World cereal consumption has more than doubled in the last 30 years, while meat consumption has tripled since 1961 and is increasing at a linear rate.

The agricultural success story is that rising demand has been met; more people are now better fed than they were a generation ago.

One of the many environmental consequences, only now becoming clear, is significant disruption of the global nitrogen cycle.

• In the past half century, the application of inorganic nitrogen fertilizers world-wide has increased more than ninefold, and the number of livestock has more than doubled since 1960.
• Fertilizers and animal manures have increased and concentrated, respectively, the amount of nitrogen entering soils, freshwater and marine ecosystems.
• Human activity has actually doubled the natural annual rate of nitrogen fixation, and by far the largest single cause is agriculture.

Most agricultural experts believe that increasing global demand for cereals and meat can be met, and forecast that grain production will rise by about 15 percent by 2010, and by 25 to 40 percent by 2020.

More fertilizer will be needed to produce the additional cereals and fodder crops for animals. Looking ahead just 12 years, if current practices persist, global fertilizer consumption will increase by at least 55 percent by 2010.

• In some under-fertilized regions, such as South America and Africa, this could be an entirely positive development.
• In others, notably parts of South and East Asia, nitrogen saturation will approach the levels already experienced in northwestern Europe and parts of the United States.
• The incidence and severity of nitrate contamination of drinking water, ground-level ozone formation, crop damage, forest die-back, and damage to coastal fisheries from algal blooms ("red" and "brown" tides) can all be expected to increase dramatically.

Opportunities for change

Some reduction in consumer demand for meat might be possible, particularly where per capita consumption is high enough to generate some health concerns.

Currently, well under half the nitrogen applied to crops world-wide in fertilizer is actually utilized by growing plants. The rest becomes a pollutant, wasting farmers' money and imposing heavy costs on society in terms of clean-up requirements and lost productivity. Animal manure, rather than substituting for inorganic fertilizers, is increasingly added to them, or simply disposed of as a waste product.

Economic and regulatory incentives for more timely and efficient use, research which improves understanding of fertilizer application and uptake by crops, agricultural extension and outreach programs which encourage farm management practices to reduce nitrogen run-off are all urgently needed so that food production can rise without further contamination of soils, water supplies, and coastal zones.