Contributions of Fertilizer Nitrogen in Global Cereal Production; Soil Organic Matter Status and Nitrogen Balance

摘要

Presently, 50 percent of the human population relies on synthetic nitrogen (N) fertilizer for food production. In the subsistence agriculture of the pre-chemical era, biological N2 fixation (BNF) was the primary source of reactive N but, in recent years, chemical N fixation (synthetic N) has become more important in global agriculture. Today, the Haber-Bosch and cultivation-induced BNF processes of converting N2 from the atmosphere to ammonia introduce reactive N of over 100 Tg N/year into the globalenvironment to increase food production (Galloway et al., 2004). Although this has sustained the large human population of Earth in meeting dietary needs, a large population in the world still lacks available N to sustain crop production. This togetherwith increasing population obviously means that the future global demand for reactive N is bound to grow substantially (Cass-man et al., 2003; Wood, Henao and Rosegrant, 2004). However, since a substantial amount of N created for food production is lostto the environment, this has also greatly increased the contribution of reactive N to a wide variety of environmental problems (Galloway etal., 2004; Vitousek ef al., 2010). 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 (i) analyses the global consumption and demand for fertilizer N in relation to cereal production, (ii) evaluates the nitrogen-15 (15N) and N difference methods to determine synthetic N recovery efficiency in current and succeeding crops grown across agro-climatic regions, (iii) examines long-term use of N on the sustenance of soil organic matter (SOM), (iv) constructs global N balances, and (v) analyses various strategies available to improve the overall use efficiency of N.