GCZSC - Postdoc in Emerging Phosphorus Limitations in shifting Cultivation Systems and Implications

About this position

Job Title: GCZSC – Postdoc in Emerging Phosphorus limitations in shifting cultivation systems and implications for cash crops yields and carbon sequestration

Area of specialization: Critical Zone is the “heterogeneous, near-surface environment in which complex interactions involving rock, soil, water, air, and living organisms regulate the natural habitat and determine availability of life-sustaining resources”. Its limits range from the top of the canopy down to the bottom of the aquifer. The successful applicant to this position will join the Global Critical Zone Science Chair to develop and conduct a research program to strengthen the understanding of:

Emerging Phosphorus limitations in shifting cultivation systems and implications for cash crops yields and carbon sequestration

This postdoctoral position, jointly hosted by LSCE (France) and UM6P (Morocco) sharing his (her) time between the two countries, investigates emerging phosphorus limitations in shifting cultivation systems of Central Africa. The successful candidate will use advanced land surface modeling calibrated to observations from field trails and satellites to assess implications for crop yields and carbon sequestration under accelerating land-use pressures.

Background

Shifting cultivation, also called slash and burn agriculture is a widespread traditional cultivation practice in wet tropical forests of central Africa. Small-holder farmers will burn and clear forests in dry seasons, followed by cultivation of diverse cash crops for periods ranging between 15 and 35 years, after which secondary forest regrow. During forest regeneration ecosystems accumulate carbon and restore nitrogen and phosphorus availability via re-distribution within different forms of nutrients present in soils, reduced losses, and inputs from biological N fixation, rock weathering, atmospheric deposition).

A growing concern is that shifting cultivation is expanding into the Congo basin driven by an increasing population & food demand. This leads to an expansion of small clearings and to an acceleration of rotation between forests and crops, with shortening forest regrowth intervals between crop cultivations. The implications are poorly known but accelerated rotations & expansion of shifting cultivation in space are expected to reduce carbon stocks in biomass and soils, and enhance nitrogen and phosphorus losses in Central Africa.

When soil fertility declines are not treated more land will be required to maintain food production. Adequate and timely input of the right type of fertilizers and target crop management (e.g. residues) can help to alleviate, or even avoid, this limitation, with direct benefits for yield stability and food security, and indirect benefits for reducing deforestation and enhancing ecosystem level time averaged carbon storage in soils and forest biomass of shifting cultivation systems.

The proposed postdoctoral subject is to use the land surface model ORCHIDEE CNP model which resolves major processes governing the ecosystem balance of carbon, nitrogen and phosphorus and their internal cycling between minerals, soils (incl. microbes) and plants. We will use the model to simulate the evolution of biogeochemical cycles under shifting cultivation with varying time for forest regeneration. A prior model calibration to crop yield and yield response from fertilizers trials (in collaboration with OCP Nutricrops) and satellite observed forest biomass recovery will enhance the model accuracy.

The model will be integrated for different environmental conditions (e.g. soil background phosphorus availability), and tested for different achievable yields and assumed forest rotations times between two successive cultivation cycles. This will lead to a first publication analyzing carbon and nutrient budgets at system level, that is not only crops but crop and forest shifting cultivations systems. In a second step, the model will be integrated with phosphorus fertilizer practices in subsistence cropping systems, to quantify the benefits for yields and the impacts on carbon storage from a system perspective, including cropland soils and secondary forest biomass.

Simple empirical calculations of how carbon credits potentially generated by improved shifting cultivation management practices could bring revenues to farmers and leverage their access to more efficient fertilizers and cultivation practices, in order to reduce agricultural land requirements and avoid indirect land use emissions from the clearing of new forests.

Requirements

• Programming skills, preferably in Fortran, Python / R
• Knowledge of remote sensing data processing and analysis
• Knowledge of biogeochemical cycles
• Experience with process-oriented modeling

Selection Criteria

• PhD degree or Master degree in a field such environmental sciences, agronomy, applied mathematics, computer science or equivalent.
• Autonomy, ability to work in a team and time management skills.
• Experienced in multidisciplinary team-based activities with the ability to effectively communicate with colleagues and with staff from the partners of a project.

Academic supervision:

UM6P: Global Critical Zone Science Chair (Institut for Advanced Studies) located at the campus Benguerir is a young chair (created in 2024) and devoted to the understanding of the soil as an integral part of a whole, a complex system called the Critical Zone, where interactions and feedbacks are intertwined. What are and will be the impacts of climate on soil–water systems? but also of these systems on the climate? The Chair considers deep water/rock interactions, water-soil mineral interactions, and interactions between water and litter, between soil and plants, and between plants and the atmosphere.

These interactions operate continuously, but not all at the same rate, which complicates the study of biogeochemical mechanisms. The misuse of arable land and land use changes have had devastating adverse impacts on soil health, on climate, on forests. More generally, human activity for the industrial and economic development of societies has resulted in alterations to the carbon, nitrogen, and phosphorus cycles, as well as changes in the status of water within its cycle.

These changes have intensified considerably over the past 15 years. The next decade is the defining decade to reverse that sobering reality and to make soils healthy, to restore forests, to mitigate global warming,

The Chair was created to contribute to the objectives and vision of OCP Nutricrops as defined in its Capstone Doctrine and for that it proposes 2 years-postdoc fellowships covering most aspects of the Critical Zone to study through different methods. It is dedicated to studying the biogeochemical mechanisms that govern the functioning of the Critical Zone, at the heart of which lies healthy soil. Professor Daniel Nahon is head of the GCZS Chair, he is a soil geochemist specialized on tropical deep soil and weathering of rocks.

LSCE- https://www.lsce.ipsl.fr

Is a world-class research laboratory established and a collaboration between CEA, CNRS and the University of Versailles Saint-Quentin -UVSQ. The LSCE hosts approximately 300 researchers, engineers and administrative staff including many PhD and master’s students. This project will provide the employee with the opportunity to work directly on advanced methods with re- searchers from the LSCE and other institutions.

Location: about 20 km from the heart of Paris, in the Orme des Merisiers green area. The main supervisor will be Daniel Goll, Researcher at LSCE and Philippe Ciais, Research director at LSCE and Académie des Sciences Paris and “Corresponding Professor” at the GCZSChair.

How to apply: Applicants should submit a complete application package to UM6P. The application package should include (1) a curriculum vitae including e.g. important recent publications / projects, (2) statement of motivation (3) answers to the selection criteria above (4) names, addresses, phone numbers, and email addresses of at least two references.