As shown before, there are methods to estimate nutrients (N and P in particular) in organic fertilisers, as well as the availability of N to crops. In a second step, a relation to the UAA available and to specific crops can be established, to get an impression on the fertilising intensity with organic fertilisers.
There are crops which can utilise organic bound nutrients better,e. g. corn/maize (main and strong growth period in the warm season, when there is increased mineralisation) or not as good, e. g. sugar beet, where N-fertilisation should be resticted to avoid negative influence on the harvestable sugar yield. On grassland, especially when used as pasture, due to hygienic reasons, manure fertilisation should only be applied in combination with a waiting period. Therefore, it makes sense to divide the available organic fertiliser according to the actual crop pattern of the area to be examined (Member State, region or farm).
For smaller areas (farm, field), agricultural surveys could be used to learn about farming practices and to estimate the most fertilised crops. In France, grassland and corn silage are the two crops that receive the most organic fertilisation according to surveys (in frequency and quantity).
Organic fertilisation/ha could therefore be used as indicators for nitrogen leaching, especially in intensive breeding areas. The risk of nitrogen leaching increases with the rate organic fertilisers are applied but also with the percentage of less-availabe nitrogen.