C172 pilot reported an off airport landing was caused by engine malfunctions after maintenance.

Narrative

After retrieving my aircraft from maintenance for a cylinder replacement and subsequent oil change; I opted to perform a local flight around the area. During this flight I was closely monitoring the performance of the aircraft; including frequent scans of oil pressure and temperature.Approximately half an hour into the flight while circling over my farm; I observed the oil pressure gauge read zero. There was no change in engine performance or noise; and I decided to make a precautionary landing. I was receiving VFR traffic advisories and flight following from the local class Charlie airport; and I informed the Controller that I was going to land at my farm and requested a frequency change. I did not inform them why I was landing; nor did I declare any sort of emergency.I have landed at my farm several times and I was familiar with the field conditions. The area I selected for my landing is an alfalfa field approximately 2500 ft. in length and very suitable for landing this aircraft. The landing was uneventful.Upon landing; I shut down the airplane and assessed the situation. The left landing gear leg; belly; and engine compartment aft of the baffles were covered in oil. I contacted the Mechanic who performed the work on the aircraft to let him know what happened; and he subsequently met me on the property to diagnose the issue. We towed the aircraft to a more appropriate place on the property to investigate closer.When we removed the cowl from the aircraft; we identified the source of the leak to be the fiber gasket where the spin-on oil filter adapter meets the oil sump of the engine. The gasket was protruding from the joint; and the oil filter adapter was loose and could be moved by hand.We drained the remaining oil from the airplane and determined there were approximately two quarts remaining in the sump. We removed the oil filter adapter from the airplane and performed [the] AD in accordance with the manufacturer's instructions; replacing all gaskets on the oil filter adapter with copper crush washers; properly torquing the assembly; and affixing it with safety wire. We refilled the engine with oil and performed a run up; confirming the oil pressure and temperature were normal and there were no leaks. The airplane was closely inspected and reassembled and towed back to the field; and I took off and returned to the local class Charlie airport; which is my home field and where the airplane is based.Since this event; I have flown this aircraft approximately six hours with no further issues. An oil change will be performed at 10 hours and the oil sent out for analysis and filter closely examined.A few things I could have done differently:In the future; after maintenance of this nature I will remain closer to the airport to ensure I have an appropriate place to land in the event of an issue.Also; if I have an issue of this nature in the future; I will let ATC know so they can provide assistance if needed. I did not declare an emergency or let them know what was happening for fear of alarming family members who often listen to online ATC audio; as well as drawing unwanted attention to something that I felt was not an emergency since this was my own field and I had landed here before. The news of a small airplane losing oil pressure and landing in a field often makes the news and is described as a crash; even when it isn't.