Biochar application has the potential to foster a soil environment conducive to improved plant growth by enhancing soil fertility and quality. However, studies focusing on its effects in carbon-poor calcareous soils are notably limited. This study aimed to determine the chemical and microbial properties of a calcareous clayey soil amended with maize biochar and its subsequent effects on barley (Hordeum vulgare L.) growth. Three biochars were prepared from maize stalks at 200, 400, and 600 degrees C by slow pyrolysis, and their influences on soil chemical/microbial properties and barley biomass were evaluated in a 120-day pot experiment under greenhouse conditions. Results showed that application of maize biochar significantly enhanced soil moisture content at field capacity, organic carbon content and decreased soil pH when compared with the control soil without biochar addition (p <= .05), depending on the pyrolysis temperature. Biochar application increased soil microbial biomass and respiration and enzymatic activity but decreased alkaline phosphatase activity (p <= .05). The nitrogen, phosphorus and potassium contents in barley biomass (shoot and root) increased with the addition of biochar (p <= .05), depending on the pyrolysis temperature. However, maize biochar application had no significant effect on barley growth and biomass production (p >= .05). This study provides evidence that biochar application can significantly improve soil chemical and microbial properties of clayey soils, without significantly affecting barley growth. This finding suggests that improved soil quality and plant nutrient content following biochar application may not immediately translate into plant biomass gains in barley in the short term. The major co-benefits of maize biochar application were (i) the improved quality of the study's clayey soil as a sustainable management practice, and (ii) the enhanced soil carbon sequestration as an ecological tool for climate change mitigation.

Soil water repellency (SWR) is a widespread natural phenomenon that results from a complex interplay between the hydrosphere, lithosphere, biosphere, atmosphere, and anthroposphere. Sewage sludge application can induce soil water repellency (SWR), impacting soil hydraulic properties. This research examined the effect of soil microbial manipulation (removal and addition) on SWR and water retention in a silty-clay-loam soil amended with varying sludge amounts. Three levels of water repellency (zero, weak and strong) were artificially created in a silty clay loam soil by adding urban sewage sludge. The results showed that the elimination of soil microorganisms such as fungi and bacteria and their interactions significantly (P≤0.01) affect the hydrophobicity, soil water retention curve (both wetting and drying) of the sludge-treated soils. Microbial exclusion significantly reduced SWR (21-49%), suggesting that microbial activity contributes to the formation of hydrophobic compounds. Conversely, microbial inoculation increased SWR (27.5-50%), indicating microbial production or transformation of hydrophobic substances. It is concluded that soil microorganisms can increase soil water repellency. Also, soil microorganisms can affect the soil water retention curve through their influence on soil water holding capacity, depending on microbial diversity. These findings highlight the critical influence of microbial activity on SWR and water holding capacity in sludge-treated soils.

Biochar may affect nitrogen (N) cycling processes and, therefore, plant-available forms of soil N by modifying the activity and composition of the soil microbial community. However, it is unclear how biochar addition can influence microbial N cycling and availability in saline polluted soils. The present study investigated the impact of sugarcane bagasse biochars (SBBs) produced at 400 and 600 degrees C on potential net ammonification, nitrification and N mineralization, microbial biomass N (MBN), and urease activity in a calcareous soil polluted with lead (Pb) under different levels of NaCl salinity (6 and 10 dS m-1 ) during a 120-day incubation period. NaCl salinity increased soil available Pb concentration, with a greater increase at high than low salinity level. The application of SBBs increased soil organic carbon (SOC, 96-101 % relative to controls), dissolved organic carbon (DOC, 14-110 %), total nitrogen (TN, 6-25 %), cation exchange capacity (CEC, 12-20 %), and immobilized soil Pb (10-25 %). Lead immobilization, which largely resulted from increased soil CEC, was greater with addition of 600 degrees C (20-25 %) than 400 degrees C (15-20 %) biochar in saline soils. Addition of SBBs decreased the availability of soil Pb that was enhanced by salinity. Biochar application stimulated potential net ammonification (177-218 %), nitrification (70-83 %) and N mineralization (92-110 %), MBN (114-221 %) and urease activity (66-79 %) in saline Pb-polluted soils. Redundancy analysis revealed that increased DOC, increased TN and Pb immobilization were the most significant factors contributing to the enhanced N bio-transformations, MBN, and urease activity in saline polluted soils amended with SBBs. Our highlights the potential benefits of low-temperature SBBs as an amendment to minimize the impact of metal toxicity associated with salinity on microbial N cycling processes in Pb-polluted soils. In conclusion, biochar application could be a useful practice for enhancing the N turnover rate in saline Pb-polluted soils by increasing substrate availability and decreasing Pb mobility.

