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Leader: Florent Levavasseur (ECOSYS).      Project type: innovation (2016-2020)     Project acronym: LEADER PROLEG

The peri-urban areas of Ile-de-France are mainly oriented towards large-scale farming and consume mineral fertilizers, the synthesis of which has a strong environmental impact (greenhouse gas emissions, depletion of fossil resources). At the same time, urban areas produce organic waste products (abbreviated to OWP: biowaste, green waste, sewage sludge, etc.) that can be spread in agriculture, either raw or after treatment (composting, methanization, etc.). This recycling of biowaste can allow a substitution of mineral fertilizers and thus a reduction of the associated impacts, while providing various additional services (soil fertility, carbon storage, etc.). In order to optimize the recycling of OWPs in agriculture, it is necessary to know their fertilizing and amending values. Numerous references exist on the values of these PROs, but these can be quite variable depending on the pedoclimatic context and the cropping systems. Moreover, there are still few references on certain recently developed OWPs (digestate, for example). The objective of the project was therefore to acquire references on the OWPs of a small peri-urban area, the Saclay plateau, via the implementation of various field trials over a period of 4 years.

The partners in charge of the field trials were the INRAE/AgroParisTech ECOSYS laboratory, the Chamber of Agriculture of the Ile-de-France region and the farmers of the territory where the trials were carried out. The beneficiaries of the project results were the farmers of the territory and of the neighboring territories, the producers of OWPs and the research for the capitalization of new references.

The main results obtained concern the obtaining of fertilizer equivalence coefficient values for the different current or potential OWPs of the territory. These coefficients will be able to help farmers in the management of their nitrogenous fertilization, both at the local level, but also more widely (feedback to COMIFER in progress). The mineral nitrogen content of the OWPs appeared to be the main determinant of the fertilizing value of the PROs. A multi-year trial also showed that similar yields could be obtained with a fertilization based on OWP only (methanization digestate) compared to a mineral fertilization in the cropping systems of the territory.

Spreading of digestate from methanization on rapeseed

The BASC LEADER co-financing of this work has made it possible to test new OWPs that would not have been tested a priori in the framework of the PSDR PROLEG project in which this project was included. It has also helped to maintain a positive dynamic on the subject of PROs with the farmers of the Saclay plateau. Finally, it contributed to the emergence of a specific project on the valorization of human urine, in particular on the realization of new field trials with urine with the same actors involved (INRAE, chamber of agriculture, partner farmer).

Following this project, many perspectives exist on the theme of the valorization of OWPs. Various projects on the valorization of methanization digestates or human urine are underway or under construction. Discussions with farmers are ongoing to identify new topics of interest to be further explored.

Oral communications:

> Levavasseur F., Dion C., Houot S., 2020. Des essais au champ pour mieux évaluer l’intérêt des produits résiduaires organiques en zones de grandes cultures péri-urbaines. Symposium PSDR 4, 28-30 octobre 2020.

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The researcher explains the project and its RESULS in VIDEO (LabEx BASC scientific days, December 17, 2020)