The Pasifika Safe Shelter Trust has sent several reconditioned tractors to Tonga since the Hunga Tonga-Hunga Ha'apai volcano erupted last year, smothering fields with tonnes of ash.
Chairman Peter Rodwell said a year or so on there was still a need for equipment to mix the ash into the soil and allow crops to flourish.
"The volcanic ash is actually quite rich in elements."
He said the charity was keen for more non-electronic tractors, particularly old Massey Fergusons because they were relatively easy to fix.