Certified Crop Advisor Practice Exam

What is the primary cause of nutrient leaching in sandy soils?

1. High organic matter

2. Low water-holding capacity

3. High clay content

4. Low pH

The correct answer is: Low water-holding capacity

The primary cause of nutrient leaching in sandy soils is closely related to their low water-holding capacity. Sandy soils are composed of larger particles, resulting in larger pore spaces, which allow water to flow through them quickly. This rapid drainage means that any dissolved nutrients present in the soil can be washed away easily with rainfall or irrigation water before the plants can uptake these essential nutrients. In contrast, soils with high organic matter or high clay content tend to retain water more effectively, which decreases the likelihood of nutrient leaching. High organic matter can bind nutrients and water, while clay particles have a smaller size and greater surface area, which helps retain moisture and nutrients in the soil matrix. Similarly, low pH, which indicates acidity, does not directly relate to the physical properties of sandy soils that facilitate leaching. Therefore, the inherent characteristics of sandy soils, particularly their low water-holding capacity, are the leading factor contributing to increased nutrient leaching.