Fertilisers use in agriculture
The application of nitrogen and phosphorus fertilisers in the European Union is nowadays lower than in the ‘80s. However, fertilisers use has remained almost stable in the last decade ( EUROSTAT, 2018 ).
Long-time data series indicate that in Western European countries the consumption of fertilisers has substantially grown from the ‘60s to the ‘90s, but thereafter it started to decrease. In Eastern European countries, a drastic drop in fertilisers consumption has been recorded at the beginning of the ‘90s, in conjunction with the collapse of the Soviet Union, followed by a gradual increase in the last 10 years. This happened for example in Bulgaria, Slovakia, Poland, Estonia and Latvia ( ).
Estimations of the spatial distribution of fertiliser applications across Europe (based on EUROSTAT data, and ) show that some agricultural intensive regions still receive high nutrients inputs. This occurs for example in the Netherlands, Belgium, Northern Italy and France. Local elevated rates are the result of combined applications of mineral fertilisers and manure from intensive breeding farms.
Pressures on freshwater quality
How do fertiliser inputs become a threat for water quality and aquatic ecosystems?
The excess of nutrients from fertilisers that are not used by the plants nor retained in the soil can be lost to the atmosphere or to the water system. Nitrogen and phosphorus can be washed off to surface waters transported in surface runoff together with sediments, or can percolate through the underground and reach groundwater aquifers. In the river basin, groundwater and surface waters are connected, and nutrients can flow from the fields to the river system and the coastal waters ().
At the farm or regional scale, a nutrient balance can be computed considering total nutrient inputs, e.g. mineral and organic fertilisers (plus biological fixation and atmospheric deposition for nitrogen), less nutrient content in the agricultural outputs, represented mainly by crop yields and grazed biomass. The nutrient balance can be used as an indicator of the excess of nutrients on agricultural soils (EUROSTAT fact sheet). A positive nutrient balance is also indicated as “nutrient surplus”. Large nutrient surplus points to high risk of diffuse water pollution from agriculture.
To decrease nutrient surplus without compromising agricultural production, the nutrient use efficiency (NUE, i.e. the nutrient outputs/inputs ratio) of the agricultural system needs to improve. This can involve a proportional reduction of fertilisers, an increase of agricultural yield, or both. In the last two decades countries like Belgium, Netherlands, Germany, Denmark, Sweden, Ireland and Greece, lowered their nitrogen surplus reducing the nutrient fertilisers while keeping the agricultural production at the same level. Conversely, in Hungary and Slovenia nitrogen surplus has diminished despite the increase in fertilisers applications, because the agricultural production has grown more than proportionally to the additional nutrient inputs. In other countries, such as in France, Italy and Spain, the nitrogen surplus has remained almost stable in the last two decades.
Time series of nitrogen and phosphorus input, output and balance per country
The excess of nutrients severely impairs the quality and use of water. Concentrations of nitrate higher than 50 mg/l are dangerous for human consumption and health (EU Drinking Water Directive). Elevated and unbalanced concentrations of nutrients in rivers, lakes and coastal waters can feed a proliferation of harmful weeds and algae (phenomenon of eutrophication), destroying the aquatic life and biodiversity, and also damaging recreational and economic activities. Nitrate concentrations in surface waters vary across European regions in space and time. They are related to the climate and hydrological condition in the river basins and to the nitrogen sources of pollution, including fertilisers from agriculture and discharges from waste water treatment plants.
Similarly, phosphate concentrations in surface waters in Europe differ according to regional conditions. Nitrogen and phosphorus concentrations in rivers and lakes are the results of biogeochemical processes of transport and transformation along the river continuum, including the nutrient uptake by algae and aquatic plants.
Fertilisers and freshwater quality in river basins
Estimations of average fertilisation rates in the EU river basins provide an indication of the pressure represented by agriculture on water resources. Changes over the last 20 years indicate some improvements, but in some large agricultural river basins the pressure remains high.
In a river basin the relationship between fertilisers application and the nitrate concentration in water is not always straightforward. Biogeochemical processes and long retention time in soils and groundwater might delay the response of water quality to change in fertilisation. Further other sources of nutrients (e.g. industries and waste water discharges, urban areas or forest land) may contribute to nutrient pollution in different amount.
A trend analysis in 76 large river basins in Europe has showed that in the last two decades an improvement of nitrate concentration at the river mouth associated with a reduction of fertilisers in the basin has been observed in 8% of the cases (the analysis does not account for climatic variability).