Organic carbon pools and soil biological fertility are affected by land use intensity in Mediterranean ecosystems of Sardinia, Italy

Restoration of soil multifunctional indicators requires more than thirty years in degraded shrubland of a semi-arid mountainous ecosystem

Vegetation degradation in natural environments leads to considerable fluctuations in soil function indicators, particularly in the sensitive and delicate habitats of semi-arid regions. In this study, the dynamic of both litter and soil properties was examined in northern Iran, in sites with Crataegus melanocarpa and Berberis integerrima dominance. The chosen sites have been degraded in 1993 due to exploitation for fuel production. Litter and soil (0-10, 10-20 and 20-30 cm depths) samples were collected in sites that have been degraded [i.e., 10-years post-degradation (2003), 20-years post-degradation (2013), and 30-years post-degradation (2023)]. A site not to exposed to degradation (year 2023) was also included as a control. In total, 48 litter samples (4 study sites × 12 samples) and 144 soil samples (4 study sites × 3 depths × 12 samples) were collected. Our findings showed a significant reduction of approximately 60-70% in the chemical characteristics of the litter, such as phosphorus (P) and magnesium (Mg) after 10-years post-degradation (2003) compared to the control site. Soil fertility indicators were also reduced 2-6 times as a result of habitat degradation. Aligned with this, the biota population in the 10-year post-degradation site showed a decrease of 70-90% with respect to the control. Moreover, the densities of fungi and bacteria decreased by approximately 30%-70% and 45-80% respectively compared to the 30-year post-degraded site. The peak activation of soil enzymes including urease, acid phosphatase, arylsulfatase, and invertase was found in the site that was not subjected to degradation, being 3.5, 5.8, 6.7 and 6.7- times higher in comparison to the 10-year post-degradation site. Overall, the results showed that in the non-degraded ecosystems, the input of plant-based organic matter was accompanied by an increase in soil fertility, organism population and soil function. This pinpoints the importance of protecting plant species in these areas, while in degraded areas planting native species adapted to the region's climate and fertilization could significantly contribute to restoring these areas.

Can soil health in degraded woodlands of a semi-arid environment improve after thirty years?

In natural habitats, especially in arid and semi-arid areas that are fragile ecosystems, vegetation degradation is one of the most important factors affecting the variability of soil health. Studying physicochemical and biological parameters that serve as indicators of soil health offers important information on the potential risk of land degradation and the progression of changes in soil performance and health during recovery periods. This study specifically examines the impact of vegetation degradation on soil health indicators and the duration needed to improve the physical, chemical, and biological parameters in a semi-arid mountainous area site types with the dominance of Quercus macranthera Fisch & C.A. Mey and Carpinus orientalis Miller in northern Iran. In different years (2003, 2013, and 2023), litter and soil samples (at depths of 0-10, 10-20, and 20-30 cm) were collected in different types of degraded sites. Additionally, in 2023, a non-degraded site was chosen as a control and similar samples were collected. A total of 48 litter (12 samples for each of the study site types) and 144 soil (4 study site types × 3 depths × 12 samples) samples were collected. In order to investigate the spatial changes of soil basal respiration (or CO2 emission), which is involved in global warming, from each site type, 50 soil samples were taken along two 250-meter transects. The findings showed that litter P and Mg contents in the non-degraded site were 1.6 times higher than in degraded site types (2003). Following vegetation degradation, soil fertility indicators decreased by 2-4 times. The biota population was lower by about 80 % under the degraded site types (2003) than in the non-degraded site, and the density of fungi and bacteria in the degraded site types was almost half that of the non-degraded site types. Geostatistics showed the high variance (linear model) of CO2 emissions in areas without degradation. In addition, vegetation degradation significantly reduced soil carbon and nitrogen mineralization. Although soil health indicators under the degraded vegetation have improved over time (30 years), results showed that even thirty years is not enough for the full recovery of a degraded ecosystem, and more time is needed for the degraded area to reach the same conditions as the non-degraded site. Considering the time required for natural restoration in degraded site types, it is necessary to prioritize the conservation of vegetation and improve the ecosystem restoration process with adequate interventions.

