Available Phosphorus Assessment of Gharb El-Mawhoob Soils, El-Dakhla Oasis, Egypt

Thirty-four soil samples were collected from Garb El-Mawhob soils, northwest of El-Dakhla oasis, New Valley governorate, Egypt to evaluate the soil available phosphorus and its relation with the properties of these soils. These samples were taken from the surface (0-30 cm) and subsurface layers (30- 60 cm) of 17 soil profiles covered the study area. Most of the soil samples had a texture of loamy sand, sandy clay loam and clay. In most cases, the studied soils showed mild alkaline pH (7.4 to 7.8) values. The electrical conductively (EC_e) and CaCO₃ of these soils varied from low to high levels and ranged from 1.05 to 163 dS/m and from 2.2 to 57.58%, respectively. The soil organic matter content differed from 0.08 to 2.27%. Also, the soluble cations and anions in most of the studied soils followed the order of Ca⁺² >Na⁺> Mg⁺² > K⁺ and Cl^- > SO₄⁼ > HCO₃^-, respectively. The cation exchange capacity (CEC) and sodium adsorption ratio (SAR_e) of these soils were ranged from 6.58 to 57.49 cmolcÅ/kg and from 0.11 to 45.18%, respectively.
The NaHCO₃-extractable soil phosphorus of these soils varied from 2.25 to 65.35 mg/kg in the surface layer and from 3.34 to 24.49 mg/kg in the subsurface one. In general, about 50% of the studied soil samples had a low level of available P (< 6 mg/kg), 24% of them showed a medium level (6 -10 mg/kg) and 26% of them contained a high level of available P (>10 mg/kg). Moreover, the studied soil samples that had clay and clay loam textures contained a high level of available P than those having other textures. The available P showed highly significant positively correlation, with some  soil properties, such as OM, HCO₃^-, CEC and silt contents, while it was negatively correlated with EC_e, Na⁺,CaCO₃ and Ca⁺².