RL1. Optimizing organic waste recycling in agriculture

Organic waste recycling in agriculture makes possible the partial substitution of mineral fertilisers and may contribute to increase soil organic carbon (C) stocks in soil and improve related soil properties. Various contaminants (pathogens, organic and inorganic) may enter the soils with the use of OWPs and be transferred to crops and/or waters and have ecotoxic impacts. Other environmental impacts may occur in relation with their potential benefits such as nitrate leaching, gas emissions (ammonia volatilisation, greenhouse gas - GHG and volatile organic compounds - VOC emissions). All effects vary with (i) the characteristics of the applied OWPs, in relation with their origin and potential applied treatment, (ii) the pedoclimatic conditions (soil, climate characteristics, geomorphological environment…) and (iii) crop succession and period of application. Furthermore, their potential use in fertilisation practices depends on their local availability.

The “Soil” team has gained expertise since more than 20 years leading to implication in national scientific animation and expertise for decision makers. During the last 5 years:

• The network of long-term experiments (SOERE-PRO) dedicated to the study of impacts of organic waste recycling on agro-ecosystem (soil, crop, water, air) has extended with participation of INRAE, CIRAD and IRD, including now 5 long-term monitored sites. All data are integrated in a common information system. The SOERE- PRO has been integrated to ANAEE-France (Investment for the future supported by ANR) as “service” opened to external use favouring collaborations (e.g. Paetsch et al., 2016; Van den Nest et al., 2016). Annual meetings of the SOERE-PRO, results and monitoring information are reported on the website https://www6.inrae.fr/valor-pro_eng/
• We organized the international 15th RAMIRAN meeting in Versailles (June 2013) and co-coordinated the national expertise on benefits and environmental impacts of organic waste recycling (Cambier et al., 2013; Houot et al., 2016).

The long-term impacts related to repeated application have been addressed, with results obtained from the SOERE- PRO. During the last 5 years:

• We focussed on environmental impacts related with emerging organic contaminants (see Highlights 2: Bourdat- Deschamps et al., 2017). Low impacts on soil and water contents have been quantified. The potential ecotoxicological impacts have been determined as very low, but pointing out the lack of information on terrestrial ecotoxicity for such question. This work implicated both the Soil and Ecotox teams.
• Trace element concentrations may increase in leachates of amended soils, in spite of increased metal retention by soil organic matter. Dissolved organic carbon favoured Cu leaching. However, pH increase with some OWP decreased the solubility and leaching of Zn (Cambier et al., 2014).
• Emitted VOC were modified but the total amount of VOC was not significantly different compared to mineral fertilisation. Differences among the OWPs were related with their physico-chemical characteristics (Abis et al., 2018). Both “Soil” and Eco&Phy teams were implicated.
• Depending on organic matter characteristics and doses of OWPs, soil organic C storage increased, more in particulate (where compost organic characteristics remained noticeable) than in clay fraction that remained the largest stock of organic C in soil with a microbial origin in this fraction, confirming the role of microbial activity in the integration of OWP organic matter in soil organic matter (Paetsch et al., 2016). Plant available water increased with organic C stocks (Eden et al., 2017; PRO-EXTERN project).

The characteristics of applied OWPs vary with the origin and applied treatment. To optimise the recycling of OWPs, both treatment and application need to be considered. We focussed on C and N behaviours for benefits and organic contaminants for environmental impacts. Recently, anaerobic digestion has intensively developed as an interesting process to produce renewable energy. The digestates are valuable fertilisers or amendments which request better understanding of their behaviour in soils after application. During the last 5 years:

• We demonstrated that the origin of treated wastes and post-treatment after anaerobic digestion both affected the potential efficiency for C storage and N availability of digestates (Askri et al., 2013, ANR DIVA). Post treatment decreased GHG emission after application (Askri et al., 2016; collaboration with “Eco&Phy” team)
• With INRAE LBE, we developed a new protocol of organic matter fractionation to predict both methane production and potential C storage after application (Jimenez et al., 2017)
• Similar fractionation approach contributed to understand the behaviour of organic contaminants (PAHs) during anaerobic digestion (Aemig et al., 2016) and was used to simulate the behaviour of organic contaminants during composting (Lashermes et al., 2013; Brimo et al., 2018) and after application of compost to soil (Geng et al., 2015).
• Drying and liming, other treatments used to stabilise and sanitize sewage sludge before application, did not modify the extractability of pharmaceuticals, leading to potential leaching risks in soils or during storage before application (Geng et al., 2016).