Soil microbial community composition and functions are disrupted by fire and land use in a Mediterranean woodland

The intersection of fire, land use transformations, and climate change is putting Mediterranean climate-type ecosystems at risk of soil degradation and loss of ecosystem services. Ondik et al. (2022b) showed that in a Mediterranean dry sclerophyll woodland of South Australia, high severity fire and clearing and grazing practices impacted both physicochemical and biological soil quality indicators. Building upon the work of Ondik et al. (2022b) this study aims to 1) identify soil physicochemical properties impacted by fire and land management that are indirect drivers of changes to soil microbial community composition and 2) determine whether the observed changes to soil microbial community composition affect soil microbial functions. Via a redundancy analysis, we identified fire and management-induced changes to pH, soil water repellency, nutrient stoichiometry, and total nutrient content as significant drivers of the composition of soil microbial communities. We then measured basal respiration, substrate induced respiration, and the carbon mineralisation quotient, and calculated functional trait distributions among microbial communities by linking 16S and 18S rRNA sequences to respiration modes and functional guilds, respectively. We found that fire reduced soil microbial respiration and the relative abundance (RA) of microbial symbionts, anaerobic bacteria, and microaerophilic bacteria, while increasing the RA of aerobic bacteria. Furthermore, management increased the RA of post-fire ectomycorrhizal fungi and may have reduced pathogenic load, microbial efficiency, and wood saprotrophs, while increasing litter, soil, and other saprotrophic species that are adapted to grasslands. This study shows that, through changes to microbial community composition, high severity wildfire and land management affected soil respiration rates, bacterial modes of respiration, prevalence of symbiotic bacteria and fungi, and microbial substrate preference. Having identified the main physicochemical drivers of changes to microbial community composition, we provide valuable insights into how fire and land management can impact soils in Mediterranean woodland.

Impact of Natural Forest Succession on Changes in Soil Organic Carbon in the Polish Carpathian Mountains

The main driver of the Carpathian landscape is the process of natural forest succession on the semi-natural meadows unique to the region. Moreover, these semi-natural mountain meadows contribute to ecosystem services, although increasing forest areas are recommended by current international policy agendas. The purpose of this study was to examine the impact of natural forest succession in the Polish part of Carpathian on changes in soil organic carbon and assess the influence of different soil properties on organic carbon content across three land uses. Soil samples were taken from 10 transects consisting of semi-natural mountain meadow, natural successional forest and old-growth forest, selected in three Polish Carpathian national parks. Measurements of organic carbon, dissolved organic carbon, microbial properties, such as microbial respiration, and enzyme activities were made; additionally, biochemical indicators were calculated. To describe the influence of measured soil parameters and calculated indicators of soil organic carbon changes, the organic carbon dependent variable regression equations across all studied soils and for the individual land use and examined layers were evaluated. The overall regression equation indicated that changes in organic carbon general to all investigated soils depended on microbial biomass carbon content, microbial quotient, dissolved organic carbon content and metabolic quotient. The regression models obtained for the individual land use variants and soil layers explained 77% to 99% of the variation in organic carbon. Results showed that natural forest succession caused a decrease in microbial biomass carbon content, and successional forest soils characterized less efficient use of organic substrates by microbial biomass.

Towards sustainable management of forest residues in the southern Apennine Mediterranean mountain forests: a scenario-based approach

KEY MESSAGE

Managing forest residues according to the carbon content of the soil helps to minimize the ecological footprint of their removal.

CONTEXT

In Mediterranean mountain ecosystems, unsustainable harvesting of wood residues might contribute to land degradation, carbon, and nutrient depletion in forest soils.

AIMS

This study aimed to assess the amount of forest biomass residues that should be left on-site to minimize the depletion of soil fertility.

METHODS

We estimated the availability of biomass residues in the public forest land of the Basilicata region of Southern Italy by collecting stand-scale inventory attributes from forest management plans. Subsequently, we quantified the amount of forest biomass residue released by implementing a scenario-based approach.

