Nitrogen Cycle

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The nitrogen cycle is arguably the second most important cycle, after the carbon cycle, to living organisms. Nitrogen is essential to plant growth, and therefore is a significant contributor to the human food chain, but its presence in the environment is strongly influenced by anthropogenic activities. During the twentieth century land-use changes, such as intensive agriculture, over-fertilization, deforestation, biomass burning, combustion of fossil fuels, industrial activities, and energy production, have significantly disturbed ‘natural’ N biogeochemical cycling. Natural reservoirs now cannot provide nitrogen in the quantity required for global food production. In 1890, total anthropogenic N production was approximately 15×109kgN year−1, but by 1990 this had risen by an order of magnitude to approximately 140×109kgN year−1. The consumption of meat protein is a major driver behind N use in agriculture. Without changes in diet or agricultural practices, fertilizer use will increase over the next 30 years, and fluxes to coastal oceans may increase by another 30%. Solving the problem of nutrient enrichment of surface waters cannot be seen in the short-term. Long-term land-use change is needed. Taking farm land immediately adjacent to water courses out of production is one option that could go some way to allow modern agriculture and water supply to coexist in the same basin. Such proposals inevitably raise questions about who pays for them – farmers, water supply companies, or the taxpayers.