Soil Fertility and Analysis Flashcards

A corn crop yielding 200 bu/ac removes approximately how many pounds of nitrogen per acre in the harvested grain?

Answer: 150–170 lb

Corn grain contains roughly 0.75–0.85 lb N per bushel, so 200 bu/ac removes approximately 150–170 lb N/ac in grain alone.

Sulfur deficiency symptoms in corn most commonly appear:

Answer: On younger leaves as uniform yellowing

Sulfur is relatively immobile in the plant, so deficiency symptoms appear first on young (upper) leaves as uniform yellowing.

Which soil property most directly determines the lime requirement (LR) to raise pH to a target level?

Answer: Buffer pH (buffering capacity)

Buffer pH measures the soil's resistance to pH change; soils with high buffering capacity (high CEC, organic matter) require more lime to achieve the same pH increase.

Denitrification occurs most rapidly under which soil conditions?

Answer: Wet, anaerobic, warm temperature

Denitrifying bacteria convert NO3- to N2 gases under anaerobic (waterlogged) conditions, and the process accelerates as soil temperature rises.

A soil has a CEC of 20 meq/100g and is 70% base-saturated. How many meq of bases per 100g of soil are present?

Answer: 14

Base saturation (%) × CEC = meq of bases, so 0.70 × 20 meq/100g = 14 meq/100g.

When comparing urea (46-0-0) and anhydrous ammonia (82-0-0) as N fertilizer sources, which statement is accurate?

Answer: Urea has a higher risk of volatilization loss when surface-applied without incorporation

Surface-applied urea can lose significant N as ammonia gas through urease-driven hydrolysis, especially at warm temperatures and high pH; incorporation or urease inhibitors reduce this risk.

The Bray P-1 soil test is NOT recommended for use in soils with pH above 7.4 because:

Answer: It underestimates P by dissolving calcium phosphates poorly

Bray P-1's dilute acid is neutralized quickly by free carbonates in calcareous soils, preventing full extraction of available P and causing underestimation.