RESULTS

Approximately 5800 m³ year^-1 of forest residues could be potentially available for bio-based industries at the regional scale within the next 10 years. Such residues mainly belong to broadleaved forest types, having a high variability in their soil organic stock (228.5-705.8 Mg C ha^-1) and altitudinally spanning from 400 to 1500 m a.s.l. In these forests, the simulated scenarios displayed a wide range of average harvestable residues from 2.5 to 5.5 m³ ha^-1, containing approximately 1.1 to 2.1 Mg ha^-1 of organic carbon.

CONCLUSION

Our study suggests that forest management plans are a useful source of information to estimate the available forest biomass residues consistently. In southern Mediterranean mountain forests, the management of forest residues according to soil carbon content helps to minimize the environmental impact and increase their sustainability.

Critical range of soil organic carbon in southern Europe lands under desertification risk

Soil quality is fundamental for ecosystem long term functionality, productivity and resilience to current climatic changes. Despite its importance, soil is lost and degraded at dramatic rates worldwide. In Europe, the Mediterranean areas are a hotspot for soil erosion and land degradation due to a combination of climatic conditions, soils, geomorphology and anthropic pressure. Soil organic carbon (SOC) is considered a key indicator of soil quality as it relates to other fundamental soil functions supporting crucial ecosystem services. In the present study, the functional relationships among SOC and other important soil properties were investigated in the topsoil of 38 sites under different land cover and management, distributed over three Mediterranean regions under strong desertification risk, with the final aim to define critical SOC ranges for fast loss of important soil functionalities. The study sites belonged to private and public landowners seeking to adopt sustainable land management practices to support ecosystem sustainability and productivity of their land. Data showed a very clear relationship between SOC concentrations and the other analyzed soil properties: total nitrogen, bulk density, cation exchange capacity, available water capacity, microbial biomass, C fractions associated to particulate organic matter and to the mineral soil component and indirectly with net N mineralization. Below 20 g SOC kg^-1, additional changes of SOC concentrations resulted in a steep variation of all the analyzed soil indicators, an order of magnitude higher than the changes occurring between 50 and 100 g SOC kg^-1 and 3-4 times the changes observed at 20-50 g SOC kg^-1. About half of the study sites showed average SOC concentration of the topsoil centimetres <20 g SOC kg^-1. For these areas the level of SOC might hence be considered critical and immediate and effective recovery management plans are needed to avoid complete land degradation in the next future.

Soil Biochemical Indicators and Biological Fertility in Agricultural Soils: A Case Study from Northern Italy

Industrial farming without considering soil biological features could lead to soil degradation. We aimed to evaluate the biochemical properties (BPs) and biological fertility (BF) of different soils under processing tomato cultivation; estimate the BF through the calculation of a simplified BF index (BFIs); determine if the crop was affected by BP and BF. Three farms were individuated in Modena (MO), Ferrara (MEZ) and Ravenna (RA) provinces, Italy. Soil analysis included total and labile organic C, microbial biomass-C (Cmic) and microbial respiration measurements. The metabolic (qCO2), mineralization (qM) and microbial (qMIC) quotients, and BFIs were calculated. Furthermore, plant nutrient contents were determined. The low Cmic content and qMIC, and high qCO2 found in MEZ soils indicate the occurrence of stressful conditions. The high qMIC and qM, and the low qCO2 demonstrated an efficient organic carbon incorporation as Cmic in MO soils. In RA soils, the low total and labile organic C contents limited the Cmic and microbial respiration. Therefore, as confirmed by the BFIs, while MO showed the healthiest soils, RA soils had an inefficient ecophysiological energy state. However, no effects on plant nutrient contents were observed, likely because of masked by fertigation. Finally, BP monitoring is needed in order to avoid soil degradation and, in turn, crop production decline.

Effects of organic fertilizers via quick artificial decomposition on crop growth

Applying organic matters into the soil would help to improve soil quality and sustain crop production. In addition, the small molecular organic matters could be active in influencing soil nutrient cycling and crop development. Thus, this study has firstly induced a new technology of quick artificial decomposition to produce fertilizers containing small molecular organic compounds from crop residues and other biological wastes. The fertilizers were produced via the quick artificial decomposition from biological wastes. The small organic species in the fertilizers were identified by the LC-MS. Field experiments of kiwifruit were conducted to test the effects of fertilizers. In total, 341 species of small organic matters have been determined in the produced fertilizers. The results showed that the organic fertilizers could significantly increase the yields of kiwifruit by 15.2% in contrast with mineral fertilizer treatments. Whereas, the organic fertilizers could enhance the contents of nutritive components in kiwifruits. These results proved that the organic fertilizers containing more small organic matter could be more efficient in promoting crop production.

