Step 1: Understanding the Question:
This question tests knowledge of alley cropping systems.
Step 2: Detailed Explanation:
In the alley cropping system, the space between rows of trees is used for agricultural crops.
Trees are planted in rows, and agricultural crops are grown in the alleys.
Vegetable crops (A): Can be grown but not the general term.
Short rotation tree crops (C): Not typically grown in alleys.
Fruit trees (D): Not the main crop in alleys.
Thus, the correct answer is agricultural crop.
Step 3: Final Answer:
Thus, the space between rows is used for agricultural crops, which corresponds to option (B).
[0.5cm]