I want to make the falling autumn leaves. I did a system of particles that rotate in flight.
How can I make them not rotate after lay on the surface?
You could possibly make the Particles die on contact (by checking the option in the collision tab) and display dead Particles (In Particle Settings)
Go the collision settings for the surface the leaves are landing on and increase the friction setting as high as possible. If the particles are still rotating upon collision you can increase the particle's friction as well.
I have other idea: Decrease Lifetime to end up particle animation and tick Died under Particle Render tab.