Linkages among Soil Properties and Litter Quality in Agroforestry Systems of Southeastern Brazil

Agroforestry systems have been promoted as a solution to address trade-offs between environmental conservation efforts and the need for increased agricultural productivity on smallholder farms in Brazil. However, the impact of land use change from degraded pasture to agroforestry on soil properties remains unclear. The objectives of this research were to: (1) assess soil chemical, physical and biological properties across distinct land uses (degraded pasture, agroforestry and secondary forest); and (2) understand relationships between litter quality, soil organic matter (SOM) and key soil quality parameters in the Brazilian Atlantic Rainforest. Soils, macroinvertebrates and litter were collected in April and September of 2018 under five land uses, including: three types of agroforestry systems, a degraded pasture and a secondary forest in Sapucaia, Rio de Janeiro, Brazil. Our results showed that soil properties clearly separated the three agroforestry systems plots (AS1, AS2, AS3) from the forest and pasture plots. Moreover, litter quality and SOM likely influence multiple biological and physiochemical soil properties under agroforestry systems and secondary forest. Our findings suggest that agroforestry systems can help support soil biological, chemical and physical properties and that the litter quality may be an important driver of their effects and potential contributions to soil restoration in the region.

The relationship between bacterial diversity and organic carbon mineralization in soft rock and sand compound soil

The soil organic carbon (SOC) mineralization rate in sandy soil plays an important role in improving soil quality, and a research is needed to determine management practices that optimize the mineralization rate. When sandy soil is improved by adding soft rock, the specific promotion process of bacterium to SOC mineralization remain unclear. To investigate these mechanisms, we selected four treatments with soft rock to sand volume ratios of 0:1 (CK), 1:5 (C1), 1:2 (C2) and 1:1 (C3) to study. The mineralization rate of organic carbon was measured using the lye absorption method. High-throughput sequencing and scanning electron microscopy were used to determine the bacterial community structure and soil microstructure, respectively. The results showed that the organic carbon content of the sandy soil increased significantly (182.22-276.43%) after using the soft rock treatments. The SOC mineralization rate could be divided into two stages: a rapid decline during days 1-8 and a slow decline during days 8-60. With increased incubation time, the intensity of the cumulative release of organic carbon gradually weakened. Compared with the CK treatment, the SOC mineralization accumulation (Ct) and the potential mineralizable organic carbon content (C₀) in the C1, C2, and C3 treatments increased significantly, by 106.98-225.94% and 112.22-254.08%, respectively. The cumulative mineralization rate (Cr) was 18.11% and 21.38% smaller with treatments C2 and C3, respectively. The SOC mineralization rate constant (k) decreased significantly after the addition of soft rock, while the half-turnover period (Th) changed inversely with k. Compared with the CK treatment, the number of gene copies of the soil bacteria increased by 15.38-272.53% after adding soft rock, with the most significant increase in treatment C3. The bacterial diversity index also increased significantly under treatment C3. The three dominant bacteria were Proteobacteria, Actinobacteria, and Chloroflexi. The correlation between C_r and one of the non-dominant bacteria, Firmicutes, was large, and the bacteria had a significant positive correlation with k. At the same time, the abundance of Firmicutes under treatments C2 and C3 was small. As the proportion of soft rock increased, the soil particles changed from point contact to surface contact, and the adhesion on the surface of the particles gradually increased. Results from this study show that the retention time of SOC can be increased and the carbon sequestration effect is better when the ratio of soft rock to sand is set to 1:2.

