Here, a degraded soil, located in a semi-arid Mediterranean region, was characterized 17 years after organic amendment with sludge or compost (differing in their stabilization degree) for restoration purposes. To do this, (i) soil physicochemical properties and plant cover, (ii) soil organic matter (SOM) content and composition, (iii) soil basal respiration and enzymatic activities, and (iv) abundance, taxonomic composition, and functionality (shotgun metagenomics) of microbial communities were studied. Increased SOM and nutrient contents were found in soil from amended plots with respect to the control, with no differences between amendment types. This is explained by the lasting effects of organic amendments and the higher plant cover. Thermal and pyrolytic analyses showed that the restoration process enriched soil mainly with SOM of intermediate recalcitrance and of high chemical diversity. SOM composition did not differ between amendment types. Increased microbial abundances and activities were found in the amended plots, without differences between compost and sludge. Shotgun metagenomics showed that microbial communities changed in taxonomic and functional terms between amended and unamended plots, but these differences were rather limited. The taxonomic differences between treatments were mainly driven by increasing abundances of Actinobacteria and decreasing abundances of Proteobacteria in soil from amended plots. Soil microbial communities in amended plots showed some functional adaptation to the increased nutrient contents and predominant nutrients forms. This, together with the higher microbial abundances detected, explained the conspicuous soil enzymatic activities reported in amended plots. The effectiveness of the studied soil restoration process was confirmed here from an integrative perspective.

This publication is part of the I + D + I project PID2020-114942RB-I00 funded by MCIN/AEI/10.13039/501100011033. This study formed part of the AGROALNEXT programme and was supported by MCIN with funding from European Union NextGenerationEU (PRTR-C17.I1) and by Fundación Séneca with funding from Comunidad Autónoma Región de Murcia (CARM). J.A.S acknowledges the support of the program “Juan de la Cierva Incorporación” of the “Ministerio de Ciencia, Innovación y Universidades” (agreement no. IJC2018-034997-I). We thank A. Vera (CEBAS-CSIC) for assistance on FAME analysis. EJP Soil has received funding from the European Union's Horizon 2020 research and innovation programme: Grant agreement No 862695.

14 páginas.- 4 figuras.- 4 tablas.- referencias.- Supplementary data to this article can be found online at https://doi.org/10.1016/j.apsoil.2024.105383

Peer reviewed