K. Ladha1 and Debashis Chakraborty2
1International Rice Research Institute, Makati city 1226, Philippines,www.irri.org, [email protected]
2Indian Agricultural Research Institute, New Delhi 110012, India
Presently, 50 percent of the human population relies on synthetic nitrogen (N) fertilizer for food production. In agriculture of subsistence during pre-chemical era, biological N2 fixation (BNF) was the primary source of reactive N but, in recent decades, chemical N fixation (synthetic N) has become more important in global agriculture. Today, synthetic N fertilizer introduces reactive N of over 100 Tg N year-1 into the global environment to increase food production. Although this has sustained the large human population in meeting dietary needs, a large agriculture area in the world still lacks available N to sustain the crop production. This together with a larger growing population obviously means that the future global demand for synthetic N is bound to grow markedly. However, since a substantial amount of N applied for food production is lost to the environment, this has also caused a web of problems causing air and water pollution and contributing to climate change. Unlike nonreactive gaseous N2, reactive N has magnified the adverse effects because the same atom of N can cause multiple effects in the atmosphere, in terrestrial ecosystems, in freshwater and marine systems, and on human health. This paper, while focusing three major cereals (maize, rice and wheat) of global importance, (i) analyses the global consumption and demand for fertilizer N, (ii) evaluates synthetic fertilizer N recovery efficiency and losses, (iii) examines long-term effects of continuous N fertilization on changes in soil N reserves, (iv) constructs global N budgets, and (v) analyses various strategies available to improve the overall use efficiency of N.