Does nitrogen cycle ? : changes in the spatial dynamics of nitrogen with industrial nitrogen fixation

Industrialization of the N cycle after World War II made new spatial dimensions in the movement of N in agriculture and society possible. Nitrogen fertilizer consumption in the USA increased from less than 0.5 million tons/yr in 1940 to more than 11 million tons/yr in 1980. Not only were crop and animal productivity increased with the increased availability, but specialized crop production and animal production regions developed. With N fertilizer available, N in feeds imported to animal production regions does not have to be returned to sustain crop production. Therefore, understanding the biology of N in the farm-level N cycle in either type of production region will be insufficient to understand the consequences of the one-way transfers of N between production regions. An environmental issue associated with the industrialization of N fixation is the depletion of nonrenewable fossil energy reserves to produce and transport fertilizers and agricultural products. Another is the reduced efficiency of N use in crop production as a result of increasing N inputs and the extent of the areas planted to N-fertilized crops. Nitrogen accumulation in manure in animal production regions poses another threat to the environment. Resolving contentious environmental issues may depend on research and management approaches that are consistent with the new spatial dimensions of N movement and the interests of all stakeholders