Assessment of Hydraulic conductivity in Iraqi soils (Articular review)

Abstract

    Given the importance of hydraulic conductivity in agriculture—particularly in determining soil’s ability to transport water through its pores—understanding this property is essential for improving productivity, minimizing water and nutrient loss, enhancing soil aeration, selecting suitable crops, managing salinity, and optimizing fertilizer efficiency. Therefore, this article aims to assess hydraulic conductivity and highlight the key factors influencing it. The average hydraulic conductivity values in different regions of Iraq were recorded as follows: 3.36 cm•h⁻¹ in the north, 2.24 cm•h⁻¹ in the central and southern regions, and 2.95 cm•h⁻¹ in the west. A review of previous studies indicates that gypsum and its concentration significantly affect hydraulic conductivity. When added to the soil, gypsum increases pore size, thereby enhancing hydraulic conductivity. Additionally, the dissolution of small gypsum crystals in moist soils leads to soil disintegration and an increase in pore spaces, which improves soil permeability and consequently enhances hydraulic conductivity. The presence of salts also influences hydraulic conductivity, depending on the dominant salt type. Calcium and magnesium salts promote soil particle aggregation, increasing hydraulic conductivity. In contrast, monovalent ions such as sodium cause soil swelling and particle dispersion, leading to reduced conductivity. This effect is exacerbated in soils dominated by 2:1 clay mineral, unlike 1:1 clay mineral, which are less affected by increased SAR (Sodium Adsorption Ratio) and ESP (Exchangeable Sodium Percentage). The impact of sodium begins at 5% and worsens at 15% or more, particularly in soils with higher clay content, which increases bulk density and decreases hydraulic conductivity. Tillage practices and the type of plow used also significantly influence hydraulic conductivity. Studies show that chisel plows yield the highest conductivity values compared to other plows across different soil types. Additionally, conductivity values tend to decrease with soil depth. Research further indicates that incorporating organic residues—regardless of type and source—or biochar (whether derived from plant or animal materials) enhances hydraulic conductivity. Moreover, hydraulic conductivity is not only affected by the solid phase of the soil but also by the type and properties of the infiltrating fluid, as it depends on the density and concentration of the percolating liquid.