A growing interest has been shown recently in the dymanics of nitrogen in agricultural and natural ecosystems. This has been caused by increasing demands for food and fibre by a rapidly expanding world population, and by a growing concern that increased land clearing, cultivation and use of both fertilizer and biologically fixed nitrogen can have detrimental effects on the environment. These include effects on water quality, eutrophication of surface waters and changes in atmospheric composition all caused by increased cycling of nitrogenous compounds. The input and availability of nitrogen frequently affects the productivity of farming systems more than any other single management factor, but often the nitrogen is used inefficiently. Much of the fertilizer nitrogen applied to the soil is not utilised by the crop: it is lost either in solution form, by leaching of nitrate, or in gaseous forms as ammonia, nitrous oxide, nitric oxide or dinitrogen. The leached nitrate can contaminate rivers and ground waters, while the emitted ammonia can contaminate surface waters or combine with atmospheric sulfur dioxide to form aerosols which affect visibility, health and climate. There is also concern that increased evolution of nitrous oxide will deplete the protective ozone layer of the stratosphere. The possibility of a link between the intensity of agricultural use of nitrogen, nitrous oxide emissions and amounts of stratospheric ozone has focussed attention on these interactions.

The study of soil nitrogen has long been an active field, but it was generally pivoted on agricultural and forestry production, and animal husbandry. With the rapid increase in the use of fertilizer nitrogen, more attention has been paid to the relationship between nitrogen management and environmental quality and human health. In addition, the study of soil nitrogen has become more comprehensive with the development of related sciences. The quantitative study of the processes of nitrogen cycling and their interrelationships has been an important part of this project and has attracted the attention of scientists all over the world. Nitrogen is one of the most important nutrients for plant growth and the application of fertilizer nitrogen is playing an important role in agricultural production. The annual consumption of fertilizer nitrogen in the world has reached 70 million tons, and China has an annual consumption of more than 15 million tons and is the largest fertilizer nitrogen consumer in the world. However, the efficiency of fertilizer nitrogen is low and losses are large. It is estimated that nitrogen losses from agriculture in China can be as high as 40-60% of the nitrogen applied. Some of the lost nitrogen enters the atmosphere and contributes to the greenhouse effect and some enters water bodies to pollute the water. Consequently, it is important for scientists all over the world to improve the efficiency of use of fertilizer nitrogen, to promote the biological fixation of nitrogen and to increase the nitrogen-supplying potential of soils.

Increasing stress is being placed on the environment by man's activities including those of changing land usage for increased food production and the release of carbon dioxide due to fossil fuel combustion. Further stresses may occur if agricultural practice is modified by using plant products for liquid fuels. Rational management of these activities can only occur if there is a thorough under standing of the biogeochemical cycles of the major plant nutrients, carbon, nitrogen, sulfur and phosphorus. A vital part of this understanding concerns the interactions between these cycles, where in various limiting processes the cycle of one element exerts a controlling influence over the cycle of one or more of the other elements. A well known example of this interaction is the role of sulfur, nitrogen and phosphorus as limiting factors in plant growth i.e. carbon uptake by the biosphere. A related effect is the suggested increase in nitrogen fixation by legumes due to CO2 enrichment in the atmosphere. Other interactions occur during the mineralisation of nitrogen, sulfur and phosphorus associated with the release of organic carbon during the decay of plant material and between the carbon substrate and mineral forms of nitrogen and sulfur during denitrification and bacterial sulfate reduction. Increased sulfur dioxide and nitrogen oxide emissions to the atmosphere in some areas are causing acid rain which appears to be affecting the productivity of some land and aquatic ecosystems."

A growing interest has been shown recently in the dymanics of nitrogen in agricultural and natural ecosystems. This has been caused by increasing demands for food and fibre by a rapidly expanding world population, and by a growing concern that increased land clearing, cultivation and use of both fertilizer and biologically fixed nitrogen can have detrimental effects on the environment. These include effects on water quality, eutrophication of surface waters and changes in atmospheric composition all caused by increased cycling of nitrogenous compounds. The input and availability of nitrogen frequently affects the productivity of farming systems more than any other single management factor, but often the nitrogen is used inefficiently. Much of the fertilizer nitrogen applied to the soil is not utilised by the crop: it is lost either in solution form, by leaching of nitrate, or in gaseous forms as ammonia, nitrous oxide, nitric oxide or dinitrogen. The leached nitrate can contaminate rivers and ground waters, while the emitted ammonia can contaminate surface waters or combine with atmospheric sulfur dioxide to form aerosols which affect visibility, health and climate. There is also concern that increased evolution of nitrous oxide will deplete the protective ozone layer of the stratosphere. The possibility of a link between the intensity of agricultural use of nitrogen, nitrous oxide emissions and amounts of stratospheric ozone has focussed attention on these interactions.