A farmer in Kenya grows maize in the same field year after year. The yield decreases over time. Which of the following best explains this observation?

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Question

A farmer in Kenya grows maize in the same field year after year. The yield decreases over time. Which of the following best explains this observation?

Accepted Answer

The soil has become depleted of nitrates which are not being replaced — Award 1 mark for correct answer. Plants absorb nitrates for protein synthesis and continuous cropping removes nitrates without replacement. A is incorrect because denitrifying bacteria reduce nitrogen content. C is incorrect because atmospheric nitrogen is not converted directly to nitrates, and this would increase yield not decrease it. D is incorrect because decomposers break down organic matter to release nutrients, not remove them.

Answer

Denitrifying bacteria have increased the nitrogen content of the soil

Answer

Nitrogen-fixing bacteria have converted all atmospheric nitrogen to nitrates

Answer

Decomposers have removed all the organic matter from the soil

Answer

The soil has become depleted of nitrates which are not being replaced

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