Speaker
Description
Nitrogen (N) losses from agroecosystems threatens the environment. Regions with high livestock densities, such as Brittany (France), are particularly sensitive to this issue. In addition, N losses are expected to increase under the rising intensity and frequency of extreme weather events. Silvopastoral systems, i.e., combination of trees and pastures, are a promising solution to prevent N losses in the short- and long-term. If recent studies highlighted the potential of silvopastures to limit N losses in the close vicinity of trees (e.g., (Zhu et al. 2020), their contribution remains ambiguous at farm and territory level.
This study aims to disentangle the relations between silvopastoral systems and the regulation of N losses by assessing the farm-gate N balance (FGB; kg N ha-1 yr-1) in a gradient of dairy farms of Brittany that either maintained and/or planted hedges and alley-cropping silvopastures. We hypothesized that the farms which adopted silvopastures the most would present lower N surplus due to (i) direct impact of the presence of trees, and (ii) the adoption of farming systems with low N inputs.
Thirty-three farms were surveyed and modelled in order to assess their FGB as a proxy for risk of N losses. FGB was calculated as the difference between N inputs and outputs; with inputs including N from fertilizers, biological N fixation, atmospheric depositions, soil N fixation by free living soil organisms, animal feed, and litter; and outputs including N from exported crops, animal products, manure, and wood. Farms were then classified through hierarchical clustering based on variables of N inputs, outputs, FGB and surface planted with trees. Variation partitioning of the FGB was performed in order to disentangle the impact of trees as compared to the impact of the management of N inputs and outputs.
The variation partitioning revealed that N inputs alone contributed the most to explain the variation of FGB (55.6%), while tree variables alone did not explain its variation. Yet, these latter contributed to explain the variability of FGB when considering their interaction with practices on N inputs (8.0%) and both N inputs and outputs (15.3%). Furthermore, the hierarchical clustering resulted in four clusters with a gradient of farming systems from extensive farming systems with high plantation of silvopastoral systems and low N surplus to intensive farming systems based on high external N inputs and maintaining old hedges.
Our results suggested that the adoption of silvopastoral systems was not in itself a major lever to limit N losses. Yet, synergies between the adoption of silvopastures and the management of N inputs led to lower N surplus at farm scale (e.g. no fertilization on the areas planted with trees). The adoption of further practices would enhance the positive impact of silvopastoral systems on the limitation of N losses (Komainda et al. 2023; Papanastasis et al. 2008). Moreover, farmers that adopted silvopastures favored the stability of N-related processes towards extreme climates events through the use of organic fertilization and the plantations of trees (Mettauer et al, in prep). The conception of silvopastoral systems that take further advantages from the synergies between presence of trees and regulation of N inputs (e.g., reduction of fertilizers inputs next to the trees or use of tree branches as fodder; (Komainda et al. 2023; Papanastasis et al. 2008)) is promising way to limit N losses in the short- and the long-term for regions with high livestock densities.
References :
Komainda, Martin, Rahel Sutterlütti, Manfred Kayser, and Johannes Isselstein. 2023. « Adjusting Nitrogen Fertilization to Spatial Variations in Growth Conditions in Silvopastoral Systems for Improved Nitrogen Use Efficiency ». Nutrient Cycling in Agroecosystems, novembre. https://doi.org/10.1007/s10705-023-10317-6.
Papanastasis, V. P., M. D. Yiakoulaki, M. Decandia, and O. Dini-Papanastasi. 2008. « Integrating woody species into livestock feeding in the Mediterranean areas of Europe ». Animal Feed Science and Technology 140 (1): 1‑17. https://doi.org/10.1016/j.anifeedsci.2007.03.012.
Zhu, Xiai, Wenjie Liu, Jin Chen, L. Adrian Bruijnzeel, Zhun Mao, Xiaodong Yang, Rémi Cardinael, et al. 2020. « Reductions in Water, Soil and Nutrient Losses and Pesticide Pollution in Agroforestry Practices: A Review of Evidence and Processes ». Plant and Soil 453 (1): 45‑86. https://doi.org/10.1007/s11104-019-04377-3.
| Keywords | Alley-cropping agroforestry; Hedgerow; Nitrogen balance; Dairy farms |
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