Response of organic carbon mineralization and bacterial communities to soft rock additions in sandy soils

Bacteria play a vital role in biotransformation of soil organic carbon (SOC). However, mechanisms of bacterium and organic carbon mineralization remain unclear during improvement of sandy soil using soft rock additions. In this study, four treatments with differing ratios of soft rock to sand of 0:1 (CK), 1:5 (C1), 1:2 (C2) and 1:1 (C3) were selected for mineralization incubation and high-throughput sequencing. The results showed that SOC, total nitrogen (TN), available phosphorus (AP), nitrate nitrogen (NO\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}${}_{3}^{-}$\end{document}3−-N), and mass water content (WC) of sandy soil increased significantly after addition of soft rock (P < 0.05). Compared with the CK treatment, cumulative mineralization and potential mineralized organic carbon content of C1, C2 and C3 increased by 71.79%–183.86% and 71.08%–173.33%. The cumulative mineralization rates of organic carbon treated with C1 and C2 were lower, 16.96% and 17.78%, respectively (P > 0.05). The three dominant bacteria were Actinobacteria, Proteobacteria and Chloroflexi, among which Proteobacteria was negatively correlated with mineralization of organic carbon (P < 0.01). The mineralization rate constant (k) was positively correlated and negatively correlated with Cyanobacteria and Nitrospirae, respectively. Under C2 treatment, Proteobacteria and Nitrospirae had the largest increase, and Cyanobacteria had the largest decrease. Compared with other treatments, C2 treatment significantly increased bacterial diversity index, richness index and evenness index, and the richness index had a negative correlation with k value. In conclusion, when the ratio of soft rock to sand was 1:2, the k of SOC could be reduced. In addition, the retention time of SOC can be increased, and resulting carbon fixation was improved.

Assimilating atmospheric carbon dioxide in tea gardens of northeast India

Carbon dioxide (CO₂) is the most important greenhouse gas in the atmosphere and phyto-assimilation is the most effective technique to mitigate global warming effect of CO₂ gas in the atmosphere. Tea is an evergreen perennial plant and cultivated worldwide under subtropical humid climatic condition for harvesting its tender shoots. Tea bushes of different cultivars and ages are grown in combination to minimize possible adverse effect of biotic and abiotic stresses; hence distribution of tea plantation in a tea garden is complex in nature. Large shade trees are also an integral part of tea garden. Those plantations in tea garden have huge potential to capture atmospheric CO₂; however, ability of tea bushes to mitigate global warming while producing tea shoots is not quantified before. The objective of this study was to quantify the potential of tea plantation to mitigate greenhouse effect (global warming mitigation potential, GWMP) due to assimilation of atmospheric CO₂ gas. High yielding TV23 cultivar assimilated significantly higher amount of CO₂ as compared to quality tea producing cultivars (S3A/3) and mature 25-30 years old tea bushes absorb more CO₂ from the atmosphere as compared to younger tea bushes. Considering the mixed population of cultivars in tea gardens, overall, tea bushes sequestrated 5134.4 ± 831.6 kg CO₂ ha^-1 yr^-1 in their biomass and had GWMP 3.47 ± 0.64 kg CO₂ KMTH^-1 yr^-1. Shade trees sequestrated 4037.4 ± 589.9 kg CO₂ ha yr^-1 from the atmosphere. Hence, the GWMP of whole plantation ((both tea bushes and shade trees) was 6.19 ± 1.7 kg CO₂ KMTH^-1 yr^-1. In this study, tea bushes sequestrated 52.7-61.3% of the total CO₂ sequestrated by the plantations in tea garden. This study enabled to understand that tea bushes play significant role in mitigating global warming by assimilating and sequestrating atmospheric CO₂ and the estimated value of global warming mitigation potential may be used for direct estimation of C sequestration by plantations in tea garden using its productivity value.

Soil Biological Fertility and Bacterial Community Response to Land Use Intensity: A Case Study in the Mediterranean Area

