MANAGING NITROGEN FOR SUSTAINABLE CROP PRODUCTION

This paper discusses the influence of N resources (fertilizer, legume, soil) on sustainable agriculture in temperate/boreal ecosystems (exem plified by the Canadian prairies), and in the humid, subhumid and semi -arid tropic (exemplified by southeast Asia and central and south Amer ica). A sustainable agricultural system is one that is economically vi able, provides safe, nutritious food, and. conserves or enhances the e nvironment. Consequently, we discuss the impact of N on crop yields, n itrogen use efficiency (NUE), food quality, environmental quality and on socioeconomic factors. Considerably more long-term research has bee n conducted in the temperate regions, consequently this was where most information was available. However, the principles governing the beha viour of N are very similar in all ecosystems. It is mainly the rates of nutrient cycling and the socioeconomic constraints that differ. Leg umes and N fertilizers, used in a responsible manner, will increase cr op production, provide quality food, increase net returns, reduce risk of monetary loss, improve soil quality, and reduce N loss via leachin g and gaseous means. The key to sustainable management of N is to sync hronize N supply with N use by the crop. Because societies in most tem perate ecosystems are more affluent they are better positioned to enco urage adoption of management techniques that promote sustainability. I n contrast, most producers in the tropics are, subsistence farmers; co nsequently, their immediate goal is economic survival, not preservatio n of the environment.