CCA - Certified Crop Advisor Fertilizer Sources and Application Questions and Answers

Question 1

A producer plans to topdress urea (46-0-0) on an established cool-season grass pasture. Warm, breezy conditions are forecasted with no chance of rain for several days. Which of the following describes the primary nitrogen loss pathway of concern and the best management practice to mitigate it?

Accepted Answer

Volatilization of ammonia; use a urease inhibitor or time the application just before a significant rainfall event.

Answer

Urea applied to the soil surface is converted to ammonium by the urease enzyme. In warm, moist, and breezy conditions, especially on high-residue surfaces like a pasture, this ammonium can rapidly convert to ammonia gas and be lost to the atmosphere. This process is called volatilization. A urease inhibitor slows the enzymatic conversion of urea, allowing more time for rainfall or irrigation to move the intact urea into the soil profile where the resulting ammonium will be protected from volatilization.

Question 2

Which of the following statements accurately compares the initial soil reaction of monoammonium phosphate (MAP, 11-52-0) and diammonium phosphate (DAP, 18-46-0) when applied as a granular fertilizer?

Accepted Answer

MAP creates an acidic reaction in the soil immediately around the granule, while DAP creates an alkaline reaction.

Answer

When MAP dissolves, it creates an acidic reaction (pH around 3.5-4.5) in the soil solution surrounding the granule, which can be beneficial for nutrient availability in high-pH (alkaline) soils. Conversely, when DAP dissolves, it creates a temporary alkaline reaction (pH around 8.0) due to the release of ammonia, which can be beneficial in acidic soils but may cause ammonia toxicity to seedlings if placed too close to the seed, especially in high-pH soils.

Question 3

A grower is planting corn into a cool, high-residue, no-till field. A recent soil test indicates low phosphorus (P) levels. Which fertilizer placement method would be most efficient for providing phosphorus to the young corn plant?

Accepted Answer

Banding the phosphorus fertilizer 2 inches to the side and 2 inches below the seed at planting.

Answer

Phosphorus is relatively immobile in the soil, and its availability is often reduced in cool, moist, no-till conditions. Banding the fertilizer in a 2x2 placement concentrates this immobile nutrient near the developing root system of the seedling. This ensures the young plant has access to adequate phosphorus for critical early-season growth, which often results in better plant vigor and can lead to increased yield.

Question 4

A grower is selecting a fertilizer for an in-furrow (pop-up) application at planting. Which of the following common fertilizer sources has the highest salt index, posing the greatest risk of seedling injury if applied at excessive rates?

Accepted Answer

Potassium Chloride (KCl)

Answer

The salt index measures a fertilizer's effect on the osmotic potential of the soil solution. A high salt index can cause 'fertilizer burn' by drawing moisture out of seedling roots. Potassium chloride (0-0-60), also known as muriate of potash, has one of the highest salt indices among common fertilizers (around 116) and must be used with extreme caution for in-furrow applications. By comparison, Urea is high (75), MAP is low (30), and TSP is very low (10).

Question 5

A farmer incorporates a large amount of mature cereal rye cover crop residue, which has a high carbon-to-nitrogen (C:N) ratio, into the soil shortly before planting corn. What is the most likely immediate effect on nitrogen availability for the corn crop?

Accepted Answer

A temporary decrease in available soil nitrogen due to microbial immobilization.

Answer

Residues with a high C:N ratio (typically >25:1 or 30:1) do not contain enough nitrogen to meet the needs of the soil microbes that decompose them. The microbes will take up available inorganic nitrogen (nitrate and ammonium) from the soil to break down the carbon-rich residue. This process, called immobilization, temporarily 'ties up' soil nitrogen, making it unavailable to the cash crop until the microbes die and the nitrogen is re-released (mineralized).

(CCA) Certified Crop Advisor Practice Test

(CCA) Certified Crop Advisor Practice Test

CCA - Certified Crop Advisor Fertilizer Sources and Application Questions and Answers