Technosol’s aggregation patterns according restoration treatments in limestone cement quarry in a semi-arid environment

Abstract The creation of Technosols with waste amendments has proved to be a viable option for restoring soils affected by mining activities in arid and semi-arid zones. As an indicator of soil quality, structure is being studied 5 years after the application of restoration treatments in a limestone cement quarry (Almería province, Spain). There, 18 experimental plots (Technosols) of 50 m2 (10 m × 5 m) were installed in 2018, with the aim of applying organic amendments obtained from residues to the sandy-clay substrate of the quarry, namely: i) compost from greenhouse remains; ii) compost from garden pruning remains; iii) stabilized urban sludge; iv) mixtures of plant compost and sludge. Experimental plots without organic amendments were also set up. Each treatment was replicated 3 times and 40 plants of Stipa tenacissima L. were planted in each plot. Structural stability was assessed and used approach is based in particular on Transmission Electronic Microscopy characterization of <20 μm microaggregates sampled according a gradient from root/soil interface to rhizospheric soils further away. Results showed that in these soils, i) there is macroaggregation due to root biomass, thus underlining the positive impact of organic amendments on soil stability due to the increase in root biomass and ii) there is microaggregation, due in particular to the microbial contribution, through their role in the biodegradation of organic matter, which generates aggregating organic matter and through their production of exopolymers. According to the different aggregation patterns between treatments, it appears that a macro/micro-aggregation balance needs to be found in terms of the amendment to be applied, so as to favor biomass without all the microbial activity mineralizing the organic matter present, in order to promote soil stability.