Certified Professional Horticulturist (CPH) Practice Exam

Which of these soil types has the smallest particle size?

1. Silt

2. Sand

3. Loam

4. Clay

The correct answer is: Clay

The soil type that has the smallest particle size is clay. Clay particles are less than 0.002 millimeters in diameter, making them significantly finer than other soil types like sand and silt. This small particle size provides clay with unique properties, such as a high surface area to volume ratio, which allows it to hold water and nutrients effectively. Clay's fine texture also results in a high cohesion between particles, leading to compacted soils that can inhibit drainage and root penetration. Understanding clay's characteristics is essential for plant growth and soil management since these properties influence water retention, nutrient availability, and soil structure. In contrast, sand consists of larger particles, followed by silt, which has an intermediate size, and loam, which is a mixture of sand, silt, and clay, without being defined by the smallest particle size.