BeCareful!: 3-Slot Scales

Looking the same, but having different wieghts, we have 50 balls. We also have a 3-slot scales. This scales can sort 3 balls from least to most in weight with a single measurement and it only accepts 3 balls (no more no less) at a time.
The question then is, how many measurements (at minimum) we need to perform to find the 2nd lightest ball?