Biochar as an efficient strategy for the improvement of soil properties and organic waste management may reduce the potential effects of abiotic stresses and increase soil fertility. However, the effects of this organic amendment on soil microbial indicators under combined salinity and pollution have not been studied yet. Therefore, the objective of this study was to evaluate the influence of sugarcane bagasse biochar on some soil bioindicators in a Cd-polluted soil under saline and non-saline conditions. A factorial experiment was carried out with two factors, including NaCl salinity (control, 20 and 40 mM NaCl) and sugarcane bagasse biochar (soils unamended with biochar, amended with uncharred bagasse, 400 oC biochar, and 600 oC) at 1% (w/w) using a completely randomized design. Results showed that salinity increased the mobility of Cd (12-17%), and subsequently augmented its toxicity to soil microorganisms as indicated by significant decreases in the abundance and activities of the soil microbial community. Conversely, sugarcane bagasse biochar application reduced the concentration of soil available Cd (14-18%), increased the contents of soil organic carbon (89-127%), and dissolved organic carbon (4-70%), and consequently alleviated the effect of both abiotic stresses on soil microbial community and enzyme activity. In conclusion, this experiment demonstrated that the application of sugarcane bagasse biochar could reduce the salinity-induced increases in available Cd and mitigate the interaction between salinity and Cd pollution on the measured soil bioindicators.

Soil quality assessment at landscape level can be used as an effective tool to monitor soil functioning and sustainability. This study aimed to develop a soil quality index (SQI) model for assessing landscape-level topsoil quality along slope positions in a commercial almond plantation. Topsoil samples (0–30 cm) were collected from four discrete slope positions (summit, backslope, footslope and toeslope) on north-facing and south-facing slopes in almond orchards established on an undulating landscape in West Central Iran, and analyzed for 16 soil properties. Four out of 16 soil properties, including microbial biomass carbon, and available forms of nitrogen, potassium and phosphorus, all important for soil functions such as nutrient cycling and supply, were identified as the most representative indicators for the minimum data set. The relative contribution of soil microbial biomass to the SQI value was maximum (43%) followed by available nitrogen (25%), potassium (16%) and phosphorus (16%). The SQI values were lower in the backslope positions (0.51 ± 0.02) than the summit (0.71 ± 0.04), footslope (0.73 ± 0.03) and toeslope positions (0.73 ± 0.04), while north (0.69 ± 0.03) and south (0.65 ± 0.03) slopes showed similar SQI values. This study illustrated a relatively high spatial variability of landscape-level soil quality along the toposequence in almond orchards. Backslope positions with a steep slope would contribute to a decline in soil quality, largely due to low microbial biomass and nutrient availability resulted from surface soil movement and water erosion. The soil microbial biomass and nutrient availability were the potential indicators that could reflect the spatial variability of soil quality along landscape positions.

