[PhD defence] 22/10/2024 - Lucas PETIT DIT GREZERIAT: "Improving the fertility of wine-growing soils by massive inputs of organic matter and inoculation with earthworms" (UMR IMBE)

Mr Lucas PETIT DIT GREZERIAT will publicly defend his thesis entitled "Amélioration de la fertilité des sols viticoles par apports massifs de matière organique et inoculation de vers de terre", on Tuesday 22 October 2024 in Avignon.

Laboratory

UMR 7263 IMBE - Mediterranean Institute of Biodiversity and Ecology EECAR

Composition of the jury

Ms MAGALI RAULT	Avignon University, IMBE	Thesis supervisor
Ms Cornelia RUMPEL	UMR IEES, CNRS	Rapporteur
Mr Manuel BLOUIN	UMR Agroecology, Institut Agro	Rapporteur
Ms Céline PELOSI	UMR EMMAH, INRAE	Thesis co-director
Mr Raphael GROS	Aix Marseille university, IMBE	Examiner
Mr Jean-Yves CORNU	UMR ISPA, INRAE	Examiner

Summary

Soil degradation is a major environmental issue of growing concern, prompting the scientific community to look into the possibilities of restoring these ecosystems. Wine-growing soils are affected by this phenomenon, particularly because of low levels of organic matter (OM), copper contamination and often impoverished biodiversity. This biodiversity includes generally low abundances of soil-engineering organisms such as earthworms, reflecting potentially reduced biological fertility. This thesis investigates the potential application of an ecological engineering method based on the inoculation of earthworms and the addition of OM to improve the fertility of wine-growing soils in the Mediterranean region. In particular, the aim was to answer four questions: (1) Is the earthworm inoculation method effective in enabling species to establish themselves in the field? (2) What are the key soil functions impacted by the application of this method? (3) How do inter-species interactions affect the life history traits of earthworms in the presence of OM? (4) What are the effects of earthworms on soil microbial enzymatic and respiratory activities as a function of OM inputs? In the first chapter, we carried out a quantitative literature review (meta-analysis) to assess the optimum parameters for successful earthworm inoculation. The results of this meta-analysis demonstrated the benefits of inoculating at a minimum density of 150 individuals per m², preferably of several species, with positive effects observable after 2 years. In the second chapter, different species of earthworms (Aporrectodea nocturna, Aporrectodea caliginosa, Allolobophora chlorotica and Lumbricus terrestris) were inoculated in November 2021 on different vineyard plots depending on OM inputs or the inter-row management method (grassing or tillage). After two years, A. nocturna is the species that seems to be establishing itself best on the Valabre experimental site (Gardanne, 13). Moreover, the earthworm communities were largest in the MVA (non-composted OM used in the form of mulch, 200 t ha-¹). Earthworm inoculation increased the amount of copper and potassium bioavailable to the plant, as well as labile carbon. MVA also increased the amount of bioavailable magnesium, as well as nitrogen and total soil organic carbon. With regard to the effect of tillage, assessed on two other plots, inoculations increased earthworm densities in the short term on the two sites monitored (1 year maximum), particularly in the grassed inter-rows. In the third chapter, positive interactions between A. nocturna and A. caliginosa on the reproduction of A. caliginosa were identified, underlining the importance of the choice of species when applying this type of method. In addition, in the fourth chapter, soil respiratory activities were generally increased in the presence of earthworms. With the addition of MVA, the presence of the species A. nocturna also made it possible to increase enzymatic activities linked in particular to the carbon cycle. This thesis therefore provides fundamental and applied information on the implementation and functional consequences of the proposed soil engineering method. Initial effects on soil functioning have been identified, enabling winegrowers to assess whether such a method can meet their needs in the vineyard.

Keywords Earthworms, Organic matter, Fertility, Vine, Inoculation, Restoration