DEPENDENCE OF THE DEGREE OF LINEAR POLARIZATION IN SCATTERED VISIBLE LIGHT ON SOIL TEXTURAL FRACTIONS

Soil texture is an important factor for determining input information about agricultural projects such as irrigation designs, fertilization treatments, and power requirements of farm machinery. Determination of soil textures in the laboratory using traditional methods is labor and time intensive. A quick and relatively easy method was developed to achieve this purpose using light polarization. Preliminary measurements based on Stokes polarimetry were made to examine the feasibility of estimating soil texture by measuring the degree of linear polarization (P) in light scattered by soil surface layer (0–30 cm) samples. Samples were collected at 18 locations along a transect from Alexandria to Sidi Barrani on the northwestern coast of Egypt. These samples represent a broad range of soil types and textures. The results from this study show that the soil textural fractions (% sand, % silt, and % clay) were linearly related to P in the scattered visible light. For a given particle size fraction, the relationship was especially strong for a preferred wavelength. The best-fitted regression lines (R2 > 0.99) were % sand = 66.53 − 64.10 P for 470 nm, % silt = 10.35 + 40.65 P for 420 nm, and % clay = 4.92 + 44.44 P for 410 nm. These findings indicate that there is potential for development of a laboratory procedure to rapidly determine the texture of soil samples. However, the results also raised questions about the effects that need to be investigated so that they can be more fully understood and the steps in the procedure can be standardized.