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.
"They have found with all the new tractors sent over, the new Chinese tractors which look great and big and all the rest of it, they're breaking down and they can't fix them because they're all computerised and there's no computer fixers over there.
"There's a lot of new tractors sitting in the ditch on the side of the road."
With many young men encouraged to join seasonal labour gangs in Australia and New Zealand, farming has been left largely to women, another reason for the need, Rodwell said.
"It's mostly women now tending the land."
The trust was working with a charity in Tonga to train women to drive the tractors, plough and generally skill them up in agriculture.
The local partner was also setting up a system to ensure the poorest farmers have better access to tractors.
"In the past, the difficulty has been a limited number of tractors and the people who get the tractors have been the big landholders.
"They control the tractors and if they want the tractor they get it first so the poor people end up missing out so we have made a general rule that the people who can't afford the tractor get it first."
Rodwell suggested instead of using old tractors as an anchor for irrigation lines in the paddock, farmers might like to send them off to be reconditioned and put to use in Tonga.
The charity would love to hear from people who may have a Massey Ferguson, particularly a classic of the 100 or 200 series.
Ford tractors would be good too as well as disc ploughs and relatively narrow slasher mowers, he said.