ABSTRACT
Energy and climate change are beginning to dominate the global political agenda and will drive policy formation that will shape the future of agriculture. Energy issues threaten national security and economic stability, as well as access to lowcost nutrient inputs for agriculture. Climate change has the potential to cause serious disruption to agricultural productivity. Paradoxically, nutrient use in agriculture to increase crop yields has the potential to negatively impact climate. This chapter will discuss recent and future energy and climate trends, the relationships between agricultural nutrient use efciency and biofuels, and how global land limitations will shape agriculture in the future. Comparative gross energy yield and nitrogen use efciency for ethanol production from crop residue, switchgrass, grain sorghum, sweet sorghum, and corn grain is presented, showing small differences in nitrogen use efciency, but large differences in gross energy yields. In addition to considering the need to increase crop productivity to meet the demands of a growing population and bioenergy, agricultural nutrient use efciency must be reconsidered with respect to the important energy and climate challenges shaping agriculture today.
