Certified Professional Horticulturist (CPH) Practice Exam

What composition best describes the ideal soil?

1. 80% minerals, 2% organic materials, and the rest is pore space

2. 50% minerals, 2% organic materials, and the rest pore space

3. 25% clay, 25% sand, 25% silt, 25% pore space

4. 50% organic materials, 50% pore space

The correct answer is: 50% minerals, 2% organic materials, and the rest pore space

The ideal soil composition for most gardening and agricultural applications typically consists of a balanced mix that promotes both plant growth and healthy soil ecology. The answer that describes this best contains 50% minerals, 2% organic materials, and the remaining portion as pore space. Minerals in the soil are essential because they provide nutrients that plants need for growth. A composition where minerals make up half of the soil indicates a rich mineral content that can support a variety of plant life. The presence of organic materials, even at a modest 2%, is crucial as these contribute to soil structure, nutrient cycling, and overall fertility. Organic matter improves the soil's ability to retain moisture and provides food for beneficial microorganisms, which are vital for a healthy ecosystem. In addition, pore space is important for aeration and water infiltration. Having the correct balance of solids and pore space allows roots to access the necessary air and water while providing structure for the soil. Other options do not align with this ideal balance. For instance, an overabundance of organic matter or a specific ratio of clay, sand, and silt without the mention of adequate minerals can lead to deficiencies in nutrient availability or poor drainage, which may not support optimal plant growth.