GT4 (Leader USC, other partners: INRA, FCTUC, UCP-CRP, LNEG)

GT4 (Leader USC, other partners: INRA, FCTUC, UCP-CRP, LNEG)

The objective of GT4 is to assess improvements in soil processes after implementing phytomanagement, focusing on:

  • General physicochemical properties,
  • Dynamics of soil organic matter,
  • Soil fertility and nutrient cycling,
  • Total and available soil contaminants,
  • Soil structure and water retention and filtration, and
  • Weathering of minerals in the rhizosphere soil.

The main objective of GT4 is to evaluate, using harmonized methodology, the effect of phytomanagement on soil functions and processes associated with the main ecosystem services in a variety of environmental conditions, including types of soil degradation/contamination and phytomanagement options. Soil sampling campaigns were successfully completed at all sites (campaign 2016) for an initial characterization of the physicochemical soil conditions (joint management between GT1 and GT4). In each experimental plot, a sample of the surface soil (arable layer of 0-20 cm or less if the superficial layer is less) obtained from the combination of 5 sub-samples collected according to a predesigned pattern was analyzed. The following parameters were determined: pH, texture (5 fractions), density, organic C, total N content, extractable P (Olsen), CIC (hexamin-Co method and / or unbuffered NH4Cl) and exchangeable cations, carbonates, water retention capacity, etc. In the first year of the project, the total organic matter content was determined in soils collected from the 8 main field sites during the first sampling campaign (2016) and in the soil samples collected for the study of long-term sites (S1, S2, S7 and S8). In all cases, a significant increase in organic matter has been observed after the application of the soil amendments. During the second year of the project a more complete characterization is foreseen, by means of physical and / or chemical fractionation protocols (in the harmonization phase), in the sites with long-term phytomanagement trials and during the second sampling campaign (2017) and third sampling (2018). This will coincide with the biological characterization of the soil (GT2). The pseudo-total concentration of the trace elements (TE) in the soil samples was analyzed at all sites by exhaustive chemical extractions. In addition, sequential extraction protocols were applied to obtain the fractions of the operationally defined TE (exchangeable TE, associated with carbonates, iron and manganese oxides, organic matter + metal sulphides or to silicates) in the S4 and S8 sites. The bioavailability of the TE is being assessed using simple non-exhaustive chemical extractions (0.05 M EDTA, NH4NO3).

Another aspect that is being studied in GT4 is the bioavailability of organic pollutants. A low bioavailability of organic contaminants in the soil is one of the most important factors limiting their biodegradation. The incorporation of organic amendments within the different options of phytomanagement can, despite improving conditions for plant development, interact with these pollutants and reduce their bioavailability, thus increasing the time necessary for decontamination. Therefore, we have initiated a series of studies, on a laboratory scale, that seek to increase the bioavailability and speed of biodegradation of hydrocarbons in contaminated soils. On the one hand, we evaluate the effect of the addition to the soil of different synthetic surfactants on contaminant desorption. On the other hand, we carried out a screening to identify bacterial isolates with the capacity to produce biosurfactants and degrade hydrocarbons.

During the second year of PhytoSUDOE, the initial characterization of the physico-chemical parameters of all sites included in the PhytoSUDOE network was concluded. The following parameters were analyzed: pH, texture (5 fractions), density, organic C, total N content, extractable P (Olsen), CIC (hexamin-Co method and / or unbuffered NH4Cl) and cation Exchange capacity, carbonates, and water retention capacity. A more complete characterization of organic matter was carried out in selected long-term sites in the second sampling campaign. The total C content and carbon forms of different stability were determined: from labile forms, important in biological processes and the cycling of nutrients, to very stable forms, with long residence times in the soil, which play an important role in its structure and water retention capacity, as well as carbon sequestration. Additionally, in the soils of the long-term sites, a sequential fractionation of P and the main heavy metals was completed.

In the final months of the project, a “Methodology for the evaluation and monitoring of key edaphic processes in phytomanaged sites of the SUDOE region” was prepared and it is available in the publications section.

In October, 2018, PhytoSUDOE officially ended. The Project deliverables were finalized along January-February, 2019, including the Layman report and the project’s video that were uploaded to the webpage’s news section (blog). Other relevant publications can be accessed also in the web along with the presentations (PDF) of the series of events organized by PhytoSUDOE. This website will be online until 2023.