Step 1: Understanding the Question:
This question tests knowledge of poplar-based agroforestry systems in India.
Step 2: Detailed Explanation:
Poplar-based agroforestry in north India is primarily in the form of block planting.
Farmers grow poplar trees in blocks along with agricultural crops.
Bund planting (A): Not common for poplar.
Alley cropping (B): Used for some species but not poplar.
Scattered planting (C): Not common for poplar.
Thus, the correct answer is block planting.
Step 3: Final Answer:
Thus, poplar-based agroforestry is in the form of block planting, which corresponds to option (D).
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