i sure would make sure that the equipment that he left at your house is not able to be removed before you straighten things out. i don't know what kind of equipment we're talking about here, but just as an example, if it's a tractor, take the key out of the ignition, remove the battery, whatever. (i'm not mechanically inclined, so i'm just making things up, but you get my point.) if this was not a huge misunderstanding, and he plans on keeping your hay, tell him you plan on keeping his equipment. otherwise you might come home and discover he picked up his stuff, and you may never hear from him again.
maybe this is not doable depending on exactly what equipment he left there, and maybe it's not even legal to do, but it's the very first thing that popped into my head when you said he left his stuff there. hold his stuff for ransom, if you will.
if it is just a mistake, you could easily hook things back up before he gets back to you with your hay.