I was lucky enough as a young child to see one of these working a high country farm - it was operating off a sloped runway and I was convinced it was going to crash as it landed uphill, then convinced it was going to crash after it took off after reloading due to how slowly it climbed - I can't find a definitive number, but I vaguely recall it had a take off speed that lurked around 50kt...

On the subject of top-dressers... ...I was privileged to see a turboprop equipped Fletcher FU-24 in action a couple of weeks ago, those pilots are very darn good at flying very low in hill country. Very loud and notable engine sound.

https://en.wikipedia.org/wiki/Fletcher_FU-24

50 knots rotation is perfectly fine for a plane that size. A Cessna Skyhawk is certified to rotate at 55 knots fully loaded (and since the stall speed is around 40knots, for specialty take-offs like soft fields it's much lower, 50knots is more than enough).