1. Fertilizer rates in the Yaqui Valley have grown over the past several decades from 172 kg/ha (range: 0 to 280 kg/ha) in 1981 to ∼250 kg/ha of fertilizer N (range: 151 to 396 kg/ha) in 1996 (2) and are now considerably higher than those in many of wheat systems of the United States and Europe. In contrast many of the irrigated rice and wheat systems of Asia have half the fertilizer N application rates of the Yaqui Valley and substantial increases in fertilizer use are expected there [International Fertilizer Industry Association (IFA)/Food and Agriculture Organization (FAO)/International Fertilizer Development Center (IFDC) Fertilizer Use by Crop (FAO Rome 1992); K. G. Cassman and P. L. Pingali GeoJournal 35 299 (1995); P. R. Hobbs K. D. Sayre J. I. Ortiz-Monasterio Increasing Wheat Yields Through Agronomic Methods (Natural Resources Special Report CIMMYT Mexico DF 1997)].
2. C. A. Meisner et al. Wheat Production and Grower Practices in the Yaqui Valley Sonora Mexico (Wheat Special Report No. 6 CIMMYT Mexico DF February 1992); unpublished surveys over the period of 1981 to 1991 carried out by the CIMMYT Economics Program Mexico DF.
3. FAO Fertilizer Yearbook United Nations (1990); United Nations United Nations Statistical Yearbook International Economic and Social Affairs Department (1992); Environmental Protection Agency (EPA) Greenhouse Gas Emissions from Agricultural Ecosystems (Intergovernmental Panel on Climate Change Report Washington DC 1990); B. L. Bumb and C. A. Baanante The Role of Fertilizer in Sustaining Food Security and Protecting the Environment to 2020 (International Food Policy Research Institute Washington DC 1996).
4. Nitrogen fixation: Anthropogenic enhancement-environmental response
5. R. T. Watson L. G. Meiro Filho E. Sanhueza A. Janetos in Climate Change 1992—The Supplementary Report to the Intergovernmental Panel on Climate Change Scientific Assessment (Cambridge Univ. Press New York 1992) pp. 25–46.