Historical Context

European agriculture is relatively new (<130 years) to many of the industrialized, grain-exporting countries such as the USA, Canada, Australia, Argentina and others. Grain production in these countries has relied, to a significant extent, on indigenous soil N supplies, and this "N mining" effect is well documented (e.g. Campbell et al. 1990). For example, in western Canada (Manitoba, Saskatchewan and Alberta), a deficit of approximately 25 million t of N was created between 1883 and 1990 through crop production (Morrison, Kraft 1994). Similar observations were made after cropping for less than 50 years in Australia (Grace et al. 1995). The need to "replace" some of this lost N has been recognized for some time, and it was discussed in 1924 at a special conference organized by the American Society of Agronomy entitled: "The legume problem". The goal of the conference was to identify opportunities for including legumes in USA dryland cropping systems. This goal is still important today, since rebuilding soil biological fertility with inorganic fertilizer N has been found to be uneconomical in many areas, especially those where water is limiting (Morrison, Kraft 1994).

A second important reason for emphasizing BNF in industrialized cropping systems is to reduce reliance on fossil-fuel energy, which is currently used in inorganic N production.

It must be recognized that while some crop production regions are starved for N (e.g. dryland regions of western North America and Australia), other agricultural regions often suffer from an excess amount of N. Therefore, the need for BNF in industrialized countries is not uniform across nations, or even within nations.

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