Gce Model Questions Vol1 2020 Agricultural Science Question 49

Practice objective / multiple choice question 49 from the 2020 Gce Model Questions Vol1 Agricultural Science examination.

Gce Model Questions Vol1 2020 Agricultural Science Objective / Multiple Choice Medium Difficulty
Question 49 GCE_MODEL_QUESTIONS_VOL1 • 2020 • AGRICULTURAL_SCIENCE • objective

A farmer practices a 4‑year crop rotation: Year 1 wheat, Year 2 legume, Year 3 wheat, Year 4 legume. Wheat requires 120 kg N ha⁻¹; legumes fix 80 kg N ha⁻¹ but use 30 kg N ha⁻¹ for their own growth. The soil initially contains 50 kg N ha⁻¹. No external N fertilizer is applied unless needed to meet the wheat requirement. (a) What is the net change in soil nitrogen after the 4‑year cycle? (b) To keep at least 60 kg N ha⁻¹ in the soil before each wheat year, how much additional nitrogen fertilizer must be applied each wheat year?

Answer Options

A. (a) Net change is -5 kg N ha⁻¹ (soil slightly decreases). (b) An extra 5 kg N ha⁻¹ must be applied each wheat year, so 70 kg fertilizer per wheat year.
B. (a) Net change is -20 kg N ha⁻¹ (soil decreases). (b) An extra 15 kg N ha⁻¹ must be applied each wheat year, so 90 kg fertilizer in total per wheat year.
Correct Answer C. (a) Net change is 0 kg N ha⁻¹ (soil returns to the initial 50 kg). (b) An extra 10 kg N ha⁻¹ must be applied each wheat year, so 80 kg fertilizer in total per wheat year.
D. (a) Net change is +30 kg N ha⁻¹ (soil increases). (b) No additional fertilizer is needed each wheat year.
Correct Answer
C
Correct Option:
(a) Net change is 0 kg N ha⁻¹ (soil returns to the initial 50 kg). (b) An extra 10 kg N ha⁻¹ must be applied each wheat year, so 80 kg fertilizer in total per wheat year.

About This Question

This is Gce Model Questions Vol1 2020 Agricultural Science Question 49. It is one of the objective questions from the 2020 Gce Model Questions Vol1 Agricultural Science examination.

Difficulty level: Medium .

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