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We investigated the effect of Serendipita indica, an endophytic fungus, inoculation of different wheat (Triticum aestivum) cultivars on the rhizosphere physical quality. S. indica inoculated and uninoculated seedlings of wheat cultivars (Roshan, Ghods, Kavir and Pishtaz) were grown in rhizoboxes. Plants were harvested and intact samples were taken from the rhizosphere to measure soil organic carbon (SOC), hot-water soluble carbohydrates (HWSC), carbon mineralization rate (CMR), water repellency index (RI) by the sorptivity method, and aggregate stability by the high energy moisture characteristic (HEMC) method. Root mucilages of inoculated and uninoculated seedlings were also collected for measuring total polysaccharides (TPmucilage). The SOC, HWSC, and RI were increased by 146, 83, and 40% and CMR was decreased by 56% in planted treatments, which consequently increased the HEMC aggregate stability indices. S. indica increased SOC, HWSC, RI, and structural stability, and improved the physical quality especially in soil with Roshan and Ghods, which had more extensive root distributions and higher TPmucilage. The changes of soil-physical and hydraulic properties among different wheat cultivars imply that both quantitative and qualitative properties of root exudates have significant effects on soil quality. Soil with Roshan had the highest SOC, HWSC, and root distribution and the lowest aggregate stability. However, soil with Ghods had almost the same SOC and HWSC, but it had the highest stability indices. S. indica inoculation of different wheat cultivars, by increasing SOC and inducing water repellency in the rhizosphere, can improve the aggregate stability and soil physical quality.

This study was conducted to determine the effect of arbuscular mycorrhizal fungi (AMF) symbiosis on plant growth and nutrient uptake under combined drought and salinity stresses. A pot experiment was carried out with a factorial arrangement of treatments in a completely randomized design with three replications. Experimental treatments included two plant types ( Atriplex canescens and Haloxylon ammodendron) with three levels of inoculation of fungal species ( Funneliformis geosporus, Funneliformis mosseae, and control), two levels of soil salinity stress (7 and 14 dS m–1), and two levels of drought stress (50% and 80% of management allowable depletion). Vegetative parameters, as well as root N, P, and K concentrations and uptakes, mycorrhizal growth response, mycorrhizal nitrogen response, mycorrhizal phosphorus response, mycorrhizal potassium response, and root colonization were measured. The results showed that the application of AMF increased the plant growth variables such as stem diameter, root length, shoot dry weights, and shoot to root ratio as well as nitrogen and phosphorus uptakes. The application of both AMF types was effective as compared to the control. However, F. mosseae indicated better performance especially, in terms of the effect on plant growth variables. Also, F. mosseae was more effective to relieve stress (i.e., salinity and drought) than F. geosporus. There was a significant difference between plant types and H. ammodendron had better efficiency than A. canescens under drought and salinity stresses. Based on the results, planting of H. ammodendron inoculated with F. mosseae might be recommended for soil conservation in the arid environments.

Soil characteristics, especially clay content and clay type, have significant impacts on splash erosion. This investigation was conducted to determine the effects of clay content and clay type (zeolite, phlogopite, bentonite, and kaolinite) on the shear strength and splash erosion of clay–sand mixtures compared with a clay soil under controlled conditions. Clay–sand mixtures were prepared by mixing 15, 30, and 45 kg 100 kg−1 of the selected clays with pure sand and a clay soil; these mixtures were pre-treated with three levels of wetting and drying (W&D) cycles, and then shear strength was measured. The splash erosion rate was measured at three levels of water status: air-dry, plastic limit (PL), and liquid limit (LL). The highest values of splash erosion were observed in the samples without the W&D cycle, and after applying the W&D cycles, splash erosion decreased. Moreover, splash erosion was higher in the air-dry and LL groups. Splash erosion decreased with increased clay content because of the structure development in the mixtures. In general, as clay content increased, splash erosion was reduced and shear strength was significantly increased. From the highest to lowest mean of cohesion, the results showed the following order: bentonite > kaolinite > phlogopite > clay soil > zeolite. However, splash erosion showed the following order for the studied clays: zeolite > clay soil > phlogopite > kaolinite > bentonite. Nonlinear power models, best-fitted relations between splash erosion and shear strength, and the shear strength could explain about 30–33% of the splash erosion variability in this study.

There is little information about the role of fungal endophytes on plant performance under oxygen-limited conditions. This study aimed to investigate the effect of Epichloe endophyte symbiosis on tall fescue responses to oxygen stress in a greenhouse experiment. The experiment was conducted with seven air-filled porosity levels in a sandy loam soil using genotypes (75C and 75B) of tall fescue (Festuca arundinacea) infected with and without endophytic fungus Epichloe coenophiala (E+ and E–, respectively). Growth and physiological variables were determined to characterize plant response to oxygen-limited conditions, after nine-month application of the treatments. The results showed that E+ 75B plants benefited from endophytic symbiosis in all air-filled porosity levels, showing a higher plant biomass, better water status and lower catalase and ascorbate peroxidase activity than E– 75B plants. In contrast, a reverse trend was observed for the genotype 75C. The E– plants also coped with poor aeration by forming adventitious roots at the soil surface, aerenchyma formation within the root tissue, and increased alcohol dehydrogenase activity. The presence of endophyte improved the genotype 75B performance under anaerobic conditions, while endophyte had an adverse effect on the performance of genotype 75C. This is probably due to incompatibility between Epichloe endophyte and genotype 75C. Epichloe endophyte is likely to decrease the flooding-induced oxidative stress and prevented the over-accumulation of reactive oxygen species in the genotype 75B. Epichloe endophyte probably maintained oxidative conditions around the roots, and consequently, E+ plants required lower level of flooding-tolerance mechanisms.

