Macronutrient triad check:\nWhich of the following is not necessarily a major (primary) nutrient component that must be present in every fertilizer product?

Introduction / Context:
Primary macronutrients for plants are nitrogen (N), phosphorus (P), and potassium (K). Many commercial fertilizers supply one, two, or all three of these, depending on soil tests and crop needs. Sulphur (S) is an essential nutrient but is classified as a secondary macronutrient, and not all fertilizers include it by default.

Given Data / Assumptions:

• We distinguish between “primary” (N, P, K) and “secondary/micronutrients”.
• The question asks which is not necessarily required in every fertilizer.
• Some products are straight fertilizers (e.g., urea) with only one primary nutrient.

Concept / Approach:
Fertilizers are tailored: a bag may be N-only (46-0-0 urea), NP (DAP 18-46-0), or NPK in various ratios. None of these necessarily includes sulphur unless specifically formulated (e.g., ammonium sulphate provides S). Therefore, sulphur is not a component that must be present in every fertilizer product, although it can be agronomically important in sulphur-deficient soils.

Step-by-Step Solution:
Recall the primary nutrients: N, P, K.Recognize sulphur as a secondary nutrient in labeling conventions.Conclude that sulphur is not mandatory in every fertilizer formulation.

Verification / Alternative check:
Common SKUs: Urea (N only), MOP (K2O only), DAP (NP), SSP (P with some S), each illustrating that sulphur is optional and product-specific.

Why Other Options Are Wrong:
Nitrogen, phosphorus, and potassium are the primary macronutrients considered core to fertilization programs; “All of N, P, and K must always be present” is false because single-nutrient fertilizers are widely used.

Common Pitfalls:
Equating “essential” with “always included”; essentiality refers to plant biology, while product composition depends on agronomic prescriptions and manufacturing.

Final Answer:
Sulphur