Certified Crop Advisor Practice Exam

What is the best measure of plant available P in a soil?

1. Soil pH

2. Soil texture

3. Soil test P

4. Soil moisture

The correct answer is: Soil test P

The best measure of plant available phosphorus (P) in soil is soil test P. This measurement is conducted through a series of standardized laboratory tests that assess the concentration of phosphorus present in the soil that is readily available for plant uptake. These tests typically involve adding a specific chemical extractant to a soil sample, which helps to solubilize phosphorus compounds. The amount of phosphorus extracted gives a clear indication of how much is available for plant use. Soil test P is essential for determining the need for phosphorus fertilization in agricultural practices. Regular soil testing allows growers to make informed decisions regarding nutrient management, ensuring that crops receive sufficient phosphorus to support healthy growth and maximize yields. In contrast, soil pH can influence phosphorus availability but does not directly measure it. Soil texture affects nutrient retention and drainage but is not a direct measure of phosphorus availability. Soil moisture is important for overall plant health and nutrient transport but does not provide specific information about phosphorus levels in the soil. Therefore, soil test P is the most accurate and reliable indicator of how much phosphorus is available to plants.