Farm tax write-offs may come sooner

Farmers could get tax breaks for new fences and dams a year earlier than promised in the budget.

The accelerated depreciation measure unveiled on Tuesday for water facilities, fodder storage and fencing is meant to start in mid-2016.

That is too long a wait for some drought-hit farmers who've expressed concern and confusion about the delay.

"It will leave small businesses like rural supply stores hanging on," National Farmers Federation president Brent Finlay said.

Treasurer Joe Hockey has been under pressure from the Nationals, including Agriculture Minister Barnaby Joyce, about the timeline.

He is now considering bringing forward the start date.

"Many farmers are telling us that they want to start as soon as possible to build the fences, dams and irrigation systems they need," a spokeswoman for the treasurer told AAP in a statement on Thursday.

The opposition used the delay to attack the government's sincerity in helping struggling farmers.

Labor's agriculture spokesman Joel Fitzgibbon said Mr Joyce was lobbying the treasurer to change a budget policy only hours after it was announced.

"This is a government not properly focused on the real problems being faced by people on the land," he said.

The tax deduction measure is designed to assist farmers manage periods of drought better and comes as a top-up to the $333 million additional drought support package announced by the government last weekend.