Using the helicopter, get closer to the pallet with solid fertilizers and press the R button. Then, when you're done with that, fly over the fields, left mouse button to go up, right mouse button to go down. W button to move forward, S button to move backward, D button to turn right and A button to turn left. When you're over the fields, just turn on the fertilizer spreader with the B button, and that's it.
This mod supports multi-user mode and will probably run on a dedicated server with this script. The mod script can be freely used to create additional aircraft. For example, you can make a helicopter out of a wooden barrel.
In 1.0.0.1, I will fix the rotation so that it rotates more smoothly. You can find a helipad among the misplaced items that can be placed.

In version 1.0.0.4:
- Improved cornering control.