CFA Soil Science & Fertilizer Chemistry 3

Question 1

Which form of phosphorus is most available for plant uptake in the soil solution?

Accepted Answer

H2PO4-

Answer

H2PO4- (dihydrogen phosphate) is the dominant plant-available form in the slightly acid to neutral pH range (6.0–7.0) where P availability peaks.

Question 2

Sulfur deficiency symptoms in plants most closely resemble deficiency of which other nutrient?

Accepted Answer

Nitrogen

Answer

Both sulfur and nitrogen deficiencies cause yellowing (chlorosis) of leaves, but sulfur deficiency appears first on younger leaves while nitrogen deficiency starts on older leaves.

Question 3

The bulk density of a compacted soil is 1.6 g/cm³. Assuming particle density of 2.65 g/cm³, what is the total porosity?

Accepted Answer

About 40%

Answer

Porosity = (1 - Db/Dp) × 100 = (1 - 1.6/2.65) × 100 ≈ 39.6%, approximately 40%.

Question 4

Which soil order is characterized by a spodic horizon containing illuviated organic matter, aluminum, and iron?

Accepted Answer

Spodosols

Answer

Spodosols are defined by their spodic horizon (Bs or Bhs), where leached humus, Al, and Fe accumulate in a distinct subsurface layer.

Question 5

When diammonium phosphate (DAP, 18-46-0) dissolves near a seed, the pH of the fertilizer band temporarily:

Accepted Answer

Rises to approximately 8

Answer

DAP dissolution releases NH3 gas initially, raising the localized pH to about 7.5–8.5 before nitrification proceeds.

CFA Practice Test

CFA Practice Test

CFA Soil Science & Fertilizer Chemistry 3