N supply and timing must be matched with the crop demand. The use of nitrogen needs particular care because nitrogen leaching and evaporation have significant environmental consequences.
A N fertilization plan must be established that specifies for every crop and plot the N sources and available amounts and shows how the crop demand is met. Taking into account:
Hidden nutrient sources such as importation through polluted air (N).
The soil mineral N status before cropping season.
Mineral N and N mineralisation from organic sources.
IP guidelines have to define for each crop the maximum nitrogen input, (expressed in kg N/ha/year or crop rotation component), and specify eventually the time-window of adequate N application.
The chemical content of at least NPK in all inorganic and organic fertilizers must be known and documented.
Where possible and appropriate N fertilization systems must be used that enable split applications based on N status of soils and or plants.