Certified Crop Advisor Practice Exam

Which of the following increases as a soil's clay content increases?

1. drainage capacity

2. surface area

3. organic matter

4. water retention

The correct answer is: surface area

The choice that identifies the increase in a soil's clay content as benefiting the surface area is accurate because clay particles are extremely small and have a high surface area relative to their volume. This vast surface area is significant because it allows for greater interaction with water, nutrients, and organic matter. The fine particles of clay create more sites for chemical reactions and bonding, leading to enhanced soil fertility and nutrient retention capabilities. In contrast, drainage capacity generally decreases with increased clay content due to clay's ability to compact and create denser soil structures, leading to reduced pore space and slower movement of water through the soil. While a higher clay content can allow clay minerals to hold onto organic matter, it does not directly result in an increase in the amount of organic matter present. Lastly, water retention does increase with higher clay content, but it is not the correct option here, as the question focuses specifically on surface area. Hence, the significant surface area that comes with increased clay content distinguishes it as the most relevant factor among the provided choices.