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Farms represent operational units which determine N-use efficiency and incorporation into products and, collectively, at the wider scale, determine the extent of environmental losses from agriculture.
The basic principles and objectives of using N, from whatever source, pertain to different systems across the wide range of farming types across Europe.
In addition to managing external inputs (fertilisers), there is much opportunity to improve N transfers within the farm. Mineral fertilisers are added to balance supply/demand for crops. Some systems rely on legume-N which, once incorporated into farm cycles, behaves in the same way as other N forms.
Farm N cycles, their constituent parts and controlling influences are described and generalised principles identified.
Farm budgets for a range of systems, focussing on typical practice in NW Europe are shown which illustrate some general, important differences between farming systems.
Key findings/state of knowledge
Benefits of using N effectively are far reaching with immediate impact in promoting production. Use of N also provides an effective and flexible management tool for farmers.
Crop N requirements are determined from response curves and economic optima. Advice is supplied to farmers from various sources but the extent to which it is taken depends on many factors. New technologies are available to improve N-use efficiency. The basis of good N management is to optimise efficiency of added and soil N by increasing the temporal and spatial coincidence between availability and uptake of N.
A large part of agricultural soils in Europe are exposed to high N inputs because of animal manure and chemical fertiliser use. Large parts of the European natural soils are exposed to high atmospheric N deposition.
High N inputs threaten soil quality, which may negatively affect food and biomass production and biodiversity and enhance emissions of harmful N compounds from soils to water and the atmosphere.
An overview of the major soil functions and soil threats are presented, including a description of the objectives of the European Soil Strategy.
The major N threats on soil quality for both agricultural and natural soils are related to changes in soil organic content and quality, soil acidification, and loss of soil diversity. These threats are described using literature.
Key findings/state of knowledge
Generally, N has a positive effect on soil quality of agricultural soils, because it enhances soil fertility and conditions for crop growth. However, it generally has a negative effect on soil quality of natural soils, because it results in changes in plant diversity.
Soil acts as a filter and buffer for N, and protects water and atmosphere against N pollution. However, the filter and buffer capacity of soils is frequently exceeded by excess of N in both agricultural and natural soils, which results in emission of N to the environment.
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