CFA Soil Properties and Testing Questions and Answers 1 — Questions and Answers
Question 1: A soil test report for a sandy loam field indicates a low Cation Exchange Capacity (CEC). Which of the following fertilizer application strategies is most appropriate for this field?
- A single, heavy application of fertilizer prior to planting.
- Split applications of fertilizer in smaller, more frequent doses throughout the growing season. (Correct answer)
- A large application of lime to dramatically increase the soil pH.
- Applying fertilizer only in the fall to allow it to incorporate over the winter.
Correct answer: Split applications of fertilizer in smaller, more frequent doses throughout the growing season.
Soils with a low Cation Exchange Capacity (CEC), such as sandy soils, have a reduced ability to hold onto positively charged nutrients (cations) like potassium and ammonium. This makes them prone to nutrient loss through leaching. Split applications of fertilizer in smaller, more frequent doses ensure that nutrients are available to the crop when needed and minimize the risk of them washing away.
Question 2: Which of the following soil properties has the most significant influence on the availability of nutrients to plants, often referred to as the 'master variable' in soil fertility?
- Soil texture
- Soil organic matter
- Soil pH (Correct answer)
- Bulk density
Correct answer: Soil pH
Soil pH is often called the 'master variable' because it directly controls the chemical reactions that determine whether nutrients are in a form that plant roots can absorb. For example, in highly acidic soils, phosphorus can become 'locked up' with iron and aluminum, making it unavailable. Conversely, in highly alkaline soils, micronutrients like iron and manganese become less available.
Question 3: A farmer receives a soil test result showing an optimal pH and adequate potassium levels, but a very low level of organic matter. Which of the following issues is most likely to be a concern for fertilizer management on this field?
- Increased risk of phosphorus fixation.
- Poor water infiltration and increased runoff potential. (Correct answer)
- Toxicity from an overabundance of micronutrients.
- Difficulty in adjusting the soil's pH with liming agents.
Correct answer: Poor water infiltration and increased runoff potential.
Soil organic matter is crucial for creating good soil structure by binding soil particles into aggregates. This improves porosity, which allows for better water infiltration and reduces the likelihood of surface runoff and erosion. Low organic matter can lead to a compacted soil surface, causing water and surface-applied fertilizers to run off the field instead of soaking in.
Question 4: When interpreting a soil test report, the values for phosphorus (P) and potassium (K) are typically listed as 'low', 'optimum', or 'high'. If a soil test comes back in the 'high' range for phosphorus, what is the general recommendation for phosphorus fertilizer application?
- Apply a starter fertilizer high in phosphorus to boost early growth.
- Apply the standard recommended rate for the crop to be grown.
- No phosphorus fertilizer is needed, and application should be avoided. (Correct answer)
- Double the application rate to build soil reserves for future crops.
Correct answer: No phosphorus fertilizer is needed, and application should be avoided.
A 'high' soil test level indicates that the soil already contains sufficient phosphorus to meet the crop's needs, and adding more fertilizer is unlikely to increase yield. In fact, applying unnecessary phosphorus can have negative environmental consequences, such as contributing to water pollution. Therefore, no additional phosphorus fertilizer is recommended.
Question 5: A certified applicator is preparing to fertilize a field with a heavy clay texture. Compared to a sandy soil, what is a key consideration for managing fertilizer on the clay soil?
- It will require more frequent fertilizer applications due to rapid leaching.
- It has a lower capacity to store nutrients like potassium and calcium.
- There is a higher potential for nutrient loss through runoff if not incorporated.
- Nitrogen will be converted to plant-available forms more slowly. (Correct answer)
Correct answer: Nitrogen will be converted to plant-available forms more slowly.
Clay soils have smaller particles and less pore space compared to sandy soils, which can lead to slower drainage and aeration. While clay soils have a high CEC and can hold nutrients well, fine-textured soils can become compacted and have poor water infiltration. This increases the risk that surface-applied fertilizers, especially phosphorus, can be washed away by rainfall before they can move into the soil profile.
Question 6: A soil test report indicates a pH of 5.2. At this pH level, which of the following nutrient availability issues is most likely to occur?
- Iron and manganese may become less available.
- Phosphorus availability is likely to be reduced. (Correct answer)
- Molybdenum availability will be at its peak.
- Potassium will be held more tightly by the soil colloids.
Correct answer: Phosphorus availability is likely to be reduced.
In strongly acidic soils (pH below 5.5), phosphorus readily reacts with iron and aluminum to form insoluble compounds, making it 'fixed' and unavailable for plant uptake. While some micronutrients like iron and manganese become more available (and potentially toxic) at low pH, phosphorus availability is significantly reduced.
CFA Soil Properties and Testing Questions and Answers 1
A soil test report for a sandy loam field indicates a low Cation Exchange Capacity (CEC).
Which of the following fertilizer application strategies is most appropriate for this field?