Future food, fiber, and fuel demands cannot be met by expanding cropland; continued advances in nutrient use efficiency will be essential. With a growing population, dwindling arable land, and rising biofuel demand, the world must rely on genetic improvements in crop productivity, soil conservation, and nutrient efficiency rather than expansion of harvested area. This CAST Issue Paper examines the background to current conditions and addresses requirements for world food production over the next 40 years, demonstrating why research in nutrient use, recovery, and recycling is crucial.