If the world’s farmers are to grow enough food to feed 9 billion people by the year 2050, they’d better get a move on.

A study released at the World Food Prize’s Borlaug Dialogue in Des Moines, IA says the growth rate of agricultural productivity is lagging behind that needed to feed an additional 3 billion people.

The Global Harvest Initiative’s 2010 GAP Report, developed with the Farm Foundation and USDA’s Economic Research Service, was designed to gauge the pace of global agricultural productivity growth against future needs for food.

Doubling agricultural output to meet global demand by 2050 will require and annual average growth of at least 1.75% in total factor productivity, according to Neil Conklin, president of the Farm Foundation and author of the report.