Agriculture

Abstract

Agriculture is a main contributor of nitrogen (N) and phosphorus (P) to the marine environment, and thereby a main cause of eutrophication of marine ecosystems. By the end of the twentieth century, roughly half of the total N and P input into the aquatic environment originated from agriculture. The relative contribution of agriculture has increased by a factor of 8 for N, and by a factor of 1.6 for P during the last century. As a result, the N/P ratio of the inputs have strongly increased. Contributions from agriculture increased especially from the 1960s, following the rapid rise in fertilizer use and manure production. Enlarged areas of agricultural land at the expense of natural areas including forests have also contributed. Leaching and runoff are the main pathways for N losses, while runoff is the main pathway for P losses from agriculture to sea.

There are huge differences between countries in N and P use efficiencies and N and P surpluses, and hence in N and P losses. In Sub-Saharan countries, N and P surpluses are small or negative. Surpluses are high and increasing in countries in transition (China, India, Brazil). Many affluent countries (US, EU) have relatively high but decreasing surpluses, following the implementation of good agricultural practices and environmental regulations in practice.

Forecasts indicate that global food production may have to increase by 50% or more relative to the production level in 2010 during the next five decades, while N and P losses will have to decrease at the same time, to halt eutrophication and biodiversity losses. For this to happen, N and P use efficiencies in food production have to increase drastically, and N and P from manure, sludge, and wastes have to be recycled and reused more effectively.