US farmers are set to sow fewer acres this spring with crops such as corn and wheat, breaking a string of four years of increases in a move likely to support agricultural commodities prices through the economic crisis.

The US Department of Agriculture will reveal its first acreage estimate on Tuesday in its Prospective Plantings report. Because the country exports half the world’s corn, a third of world soyabeans, and a fifth of the world’s wheat, changes in acreage and hence in output have a huge impact in global food prices.