Free CFA Soil Science and Testing Questions and Answers 1 — Questions and Answers
Question 1: A soil test report indicates a Cation Exchange Capacity (CEC) of 5 meq/100g. What does this value suggest about the soil's properties and nutrient management requirements?
- The soil is likely sandy, has a low capacity to hold nutrients, and requires frequent, smaller applications of fertilizer. (Correct answer)
- The soil is likely a heavy clay, has a high capacity to hold nutrients, and can be fertilized less frequently with larger amounts.
- The soil has a high organic matter content, excellent water retention, and minimal risk of nutrient leaching.
- The soil has a neutral pH, and most nutrients are readily available without the need for significant amendments.
Correct answer: The soil is likely sandy, has a low capacity to hold nutrients, and requires frequent, smaller applications of fertilizer.
A low Cation Exchange Capacity (CEC), typically below 10 meq/100g, indicates a soil with fewer negatively charged sites to hold onto positively charged nutrients (cations) like potassium, calcium, and magnesium. This is characteristic of coarse-textured, sandy soils. Because the soil cannot retain these nutrients well, they are more susceptible to leaching. Therefore, the best management practice is to apply smaller amounts of fertilizer more frequently to ensure nutrients are available when the crop needs them without excessive loss to the environment.
Question 2: A farmer plans to grow alfalfa, which thrives in a soil pH range of 6.5 to 7.5. A recent soil test shows the field has a pH of 5.5. Which of the following problems is the farmer most likely to encounter if the soil is not amended?
- Increased toxicity of aluminum and manganese, and reduced availability of phosphorus and calcium. (Correct answer)
- Deficiencies of iron and zinc, as they become less available in acidic conditions.
- Excessive availability of nitrogen, leading to overly vegetative growth and poor forage quality.
- Improved soil structure and water infiltration due to the acidic conditions.
Correct answer: Increased toxicity of aluminum and manganese, and reduced availability of phosphorus and calcium.
A soil pH of 5.5 is considered acidic. In highly acidic soils (generally below 6.0), the availability of essential macronutrients like phosphorus, calcium, and magnesium decreases. Conversely, the availability of certain metals, such as aluminum and manganese, increases to levels that can be toxic to many plants, including alfalfa. Iron and zinc availability actually increases in acidic soils, so deficiencies are unlikely. Nitrogen availability is also impacted, but not typically in a way that leads to excessive uptake.
Question 3: Which of the following soil components has the greatest influence on increasing both Cation Exchange Capacity (CEC) and water-holding capacity?
- Silt
- Sand
- Clay
- Organic Matter (Correct answer)
Correct answer: Organic Matter
Organic matter has a very high Cation Exchange Capacity (CEC), often ranging from 250 to 400 meq/100g, which is significantly higher than clay minerals. It also acts like a sponge, absorbing and holding large amounts of water, thereby greatly increasing the soil's water-holding capacity. While clay also contributes significantly to both CEC and water retention, the contribution of organic matter on a per-unit-weight basis is much greater.
Question 4: A soil test report shows a phosphorus (P) level of 15 ppm using the Mehlich-3 extractant. The recommendation is to apply 60 lbs of P2O5 per acre. The applicator has a fertilizer blend of 18-46-0. How many pounds of this fertilizer are needed to meet the phosphorus recommendation for one acre?
- 300 lbs
- 130 lbs (Correct answer)
- 60 lbs
- 46 lbs
Correct answer: 130 lbs
The fertilizer grade 18-46-0 means it contains 18% Nitrogen (N), 46% Phosphate (P2O5), and 0% Potash (K2O). To find the amount of fertilizer needed, divide the recommended amount of nutrient by the percentage of that nutrient in the fertilizer blend. Calculation: 60 lbs P2O5 / 0.46 = 130.4 lbs. Therefore, approximately 130 lbs of 18-46-0 are needed per acre.
Question 5: Which soil property is a measure of the soil's ability to resist changes in pH?
- Soil Texture
- Bulk Density
- Buffering Capacity (Correct answer)
- Porosity
Correct answer: Buffering Capacity
Buffering capacity is the ability of a soil to resist changes in pH. Soils with high clay content and high organic matter have a higher buffering capacity because they have a higher Cation Exchange Capacity (CEC). These soils require larger amounts of liming material to raise the pH compared to sandy soils with low CEC. Soil texture influences buffering capacity, but buffering capacity is the direct term for this resistance to pH change.
Question 6: An applicator is managing a field with coarse-textured soil and low organic matter. Which of the following is the most significant challenge they will face regarding nutrient management?
- Poor soil aeration leading to root diseases.
- High potential for nutrient leaching, especially nitrogen. (Correct answer)
- Difficulty in tilling the soil due to compaction.
- Excessive retention of phosphorus, making it unavailable.
Correct answer: High potential for nutrient leaching, especially nitrogen.
Coarse-textured soils, such as sands, have large particles and high porosity. This structure, combined with low organic matter, results in a low Cation Exchange Capacity (CEC) and poor water-holding capacity. Consequently, water and soluble nutrients like nitrate-nitrogen move rapidly through the soil profile, leading to a high potential for leaching beyond the root zone. This makes nutrient management challenging and requires strategies like split applications.
Free CFA Soil Science and Testing Questions and Answers 1
A soil test report indicates a Cation Exchange Capacity (CEC) of 5 meq/100g.
What does this value suggest about the soil's properties and nutrient management requirements?