Soil Fertility — Soil Science Reviewer Questions

17 board-style Soil Fertility items for the Agriculturist Licensure Examination, free and open to every examinee. Texture drives water, water drives aeration, and aeration drives nutrient availability. Reason down that chain and most items unlock.

17 questions in this topic · part of Soil Science · every answer explained

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Sample Soil Fertility questions with answers and explanations

Board-style items taken from the Soil Science bank. Every answer is explained, which is the part that makes a review question worth doing twice.

A recommendation calls for 90 kg N/ha and the only source is urea (46-0-0). How much urea is needed?
- A. 414 kg/ha
- B. 196 kg/ha correct
- C. 41 kg/ha
- D. 90 kg/ha
Why: Divide the nutrient requirement by the grade expressed as a decimal: 90 / 0.46 = 195.7, rounded to 196 kg/ha. Multiplying by 0.46 instead gives 41 kg and would supply less than a quarter of the nitrogen the crop was recommended.
A farmer applies 300 kg/ha of complete fertiliser (14-14-14). How much actual nitrogen is supplied?
- A. 300 kg N/ha
- B. 14 kg N/ha
- C. 42 kg N/ha correct
- D. 21 kg N/ha
Why: 0.14 x 300 = 42 kg N/ha, and the same 42 kg each of P2O5 and K2O. The grade is a percentage of the BAG, so the nutrient delivered always depends on how much material is spread, not on the analysis alone.
A recommendation is 60-40-40 kg NPK/ha. If 286 kg/ha of 14-14-14 is applied as basal, how much additional N must come from urea (46-0-0)?
- A. 20 kg/ha of urea
- B. 96 kg/ha of urea
- C. 130 kg/ha of urea
- D. 44 kg/ha of urea correct
Why: The complete supplies 0.14 x 286 = 40 kg each of N, P2O5 and K2O, meeting P and K exactly. The nitrogen shortfall is 60 - 40 = 20 kg N, and 20 / 0.46 = 43.5, rounded to 44 kg of urea. Answering 20 kg confuses the NUTRIENT needed with the MATERIAL that carries it.
A soil test recommends 100 kg P2O5/ha. Expressed as elemental phosphorus, how much is that?
- A. 43.6 kg P/ha correct
- B. 229 kg P/ha
- C. 83.0 kg P/ha
- D. 100 kg P/ha
Why: P = P2O5 x 0.436 = 43.6 kg/ha. The factor exists because fertiliser grades are stated as oxides by long convention while plant uptake and soil test reports are often elemental -- mixing the two conventions is a frequent and expensive error.
A farmer needs 90 kg K2O/ha and uses muriate of potash (0-0-60). How much material is required?
- A. 54 kg/ha
- B. 150 kg/ha correct
- C. 90 kg/ha
- D. 180 kg/ha
Why: 90 / 0.60 = 150 kg/ha. That also delivers roughly 75 kg of chloride, which matters for chloride-sensitive crops such as tobacco -- a reason sulphate of potash is sometimes chosen despite its higher cost.
Ammonium sulfate is 21-0-0 and urea is 46-0-0. To supply 84 kg N/ha, how much MORE material must be spread if ammonium sulfate is used instead of urea?
- A. 400 kg/ha more
- B. 183 kg/ha more
- C. 217 kg/ha more correct
- D. 62 kg/ha more
Why: Ammonium sulfate: 84 / 0.21 = 400 kg; urea: 84 / 0.46 = 183 kg. The difference is 217 kg/ha of extra material to buy, haul and spread. Ammonium sulfate can still be preferred where its sulfur or its acidifying effect is wanted, which is a judgement the arithmetic informs rather than settles.
A recommendation is 120 kg N/ha for one hectare. A farmer's plot measures 40 m x 50 m. How much urea (46-0-0) should be applied to the plot?
- A. 261 kg
- B. 24 kg
- C. 120 kg
- D. 52 kg correct
Why: The plot is 2,000 m2, or 0.2 ha, so it needs 24 kg N. As urea: 24 / 0.46 = 52 kg. Two conversions are required -- area to hectares and nutrient to material -- and skipping either produces a rate that is wrong by a factor of five or of two.
Rice yielding 5 t/ha removes about 15 kg N per tonne of grain. If fertiliser nitrogen is only 40% recovered, how much N must be applied to replace the removal?
- A. 188 kg N/ha correct
- B. 75 kg N/ha
- C. 30 kg N/ha
- D. 125 kg N/ha
Why: Removal = 5 x 15 = 75 kg N/ha. Because only 40% of applied N reaches the crop, the rate needed is 75 / 0.40 = 187.5, rounded to 188 kg N/ha. Recovery efficiency is the step that separates crop REMOVAL from a fertiliser RECOMMENDATION, and it is why split application, which raises recovery, lowers the rate needed.

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Soil Fertility — Soil Science Reviewer Questions

Sample Soil Fertility questions with answers and explanations

A recommendation calls for 90 kg N/ha and the only source is urea (46-0-0). How much urea is needed?

A farmer applies 300 kg/ha of complete fertiliser (14-14-14). How much actual nitrogen is supplied?

A recommendation is 60-40-40 kg NPK/ha. If 286 kg/ha of 14-14-14 is applied as basal, how much additional N must come from urea (46-0-0)?

A soil test recommends 100 kg P2O5/ha. Expressed as elemental phosphorus, how much is that?

A farmer needs 90 kg K2O/ha and uses muriate of potash (0-0-60). How much material is required?

Ammonium sulfate is 21-0-0 and urea is 46-0-0. To supply 84 kg N/ha, how much MORE material must be spread if ammonium sulfate is used instead of urea?

A recommendation is 120 kg N/ha for one hectare. A farmer's plot measures 40 m x 50 m. How much urea (46-0-0) should be applied to the plot?

Rice yielding 5 t/ha removes about 15 kg N per tonne of grain. If fertiliser nitrogen is only 40% recovered, how much N must be applied to replace the removal?

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