CCA - Certified Crop Advisor Soil Fertility and Analysis Questions and Answers 1 — Questions and Answers
Question 1: A soil test report for a field with a history of corn production indicates a Cation Exchange Capacity (CEC) of 8 meq/100g. Which of the following management strategies is most appropriate for this field?
- Applying higher rates of nitrogen fertilizer less frequently.
- Utilizing split applications of nitrogen and potassium fertilizers. (Correct answer)
- Incorporating large amounts of sand to improve drainage.
- Liming to significantly increase the soil pH above 7.5.
Correct answer: Utilizing split applications of nitrogen and potassium fertilizers.
A CEC of 8 meq/100g is relatively low, characteristic of a sandy or low organic matter soil. [3, 4] This indicates a lower capacity to hold positively charged nutrients (cations) like potassium (K+) and ammonium (NH4+). [2, 35] Therefore, nutrients are more susceptible to leaching. Split applications of mobile nutrients like nitrogen and potassium ensure a more continuous supply to the crop throughout the growing season and minimize losses. Applying high rates at once would increase the risk of leaching beyond the root zone.
Question 2: A farmer observes interveinal chlorosis on the newest, upper leaves of his soybean plants. The field has a soil pH of 7.8. Which nutrient deficiency is the most likely cause of these symptoms?
- Nitrogen (N)
- Potassium (K)
- Magnesium (Mg)
- Iron (Fe) (Correct answer)
Correct answer: Iron (Fe)
Iron (Fe) deficiency is commonly characterized by interveinal chlorosis (yellowing between the veins) on the youngest or uppermost leaves because iron is immobile within the plant. [9] This condition, often called iron deficiency chlorosis (IDC), is frequently observed in high pH (alkaline) soils, as high pH reduces the availability of iron for plant uptake. [9, 31] Nitrogen, potassium, and magnesium are mobile nutrients, so deficiency symptoms would typically appear first on the older, lower leaves. [10]
Question 3: Which of the following soil sampling strategies is best suited for a large, non-uniform field with significant variations in soil type, topography, and past yield, where the producer has variable-rate application technology?
- Composite sampling using a random zigzag pattern across the entire field.
- Grid sampling. (Correct answer)
- Sampling only the historically high-yielding areas.
- Taking a single composite sample from the center of the field.
Correct answer: Grid sampling.
Grid sampling involves dividing a field into a grid of smaller, uniform-sized areas (e.g., 1-4 acres) and collecting a separate composite sample from each grid cell. [11, 17] This method is ideal for identifying and mapping in-field variability of nutrient levels and other soil properties. The resulting data can be used to create prescription maps for variable-rate applications of fertilizers and lime, targeting inputs precisely where they are needed, which is highly effective for large, non-uniform fields. [11]
Question 4: A routine soil analysis report indicates a soil pH of 5.2. At this pH, which essential macronutrient's availability is most likely to be significantly limited?
- Iron (Fe)
- Manganese (Mn)
- Phosphorus (P) (Correct answer)
- Zinc (Zn)
Correct answer: Phosphorus (P)
In strongly acidic soils (pH below 5.5), the availability of essential macronutrients like phosphorus (P), potassium (K), sulfur (S), calcium (Ca), and magnesium (Mg) is significantly reduced. [16] Phosphorus, in particular, becomes less available due to fixation by aluminum and iron compounds, which are more soluble at low pH. While micronutrients like iron, manganese, and zinc are generally more available at lower pH, macronutrient availability is a primary concern in this range. [16, 26, 31]
Question 5: When interpreting a soil test report, what does the 'Buffer pH' value primarily help determine?
- The amount of readily available nitrogen in the soil.
- The soil's Cation Exchange Capacity (CEC).
- The amount of lime required to raise the soil pH to a desired level. (Correct answer)
- The potential for phosphorus runoff from the field.
Correct answer: The amount of lime required to raise the soil pH to a desired level.
The buffer pH test is performed when the initial soil pH is acidic (typically below 6.0). [24] It measures the soil's resistance to a change in pH, which is also known as its buffering capacity. This value is used by soil testing labs to provide a precise recommendation for the amount of agricultural lime needed to neutralize the soil's acidity and raise the pH to the target level for the intended crop. [24]
Question 6: Which of the following is considered a primary macronutrient essential for corn growth and is required in quantities similar to nitrogen?
- Sulfur (S)
- Potassium (K) (Correct answer)
- Calcium (Ca)
- Zinc (Zn)
Correct answer: Potassium (K)
The primary macronutrients are Nitrogen (N), Phosphorus (P), and Potassium (K). [18, 20] Corn requires large quantities of potassium, with total crop uptake levels often similar to those of nitrogen. [27] While secondary macronutrients like sulfur and calcium and micronutrients like zinc are essential, they are required in smaller amounts than N and K. [20, 27]
CCA - Certified Crop Advisor Soil Fertility and Analysis Questions and Answers 1
A soil test report for a field with a history of corn production indicates a Cation Exchange Capacity (CEC) of 8 meq/100g.
Which of the following management strategies is most appropriate for this field?