Introduction

Agriculture worldwide faces a variety of challenges. In some regions, production must be expanded to provide food for growing populations, in others there are surpluses and agricultural production has to be matched to effective demand. Environmental issues are increasingly constraining agricultural systems.

Often the requirements of economically viable agricultural systems and the environment appear to be in conflict. This conflict is more apparent than real and, as an aid to resolve the dilemma, representatives from the fertilizer industry and agricultural experts have agreed on a set of 'best agricultural practices', which can contribute to the development of agricultural systems that are both environmentally and economically sustainable. Ecological measures can be successfully implemented only under economically favourable conditions.

Objectives

1. To integrate the principles of economic crop production with environmental protection.
2. To create public confidence that farmers use fertilizers responsibly.
3. To provide planners and policy-makers with a sound understanding of the role of fertilizer in sustainable systems of crop production.

Crop Nutrition and Plant Nutrient Loss from Soils

Crops require adequate amounts of plant nutrients to produce optimum yields. Since many soils throughout the world are not capable of supplying adequate amounts of all nutrients, the application of mineral fertilizers and other sources of plant nutrients is required to ensure optimum crop production. Rates and timing of application and a balanced supply of nutrients for the crop are important in order to minimize the risk of leaching and thus pollution.

All crop systems result in some loss of nutrient, whether the site is fertilized or not. The loss may be to the air, to water, or the nutrients may be fixed in the soil. The quantity of nutrients lost depends not just on the nutrients applied but on the whole agricultural system, in particular the climate, soil type and cropping pattern.

Sustainable production can be achieved only if soil nutrients are maintained at satisfactory levels, supplying additional nutrients, applied at the correct rate and time, if any are lacking.

One advantage of mineral fertilizers is that they can be formulated to provide a balanced supply of the most important nutrients, readily available to the plants at a time and in quantities best suited to their requirements. They are relatively easy to transport and can be stored without risk to the environment.

Organic manures play an important role in integrated plant nutrition but they are often subject to heavy nutrient losses to the environment. Considerable amounts of ammonia are volatilized during their storage and handling. The inorganic N content of manures is highly variable and the organic N is released only slowly so that the supply of available nitrogen to the crop may be insufficient at peak growth unless supplemented with fertilizer N. The manure will normally release nitrate after harvest which may be leached unless an autumn "catch" crop is planted. Application year after year at a rate which supplies sufficient mineral N to crop will result in high soil organic levels, with a possible increase in the risk of leaching.

It is important to improve the techniques and practices for the use of manure and slurry, in order to increase their efficiency and reduce losses. Excessive application must be avoided.

Quantities of Plant Nutrients to be Applied

The amount of plant nutrients applied in fertilizers must be assessed for individual fields to ensure that it is matched to the uptake of nutrients by the plant, allows vigorous crop growth and maintains satisfatory levels in the soil.

It is important that the economic optimum for the individual field, based on a realistic assessment of the anticipated yield, should not be exceeded. Some nutrient losses, resulting from denitrification, volatilization and naturally-occurring leaching, are unavoidable. They occur whether the site is fertilized or not. But, up to the economic rate, the additional nutrient loss, compared with zero fertilizer application, can be negligible. Additional quantities should not be applied as an insurance.

The best available local techniques should be used for assessing the optimum amount of fertilizer to apply. Techniques have been developed, although some, such as the "N-min" test need further refinement and may not be generally applicable. These techniques are available either directly to the farmer or indirectly through extension services.

On the farm, accurate records of crop performance allow better yield forecasts to be made.

In areas that are particularly environmentally sensitive, standard farm practice may need to be modified, including the planting of "catch"-crops, band application of fertilizers, and so on.

Timing and Method of Application

The timing of a fertilizer application and the choice of applicator will be determined by the farming system and by the need to avoid nutrient losses to the environment and to maximize crop nutrient uptake. The provision of maximum farmer convenience is a lesser consideration.

The amount and timing of nutrient uptake by the crop depends on the variety, its planting date and the crop rotation, as well as on external factors such as soil and weather conditions. Nitrogenous fertilizers should be applied only at times when the crops can use the nitrogen or when there is a very low risk of leaching. All yield-promoting measures, such as proper tillage practices and crop protection, enhance nutrient uptake, thus improving fertilizer efficiency and reducing the risk of nutrient losses.

When applying fertilizers, unsuitable weather and soil conditions must be avoided as far as possible. Application should be made after consideration of best-available weather and soil information, likely crop performance and an assessment of alternative application technology or management which could minimize non-productive nutrient losses under adverse conditions. Fertilizer should not be applied to uncropped borders of fields or near to or directly into natural water courses.

In addition, the application equipment must give a uniform spread at the correct rate. The application equipment must be well chosen, properly adjusted and maintained.

Type of Fertilizer to be Applied

The type of fertilizer used should always take account of its environmental impact and its efficiency for economic crop production. It may be advantageous to apply ammonium-based nitrogen fertilizers with nitrification inhibitors when a high risk of leaching has been identified. Slow-release fertilizers may be appropriate for certain crop and site conditions. Both chemical form and physical characteristics must be matched to local conditions.

However, factors other than the purely agronomic, may explain the use of a type of fertilizer. In Europe, for example, history and tradition, the availability of raw materials, the established manufacturing processes, economic considerations and management aspects have influenced the types of fertilizers used. Change to a different type of fertilizer, even if agronomically more suitable, may require a period of adaptation.

For further information :

EFMA - European Fertilizer Manufacturers Association
Avenue E. Van Nieuwenhuyse 4 - 1160 Bruxelles - Belgium
Tel: +32 2 6753550 - Fax: +32 2 6753961
Web : http://www.efma.org