The interactions with soil characteristics and cropping system must also be considered in the optimisation of OWP use at the territorial scale. Classical assessment of soil characteristics (depth, particle size distribution, pH…) are considered when developing soil maps. The spatial distribution of soil content in organic C and N condition the potential increase in organic C and N availability for crops, and crop successions the potential application period and the needs in nutrients. Simulation models were used to assess the consequences of various scenarios of distribution of OWPs at the territory scale. During the last 5 years:

Strong efforts were provided on the assessment of spatial distribution of topsoil organic carbon (SOC) content, cultural operations and crop successions (GESSOL PROSTOCK, BASC SOCSENSIT, TOSCA PLEIADES-CO projects). Using classical geostatistical mapping of SOC content together with laboratory analysis and morphometric data, cokriging gave accurate model (about 3.2 g.Kg-1) in the Versailles Plain (Zaouche et al., 2017) with high local uncertainties where OWPs were applied. Airborne hyperspectral imagery with synchronous assessment of field spectra and classical laboratory analysis provided slightly less precise prediction of SOC (Vaudour et al., 2016) which could be improved with S2 images (Vaudour et al., 2017). From a 70 y-retrospective spatial assessment, land-use change could be related to variations in SOC content (Vaudour et al., 2017). Using high spatial resolution images made possible the mapping of both crop types and cultural operations at early crop stages (Vaudour et al., 2015). Soil roughness highly impact soil reflectance, thus SOC prediction (Ebengo et al., 2018). An automatic photogrammetric approach was developed to measure soil surface roughness (Gilliot et al.,2017a) and considered in the prediction of tillage operation from spectral imagery and radar sources (Vaudour et al., 2014).

• At within-field scale, Unmanned Aerial System (UAS) imagery with miniaturized multispectral cameras was used to predict SOC content with accuracy of 2 g.kg-1 (Gilliot et al., 2016; Gilliot et al., 2017b). After correction of luminosity variations on images due to varying weather conditions (Gilliot et al., 2018), 3D crop surface model was  created  using  high-resolution  RGB images to estimate maize height and grain yield was predicted with a relative error of 14.8 % (Gilliot et al., 2018 submitted)

• At the territorial scale and using agro- ecosystem models (STICS, CERES-EGC), the potential substitution of mineral N and C storage in soil was assessed considering scenarios. In the peri-urban territory of Versailles Plain (i) only 25% of cropped soils could be amended when 65% would need to, (ii) the potential available N from OWPs represented 15% of crop needs (ANR ISARD, Houot et al., 2016). The CERES-EGC model well simulated C and N dynamics in the long-term (Noirot-Cosson et al., 2016). It has been parameterized for all OWPs of the territory (Noirot-Cosson et al., 2017) and used for scenario assessment (Fig. 14, see Highlights 1: Noirot Cosson, 2017).

Finally, the integration of all effects related to OWP  insertion in fertilising practices in a multi-criteria analysis is necessary for evaluation. LCA is often used as multi-criteria analysis but mainly considers environmental impacts. We chose to develop a multi-criteria tool to assess the impacts of OWP application on soil ecosystem services (Obriot et al., 2016; see RL4 below).

Scientific stategy and project

This research line remains structured in (A) the assessment and modulation of observed effects after application considering the characteristics of OWP as explained by origin and treatment, (B) the interaction with pedo-climatic conditions and cropping systems to determine the best management of OWP application at territorial scale. This research line is directly related with the “Biomass” theme, with strong interactions with the other structuring themes. For the next years, several projects will contribute to achieve the objectives.

