We are only trying to help you.so I think I will let that one go. You asked the original question, so you must have some doubts. I operate from numerous grass strips, each a different level of difficulty. The most interesting one is where we have funnel of trees that we navigate down and through, with a telegraph wire at 50 feet across the threshold. Depending on wind shear, you either go under the wire, or over, and dive for the strip. The owner put a big orange ball in the middle of the wire so that we could see it. Very kind of him. The point we are trying to make is that there can be no set rule for this kind of flying. You must understand the issues and dangers that lie in farm strip flying. Number 1 is total recency and local knowledge. And FWIW a 20000hr ATPL friend of mine put one of my more capable planes in a ploughed field, uphill, and taxied a mile to find out his farmer friend had closed that strip, and moved it across the road. He was using a GPS, local knowledge, and the viz was 2k. He swore blind he was in the right place. He was, just not a strip anymore, but he landed;) We all make errors.

"It's another private airfield with 410 m paved runway. It is owned by a former aerobatic pilot, so I thought if he can put his fast and powerful aircraft down there, I should be able to do that with my slow kite too :"
Landing distance depends on stall speed, pilot skill, and the wind. Take-off distance depends a lot on the power available.
I could easily fly into airstrips which would require disassembly to get the aircraft out of.

Which is why I've sometimes thought there are places I could get out of easily enough - the aircraft should perform within book figures plus fudge factors - but is my skill adequate to get in there in the first place? Starting a take-off from the right spot at the right speed is easier than starting a landing by touching down at the right spot at the right speed.

@maxred: a good example to illustrate the common sense of a little phone call before taking off - even if some dislike the concept of it being mandatory, aka PPR, it is never a bad idea. We all make errors, indeed, but it is better to make them early in the flight, or even before.

@GtW: I tend to agree, but it much depends on the type of aeroplane. My own pride and beauty can certainly be flown out of any runway she can be landed into - my hardest was 190 metres, and on take-off I "rotated" (HAHAHA!) before halfway. @Maoraigh1 seems to fly a Jodel, perhaps less over-powered than my bird.