PhD offer

The French National Research Institute for Agriculture, Food and Environment (INRAE) and the French Agricultural Research Centre for International Development (CIRAD) are looking for a motivated young scientist candidate for conducting a three years PhD thesis on an exciting topic with strong implications for climate change mitigation and adaptation: crop biomass production, soil litter decomposition, nitrogen leaching and nitrous oxide emissions under extreme rainfall events, in a sub humid region of Zimbabwe, assessed through a combination of in-situ measurements, lab experiments, and modeling.

Background
Extreme rainfall events are a major characteristic of climate change that poses serious threats to agriculture. Evidence of such events has been recently observed in temperate regions, but in tropical sub humid regions, their frequency and intensity are increasing, with drought and dry spells during the cropping season, as well as erratic and very intense rainfall events. These events impact crop biomass production, the amount and quality of crop residues returned to the soil and their decomposition, as well as the dynamics of soil organic matter mineralization. They can further lead to increased loss of soil nitrogen (through leaching, erosion or gaseous emissions), with a negative impact on crop nutrition, production, and greenhouse gas balance. In the mid and long term, this decrease in biomass production may reduce soil organic carbon stock and soil fertility.

Objectives
This PhD thesis will study the impact of rainfall (from drought to extreme rainfall) on crop production and soil functioning, in a context of sustainable intensification of the agricultural practices. The focus will be on maize (Zea mays L.), one of the most common staple crops globally, in a sub-humid region of Zimbabwe where erratic and extreme rainfall events are widespread. The investigated cropping system comprises no tillage, soil cover by crop residues left on the soil surface as mulch, and mineral fertilization to enhance biomass production. The mulch limits soil water evaporation during dry periods, reduces runoff and erosion during high rainfall and consequently has effects on nitrate leaching and nitrous oxide emissions (N2O), a potent greenhouse gas. It is thus of paramount importance to improve our understanding of these processes in order to better synchronize soil mineral nitrogen availability and crop demand and avoid nitrogen losses. The project will combine an experimental approach in Zimbabwe, a laboratory approach in Reims (France), and a modeling work. An experiment will be carried out during two cropping seasons in Harare, Zimbabwe, in collaboration with the University of Zimbabwe. It will comprise three main treatments: normal rainfall, rainfall exclusion, rainfall exclusion + extreme rainfall. Mineral fertilizer labelled with stable isotope (15N) will be applied to follow its fate in the soil-crop system. The laboratory experiment in France will include soil columns (with soil coming from Zimbabwe), maize residues, with different levels of precipitation and fertilization (including timing). Greenhouse gas emissions and carbon and nitrogen dynamics will be monitored. Modeling will be done with the soil-crop STICS model calibrated with data acquired in the field and in the laboratory. This will enable long-term prediction of agronomic and environmental impacts of extreme rainfall: changes in soil organic carbon stocks, nitrogensupply and losses, crop yields, greenhouse gas emissions. As this thesis is part of the European funded project RAIZ "Promoting agro-ecological intensification for resilience building", it will strongly benefit from a framework of international collaborations. The findings of the doctoral work will make it possible to propose to farmers and their advisors useful ways to improve the management of carbon and nitrogen in cropped systems, in order to better use the positive feedback loop "nutrition - plant production - biomass restitution to the soil - organic matter and mineralization". The new knowledge and the progress made in the simulation of extreme climatic events will be used beyond this doctoral work onother tropical and temperate agricultural situations.

Keywords
Soil, nitrogen, carbon, climate change, sustainable intensification of agriculture, crop, experiment, modelling, Zimbabwe

Academic supervision
Main supervisor: Sylvie RECOUS, INRAE (sylvie.recous@inrae.fr)Co supervisors: Gwenaëlle LASHERMES, INRAE (gwenaelle.lashermes@inrae.fr)Rémi CARDINAEL, CIRAD (remi.cardinael@cirad.fr)Other supervisors: Hugues CLIVOT, Université de Reims Champagne ArdenneMarc CORBEELS, CIRADRegis CHIKOWO, University of Zimbabwe
The PhD student will be registered as a doctorate student at the Université de Reims Champagne-Ardenne, in Reims (Doctorate school ABIES). He/she will be in Zimbabwe for two cropping seasons (2022/23, 2023/24), approximately from early November to the end of April, except in 2022 where the student is expected to be in Harare in September to implement the field experiment. Flight tickets and accommodation in Zimbabwe will be covered.

Profile required and selection criteria

• A MSc/Master 2 in environmental science, soil science or agronomy
• Willingness to do field work in Africa and to do modeling
• Knowledge of R is appreciated
• Strong interest on global issues, climate and the environment
• Experience on crop modeling and in writing scientific papers is an asset

Contract and application procedure

• Fully funded PhD for three years (2022-2025)
• Starting date: The PhD student should start on 1st September 2022
• Doctoral School: ABIES (Agriculture Food Biology Environment Health)

How to apply
Applicants should submit a complete application package by email to all thesupervisors (see above) before 31st May 2022. The application package should include:

1. a curriculum vitae
2. statement of motivation
3. answers to the selection criteria above
4. names, addresses, phone numbers, and email addresses of at least two references.

Final recruitment is subject to selection by a jury of the ABIES graduate school.