|Mineral Fertilizer Use and the Environment (IFA - UNEP, 1998, 52 p.)|
Using comparisons of nutrient inputs and outputs as a yardstick for environmental correctness of fertilizing practices in scientific publications and studies started during the 1980s. Different types of nutrient balances came into use. The most common is a comparison of nutrient inputs and outputs at farm gate level (the alternative soil surface balance is more complicated). The account examines the relationship between applied nutrients and nutrients removal in the harvested crop. It considers all nutrients, whether of mineral or organic origin, which may be applied. The system ideally should also consider changes in soil nutrient levels and, in some cases, admissible losses.
Nutrient accounting is being developed by the OECD as one of the environmental indicators. These are national indicators, and, as the OECD points out these balances require careful interpretation. For example, a country may have a national surplus while experiencing nitrate pollution in some areas and nutrient depletion in others. The nutrient balance indicator needs to be used in conjunction with indicators on farm nutrient management, soil quality and water quality.
Livestock wastes contain substantial amounts of plant nutrients (see the section on Organic Materials). It is therefore evident that all sources of nutrients should be into account when determining rates of mineral fertilization.
Accounting systems based on the nutrient input and output are used in some European countries as a measure for the environmental performance of farms, particularly in countries with a manure disposal problem.
In Denmark, since 1994, farmers have had to prepare fertilization plans and the amount of nitrogen that may be applied to each type of crop is regulated. Another requirement is that 65% of the cultivated area must be covered by a green crop in winter. There are heavy fines in the event of infringement. In Germany a federal Regulation of fertilizer use model regulation came into effect in January 1996. The model must now be implemented in the individual Federal States. In Norway fertilizer plans are now compulsory. In the Netherlands a compulsory nutrient accounting scheme is starting in 1998. Nutrient applications over the maximum will be taxed.
Nutrient accounts may indicated a deficit as well as a surplus. The exercise would therefore be useful also in developing countries where soils are being mined of their nutrients. A substantial proportion of the nutrients which find their way into the manure produced by intensive livestock units originate from animal feed which has been imported from other regions of the world, thus depleting the nutrients in the soils of the exporting regions. But in many developing countries soils are also being exhausted just to provide a subsistence for their cultivators.