Large-scale organic agriculture : a green promise and a nitrogen brain teaser

Nitrogen is the key to soil fertility: without it, crop yields would be unsatisfactory. The only two major sources of nitrogen for agricultural systems are nitrogen fixation from the air by legumes, organic fertilizers (including livestock manure), and the industrial synthesis of nitrogen fertilizers. While conventional agriculture can rely on this last source, organic agriculture (OA) must do without it. OA therefore relies exclusively on legumes and the recycling of nitrogen from livestock manure. The nitrogen in livestock manure comes from nitrogen ingested by animals from crops or pastures that have themselves been fertilized. The equation is therefore complex when it comes to enabling a significant expansion of organic farming in Europe while seeking to reduce nitrogen surpluses that pollute soil and water, especially if the number of animals decreases, as several forecasts suggest.

Two Scenarios for Exploring the Future of Organic Farming

Researchers at UMR SAS have modeled nitrogen flows across the entire French agricultural system, distinguishing between organic and conventional farming. They compared the current situation with the situation in 2030, using two possible pathways to reach 25% of agricultural land under organic farming:

• Trend Scenario, extending recent trends. Livestock numbers decline slightly in conventional farming but increase in organic farming.
• Reduction Scenario, with a 50% reduction in livestock numbers, while significantly increasing organic livestock numbers. The use of manure from conventional livestock operations is prohibited for organic crops, and the use of industrial fertilizers decreases.

These two scenarios served as a framework for comparing nitrogen flows in soils, crops, pastures, and livestock operations.

The rise of organic farming is profoundly altering the balance

Less nitrogen entering the system.

With more organic farming, less animal feed is imported and less industrial fertilizer is used. As a result, total nitrogen inputs decrease by 9% (Trend) to 28% (Reduction), while nitrogen surpluses decrease by 9% and 26%, respectively, for each scenario.

More legumes… but lower productivity.

Legumes play a central role specifically in organic farming: in the Reduction scenario, they provide up to 72% of available natural nitrogen. But this strategy is not enough to maintain crop yields (–9% in Trend, –24% in Reduction), partly because there is less manure available.

Less animal production.

Since animals raised in organic farming are less productive and more numerous, while conventional livestock numbers decline, total animal protein production falls. In the Reduction scenario, it drops by about 27% (10% in the Trend scenario).

Consequences: Incompatibility with current dietary patterns

With 25% of its land area under organic farming, France can no longer, under either of these two scenarios, maintain its current level of consumption of animal products without resorting to imports.

•    In the Trend scenario, consumption of meat, milk, and eggs would need to be reduced by 5%.
•    In the Reduction scenario, the necessary reduction could reach 30%.

This dietary shift would prevent the environmental impacts from being shifted to other countries through imports.

This study shows that expanding organic farming on a large scale is associated with declines in productivity and pressures on manure availability. Future research should analyze these issues at the regional level, taking into account the specializations of France’s agricultural regions. Methodologically, further research will be conducted to strengthen the robustness of these results, particularly regarding the level of biological nitrogen fixation or the efficiency of nitrogen use in organic crops at the national level.
The roles of legumes and livestock farming thus become critical: failing to adjust practices or diets to achieve 25% of land under OA implies importing more animal products.
In summary, transforming French agriculture also requires a collective reflection on our dietary habits and on the role of animals in production systems—not only as protein producers but also in their role in transferring nitrogen to crops.