Land abandonment might be an alternative management for restoring soil conditions and C from prolonged cultivation and agricultural practices. In the present study, the influence of 18-22 years of ...land abandonment on soil properties, C dynamics and microbial biomass was evaluated in closely situated wheat and alfalfa farmlands, and abandoned lands on calcareous soils, Central Iran. Soil properties of the 0-15 and 15-30 cm depths from abandoned lands were compared to those from conventionally cultivated lands (i.e., continuous wheat-fallow and alfalfa-wheat rotation) common in calcareous soils of Central Zagros Mountains. Soil bulk density in the 0-15 and 15-30 cm layers decreased significantly while total porosity increased significantly in abandoned lands. Generally, soil aggregate stability tended to increase within the abandoned fields owing to increased water-stable macro-aggregates. Soil organic C (OC) contents (g kg^sup -1^) and pools (Mg ha^sup -1^) in the 0-15 cm soil layer increased significantly in abandoned lands compared with cultivated lands, with no effect in the 15-30 cm soil layer after 18-22 years of land abandonment, suggesting the restoration of C is pronounced in the upper 0-15 cm soil depth . The total C accumulation in abandoned lands was 7.0 Mg C ha^sup -1^ for the entire sampling depth (0-30 cm) over the 18-22 years of land abandonment, which was 26% greater relative to cultivated lands. Carbon mineralization (Cmin) followed a trend similar to organic C, whereas C turnover (Cmin/OC ratio) was slightly greater in wheat fields. However, soil microbial biomass C (MBC) did not vary considerably among the three land uses. In brief, improvements, albeit slowly, in soil properties of the top layer with the cessation of cultivation indicated that land abandonment may result in enhanced soil C sequestration, and would maintain fertility and productivity of the farmlands of semi-arid climates.PUBLICATION ABSTRACT
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.
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.
•We assessed crop cultivation effect on soil quality index (SQI) in rangelands.•Organic carbon and salinity were the key indicators of soil changes and SQ.•Assessing SQI allowed a better ...discrimination between rangeland and cropland sites.•Long-term cultivation and disturbance in native rangelands degraded severely SQ.•Cropland soils functioned at 52–64% of the potential capacity of rangelands soils.
Conversion of native rangelands to croplands potentially influences soil functions and quality. The aim of the current study was to assess soil quality (SQ) after rangeland conversion and degradation for more than 40 years using an indexing framework and integrated approach. Fifteen soil attributes were measured at two sampling depths (0–20 and 20–40cm) of paired native undisturbed and adjacent cultivated rangelands at three rangeland sites. The soil organic carbon (OC), electrical conductivity (EC) and arylsulphatase (ARY) activity were found to be the key indicators of the minimum data set and these indicators greatly affected the computed soil quality index (SQI), particularly in the soil surface. The contribution of OC, EC and ARY to the overall SQI was 77, 13 and 10%, respectively. Although rangeland conversion reduced other soil attributes (including aggregate stability, available water capacity, cation exchange capacity, microbial biomass, microbial activity and the activities of urease and invertase enzymes), in particular at the 0–20cm depth, these variables did not contribute to the estimated SQI values because of their high correlation with OC contents (i.e., strong interdependency). Cultivated rangelands were characterized by a low soil OC content, EC and ARY activity, and consequently a low SQI. A significant decline in SQI value (29–47%) was observed as a result of rangeland conversion to croplands, depending on soil depth considered and scoring function used to compute the SQI. Overall, converting native rangelands to croplands decreased SQ to 52–64% of their potential capacity using a non-linear scoring method. In summary, soil OC, EC and ARY are the most important indicators, which can be used to monitor and asses the degradation of rangeland SQ after conversion to croplands in these arid and semiarid upland environments. This finding is of especial importance because the assessment of SQ allows the successful and straightforward discrimination between rangeland and cropland ecosystems or to quantify land use conversion effects on SQ. It is concluded that the rate of soil changes can be assessed and compared more accurately in the studies of land use conversions in native rangeland ecosystems using the current indexing framework due to its simplicity and quantitative flexibility.
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.
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.
