Correct sentence:
The sentence is correct: The seed drill plants seeds in the soil in straight rows.
What it means (for a 6-year-old):
- A seed drill is a machine.
- It plants (puts) tiny seeds into the soil (the ground).
- It puts the seeds in straight rows (like neat lines).
Simple alternatives you can use:
- A seed drill plants seeds in straight rows.
- The seed drill puts seeds into the soil in straight rows.
Extra note: Your original sentence is grammatically correct. Good job!