Role of isotopes in fertilizer studies

Fertilizers play a major role in increasing and stabilising the yield of different crops throughout the world.In the farmers` field it is essential that fertilizer application to be made in such a manner that the crop will take up the maximum nutrients from the applied fertilizer.A combination of the correct placement, time of application and appropriate chemical composition of the fertilizer will ensure the greatest uptake of nutrient by the crop with minimum loss due to interaction in the soil-fertilizer processes.In the soil-plant system, it is not possible to distinguish between soil and fertilizer derived nutrients by means of classical/chemical methods.Fertilizer labelled with the appropriate stable (N-15) or radioactive (P-32, P-33) isotops provide the only direct means of following the fate of such nutrients in soils and their uptake by the plants.Fertilizer labelled with the appropriate isotops of interest will thus form an invaluable tool in an attempt to select fertilization practices for different soils and climatic conditions, to obtain quantitative information on the efficiency of the use by crops of nutrients from fertilizers, to study nutrient movement in the soil, and to avoid environmental pollution.For these reasons, the Soil Fertility, Irrigation and Crop Production Section of the Joint FAO/IAEA Division organised, beginning from 1962, field experiments with labelled fertilizers in different parts of the world, icluding the tropics.The paper deals with some of the results of the research undertaken with fertilizers labelled with stable as well as radioactive isotopes, in different countries through the Co-ordinated Research Programmes or IAEA Technical C0-operation Projects, co-ordinated by the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture.The role of isotopes in finding ways to increase the efficiency of the utilisation of fertilizer nutrients by the plants and of increasing yield per unit area of crops, such as rice, maize, wheat, soybean, sunflower, is discussed.