This study aimed to establish a soil quality index (SQI) using factor analysis (FA) and network analysis (NA) techniques for the assessment of soil quality after deforestation in Northern Iran. In this work, 16 soil properties from forest sites and adjacent cropland sites at two locations in the Hyrcanian forests of Northern Iran were used and analyzed. The minimum data set (MDS) indicators selected through the FA method were potential carbon mineralization (PCM), urease activity (URE), plant-available water and cation exchange capacity, which contributed to the SQI value by 39, 28, 19 and 13%, respectively. Soil quality indicators identified through the NA approach were URE, organic C (OC), PCM and microbial biomass C (MBC), contributing towards the SQI value by 34, 26, 23 and 17%, respectively. The PCM and URE, selected by both techniques, were the most significant indicators of soil quality to detect the deforestation impacts in Northern Iran. The computed SQIs were significantly correlated with OC stocks, validating the SQI models developed by both FA and NA methods. The SQI values computed through NA were more sensitive to deforestation than those computed through FA, suggesting the NA-screened SQI would represent changes in soil functions more adequately than the FA-screened SQI. Croplands were characterized by a lower value of SQI (62-79%), especially in the surface layer, indicating a loss of soil capacity to function well after deforestation for the expansion of farmlands. The current study shows that the SQI model developed by the NA approach would also be a useful, alternative technique for soil quality assessment after conversion of native forest ecosystems to agricultural lands. To conclude, our results confirmed a weighted correlation-based NA of the soil attributes can be used as a simple and robust tool for assessing soil quality following deforestation and loss of ecosystem services.

Biochar can reduce salinity stress and metal toxicity to soil microbial community and enzymatic activity, hence would improve soil biological fertility and quality. However, the effects of sugarcane bagasse biochar (SCB) on microbial and biochemical responses to salinity stress in metal co-contaminated soils still remain unknown. The aim of this study was to assess the impact of SCB application on microbial activity, biomass and enzymatic activities in a soil co-contaminated with cadmium (Cd) and lead (Pb) when simultaneously exposed to NaCl salinity stress during an incubation experiment. Soil samples were initially co-contaminated with cadmium (10 mg Cd kg(-1)) and lead (150 mg Pb kg(-1)) solutions, then pre-incubated for 30 days and finally salinized with three levels of NaCl solution (0, 20 and 40 mM NaCl). Two slow pyrolysis SCBs prepared at 400 and 600 degrees C were applied to the saline polluted soils at 1% (w/w) and the mixtures were incubated for 120 days under laboratory conditions. Soils amended with raw bagasse and without amendment were also used in the experiment. Results showed that soil amendment with SCBs decreased the availability of Cd by 17-19% and Pb by 11-18%, and increased the content of soil organic carbon (SOC) by 96-104% and dissolved organic carbon (DOC) by 14-164% under saline conditions. High-temperature SCB decreased metal availability and enhanced SOM content in the soil more than low-temperature SCB. Application of SCBs increased soil microbial and biochemical properties from 27 to 180%, depending on the pyrolysis temperature, salinity level and the assay itself. Biochar reduced the adverse influences of metal toxicity and salinity stresses on soil microbial and biochemical functions, most largely through immobilizing metals and improving SOC and DOC. Low-temperature SCB promoted soil microbial quality more than high-temperature SCB. This study indicated that low-temperature SCB could be used as an amendment in metal co-contaminated soils to alleviate the potential risks associated with the combined effects of metal pollution and salinity stresses on microbial and biochemical indicators of soil quality/health under arid and semi-arid conditions. The findings would have some useful implications for the soils co-contaminated with toxic metals under the stress of salinity and for rehabilitation of salt-affected soils using SCB as a cost-effective source of organic matter.

