Determinants of fertiliser effectiveness: The field effectiveness of an applied fertiliser depends on soil nature, crop type, and soil pH. It is independent of which factor, if any?
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ANature of soil (texture, organic matter, CEC)
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BType of crop and growth stage
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CSoil pH and liming status
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DNone of these (it depends on all listed factors)
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EAverage annual rainfall only
Answer
Correct Answer: None of these (it depends on all listed factors)
Explanation
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:
Evaluate soil nature: affects retention, movement, and bioavailability → critical.Evaluate crop: different species demand different NPK ratios and timing → critical.Evaluate pH: controls solubility/volatilisation and microbial steps → critical.Conclude: none of the listed factors can be ignored; choose “None of these”.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)