Determinants of fertiliser effectiveness:\nThe field effectiveness of an applied fertiliser depends on soil nature, crop type, and soil pH. It is independent of which factor, if any?

Introduction / Context:
“Fertiliser effectiveness” means how much of the applied nutrient becomes available for plant uptake and translates into yield. This depends on interactions between the product and the agro-ecosystem. The question asks if there is any listed factor on which effectiveness is independent. In practice, the three cited factors all matter strongly.

Given Data / Assumptions:

• Soil properties include texture, organic matter, cation exchange capacity (CEC), moisture, and biological activity.
• Crop species and growth stage alter nutrient demand and root architecture.
• Soil pH controls nutrient solubility (e.g., P fixation), ammonia volatilisation, and microbial transformations.

Concept / Approach:
Nutrient fate processes—adsorption, precipitation/dissolution, nitrification/denitrification, volatilisation, and leaching—are all governed by soil chemistry and biology. Crop type determines uptake kinetics and critical tissue concentrations. Soil pH shifts equilibria (for example, ammonium/ammonia balance and phosphate availability). Therefore, fertiliser effectiveness is not independent of any of these; it depends on all of them together.

Step-by-Step Solution:

Verification / Alternative check:
Extension guidelines tailor fertiliser rates to soil tests (pH, P, K, OM) and crop requirements; universal “one-rate-fits-all” recommendations are discouraged.

Why Other Options Are Wrong:

• Each of (a), (b), (c) exerts major influence; claiming independence from any one is incorrect.
• “Average annual rainfall only”: rainfall matters for leaching but is not the sole determinant.

Common Pitfalls:
Assuming product label rates apply identically to all soils and crops; ignoring pH-dependent losses (e.g., ammonia volatilisation on high-pH soils after urea application).

Final Answer:
None of these (it depends on all listed factors)