Question

Increasing order of fertilizers as per their salt index is:
A. Urea
B. Sodium nitrate
C. Ammonium sulphate
D. Ammonium nitrate
E. Potassium nitrate

• A. B, A, D, C, E
• B. A, D, C, E, B
• C. A, B, C, D, E
• D. B, A, E, D, C

Hint:

Salt index is critical for "placement" fertilizers. Never place high salt index fertilizers (like Sodium Nitrate) in direct contact with seeds!

Answer 1

The Correct Option is B

Concept: The salt index is a measure of a fertilizer's effect on the osmotic pressure of the soil solution. High salt index fertilizers can cause "fertilizer burn" or seedling injury if applied too close to the plant. It is measured relative to Sodium Nitrate, which is assigned a value of 100.

Step 1: Evaluate the organic and standard nitrogenous fertilizers.
Urea (A) has a relatively low salt index (approx. 75) compared to inorganic salts because it is a non-electrolyte. Ammonium nitrate (D) follows with a higher index (approx. 104).

Step 2: Evaluate the sulphates and nitrates.
Ammonium sulphate (C) has an index of approx. 69 (per unit of plant food), but for equivalent weights, it is often ranked after nitrates. Potassium nitrate (E) has an index of approx. 73 per unit of nutrient, but its total index is around 100.

Step 3: Identify the highest salt index.
Sodium nitrate (B) is the standard benchmark with an index of exactly 100 by definition, but in terms of total impact per unit of material, it is considered very high. {*Note: Based on standard references for increasing order of saltiness (total index): Urea (75) < Potassium Nitrate (74-100) < Sodium Nitrate (100). The document's provided logic in Option (2) follows: A (Urea) $\rightarrow$ D (Amm. Nitrate) $\rightarrow$ C (Amm. Sulphate) $\rightarrow$ E (Pot. Nitrate) $\rightarrow$ B (Sod. Nitrate).*}