Exploring optimised crop-livestock changes that promote higher efficiency and reduced N imports in three French farming systems

CONTEXT

European farming systems depend on synthetic fertilisers and feed imports. In a context of global peak oil and geopolitical crises, it is important to seek increasing independence from input imports and to reduce their environmental impact. This requires better crop-livestock integration, notably at the territorial level. However, this implies contending with the trade-offs related to agricultural production.

OBJECTIVE

The study aim was to explore, at the territorial level, how crop-livestock change can maintain or maximise agricultural production and affect N use efficiency while reducing N imports. This was investigated in three French farming systems characterised by different crop-livestock compositions: field crops (Plateau Picard), intensive dairy cattle and monogastrics (Bretagne Centrale) and extensive ruminants (Bocage Bourbonnais).

METHODS

Two multi-objective optimisation scenarios using an evolutionary genetic algorithm were applied to a farming system N balance model. These scenarios reflected two fertilisation strategies: (i) maintaining target crop yields with synthetic fertiliser or (ii) adapting crop yields to available natural and organic fertiliser. The decision variables were types of crop acreage and livestock density, which were systematically varied within a set of agronomic constraints. The optimised objectives were maximisation of crop and livestock production and minimisation of synthetic fertiliser use and imported feed.

RESULTS AND CONCLUSIONS

In Bocage Bourbonnais, no matter which strategy was used, both livestock production and crop production with no N imports increased (up to a total of +24 kgN/ha utilised agricultural acreage (UAA)/yr), in particular by increasing the proportion of monogastrics in the herd (median, +25 % with the first strategy). For these production maximums, N waste fell by up to 12.5 kgN/haUAA/yr. In the other farming systems, it was only possible to increase agricultural production (to the detriment of either crop or livestock production) without N imports (a total of +2 kgN/haUAA/yr for Plateau Picard and + 5 kgN/haUAA/yr for Bretagne Centrale). However, N waste decreased only in Bretagne Centrale (−70 kgN/haUAA/yr), with a sharp drop in livestock production (∼100 %). These production increases for the three regions showed up to 150 kgN/ha arable land/yr of symbiotic fixation by legumes.

SIGNIFICANCE

For three different farming systems at the territorial level, the results quantified the extent to which crop-livestock changes can lead to greater independence from imported inputs and reduce N waste while maintaining or increasing agricultural production. These results imply that a substantial reduction in N imports will require reconsidering the livestock place in agricultural production and reducing target crop yields.