Effects of technosols based on organic amendments addition for the recovery of the functionality of degraded quarry soils under semiarid Mediterranean climate: A field study

Monitoring of indicators and bacterial succession in organic-amended technosols for the restoration of semiarid ecosystems

Restoration of mining sites is essential to ensure ecosystem services and biodiversity. One restoration strategy employed in arid and semi-arid zones is the use of organic amendments to establishment technosols. However, it is necessary to monitor the restoration progress in order to select appropriate amendments. This study monitored the effects of compost gardening, greenhouse horticulture and stabilized sewage sludge, and their blends. We focused on soil physical and chemical indicators and bacterial community structure and diversity during the 30 months after application. Organic amendments increased total organic carbon and nitrogen within six months, staying elevated compared to natural soils over 30 months. Electrical conductivity rose then stabilized, the pH slightly decreased but stayed alkaline, and water holding capacity improved in treated technosols. Bacterial diversity increased in amended technosols compared to control. Alpha diversity varied with treatment and time, peaking at 18 months. Technosols with plant compost showed reduced bacterial richness at 30 months, while those with sewage sludge and its mixtures maintained it. The bacterial community analysis showed significant differences among treatments and times, highlighting dominant phyla like Proteobacteria and Bacteroidetes. PCoA analysis showed clear separation of bacterial communities from treated, natural, and control soils, with notable differences between plant and sludge treatments. Soil variables such as TOC, TN, EC and water holding capacity explained more than 82 % of the variation in bacterial communities. Eighty-three indicator taxa were identified that explained the differences between the microbial communities of treated and untreated soils, highlighting the importance of taxa such as Pelagibacterium spp., Roseivirga spp. and Cellvibrio spp. in preserving soil health. In short, organic amendments improve soil properties and promote the diversity and stability of beneficial microbial communities in semi-arid mined soils, underlining their crucial role in the restoration and long-term maintenance of degraded soils.

Short-term evaluation of soil physical, chemical and biochemical properties in an abandoned cropland treated with different soil organic amendments under semiarid conditions

This study evaluate the effects of four organic soil amendments on soil. Physical, chemical and biochemical properties were compared to untreated and natural (not cultivated) soils in a semiarid region (Andalusia, Spain). A large set of physical, chemical biochemical properties and, the composition of bacterial communities; and overall soil quality index (SQI) were evaluated on soils treated with organic soil amendments of animal origin (compost from sheep and cow manure [CS] or chicken manure, [CK], vegetal origin (greenhouse crop residues [CC]), and vermicompost (CV). Immediately after application, the animal origin compost significantly increased pH, electrical conductivity (EC), and total nitrogen (TN) as well as the enzymatic activities associated with the carbon (C) cycle but decreased the richness and evenness of bacterial communities. After 3 months of treatment, all measured properties recovered except for EC, TN and dehydrogenase activity (whose increase was stable over time), as did bacterial richness, which remained lower. The vegetal-originating compost increased EC and pH whereas the other effects were not significant throughout the monitoring period. CV application did not affect soil properties. The SQI was the highest for soils treated with CK compost, both immediately after application and over time. The soil treatments with the other organic amendments did not result in a significantly different SQI over time compared to both untreated and natural sites.

Different effects of taproot and fibrous root crops on pore structure and microbial network in reclaimed soil

Understanding the effects of plant roots on the pore structure and microbial community of soil is crucial to recovery and improve soil productivity in mining areas. This study aims to assess the impact of taproot (TR) and fibrous root (FR) crops on the physicochemical properties, pore structure, and microbial communities and networks in reclaimed mine soil. Results showed that reclamation positively influenced pore structure and microbial diversity. Tillage with TR and FR crops significantly increased porosity, total pore volume, and area of mining soil (p < 0.05). Compared with TR, FR produced more macropores, mesopores, and micropores. In addition, the module group, average degree, density, and connectivity of microbial network in FR cultivated soil were higher than those in TR cultivated soil. The microbial network map showed that FR had more keystone taxa than TR, and mainly consisted of Acidobacteria and Proteobacteria. In the FR microbial network, Rhizobiales, Betaproteobacteria, and Acidobacteria_Gp11 play critical roles as module hubs and Noviherbaspirillum and Zavarzinella as connectors. Furthermore, most of the key microbes were significantly correlated (p < 0.05) with the total pore area and probably tended to live in pores >75 μm and 0.1-5 μm in size. Therefore, FR crops were more effective than TR crops in improving pore structure and enhancing the development of microbial network in reclaimed soil.

Organic amendments from recycled waste promote short-term carbon sequestration of restored soils in drylands

Soils are considered as a major reservoir for terrestrial carbon and it can act as a source or sink depending upon the land management activities. In semi-arid areas, the natural recovery of soils degraded by mining activities is complicated. A possible solution to recover soil quality and functionality, plant cover and carbon sequestration capacity could be the application of organic amendments. This work focuses on a restoration carried out in 2018 by applying with different composted organic amendments (stabilized sludge, gardening and greenhouse waste) in a limestone quarry under semi-arid climate (SE Spain). The objective was to evaluate the effects of different organic amendments on net CO₂ exchange in two microcosms: soil-Stipa tenacissima and soil-spontaneous vegetation. Soil physical and chemical properties, environmental and ecological variables and their interrelationship were studied in amended and unamended soils. The results obtained under soil-forming factors in the study area showed an increase in soil organic carbon and nitrogen content, improved moisture and plant growth, and plant canopy development in amended soils. Soil moisture, soil temperature and plant cover significantly influenced net CO₂ exchange. In general, microcosms with S. tenacissima showed higher carbon sequestration rates than soils with only spontaneous plant cover. Soils treated with a vegetable-only amendments showed higher plant cover and CO₂ fixation rates after significant rainfall. On the other hand, the plots treated with sludge compost presented more soil respiration than photosynthesis, especially in the wet seasons. Soils with sludge and greenhouse compost mixed had higher CO₂ fixation rates than soils restored with a mixture of sludge and garden compost. Soils with greenhouse waste compost showed CO₂ fixation in the microcosm with plants in all campaigns, being the best treatment to promote atmospheric CO₂ sequestration in soil restoration.

