Certified Crop Advisor Practice Exam 2026 – Complete Study Resource

The choice of soil minerals as the least available source of nutrients for plants is correct because, while minerals constitute a significant reservoir of nutrients in the soil, their availability can be limited by various factors. Mineral nutrients exist in the form of solid particles within the soil matrix and must undergo weathering and other physical and chemical processes to become soluble and available for plant uptake.

Soil organic matter and plant debris are more readily available because they are made up of decomposed materials that can release nutrients like nitrogen, phosphorus, and sulfur into the soil as they break down. Fertilizers are specifically formulated to provide nutrients directly to plants in readily available forms, thus making them much more accessible than soil minerals.

Overall, while all sources play a role in nutrient availability, soil minerals typically require transformation and release processes before they can effectively contribute to plant nutrition, making them the least available in comparison to the other options listed.