Certified Crop Advisor Practice Exam

What soil pH level is generally optimal for nutrient availability in most crops?

1. 4.5-5.0

2. 5.5-6.5

3. 6.5-7.5

4. 7.5-8.5

The correct answer is: 5.5-6.5

A soil pH level of 5.5 to 6.5 is generally considered optimal for nutrient availability in most crops. At this pH range, essential nutrients such as nitrogen, phosphorus, potassium, and micronutrients are most soluble and therefore accessible to plant roots. In this slightly acidic to neutral range, beneficial soil microorganisms thrive, promoting healthy soil structure and nutrient cycling. Soil pH significantly affects chemical reactions in the soil, influencing the availability of nutrients which can be beneficial or detrimental to crop growth depending on their solubility. When pH levels drop below this range, as seen in more acidic soils (4.5-5.0), the availability of nutrients like phosphorus and calcium decreases while levels of elements like aluminum and manganese may become toxic. Conversely, in alkaline conditions (7.5-8.5), certain micronutrients may become less available due to precipitation, significantly impacting plant health and crop yields. Therefore, maintaining a soil pH of approximately 5.5 to 6.5 is key for balanced nutrition and optimal crop performance.