If it was full of rubbish? Wooden pallets, empty petrol cans, barbed wire, chicken fencing, recycling bin all in the same very muddy field as the persons horses you'd rented it to? The person who owns the horses is on notice from a horse welfare org due to neglect and lack of hay which she seems to be sorting but 4 months in the field is still utterly trashed and the horses have to move around all the debris.
If it were your field and you weren't aware would you want someone to tell you?