Differences of up to 100 kg nitrogen per hectare, depending on the country: fertilisation recommendations are not the same throughout Europe.
Excess nitrogen enters the environment when nitrogen inputs exceed crop demand. If these losses are high, the excess N concentrations have negative impacts leading to eutrophication of water bodies and coastal areas and increasing the greenhouse effect.
Recommendations for nitrogen fertilisation are one approach to reducing these losses. They rely on different methods to calculate the fertilisation requirements and indicate the maximum permitted nitrogen application rate, taking into account local conditions. The thresholds are mandatory or indicative, depending on the country.
In this context, scientists at Agropscope in collaboration with European colleagues have analysed the nitrogen fertilisation recommendations of ten Western European countries to identify similarities and differences and propose suggestions for improvement.
Methods vary in complexity
Their study revealed that three different methods are used in Europe to calculate nitrogen fertilisation recommendations:
- N mass balances (France, Italy, Spain)
- Corrected standards (Germany, Netherlands, Switzerland, Luxembourg)
- Pre-parameterised calculations, which rely on a soil N supply typology (UK, Ireland, Belgium)
In total, 16 variables were identified in the calculation methods. The more complex methods use ten (Italy, France), while the simplest rely on only three (Luxembourg). The most common variables are nitrogen uptake by the crop, availability of nitrogen in farmyard and recycled manure and nitrogen released by crop residues. In contrast, few countries explicitly consider nitrogen losses to ground and surface waters or to the atmosphere in the calculation methods.
Major differences in the recommended values
On this basis, the scientists calculated the nitrogen recommendations of the ten countries for a wheat crop grown on a farm with livestock where farmyard manure was regularly applied and the same crop on a farm with a diverse crop rotation but without livestock and few applications of farmyard manure.
They found large differences in the resulting recommendations, ranging from almost no fertilisation to up to 135 kg nitrogen per hectares in the first scenario and from 111 to 210 kg nitrogen per hectare in the second.
According to the authors of the study, these differences can be attributed mainly to the fact that the reference values for three of the variables under consideration – nitrogen availability in manure, uptake by crops and leaching – vary across the ten countries. Differences in the calculation method played only a minor role.
A regular review and widespread implementation of the methods is important
The study also showed that all the methods can improve nitrogen efficiency and reduce losses. The important consideration is to use reliable parameters or correction factors adapted to local conditions.
