Certified Crop Advisor Practice Exam

What happens to runoff as surface residue increases?

1. Runoff increases

2. Runoff remains constant

3. Runoff decreases

4. Runoff becomes unpredictable

The correct answer is: Runoff decreases

As surface residue increases, runoff typically decreases due to several interconnected factors related to how residue interacts with water and soil. Surface residue, such as crop residue or cover crops, plays a significant role in enhancing soil structure and promoting infiltration. When there is more residue on the surface, it creates a barrier that reduces the speed at which water can flow over the soil. This means that when rainfall occurs, more water is retained and allowed to infiltrate into the soil rather than running off the surface. Additionally, residue can help to slow down the water's movement, allowing for better absorption and reducing the chances of erosion. Furthermore, increased surface cover enhances soil moisture retention by reducing evaporation and protecting the soil from direct impact from raindrops, which might otherwise create compacted soil and reduce infiltration rates. In conclusion, as surface residue increases, the capacity of the soil to absorb water improves, leading to a decrease in runoff. This relationship highlights the importance of using residue management as a part of soil and water conservation practices in agriculture.