Replacing plant nutrients removed during harvests, and minimizing nutrient losses to the environment are the goals of effective fertilization. This involves both efficient and balanced fertilization to ensure adequate plant nutrition while maintaining optimum soil fertility levels.

Fertilizer Use Efficiency

In developed countries, there has been a marked improvement in the efficiency of fertilizer use over the past 30 years, triggered by economic pressures and concerns about the environment. Current fertilizer consumption in West Europe is around the same level as it was in 1970, but the average wheat yield has increased over the same period from 2.7 tonnes per hectare to 6.0 tonnes per hectare. In the United States, maize production per kilogram of nitrogen (N) applied increased from 42 kilograms in 1980 to 57 kilograms in 2000.

The efficiency of fertilizer use is improving more slowly in developing countries. For instance, in India, the efficiency of nitrogen applied to rice is only 30-35 per cent, and 20-25 per cent for phosphorus (P). In view of the large quantities involved, inefficiencies in fertilizer use not only have an environmental effect, but also represent a substantial economic loss.

Balanced Fertilization

Plant health, productivity and nutritional value are substantially influenced by a correct balance of available essential nutrients. Scientific trials clearly demonstrate that if any plant nutrient is deficient, crop growth will be affected. The proper use of fertilizers corrects imbalances or deficiencies in plant nutrients. Integrating fertilizers with manures and leguminous crops within comprehensive plant nutrition systems that are tailored to local conditions is the key to sustainable soil fertility.

Since 1960, world nitrogen consumption has increased much faster than that of phosphorus and potassium (K), jumping from 12 to 84 million tonnes between 1960 and 2000. The ratio between nitrogen (N), phosphate (P₂O₅) and potash (K₂O) changed from 1:0.95:0.73 in 1960 to 1:0.39:0.26 in 2000. This development was driven by economic and technical factors, as well as by short-term risk management considerations. The fact that nitrogen fertilizers tend to be preferred by farmers derives from their relatively low cost per unit of nutrient, their widespread availability, and the quick yield response of new varieties to nitrogen. Farmers also view nitrogen inputs as a risk-reducing factor because of its influence on growth and yield, in particular when their financial resources are limited or when their land tenure is insecure, which is the case in many developing countries.

In recent decades, farmers have tended to rely primarily on nitrogen fertilizers to maximize crop yields, rather than targeting optimal achievable yields determined by local agronomic, economic and environmental conditions. However, high levels of nitrogen fertilization without appropriate balance may result in negative effects on the soil and the environment (nitrogen losses through leaching or volatilization) and increased incidence of crop lodging, weed competition and pest attacks. In some crops, high nitrogen content decreases quality, in particular storage ability. On the other hand, too little nitrogen results in lost yields and farmer profits, inefficient use of other plant nutrients, and potential damage to the environment.

An adequate supply of phosphorus is essential because of its functions in vital molecules such as proteins and nucleic acids that govern plant's life. Phosphorus stimulates root development and is necessary for cell division. Potassium is of vital importance for cells and their enzymatic and metabolic functions. Both phosphorus and potassium help to protect plants against stress, such as that caused by pests, diseases, drought or frost. They also considerably improve the efficiency of nitrogen uptake.

Truly balanced fertilization requires supplying adequate amounts of nitrogen, phosphorus and potassium, plus other nutrients such as magnesium (Mg), sulphur (S) and micronutrients, as determined by soil tests and crop requirements.

Acid and sodic soils must undergo remediation for effective fertilizer use. Applying lime to acid soils and gypsum to sodic soils is critical to effective nutrient management.

IFA's Position

IFA considers effective fertilization as "the nutrient mix which ensures optimal nutrient uptake". This primarily means an adequate supply of nitrogen, phosphorus, potassium, sulphur and other nutrients in line with soil reserves and the crop requirements for a target yield, while preserving the environment.

IFA promotes efficient, balanced and environment friendly application of fertilizers, in accordance with scientific recommendations. In this end, IFA has prepared and distributes a World Fertilizer Use Manual with crop-specific advice, Guidelines on Best Agricultural Practices adapted to conditions in a number of regions and Codes of Best Agricultural Practices on the most frequently used fertilizers.

December 2002