing minerals that towards the secondary fraction, however, the relative high values of soil pH, active CaCO3 and Ca2+ controlled the availability of many of these nutrients, especially phosphorus and micronutrients.