Global inventories of wheat, soybeans and corn are dropping more than forecast as farmers find themselves unable to keep up with rising demand for food, livestock feed and biofuel, according to reports.

Wheat stockpile forecasts for May have been cut by 1.7 percent to 209.6 million metric tons, while soybean reserves for August are now estimated to reach a three-year low of 57.3 million metric tons, according to the U.S. Department of Agriculture. Corn is expected to reach a 16-year low of 801 million bushels.

Soybean production in Brazil and Argentina, the two biggest growers after the U.S., will drop to 115 million metric tons from 124.5 million metric tons in 2011 and the 127 million metric tons forecast in December 2011, according to the USDA. The latest number is now lower than three years ago, when the harvest was damaged by weather. Global soybean production, at 245.07 million metric tons, is also expected to be about 19 million metric tons lower than 2011, the biggest drop since 1965.

Global use of wheat in livestock feed will reach a record 131.06 million metric tons, up from the 130.66 million metric tons estimated in February, said the USDA.