Changes in soil organic matter molecular structure after five-years mimicking climate change scenarios in a Mediterranean savannah

Mediterranean savannahs (dehesas) are agro-sylvo-pastoral systems with a marked seasonality, with severe summer drought and favourable rainy spring and autumn. These conditions are forecasted to become more extreme due to the ongoing global climate change. Under such conditions, it is key to understand soil organic matter (SOM) dynamics at a molecular level. Here, analytical pyrolysis (Py-GC/MS) combined with chemometric statistical approaches was used for the molecular characterization of SOM in a five-years field manipulative experiment of single and combined rainfall exclusion (drought) and increased temperature (warming). The results indicate that SOM molecular composition in dehesas is mainly determined by the effect of the tree canopy. After only five years of the climatic experiment, the differences caused by the warming, drought and the combination of warming+drought forced climate scenarios became statistically significant with respect to the untreated controls, notably in the open pasture habitat. The climatic treatments mimicking foreseen climate changes affected mainly the lignocellulose dynamics, but also other SOM compounds (alkanes, fatty acids, isoprenoids and nitrogen compounds) pointing to accelerated humification processes and SOM degradation when soils are under warmer and dryer conditions. Therefore, it is expected that, in the short term, the foreseen climate change scenarios will exert changes in the Mediterranean savannah SOM molecular structure and in its dynamic.

Exolaccase-boosted humification for agricultural applications

Globally, phenolic contaminants have posed a considerable threat to agro-ecosystems. Exolaccase-boosted humification may be an admirable strategy for phenolic detoxification by creating multifunctional humic-like products (H-LPs). Nonetheless, the potential applicability of the formed H-LPs in agricultural production is still overlooked. This review describes immobilized exolaccase-enabled humification in eliminating phenolic pollutants and producing artificial H-LPs. The similarities and differences between artificial H-LPs and natural humic substances (HSs) in chemical properties are compared. In particular, the agronomic effects of these reproducible artificial H-LPs are highlighted. On the basis of the above summary, the granulation process is employed to prepare granular humic-like organic fertilizers, which can be applied to field crops by mechanical side-deep fertilization. Finally, the challenges and perspectives of exolaccase-boosted humification for practical applications are also discussed. This review is a first step toward a more profound understanding of phenolic detoxification, soil improvement, and agricultural production by exolaccase-boosted humification.

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Exolaccase-initiated humification is conductive to phenolic detoxification

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Multiple humic-like products are created in exolaccase-boosted humification

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Similarities and differences between artificial and natural humus are disclosed

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Humic-like products can be used to sustain soil health and increase crop yield

Recovery of Degraded Areas through Technosols and Mineral Nanoparticles: A Review

Anthropogenic sources such as urban and agricultural runoff, fossil fuel combustion, domestic and industrial wastewater effluents, and atmospheric deposition generate large volumes of nutrient-rich organic and inorganic waste. In their original state under subsurface conditions, they can be inert and thermodynamically stable, although when some of their components are exposed to surface conditions, they undergo great physicochemical and mineralogical transformations, thereby mobilizing their constituents, which often end up contaminating the environment. These residues can be used in the production of technosols as agricultural inputs and the recovery of degraded areas. Technosol is defined as artificial soil made from organic and inorganic waste, capable of performing environmental and productive functions in a similar way to natural ones. This study presents results of international research on the use of technosol to increase soil fertility levels and recover degraded areas in some countries. The conclusions of the various studies served to expand the field of applicability of this line of research on technosols in contaminated spaces. The review indicated very promising results that support the sustainability of our ecosystem, and the improvement achieved with this procedure in soils is comparable to the hybridization and selection of plants that agriculture has performed for centuries to obtain better harvests. Thus, the use of a technosol presupposes a much faster recovery without the need for any other type of intervention.

Bio-Based Waste’ Substrates for Degraded Soil Improvement—Advantages and Challenges in European Context

The area of degraded sites in the world is constantly expanding and has been a serious environmental problem for years. Such terrains are not only polluted, but also due to erosion, devoid of plant cover and organic matter. The degradation trends can be reversed by supporting remediation/reclamation processes. One of the possibilities is the introduction of biodegradable waste/biowaste substrates into the soil. The additives can be the waste itself or preformed substrates, such composts, mineral-organic fertilizers or biochar. In EU countries average value of compost used for land restoration and landfill cover was equal 4.9%. The transformation of waste in valuable products require the fulfillment of a number of conditions (waste quality, process conditions, law, local circumstances). Application on degraded land surface bio-based waste substrates has several advantages: increase soil organic matter (SOM) and nutrient content, biodiversity and activity of microbial soil communities and change of several others physical and chemical factors including degradation/immobilization of contaminants. The additives improve the water ratio and availability to plants and restore aboveground ecosystem. Due to organic additives degraded terrains are able to sequestrate carbon and climate mitigate. However, we identified some challenges. The application of waste to soil must comply with the legal requirements and meet the end of use criteria. Moreover, shorter or long-term use of bio-waste based substrate lead to even greater soil chemical or microbial contamination. Among pollutants, “emerging contaminants” appear more frequently, such microplastics, nanoparticles or active compounds of pharmaceuticals. That is why a holistic approach is necessary for use the bio-waste based substrate for rehabilitation of soil degraded ecosystems.