Wim DE VRIES
Professor, Wageningen University & Research
PhD Researcher at Environmental Systems Analysis Group, Wageningen University & Research
The Netherlands is a high-livestock density territory. How has the ratio between mineral fertilizers and manure changed over time, and what is the relative contribution of each to environmental challenges in the country?
For nitrogen, about two-thirds is applied in the form of manure (in Dutch dierlijke mest). and one third as fertilizer (in Dutch kunstmest). For phosphate, > 90% is applied as manure. Both nitrogen and phosphorus inputs have declined by ca. 40 % over the last 30 years (see figure below). Current environmental problems related to N and P are mainly caused by manure, due to the extremely high animal densities (3.8 livestock units per hectare of agricultural land as compared to an EU average of 0.8) that are sustained by high feed imports.
How can regions around the world reconcile still required N inputs to enhance crop production with concerns about N losses to air and water?
(i) Re-location strategies: reduce agricultural N inputs in areas where farmers practice is (far) above crop N demand (e.g. China, the Netherlands: give right rate) and enhance N inputs in areas where it is too low (e.g. eastern Europe, Africa, parts of Latin America) up to a level where N losses to air and water are acceptable in view of impacts on ecosystems.
(ii) Increase nitrogen use efficiency, to allow a higher crop production at lower losses (4-R strategies: right type, time and place in addition to right rate, mentioned before).
(iii) Food-chain strategies: increase recycling of nutrients (compost, manure, sludge)
(iv) Reduce food waste from field level to consumer level
You have recently completed an analysis of optimal N inputs at the EU level. What are the key messages?
Safeguarding surface water quality requires the strongest reductions in agricultural nitrogen inputs, followed by nitrogen deposition on terrestrial ecosystems, and groundwater quality.
Critical inputs are most strongly exceeded in regions with high livestock density and related high N inputs, such as Ireland, the Netherlands, Belgium and Luxembourg, Bretagne in France and the Po valley in Italy
Achieving yield potentials requires the strongest increases in N inputs in Poland, the Baltic region and Portugal.
For areas where critical N losses are exceeded, increasing NUE can be a strategy to reconcile food production with environmental targets. However, some regions require NUEs of more than 90% to meet environmental targets at current production – in these regions, reductions in inputs and thus production probably need to be accepted if we want to safeguard environmental quality.
How can modelling work help all concerned stakeholders develop innovative approaches? Would you advise a similar analysis at the global scale?
Modelling provides a consistent approach to give insights in the scale of the problem, in the spatial variation and in the relative contribution of different drivers. Within Europe, we observe strong variation in critical N inputs: in some regions, critical thresholds are already exceeded, while in other regions inputs can safely increase without threatening environmental quality. At the global scale, these differences are probably even larger, so an analysis at this scale would certainly be interesting.