Step 1: Understanding the Concept:
Soil texture refers to the relative proportions of various sizes of mineral particles in the soil.
The particles are categorized into "Soil Separates": Sand, Silt, and Clay.
The International Society of Soil Science (ISSS) system provides a standardized classification based on the diameter of these particles in millimeters (mm).
Descending order means arranging them from the largest diameter to the smallest.
Step 2: Detailed Explanation:
Let's look at the specific size ranges defined by the ISSS system:
1. Coarse Sand (D): These are the largest particles in the list. Their diameter ranges from 2.0 mm to 0.2 mm. You can easily see individual grains with the naked eye. Coarse sand provides high aeration but has very low water-holding capacity.
2. Fine Sand (C): These particles are smaller than coarse sand, ranging from 0.2 mm to 0.02 mm in diameter. They still feel gritty to the touch.
3. Silt (B): Silt particles range from 0.02 mm to 0.002 mm. They are too small to be seen individually without a microscope. Silt feels smooth and floury when dry and slippery (not sticky) when wet.
4. Clay (A): Clay consists of the finest particles, with a diameter less than 0.002 mm. Clay particles have a massive surface area and are responsible for most of the chemical activity in the soil (like nutrient retention). They feel sticky and plastic when wet.
Order of size: Coarse sand (D) > Fine sand (C) > Silt (B) > Clay (A).
Thus, the descending order is D, C, B, A.
Step 3: Final Answer:
By following the standard soil separate sizes (Coarse Sand > Fine Sand > Silt > Clay), we arrive at the sequence D, C, B, A.
The correct answer is option (C).