Why can not a field sown with cultivated plants be considered a natural ecosystem?

in addition to solar, additional energy is used.
A distinctive feature of agroecosystems is the inability to exist without a person: without watering, plowing, weeding, the field will become a meadow. Therefore, in addition to solar energy, additional energy is needed to maintain this artificial ecosystem.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.