Land-use changes in native rangelands can greatly affect nutrient cycling processes. While phosphorus (P) is the second most important macronutrient that limits plant growth and productivity in semi-arid rangelands, the effect of land-use conversions on P pools and turnover has been rarely studied. The main objective of this study was to determine soil P pools and dynamics after conversion of rangelands to rainfed wheat croplands and re-conversion of these rainfed farming systems back to rangelands (i.e., cultivation abandonment) in West Central Iran. Soil samples (0–150 and 150–300 mm) were collected from wheat-cultivated rangelands, wheat-abandoned rangelands and uncultivated rangelands on north-facing and south-facing slopes, and analyzed for P pools, P mineralization and phosphatase activities. Results showed a strong impact of land-use changes on soil P pools and turnover, which varied greatly with slope aspect. Converting rangelands to wheat fields declined soil inorganic P (46%), organic P (26%), microbial biomass P (52%), potentially mineralizable P (78%) and P-acquiring enzyme activities (15–20%). Conversely, abandonment of wheat cultivation resulted in a major recovery of P pools and cycling with greater inorganic P (36%) and organic P (21%) pools, microbial biomass P content (79%), P mineralization (191%) and P-cycling enzyme activities (4–7%) after 15 years. In summary, short-term cessation of wheat cultivation to allow secondary rangeland succession without disturbance would rebuild soil P storage, restore P cycling and supply, and hence would improve soil functions and quality. Therefore, cropland abandonment should be adopted to maintain soil P fertility and the sustainability of native rangelands in semi-arid regions.

Recovery of soil quality after wildfire is essential for soil functioning such as nutrient cycling, resistance to biochemical degradation and sustainable plant growth. Post-fire soil quality is crucial for the maintenance of ecosystem sustainability. The objective of this study was to develop a soil quality index (SQI) for assessing post-fire soil quality in upland rangeland ecosystems of a semi-arid region in Central Iran. Soil samples were collected from burnt and unburnt plots at six rangeland sites two years after a wildfire event and analyzed for 22 soil properties. The soil microbial and biochemical properties indicated a greater magnitude of post-fire changes than soil chemical properties. The contribution of microbial respiration to soil quality, obtained using factor analysis, was the highest (36%) followed by particulate organic carbon (22%), microbial biomass carbon (15%), available phosphorus (15%) and alkaline phosphomonoesterase activity (12%). This indicates that microbial properties, labile carbon and phosphorus availability are the most important soil quality indicators to detect the wildfire effects in the study rangelands. The SQI value was, on average, 28% lower in burnt rangelands (0.39-0.55) than unburnt rangelands (0.56-0.75); indicating disturbance by wildfire would be accompanied by the loss of soil functioning. This illustrates that fire decreased soil quality, which did not recover two years after fire, probably due to the high grazing pressure and climatic conditions (i.e., longer drought periods and water limitation). Apparently, a longer period of time would be required for the complete recovery of soil quality in these semi-arid rangelands. In this study, we demonstrate that an integrated SQI would be more useful to assess post-fire soil functions than single soil properties in fire-affected rangelands of semi-arid climates.

Biochar may improve soil microbial and biochemical functions under abiotic stresses. In this research, we studied changes in soil microbial properties and processes after sugarcane bagasse biochar (SCB) application (1% w/w) to a soil contaminated with Cd under saline conditions during an incubation experiment. SCB produced at 400 °C (B400) and 600 °C (B600) increased soil organic carbon (SOC) content by 89-127% and dissolved organic carbon content by 21-70%. NaCl salinity mobilized Cd by 16-19%, while biochar immobilized Cd by 14-18%, indicating the use of biochar would offset the increase in Cd availability induced by salinity. SCB application improved microbial and biochemical functions (up to 280%) in the soils contaminated with Cd under salinity stress. B400 biochar was often more effective in improving the soil microbial properties and functioning than B600 biochar. SCB application reduced the detrimental effects of salinity-induced Cd toxicity on soil microbial community and enzyme activity mainly through retaining Cd and supplying C substrate for microbial uptake and activity. The factor analysis and redundancy analysis results also confirmed that SOC and Cd availability was the most important factors and accounted for a large portion of the variation in soil microbial properties and enzyme activities in saline Cd-contaminated soils amended with SCB. This study indicated that B400 applied at 1% could be used in saline Cd-contaminated soils to protect the soil microbial communities from Cd toxicity, and to mitigate the potential stresses associated with the co-occurrence of Cd contamination and salinity on critical soil microbial and biochemical functions.