The current study was performed to investigate the effects of three different long-term land use intensities on adjacent soil plots, namely a winter wheat field, a grass-covered vineyard, and a cherry farm, on soil biochemical, microbial, and molecular parameters. The results showed the maximum content of soil organic matter (SOM) and microbial biomass carbon (MBC) observed in the grass-covered vineyard. Basal respiration (BSR) and the cumulated respiration (CSR) after 25 days of incubation were significantly higher in the grass-covered vineyard and cherry farm, respectively (BSR 11.84 mg CO2–C kg−1 soil d−1, CSR 226.90 mg CO2–C kg−1 soil). Grass-covered vineyard showed the highest soil biological fertility index (BFI) score (20) and ranked in the class IV (good) of soil biological fertility. Cereal field and cherry farm had lower BFI scores and the corresponding BFI class was III (medium). In addition, the maximum ribosomal RNA copy number and the highest abundance of oligotrophic bacterial groups (25.52% Actinobacteria, 3.45% Firmicutes, and 1.38% Acidobacteria) were observed in the grass-covered vineyard. In conclusion, the grass-covered vineyard is a more conservative system and could have a large potential to improve total carbon storage in soil, mainly because of the cover crop residue management and the low soil perturbation through the no-tillage system.

Land use shapes the resistance of the soil microbial community and the C cycling response to drought in a semi-arid area

The aim of this study was to understand the responses of the microbial community of soil under different land uses to drought in a semi-arid Mediterranean area. In a laboratory incubation, soil samples from different land uses (natural forest, drip-irrigated orchard, rain-fed almond tree cultivation and abandoned area) were maintained at 20% and 60% of the WHC. The microbial biomass and potential enzyme activities were determined after four and fifty days of soil incubation. The diversity and composition of the microbial community were studied after 50 days of incubation. The total mineralisation of soil organic C (SOC), as well as, the mineralisation of fresh organic matter (FOM) and the "priming effect" were analysed after addition of ¹³C-enriched plant tissue. Both land use and drought had significant effects in the soil microbial community, but the effect of land use was stronger than that of drought. The PLFA content (microbial biomass) of the forests soil was greater under drought. After 50 days of soil incubation, the microbial biomass and most of potential enzyme activities of the almond tree and abandoned soil samples were not significantly affected by drought contrary to those in orchard soil. The total and FOM mineralisation were on average lower in soil under drought than under optimal moisture for all land uses. However, the responses of the priming effect to drought were dependent on the land use. Overall, we conclude that the resistance to drought of the soil microbial community from an agroecosystem having a semi-arid climate is strongly influenced by the previous land use.

Cyanobacteria inoculation enhances carbon sequestration in soil substrates used in dryland restoration

Despite significant efforts to restore dryland ecosystems worldwide, the rate of success of restoration is extremely low in these areas. The role of cyanobacteria from soil biocrusts in reestablishing soil functions of degraded land has been highlighted in recent years. These organisms are capable of improving soil structure and promoting soil N and C fixation. Nevertheless, their application to restore functions of reconstructed soils in dryland restoration programs is yet to be harnessed. In this study, we used microcosms under laboratory conditions to analyse the effects of inoculating soil substrates used in post-mine restoration with a mixture of N-fixing cyanobacteria isolated from soil biocrust (Nostoc commune, Tolypothrix distorta and Scytonema hyalinum) on i) the recovery of the biocrust, and ii) the carbon sequestration and mineralisation rates of these substrates. Soils were collected from an active mine site in the mining-intensive biodiverse Pilbara region (north-west Western Australia) and consisted of previously stockpiled topsoil, overburden waste material, a mixture of both substrates, and a natural soil from an undisturbed area. Our results showed that cyanobacteria rapidly colonised the mine substrates, with biocrust coverage ranging from 23.8 to 52.2% and chlorophyll a concentrations of up to 12.2 μg g^-1 three months after inoculation. Notably, soil organic C contents increased 3-fold (P < 0.001) in the mine waste substrate (from 0.6 g kg^-1 to 1.9 g kg^-1) during this period of time. Overall, our results showed that cyanobacteria inoculation can rapidly modify properties of reconstructed soil substrates, underpinning the potential key role of these organisms as bio-tools to initiate recovery of soil functions in infertile, reconstructed soil substrates.

