Internship: Modeling nitrogen fluxes in a mixed crop–dairy cattle system

Back to jobs listing

INRAE presentation

The French National Research Institute for Agriculture, Food, and Environment (INRAE) is a major player in research and innovation. It is a community of 12,000 people with 272 research, experimental research, and support units located in 18 regional centres throughout France. Internationally, INRAE is among the top research organisations in the agricultural and food sciences, plant and animal sciences, as well as in ecology and environmental science. It is the world’s leading research organisation specialising in agriculture, food and the environment. INRAE’s goal is to be a key player in the transitions necessary to address major global challenges. Faced with a growing world population, climate change, resource scarcity, and declining biodiversity, the Institute has a major role to play in building solutions and supporting the necessary acceleration of agricultural, food and environmental transitions.

Work environment, missions and activities

You will work in the Herbivores joint research unit (UMRH). The mission of this unit is to produce, integrate and disseminate knowledge, and share expertise to design multi-performing herbivore farming systems that meet the challenges of global change (environmental, socio-economic and digital transition). The unit has 118 permanent staff and welcomes 70 non-permanent staff each year. It is organized into 4 research teams, a management team and a support team.

You will work within the Livestock Systems, Agroecological Transition, Resilience and Product Quality (STARQ) team and the Digestion, Nutrition, Feed, Metabolism and Microbes (DINAMIC) team. You will also interact with researchers and engineers from INRAE’s unit such as Experimental unit for Forage, Ruminants, and the Environment (Ferlus), joint research unit Soil Agriculture and hydrosystem Spatialization (SAS) and joint research unit Physiology, Environment and Genetics for Animals and Livestock Systems (PEGASE).

The project in which you will be involved aims to understand and model the interactions between nitrogen fluxes and natural nitrogen isotope signatures (δ¹⁵N) in an experimental mixed crop–dairy cattle system.

Nitrogen is an essential element for agricultural productivity, but its increasing use over the past century has led to a substantial decline in nitrogen use efficiency. A significant fraction of this nitrogen is lost to the environment, contributing to water eutrophication through nitrate leaching, deterioration of air quality through ammonia volatilization, and climate change through nitrous oxide emissions. Improving nitrogen use efficiency and enhancing the recycling of nitrogen within agricultural systems are therefore key levers for reducing these losses and improving the sustainability of farming systems.

Nitrogen naturally occurs as two stable isotopes: the light isotope, ¹⁴N (99.63%), and the heavy isotope, ¹⁵N (0.37%). Analysis of δ¹⁵N is a promising approach for assessing the degree of nitrogen cycling and recycling within agricultural systems. Indeed, microorganisms involved in nitrogen transformations, for example during organic matter decomposition or nitrification, generally prefer to use the lighter ¹⁴N isotope, thereby leaving a higher proportion of ¹⁵N in the remaining substrate. In particular, processes associated with nitrogen losses, such as nitrification, ammonia volatilization, and denitrification, preferentially take the lighter ¹⁴N isotope relative to ¹⁵N. These processes can therefore be associated with substantial isotopic fractionation, resulting in a relative depletion of ¹⁵N in the nitrogen forms that are lost (notably gaseous forms), and a relative enrichment in ¹⁵N in the remaining compartments, such as soils, plants, and animals.

Among these compartments, soils and animal hair are of particular interest because their relatively slow dynamics allow them to integrate the history of nitrogen cycling and record isotopic signatures reflecting the degree to which the nitrogen cycle is open or closed in livestock systems (Kriszan et al., 2014). However, the complexity of the processes determining ¹⁵N signatures means that their interpretation remains poorly documented. The challenge is therefore to link the rapid dynamics of nitrogen cycling with the slower, integrative dynamics recorded in soils and animal hair, in order to better understand the determinants of δ¹⁵N and assess its potential as an indicator of nitrogen use efficiency and the degree of nitrogen cycle closure.

This internship is part of the NATAN15 research project, which aims to analyse and model the interactions between fast and slow dynamics of the nitrogen cycle in livestock systems. The project seeks to assess the potential of δ¹⁵N signatures in ruminant hair and soils as integrated indicators of nitrogen use efficiency and the degree of nitrogen cycle closure.

The project is based on the OasYs experimental mixed crop–dairy cattle system, comparing two contrasting areas over a 12-month period: 

1. a grazed area, where direct deposition of animal excreta is expected to limit gaseous nitrogen losses;
2. a mown area, where the application of previously stored manure during winter is expected to increase such losses. 

Different compartments associated with the use of these areas—including soils, plants, animal hair, and manure—have been sampled and are currently being analysed for their δ¹⁵N signatures. The objective of the proposed internship is to adapt an existing multi-compartment mechanistic model (Poupin et al., 2014) to the context of the project, in order to describe the temporal dynamics of ¹⁵N isotope signatures in integrative compartments (animal hair and soils) based on nitrogen flux dynamics. This will ultimately allow the potential of these isotopic signatures to be assessed as indirect markers of the degree of nitrogen cycle closure.

More specifically, you will be responsible for:

1. conducting a literature review and critically analysing the available knowledge to develop an understanding of nitrogen dynamics in mixed crop–dairy farming systems, and to identify the key processes and associated parameters;
2. adapting and extending the selected multi-compartment mechanistic model through coding exercises, followed by a sensitivity analysis to identify the parameters that have the greatest influence on simulation outputs and to assess the consistency of model behaviour with the expected nitrogen dynamics in the studied system;
3. calibrating and evaluating the model using the observed δ¹⁵N values and, where available, nitrogen fluxes measured or estimated using other methods.

 

Bibliographies

Kriszan, M., Schellberg, J., Amelung, W., Gebbing, T., Pötsch, E.M., Kühbauch, W., 2014. Revealing N management intensity on grassland farms based on natural δ15N abundance. Agriculture, Ecosystems & Environment 184, 158–167. doi:10.1016/j.agee.2013.11.028

Poupin, N., Mariotti, F., Huneau, J.-F., Hermier, D., Fouillet, H., 2014. Natural Isotopic Signatures of Variations in Body Nitrogen Fluxes: A Compartmental Model Analysis. PLoS Computational Biology 10, e1003865. doi:10.1371/journal.pcbi.1003865

Special conditions of activity: Work mainly screen-based, with the possibility of visiting experimental dairy cattle facilities.

Training and skills

Recommended training: Master’s 2 student or final-year engineering student in agronomy, environmental sciences, ecology, or an equivalent field.

Required knowledge: Mixed crop–livestock farming systems, biogeochemical cycles, and mechanistic modelling.

Appreciated experience: Knowledge of simulation techniques and experience with R or Vensim software.

Skills: Teamwork, autonomy, rigor, and strong organisational skills.

INRAE's life quality

By joining our teams, you benefit from (depending on the type of contract and its duration):

- 2.5 days of leave per month worked;
- parenting support: CESU childcare, leisure services;
- skills development systems: training, career advise;
- social support: advice and listening, social assistance and loans;
- holiday and leisure services: holiday vouchers, accommodation at preferential rates;
- sports and cultural activities;
- collective catering.

The Theix site in Saint-Genès-Champanelle is served by the T2C line (route P39) and an on-demand transport service; it also has parking facilities and services designed for cyclists.

How to apply

I send my CV and my motivation letter