Biochar as an organic amendment improves soil attributes, with a potentially significant effect on soil chemical fertility and quality. The main objective of this study was to quantify the effect of biochar addition on nutrients, carbon sequestration and microbial activity and understand the mechanisms of controlling biochar effects in calcareous soils. Maize residue biochars produced at 200, 400 and 600 °C were added at 5 and 10 g kg−1 rates to sandy loam and clayey texture calcareous soils. The soil properties measured were pH and electrical conductivity (EC), plant-available potassium (K) and available phosphorus (P), total nitrogen (TN), C sequestration; and the fluorescein diacetate (FDA) hydrolysis activity. Addition of raw material and biochars increased pH (0.15–0.46 units), EC (0.14–0.38 dS m−1), TN (63–120%), K (12–41%) and FDA activity (27–280%), but tended to decrease plant-available P (23–86%). Increasing pyrolysis temperature increased soil C pool index (CPI), but decreased the FDA and the changes depended largely upon the application rate and soil texture. The positive effects of biochar addition and its pyrolysis temperature on soil C sequestration potential were more pronounced at high than low application rate and in sandy loam than clayey soils. Nevertheless, the effect of biochar addition and pyrolysis temperature on the FDA activity was higher at high than low application rates, but lower in sandy loam than clayey soils. Although biochar application may successfully improve soil processes and attributes and have a high potential for C sequestration, its effects are controlled by soil texture, pyrolysis temperature and application rate.

Salinity may increase metal mobilization with a potentially significant consequence for soil enzymatic activity and nutrient cycling. The goal of this study was to investigate changes in soil enzyme activity in response to salinization of a clay loam soil artificially polluted with cadmium (Cd) and lead (Pb) during a 120-day incubation experiment. Soil samples were polluted with Cd (10 mg Cd kg−1), Pb (150 mg Pb kg−1), and a combination of Cd and Pb, then preincubated for aging and eventually salinized with three levels of NaCl solution (control, low and high). NaCl salinity consistently increased the mobilization of Cd (12–22%) and Pb (5–16%) with greater increases at high (17–22% for Cd, 9–16% for Pb) than low (12% for Cd, 5–7% for Pb) salinity levels. While the increased Cd mobilization was greater in co-polluted (22%) than Cd-polluted (17%) soils, the increase of Pb mobilization was lower in co-polluted (9%) than Pb-polluted (16%) soils at high salinity level. The salinity-induced increases in metal mobilization significantly depressed soil microbial respiration (up to 43%), microbial biomass content (up to 63%), and enzymatic activities (up to 87%). The multivariate analysis further supported that the increased soil electrical conductivity, Cd mobilization, and pH after salinization were the most important factors governing microbial activity and biomass in metal-polluted soils. Results showed that changes in microbial biomass and mobile metal pool with increasing salinity had a major effect on enzyme activities, particularly under the combined metals. This study indicated that the secondary salinization of metal-polluted soils would impose an additional stress on enzymatic activities as biochemical indicators of soil quality, and therefore should be avoided for the maintenance of soil microbial and biochemical functions, especially in arid regions. In metal-polluted soils, the observed responses of extracellular and intracellular enzymes to salinity can be used to advance our knowledge of microbial processes when modeling the carbon and nutrient cycling.

