Trump’s proclamation reduces the duty rate on machinery like harvesters, alongside certain other equipment, from 25% to 15%.

Foreign companies can also qualify for a 10% duty rate if their manufacturing equipment contains at least 85% US steel or aluminium, the White House added in a fact sheet.

The changes take effect on June 8 and last until Dec 31, 2027.

Farmers have raised concern over rising costs ahead of key midterm elections, and face a further squeeze from the Middle East war as diesel and fertiliser prices have surged.

US-Israeli strikes targeting Iran since the end of February sparked Tehran’s retaliation that virtually blocked off the Strait of Hormuz.

The critical waterway normally sees about a fifth of the world’s oil and gas supplies pass through it, and is also essential for the global fertiliser trade.

The blockage has also driven aluminum prices higher as it is a key passageway for deliveries from the Middle East.

“Recent circumstances have affected and are affecting domestic industries that use agricultural equipment, industrial equipment and machinery, and other related products,” Trump’s order on Monday noted.

It is the latest adjustment to Trump’s steel and aluminum tariffs, after firms pushed back on onerous rules.

US tariffs on steel, aluminum and copper generally stand at 50%.

In April, Trump moved to lower tariffs on products deemed to contain substantial amounts of these metals to 25% – targeting their full value rather than the amount of the metals they contain – in a bid to simplify the system.

Besides agricultural equipment, Trump’s latest order said the lower 15% rate would also apply to certain heating, ventilation and air conditioning systems that are mainly for residential use.