Certified Professional Horticulturist (CPH) Practice Exam

What can enhance the water holding capacity of sandy soils?

1. Organic matter

2. Clay

3. Loam

4. Pebbles

The correct answer is: Organic matter

Organic matter is essential for enhancing the water holding capacity of sandy soils due to its unique physical and chemical properties. Sandy soils generally have larger particle sizes and larger pore spaces, which allows water to drain quickly, making it difficult for plants to retain moisture. Introducing organic matter—such as compost, leaf mold, or well-rotted manure—can significantly improve this situation. Organic matter increases the soil's ability to hold water by acting like a sponge. It fills in the gaps between the sandy particles, thereby increasing the surface area for moisture retention. Additionally, organic matter improves soil structure, which can enhance the formation of aggregates. This aggregation helps create smaller pore spaces that retain water more effectively while still allowing for good drainage. Furthermore, organic matter contributes to the nutrient-holding capacity of the soil, providing additional benefits for plant growth. Clay and loam can also improve soil water retention, but they function differently than organic matter. Clay has small particles that retain water but can create compaction issues, while loam is typically a balanced mixture of sand, silt, and clay, already having good water retention properties. Pebbles lack structural components to enhance water retention effectively, as they do not contribute any capacity for moisture storage. Understanding these dynamics is crucial for