Soil recovery, particularly soil organic matter (SOM), after land-use changes is crucial for the maintenance of ecosystem functioning and sustainability. The objective of this study was to investigate the influence of wheat dry-farming and subsequent abandonment of dry-farming on the quantity and quality of SOM and humic substances (HS) in a semi-humid upland pasture ecosystem. Soil samples were collected at 0-15 and 15-30 cm depths from cultivated pastures under dry-farming, restored pastures after dry-farming abandonment and never-cultivated pastures as a reference site. The samples were analyzed for total organic C (TOC), chemically labile organic C (LOC) and non-labile C (NLC) fractions; and further fractionated into conventional fulvic acid (FA), humic acid (HA) and humin (HU) components. Land-use changes in pastures altered both labile C and highly recalcitrant C fractions, depending on soil sampling depth. Long-term dry-farming reduced soil TOC (33%), LOC (64%) and NLC (29%) fractions, while dry-farming abandonment resulted in an increase in soil TOC (18-35%), LOC (45-65%) and NLC (17-33%), depending on the age of cultivation abandonment. The quantity of both FA and HU fractions decreased (40-43%) following dry-farming in pasture soils but increased (17-81%) after dry-farming abandonment when compared with cultivated pasture soils. Nevertheless, neither dry-farming nor abandonment of dry-farming affected the HA fraction. Although dry-farming practices increased the HA/FA ratio, (FA + HA)/TOC ratio and E4/E6 ratio of HA, the abandonment of dry-farming reduced these qualitative parameters of soil HS. Dry-farming abandonment in native pastures caused HA structure to be become more aromatic and stable. This study indicated that land-use changes in primary pastures can affect not only the quantity, but also the quality of SOM and its major fractions. Changes in both quantity and quality of SOM and HS could be used as sensitive indicators of soil degradation and ecological restoration in semi-humid pastures.

Soil amendment with biochar alleviates the toxic effects of heavy metals on microbial functions in single-metal contaminated soils. Yet, it is unclear how biochar application would improve microbial activity and enzymatic activity in soils co-polluted with toxic metals. The present research aimed at determining the response of microbial and biochemical attributes to addition of sugarcane bagasse biochar (SCB) in cadmium (Cd)-lead (Pb) co-contaminated soils. SCBs (400 and 600 °C) decreased the available concentrations of Cd and Pb, increased organic carbon (OC) and dissolved organic carbon (DOC) contents in soil. The decrease of metal availability was greater with 600 °C SCB than with 400 °C SCB, and metal immobilization was greater for Cd (16%) than for Pb (12%) in co-spiked soils amended with low-temperature SCB. Biochar application improved microbial activity and biomass, and enzymatic activity in the soils co-spiked with metals, but these positive impacts of SCB were less pronounced in the co-spiked soils than in the single-spiked soils. SCB decreased the adverse impacts of heavy metals on soil properties largely through the enhanced labile C for microbial assimilation and partly through the immobilization of metals. Redundancy analysis further confirmed that soil OC was overwhelmingly the dominant driver of changes in the properties and quality of contaminated soils amended with SCB. The promotion of soil microbial quality by the low-temperature SCB was greater than by high-temperature SCB, due to its higher labile C fraction. Our findings showed that SCB at lower temperatures could be applied to metal co-polluted soils to mitigate the combined effects of metal stresses on microbial and biochemical functions.

Salinity may increase metal mobilization and toxicity with a potentially significant consequence for soil enzymatic activity and nutrient cycling. The goal of this study was to investigate changes in soil enzyme activity in response to salinization of a clay loam soil artificially polluted with cadmium (Cd) and lead (Pb) during an incubation experiment. Soil samples were polluted with Cd, Pb, and a combination of Cd and Pb, pre-incubated for aging, and then salinized with three levels of NaCl solution, and were finally incubated for 120 days. NaCl salinity consistently increased the mobilization of Cd and Pb with greater increases at high than low salinity levels. While the increased Cd mobilization was greater in co-polluted than Cd-polluted soils, the increase of Pb mobilization was lower in co-polluted than Pb-polluted soils at high salinity level. The salinity-induced increases in metal mobilization and toxicity significantly depressed soil microbial respiration, microbial biomass content and enzymatic activities. The increased soil electrical conductivity, Cd mobilization and pH after salinization were the most important factors governing microbial activity and biomass in metal-polluted soils. Changes in microbial biomass and mobile metal pool with increasing salinity had the major effects on enzyme activities, particularly under the combined metals. Secondary salinization of metal polluted soils would impose an additional toxicity stress on enzymatic activities as biochemical indicators of soil quality, and therefore should be avoided for the maintenance of soil microbial and biochemical functions, especially in arid regions. In metal-polluted soils, the observed responses of enzymes to salinity can be used to advance our knowledge of microbial processes when modelling the carbon and nutrient cycling.