Native-plant amendments and topsoil addition enhance soil function in post-mining arid grasslands

One of the most critical challenges faced in restoration of disturbed arid lands is the limited availability of topsoil. In post-mining restoration, alternative soil substrates such as mine waste could be an adequate growth media to alleviate the topsoil deficit, but these materials often lack appropriate soil characteristics to support the development and survival of seedlings. Thus, addition of exogenous organic matter may be essential to enhance plant survival and soil function. Here, we present a case study in the arid Pilbara region (north-west Western Australia), a resource-rich area subject to intensive mining activities. The main objective of our study was to assess the effects of different restoration techniques such as soil reconstruction by blending available soil materials, sowing different compositions of plant species, and addition of a locally abundant native soil organic amendment (Triodia pungens biomass) on: (i) seedling recruitment and growth of Triodia wiseana, a dominant grass in Australian arid ecosystems, and (ii) soil chemical, physical, and biological characteristics of reconstructed soils, including microbial activity, total organic C, total N, and C and N mineralisation. The study was conducted in a 12-month multifactorial microcosms setting in a controlled environment. Our results showed that the amendment increased C and N contents of re-made soils, but these values were still lower than those obtained in the topsoil. High microbial activity and C mineralisation rates were found in the amended waste that contrasted the low N mineralisation but this did not translate into improved emergence or survival of T. wiseana. These results suggest a short- or medium-term soil N immobilisation caused by negative priming effect of fresh un-composted amendment on microbial communities. We found similar growth and survival rates of T. wiseana in topsoil and a blend of topsoil and waste (50:50) which highlights the importance of topsoil, even in a reduced amount, for plant establishment in arid land restoration.

Effects of Medium-Term Amendment with Diversely Processed Sewage Sludge on Soil Humification-Mineralization Processes and on Cu, Pb, Ni, and Zn Bioavailability

The organic fraction of sewage sludge administered to agricultural soil can contribute to slowing down the loss of soil’s organic carbon and, in some cases, can improve the physical and mechanical properties of the soil. One of the main constraints to the agricultural use of sewage sludge is its heavy metals content. In the long term, agricultural administration of sewage sludge to soil could enhance the concentration of soil heavy metals (as total and bioavailable fractions). The aim of this research was to evaluate the effects of medium-term fertilization with diversely processed sewage sludge on the soil’s organic carbon content and humification–mineralization processes, on the physical–mechanical properties of soil and their influence on the pool of potentially bioavailable heavy metals, in order to assess their effectiveness as soil organic amendments. After eight years of sludge administration; an increase in the concentrations of bioavailable form was evidenced in all the heavy metals analyzed; independently of the type of sludge administered. The form of sludge administration (liquid, dehydrated, composted) has differently influenced the soil humification–mineralization processes and the physical–mechanical properties of soil. The prolonged amendment with composted sewage sludge contributed to keeping the soil humification–mineralization process in equilibrium and to improving the physical and mechanical qualities of the treated soil.

Spatio-temporal topsoil organic carbon mapping of a semi-arid Mediterranean region: The role of land use, soil texture, topographic indices and the influence of remote sensing data to modelling

SOC is the most important indicator of soil fertility and monitoring its space-time changes is a prerequisite to establish strategies to reduce soil loss and preserve its quality. Here we modelled the topsoil (0-0.3m) SOC concentration of the cultivated area of Sicily in 1993 and 2008. Sicily is an extremely variable region with a high number of ecosystems, soils, and microclimates. We studied the role of time and land use in the modelling of SOC, and assessed the role of remote sensing (RS) covariates in the boosted regression trees modelling. The models obtained showed a high pseudo-R² (0.63-0.69) and low uncertainty (s.d.<0.76gCkg^-1 with RS, and <1.25gCkg^-1 without RS). These outputs allowed depicting a time variation of SOC at 1arcsec. SOC estimation strongly depended on the soil texture, land use, rainfall and topographic indices related to erosion and deposition. RS indices captured one fifth of the total variance explained, slightly changed the ranking of variance explained by the non-RS predictors, and reduced the variability of the model replicates. During the study period, SOC decreased in the areas with relatively high initial SOC, and increased in the area with high temperature and low rainfall, dominated by arables. This was likely due to the compulsory application of some Good Agricultural and Environmental practices. These results confirm that the importance of texture and land use in short-term SOC variation is comparable to climate. The present results call for agronomic and policy intervention at the district level to maintain fertility and yield potential. In addition, the present results suggest that the application of RS covariates enhanced the modelling performance.