Nutrient Management and 4Rs Flashcards
7 cards from real CFA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Nutrient Management and 4Rs flashcards as text
Which practice best exemplifies the 'Right Time' principle for phosphorus fertilization in a corn-soybean rotation?
Answer: In-furrow application at corn planting for starter effect
In-furrow starter phosphorus at planting is the best example of Right Time because it places P where the young plant can access it during early growth when soil P uptake is limited by cold temperatures.
Nitrification inhibitors like DCD (dicyandiamide) work by:
Answer: Slowing the bacterial conversion of ammonium to nitrate
DCD inhibits Nitrosomonas bacteria, slowing the first step of nitrification and keeping nitrogen in the ammonium form longer to reduce leaching and denitrification risk.
When calibrating a variable rate application (VRA) system for a field with high spatial variability, the grower must first ensure that:
Answer: GPS accuracy is sufficient for the prescription map scale being used
VRA systems depend on precise GPS positioning to match application rates to the correct management zones; insufficient GPS accuracy causes mis-application.
A high soil nitrate test (>25 ppm NO3-N) in the spring before corn planting indicates:
Answer: Significant carry-over N from the previous year, allowing a reduced N application rate
High pre-plant soil nitrate indicates carry-over from the previous crop or applied N, and growers should credit this N toward the total crop requirement to avoid over-application.
Which micronutrient deficiency in soybeans causes interveinal chlorosis on young leaves and is most common on high-pH, calcareous soils?
Answer: Iron deficiency chlorosis (IDC)
Iron deficiency chlorosis (IDC) is the classic young-leaf interveinal chlorosis on soybeans grown in high-pH calcareous soils where iron becomes unavailable.
A grower applies 200 lbs/acre of 0-46-0 (triple superphosphate). What is the total P2O5 applied?
Answer: 92 lbs P2O5/acre
200 lbs × 46% P2O5 = 92 lbs P2O5/acre; the grade indicates the percentage of the nutrient as the oxide equivalent.
Which practice is the most effective way to reduce ammonia volatilization losses from surface-applied urea?
Answer: Incorporate urea into the soil mechanically or with irrigation within 24 hours
Incorporating urea into soil within 24 hours of application moves it below the surface, where hydrolysis occurs in moist soil with no pathway for ammonia gas to escape.