The current study was conducted to determine the combined performance of soil micro- and macro-organisms to stimulate the growth and lead (Pb) uptake of Bermuda grass (Cynodon dactylon (L.) Persi.) in a soil polluted with Pb-mining activities. Plants were inoculated with a mixture of arbuscular mycorrhizal (AM) fungal species, plant growth-promoting rhizobacteria (PGPR) species, and epigeic earthworms (Eisenia fetida) either alone or in combination. Results demonstrated antagonistic interactions between AM fungi and PGPR or between AM fungi and earthworms on the growth of mycorrhizal plants by increasing the availability of both phosphorus (P) and Pb in the soil solution and the subsequent reduction of mycorrhizal root colonization following inoculation of PGPR or earthworms. Plant biomass was negatively correlated with soil-available Pb, but positively with the percentage of root colonization by AM fungi. Additionally, mycorrhizal root colonization was negatively correlated with soil-available P and Pb concentrations. The triple inoculation of AM fungi with PGPR and epigeic earthworms as a bioaugmentation tool could result in a synergistic interaction effect on plant Pb bioaccumulation and uptake, enhancing the efficiency of phytoremediation and eco-restoration of Pb-polluted sites. In conclusion, the use of Bermuda grass in association with functionally dissimilar soil organisms demonstrated a high effectiveness for Pb in situ phytoremediation, specifically Pb phytostabilization, to reduce Pb mobilization in the environment.

The aim of this research was to study the influence of land-use changes on degradation and ecological restoration of rangeland soils by quantifying 15 soil attributes and the subsequent development of a soil quality index (SQI). Soil properties were determined to establish a minimum data set (MDS) for the development of an overall weighted additive SQI. The soil attributes were measured on samples (0 to 15 and 15 to 30-cm depths) collected in undisturbed rangelands, cultivated rangelands, and restored rangelands following cultivation abandonment for 12 or 45 years in a semi-arid ecosystem, Central Iran. The selected MDS indicators consisted of the mean weight diameter (MWD), total nitrogen (TN), microbial respiration (MR), and alkaline phosphomonoesterase activity (ALP). Overall, soil aggregation, N content, microbial activity, and ALP activity were found to be the key indicators contributing considerably to the SQI of rangeland ecosystems. Soil MWD had the highest contribution (31%) to the estimated SQI values, followed by TN (27%), MR (22%), and ALP (21%). Results indicated a clear difference in soil quality among the common land uses with a significant decline of SQI after conversion of native rangelands (0.80) to croplands (0.53). Restored rangeland soils were characterized by a higher value of SQI (0.63-0.73) as compared with cultivated rangelands (0.53). This suggests a good recovery of soil capacity and functions after the abandonment of cropping activity in previously cultivated rangelands. Vegetation restoration and plant productivity appeared to be the major driver of improved soil quality of the abandoned croplands in these rangelands. Our SQI tool could be useful to determine the success of agricultural abandonment and ecological restoration of rangeland soils in the studied semi-arid environment.

