Answer: The presence of seeds that need light to germinate in the farm.
Explanation:
There are some specie of seeds that germinate best when they are exposed to light.
If these seeds are covered in soil, it is very likely they they will remain dormant and not sprout until conditions improve.
These seeds only needs to be pressed onto the surface of the soil where they can easily access sunlight and kept moist to germinate.
Once the light from the Sun hits this seed they obtain the required energy needed for them to germinate.
Therefore when the farmer ploughed the field he was unknown to him, exposing the seeds to the much needed light.
