PhD position in Soil Science, Biogeochemistry and Agroecology – “Unravelling the role of phosphorus (P) forms on the efficacy of renewable P sources to improve P availability” (OT124)

PhD position in Soil Science, Biogeochemistry and Agroecology – “Unravelling the role of phosphorus (P) forms on the efficacy of renewable P sources to improve P availability” (OT124)

Although phosphorus (P) is essential for all living organisms, it acts as a limiting nutrient for the productivity of many agrosystems due to its low availability in soil. P fertilization is therefore needed to meet the crop demand and achieve high yields. Most of the P currently used in chemical fertilizers is derived from phosphate rocks that are finite and located in only a few places on Earth. Moving towards more sustainable sources for managing P in cropping systems, renewable nutrient-rich (derived-)organic amendments (manure, sludge, compost, biochar, ashes, struvite …) are increasingly considered to replace P fertilizers produced from phosphate rocks, not only by scientists but also by politics and stakeholders. However, compared to conventional P fertilizers such as triple superphosphate, P is present in these amendments in various inorganic and organic forms which differ in their plant availability. Most of the research investigating the fate of P applied to the soil has focused on (soluble) inorganic P while the fate of other P forms has been disregarded so far. Moreover, since plant species differ in their ability to mobilize P from soil P pools, it is highly likely that the potential of recycled P fertilizers to increase plant uptake will be dependent not only on the forms of P but also on the P mobilization/acquisition strategies (e.g. soil acidification, carboxylate secretion, phosphatase release …) used by the plants. Thus, in order to optimize the use of recycled P fertilizer and to be able to predict P availability in cropping systems, there is a great challenge to elucidate the relationships between the forms of P applied to the soil, the soil properties and the plant traits involved in the P mobilization/acquisition and their consequences on P mobility and uptake by plants (Figure 1).


The main objective of this PhD project is to optimize the use of renewable P fertilizers through a better understanding of the impact of P forms on P availability in contrasted soil-plant systems (Figure 2). The first step of this PhD project will be to identify the soil constituents and properties which are involved in the sorption/desorption of P applied under different forms. The knowledge of these parameters will be of help to predict the availability of P as a function of the form which is applied and to better model the behavior of P according to the soil properties.

The second step will be to validate the results of the sorption/desorption experiments by analyzing the P uptake by plants in response to the application of various P forms. Since most of the renewable P fertilizers differ also in terms of nitrogen (N) concentration and organic carbon (C) composition (e.g. cellulose, hemicellulose, lignin) which can in turn impact physico-chemical and biological soil properties, the third step will be to evaluate the effect of these compounds on the P uptake. The final step will consist to evaluate the genericity of our data by testing the effect of “real” amendments (struvite, sludge, biochar …) with contrasted P forms on P mobility and uptake by plants. In this step, plants with different P mobilization/acquisition traits will be tested alone (single-species treatment) or in combination (multi-species treatment).

We hypothesize that the overall uptake of P will be higher in multi-species than in single-species treatments and, more importantly, the addition of a mixture of inorganic and organic P forms will result in higher P use efficiency by multi-species treatment than the addition of only one P form.

Framing: This PhD Thesis takes place at UniLaSalle in Beauvais (France). The intern will benefit of the multiple services available on the campus (100 student associations, fitness room, university restaurant…).

This PhD Thesis will be performed in the AGHYLE unit under the supervision of Dr David Houben and Dr Michel-Pierre Faucon, in co-tutelle with Prof. Gilles Colinet (ULiège, Belgium) and in collaboration with an international partner from the LaSalle network.

Academic level: Master degree (Graduate Students)

General Information:

  • Period: 3 Years
  • Starting date: October 1st 2019
  • Ending date: September 30th 2022
  • PhD Thesis grant: 1768.55€ per month (gross salary)

To reply to this PhD Thesis offer, please send:

  • Academic transcript (undergraduate/Master degree)
  • Cover letter
  • Curriculum Vitae

To: Dr David HOUBEN and Dr Michel-Pierre FAUCON  

Deadline: May 25th

The position’s decription is downloadable here.