Soil cadmium (Cd) pollution resulting from anthropogenic activities has become a major concern for microbial and biochemical functions that are critical for soil quality and ecosystem sustainability. Organic amendments can reduce Cd toxicity to the microbial community and enzymatic activity in Cd-polluted soils and thus would increase the ecological dose (ED) values. However, there has been less focus on the effect of organic amendments on microbial and biochemical responses to Cd toxicity in non-calcareous soils using the concept ED. The aim of this study was to assess the impact of compost application on microbial activity, microbial biomass, turnover rates of carbon and nitrogen, and enzymatic activities as the key ecological functions in a non-calcareous soil spiked with different Cd concentrations (0–200 mg kg−1). Results showed that soil amendment with compost decreased Cd availability by 48–76%, depending on the total soil Cd content. The application of compost reduced the negative influence of Cd eco-toxicity on most soil microbial and biochemical functions by 20–122%, depending on the Cd level and the assay itself. The ED values, derived from the sigmoidal dose-response and kinetic models, were 1.10- to 2.24-fold higher in the compost-amended soils than the unamended control soils at all Cd levels. In conclusion, the potential risks associated with high levels of Cd pollution can be alleviated for microbial and biochemical indicators of soil quality/health with application of 2500 kg ha−1 compost as a cost-effective source of organic matter to non-calcareous soils. The findings would have some useful implications for organic matter-limited non-calcareous soils polluted with Cd.

Micro- and macro-organisms are key components of sustainable soil-plant systems; and are involved in plant growth stimulation and accumulation of heavy metals in the plant, with great contribution to phytoremediation of heavy metal-contaminated soils. However, the combined effect of arbuscular mycorrhizal fungi (AMF), plant growth-promoting rhizobacteria (PGPR) and earthworms on plant growth and metal uptake is not yet clear. The main objective of this study was to examine the combined influences of these soil organisms on the growth and metal uptake by a native plant species (Stachys inflata), and subsequently on potential phytoremediation in a soil highly polluted with Pb/Zn mining activities. Metal tolerant AMF, PGPR and earthworms were used either alone or in combination in a factorial pot experiment under greenhouse conditions for 4 months. Inoculation of AMF, PGPR and earthworm led to an increase of soil Pb/Zn availability with the greatest Zn availability (about 2 times) with triple inoculation of all the organisms and the highest Pb availability (about 3 times) with co-inoculation of PGPR and earthworms. Triple inoculation of soil organisms increased the total plant biomass 3 times, total Pb uptake 6 times and total Zn uptake 5 times as compared with the uninoculated plants. The growth-stimulating effect of combined soil organisms was much greater than that of individual or dually-inoculated organisms. These results showed that it is possible to use the combination of metal-tolerant soil organisms as a potential bioaugmentation tool to accelerate metal phytoremediation rate in calcareous soils polluted by Pb/Zn mining activity under arid conditions. This could occur as a consequence of the synergistic effects of AMF, PGPR and earthworms on metal availability in the soil, S. inflata growth, metal tolerance and uptake. However, it would practically require more than hundreds of cropping cycles (360 for Pb and 250 for Zn) to achieve metal maximum permissible limits under the conditions of this pot experiment.

Abiotic stresses such as salinity and contamination individually have a negative effect on the soil enzyme activities, whereas addition of organic matter to soil can alleviate the negative impacts of stresses on the enzyme activity. However, the combined effects of these stresses (multiple stresses) on soil biochemical conditions and the role of organic matter addition in these interactions are largely unknown. The objective of this research was to explore the interaction effect of NaCl salinity and cadmium (Cd)-pollution on the activities of catalase, alkaline phosphatase, arylsulfatase and fluorescein diacetate hydrolysis in a Cd-contaminated calcareous soil treated with alfalfa residue over 3 months of incubation. A factorial experiment with 2 levels of Cd, 3 levels of salinity and 2 plant residue treatments was conducted using a completely randomized design with 4 replications. The results indicated that salinity increased the Cd availability in both uncontaminated and contaminated soils and reduced the soil enzymatic activity. Nevertheless, addition of alfalfa residue reduced the detrimental effects of salinity and Cd-pollution on the soil enzyme activities. This indicated that in saline Cd-contaminated soils with low organic matter, adding plant residues could lower the concentration of available Cd and the effect of soil salinity with a concomitant increase of enzyme activities. So, this study showed that the joint effect of NaCl salt and Cd on enzyme activity was mostly synergistic in plant residue-untreated soils, but it was antagonistic in the plant residue-treated soils.