Efficiency of fertilizer nitrogen in cereal production: Retrospects and prospects

Presently, 50% of the human population relies on nitrogen (N) fertilizer for food production. The world today uses around 83 million metric tons of N, which is about a 100-fold increase over the last 100 years. About 60% of global N fertilizer is used for producing the world's three major cereals: rice, wheat, and maize. Projections estimate that 50 to 70% more cereal grain will be required by 2050 to feed 9.3 billion people. This will require increased use of N of similar magnitude if the efficiency with which N is used by the crop is not improved. Fertilizer N-recovery efficiency by the first crop is 30 to 50%. The remaining N either remains in the soil, the recovery of which in the following crops is very limited (< 7% of applied N up to six consecutive crops), or it is lost from the soil-plant system, causing serious disruptions in ecosystem functions. Much research has been conducted during the past decades to improve N-use efficiency (NUE) by developing fertilizer management strategies based on a better synchronization between the supply and requirement of N by the crop. Importantly, some of these techniques are being adopted on a large scale by farmers. The two challenges ahead are to (1) improve farmers' knowledge and (2) ensure that these techniques are cost-effective and user-friendly so that they provide attractive options for adoption. (c) 2005, Elsevier Inc.