Establishment of an instrumented agroforestry site in Champenoux: to optimize productivity and sustainability of intensive cropping systems through symbiotic nitrogen fixation
PI : Nicolas Marron (UMR 1137 – Ecologie et Ecophysiologie Forestières – EEF)
Co-applicants : D. Epron, B. Amiaud, S. Chauchard, D. Gérant (EEF), A. Deveau (IaM), L. Saint-André (BEF)
S. Piutti (UMR 1121 Laboratoire Agronomie et Environnement (LAE))
B. Fabre (UE 1261 Unité Expérimentale Forestière de Lorraine (UEFL))
J. Gauvin (UE 1261 Unité Expérimentale Forestière de Lorraine (UEFL))
J.M. Escurat (Etablissement Public Local d’Enseignement et de Formation Professionnelle Agricole des Vosges (EPLEFPA des Vosges))
Context – Intensive tree planting aimed at producing biomass for energy purposes is not very popular at the moment: these plantations deplete the soil, are neither environmentally friendly nor competitive with herbaceous species. However, they are an important asset that could allow us to reach 20% of energy consumption from renewable resources, the objective set by the European Union for 2020. The association of species capable of fixing nitrogen from the atmosphere with species of economic interest may be a way to effectively counter the disadvantages posed by short rotation tree plantations. Biological nitrogen fixation reduces the financial and environmental cost of chemical fertilizers. The nitrogen-fixing species can be woody (black locust, alder) or grasses (alfalfa).
Objective – Our objective is to establish an instrumented plantation associating nitrogen-fixing species (alder, alfalfa) with economically interesting species (poplar, wheat) planted on an agricultural plot located at the experimental farm of La Bouzule located in Champenoux.
Approach — The plantation is composed (1) of “forest” plots (pure poplar, pure alder, mixture poplar / alder), (2) agricultural plots (pure wheat, pure alfalfa), and (3) agroforestry plots (poplar / alfalfa mixture, alder / wheat mixture) in order to assess the fertilizer effect of nitrogen-fixing species on non-fixers. The experiment was launched in April 2014.
Key results —
- The extension of the project in 2015 allowed to replant a significant number of trees that have not survived in 2014. About 500 poplars (≈18% of total) and 600 alders (≈30% of total) were planted again in April 2015.
- The instrumentation of the trial was completed with the installation of a weather station and six additional moisture / temperature soil profiles in forest plots (mixture and monocultures of the two species). The first results showed that the soil drying was more in depth to the alders because of their planting in the form of rooted plants, unlike the poplars (Master thesis of Mathilde Chardon).
- Height growth monitoring of selected trees of both species, within the three treatments (pure forest, mixed forest, and agroforestry) and the three blocks was conducted during the 2015 growing season (360 trees). Differences are already visible, trees in the agroforestry treatments showing a slower growth in height. Trees in the third block, located on a very shallow soil, are also less developed in height than in both others blocks (Master thesis of Guillaume Sabourin).
- The effect of the treatment (agricultural, forestry, agroforestry) on functional microbial indicators (related to biogeochemical cycles) is not marked two years after planting. However, these indicators appear to be relevant in assessing the demand of microorganisms in nutrients, and potentially their availability in soils. In parallel, analyzes repeated in time will allow to model the acquisition and allocation of carbon and nitrogen in plants linked to the dynamics of these elements in the soil (postdoctoral stay of Hugues Clivot).
Main findings — Two years following initial implementation, the plantation is still too young to be included in developing research projects. To date, no facilitation effects have been detected. Trees in the agroforestry plots, however, proved to be highly constrained by competition with herbaceous species at the root level.
Future perspectives — The test site is currently a candidate for integration into the SOERE F-ORE-T project in 2016. Despite protective measures such as mulch layers, anti-game protection and watering the trees during the peak of the 2015 summer drought, further replenishment will probably still be required in 2016. Site instrumentation will be further developed with the installation of a mast with an anemometer, a rain gauge, a Pyranometer, etc.