A1 - New sectors of OWP recycling to improve the looping of nutrients and C related benefits: During T. Martin PhD, the benefits and environmental impacts related to urine recycling chains will be assessed, (AGROCAPI project, collaboration SADAPT and LEESU, interaction with Eco&Phy team). The potential benefits of incorporation of biochar to compost will be explored during ML Aubertin PhD thesis (FUI ECOCHAR, collaboration IEES, Unilasalle, Agriculteurs Composteurs de France, VTGreen society).

A2 - Towards increased genericity and predicting tools for OWP effects on C and N behavior: Within the SOLEBIOM project (collaboration Agrotransfert, Agroimpact, Arvalis and Terres Inovia), we will determine parameters to predict C storage with the AMG model (largely used for advices towards farmers) when using OWPs in fertilizing practices. Several projects concern anaerobic digestion. A typology of digestate characteristics based on their inputs and process characteristics will be developed within the CONCEPT-DIG project (IRSTEA OPAALE and LBE collaboration with Agriculteurs Methaniseurs de France). Chemical and spectral characteristics of inputs and digestates will be used to predict potential biogas production and C storage efficiency and N availability from digestates (MAPPED project, collaboration with LBE, IRSTEA OPAALE, Engie and BioEntec).

A3 - Trade-off between C and N benefits and potential related environmental impacts: Soil C storage and mineral N substitution by OWPs can be compensated by increased nitrate leaching, gas emission after application but also during previous treatment. C and N mass balance and environmental assessment will be realized considering both anaerobic digestion and post treatment of digestates or composting together with field application during V. Moinard PhD thesis (Regional METAMETHA project, collaboration with UEPAO and UR soil, interaction with Eco&Phy team). Furthermore, application of OWPs may enhance VOC and secondary aerosol formation with sanitary impacts (collaboration Eco&Phy team, ANR project to be submitted).

B - Management of OWP at territorial scale: The consequences of anaerobic digestion development on cropping systems and fertilizing practices are assessed with simulated scenarios in 2 territories with contrasting pressure of animal breeding. The STICS model will be parameterized for digestates and other OWPs (Post-doc M. Crépeau, METHAPOLSOL project) and coupled with a simple model describing anaerobic digestion to assess the treatment-application entire chain (collaboration with IRSTEA OPAALE, SAS). Larger attention will be dedicated to decision rules: (i) for cropping practices and specifically for fertilizing practices by farmers; (ii) for OWP management by other actors at territorial scale (communities, waste treatment companies) during the PROLEG and PROTERR projects. Multi-criteria assessment of OWP insertion in fertilizing practices will be introduced in MAELIA, agent-based simulation platform further used to develop innovative cropping systems (see RL 4) and assess spatial evaluation of management strategies for treatment and insertion in fertilizing practices. The territories are strongly related with SOERE-PRO sites used to quantify the indicators (RL4). Innovative cropping systems will be defined in collaboration with Agronomy. At this territorial scale, the potential of OWP recycling and other practices for “carbon credit” will be assessed by considering their potential carbon storage, their associated GHG emissions and their feasibility in a small periurban area (ADEME project in collaboration with Terre & Cité and Grignon Farm). Information provided by Sentinel satellite series will be used to develop other approach for spatializing organic amendment practices and intermediate crops (PEDO_POLYPHEME project, see RL3 below). Finally, the fluxes of nutriments related to OWP and other materials will be assessed in a territorial ecology framework, to highlight the potential for closing the loop and to identify the key stakeholders implied (collaboration with SADAPT).

All modeling development (STICS, AMG, MAELIA), spatial and multi-criteria assessment of OWP insertion in cropping systems will benefit from the recent recruitment of Florent Levavasseur, dedicated research engineer, and rely on geomatic skills of the Unit. Strong interactions exist (i) with other research lines of Soil team, (ii) with the Eco&Phy team for all gas emission (NH3, N2O), with specific attention for VOC and aerosols and with ecophysiologists for consideration of plants (see “Biomass” theme) ; (iii) with the Ecotox team for assessment of terrestrial ecotoxicological impacts and unraveling of beneficial effects related with organic matter and potential impacts related with contaminants (see “contaminant” theme and project of Ecotox team).