Mineralization of soil organic matter plays a key role in supplying nutrient elements essential to plant growth. Soil cultivation and crop residue affect C mineralization and nutrient availability in ...wetland ecosystems. This study evaluated the combined impacts of soil cultivation and crop residue on C and N mineralization in a calcareous wetland soil (Luvic Calcisol) in Central Iran. Soil samples were collected from 0 to 15
cm depth in cultivated and uncultivated plots and analyzed for selected soil attributes. Wheat (
Triticum aestivum L.) and alfalfa (
Medicago sativa L.) residues were collected and analyzed for the chemical composition. Nitrogen and C mineralization rates were studied using laboratory incubations for 60 days. Results show that in this calcareous wetland soil, cultivation decreased soil total organic carbon and total N contents, while total organic carbon/total N ratio, bulk density, pH, and extractable P and available K levels remain unaffected. Cultivation resulted in a significant increase in soil C and N mineralization. Wheat residue had a significantly lower quality than alfalfa residue, and therefore decomposed more slowly. Results also indicate that plant residue has a significant impact on decomposition rate and nutrient cycling. Soil cultivation and residue quality had a significant influence on C and N cycling and nutrient contents. The combined effects of soil cultivation and crop residue play a significant role in changing the nutrient balance and availability in calcareous wetland soils with conventional agricultural practices. In summary, significant differences occurred in soil attributes and residue decomposition affecting C and nutrient dynamics, and therefore crop productivity.
•Soil organic matter (SOM) and humic substances (HS) were affected by land-use changes in upland pastures.•Changes in quantity and quality of SOM and HS could be used as indicators of soil ...degradation and restoration.•Subsurface soil layer of pasture ecosystems had a great C recovery potential after dry-farming abandonment.•SOM and HS were not completely recovered to initial level after abandonment of dry-farming for 30 years.•Abandonment of cultivation and tillage offers an opportunity for C sequestration in semi-humid-pasture soils.
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.
•Earthworms decreased soil microbial biomass content and turnover time.•Microbial activity and fungal respiration were increased by earthworms.•Earthworm effects on microbial indicators were ...decreased with sludge addition.•Modification of earthworm effects was greater with addition of endogeic species.•Interaction effect between earthworm species on microbial performance was additive.
Application of municipal sewage sludge (MSS) may modify the influence of earthworm activity on soil microbial and biochemical properties through an increase of substrate availability. However, the effect of earthworm activity on microbial community is poorly known in calcareous soils amended with MSS. Such knowledge would lead to better understanding of how earthworms and microorganisms interact following MSS application in agroecosystems. This study aimed to investigate how MSS application can modify the impact of earthworms on microbial performance and biochemical attributes of a calcareous soil amended with MSS. Experimental treatments were MSS application (without and with 1.5% MSS) and earthworm addition (no earthworm, epigeic Eisenia fetida, endogeic Aporrectodea caliginosa and a combination of the two earthworm species) setup as a 2×4 full factorial experiment using a completely randomized design with three replications for each treatment combination under greenhouse conditions over 90 days. Addition of MSS had a positive effect on the measured biochemical and microbiological indicators of the study soil. Municipal sewage sludge application resulted in a significant (p<0.001) increase in the amounts of microbial biomass carbon (MBC) and basal respiration rate (RR); but without an effect on the level of dissolved organic carbon (DOC). While the presence of earthworms decreased the quantity of DOC and MBC (p<0.001); other soil attributes such as basal respiration rate, the metabolic quotient (qCO2) and the ratio of fungal to bacterial (F/B) respiration were all increased significantly (p<0.001) with earthworm addition. Nevertheless, the magnitude of the earthworm effect was largely dependent upon the MSS treatment. Application of MSS decreased the stimulatory effect of earthworms on soil microbial indicators and this effect was less pronounced in the presence of E. fetida than A. caliginosa species. This is probably due to the preference of epigeic E. fetida to feed on MSS as an essential food resource rather than only feeding and grazing on microbial populations. In contrast, the endogeic A. caliginosa species was not dependent upon MSS as food resources. Moreover, the interaction effect between the two earthworm species on soil microbial and biochemical properties was mostly additive in nature (without interaction) in both MSS-amended and unamended soils. Results indicated that earthworm effect and its interaction with MSS were important factors for soil microbial biomass, community composition and performance and that earthworm effects should decrease in MSS-treated soils.