Rhizosphere properties would greatly depend on plants species/genotypes which might be used as criteria for screening of plants in terms of the effects on soil quality. This study was conducted to determine the effects of 41 barley genotypes from three groups of Hordeum vulgare, spontaneum and wild genotypes on the rhizosphere structural stability and quality indicators. The genotypes were planted in a research field for 8 months. Soil quality indicators including water and ethanol sorptivities (SW and SE), water repellency (R), soil oganic carbon (SOC), hot-water soluble carbohydrates (HWSC), and water-dispersible clay (WDC) were determined in the rhizosphere and bulk soils. All of the indicators changed in the rhizosphere in comparison with the bulk soil, and different genotypes showed diverse effects on these indicators. The R and SOC of the rhizosphere varied among the genotypes, and they were greater in the rhizosphere compared to bulk soil. However, there was no significant difference between the three groups in terms of water repellency. The WDC in the rhizosphere was significantly lower and its value was in the order: vulgare

The present paper is aimed at investigating the effects of land use (particularly reducing conditions of paddy fields) on soil structural stability as characterized by the high energy moisture characteristic (HEMC) method and finding the relationship between soil structural stability and available water (AW) in Amol city in Mazandaran province, Iran. Land use conversion led to a change in the soil organic matter (OM) content. The highest OM was found in the forest and pasture land uses, being significantly different from those of citrus garden and paddy field land uses. The high values of bulk density in the citrus garden and paddy fields can be attributed to intensive machinery traffic and puddling, respectively. However, bulk density was low in pasture and forest land uses because of high OM and macropores. Forest and the paddy fields had higher soil structural stability due to high OM/Clay ratio. The HEMC indices including volume of drainable pores ratio (VDPR) and stability ratio (SR) were calculated using the modified van Genuchten model, and the ratio of slopes at the inflection point of HEMCs of fast-wetted to slow-wetted soil samples (SiR) was determined using the van Genuchten model. The HEMC indices showed positive and significant correlations with OM and OM/Clay ratio. By increasing the OM/Clay ratio, greater clay became complexed with organic matter, and thus soil structure stability increased. A strong correlation was observed between VDPR and OM/Clay in citrus garden and paddy fields. Furthermore, there was a significant correlation between VDPR and AW. The highest field capacity and AW were observed in the forest and paddy fields due to high OM and the presence of smectitic clays under reducing conditions, respectively.

This study was done to evaluate the suitability of biochar-based mixtures for growth media. Biochars from agricultural wastes were produced by slow pyrolysis at 300 (B300) and 500 °C (B500). Organic substrates/biochars of sawdust (Sd), wheat straw (WS), rice hull (Rh), palm bunches (Plm) and sugarcane bagasse (SC), and inorganic substrates of vermiculite (V) and zeolite (Z) were used to prepare growth media. Based on the criteria of high water holding capacity (WHC), easily-available water (EAW), water buffering capacity (WBC), air-after-irrigation (AIR), low bulk density (BD), EC, pH, and water drop penetration time (WDPT), thirteen growth media were prepared with different volumetric ratios of individual substrates. Incorporation of biochars/inorganic components increased BD, pH, and EC of the mixtures compared to cocopeat-perlite. The EAW, WHC, and WBC were greater in the biochar-based mixtures than cocopeat-perlite. Physical properties of the biochar-based mixtures were within the optimum ranges for growth media (AIR > 10%v/v, WBC = 4‒10%v/v, WDPT

This research aimed at evaluating how different vegetation patch types and inter-patch zone affect soil properties/functions and ecological processes. Five main types of patches and one inter-patch zone were identified in an arid rangeland ecosystem in the Ghamishloo National Park and Wildlife refuge, central Iran. Next, twenty-nine soil samples were collected from the patches and the inter-patch to measure soil texture, pH, electrical conductivity (EC), total nitrogen (TN), available phosphorus, bulk density (BD), soil organic matter (SOM), particulate organic matter (POM), basal soil respiration (BSR), hot-water extractable carbohydrates (HWEC), and aggregate stability (as quantified by mean weight diameter, MWD, of water-stable aggregates). At each six patch types and inter-patch zone, eleven soil indicators were measured along three 30-m transects to estimate soil stability, infiltration, and nutrient cycling indices as proposed by the landscape function analysis method. Results indicated that SOM, TN, MWD, HWEC, BSR, POM, and silt content varied significantly between the patch and inter-patch types. Moreover, the difference between shrub patch and inter-patch zone was significant for infiltration and nutrient cycling indices but not for soil stability. Substantial input of organic carbon is required in the soils of inter-patch zone and forb patch type to achieve greater soil functioning. Patches of shrubs, shrub-forbs, and grasses improved soil quality and ecosystem functioning more efficiently than forbs and inter-patch zone; hence, preserving these patches is recommended for conservational solutions in arid fragile ecosystems. The results highlighted the importance of SOM in evaluating functional status of arid rangelands.

Investigating the relationships between vegetation dynamic and edaphic factors provide management insights into factors affecting the growth and establishment of plant species and vegetation communities in saline areas. The aim of this study was to assess the spatial variability of various vegetation communities in relation to edaphic factors in the Great Salt Desert, central Iran. Fifteen vegetation communities were identified using the physiognomy-floristic method. Coverage and density of vegetation communities were determined using the transect plot method. Forty soil samples were collected from major horizons of fifteen profiles in vegetation communities, and analyzed in terms of following soil physical and chemical characteristics: soil texture, soluble Na+ concentration, sodium adsorption ratio (SAR), electrical conductivity (EC), pH, organic matter content, soluble Mg2+ and Ca2+ concentrations, carbonate and gypsum contents, and spontaneously- and mechanically-dispersible clay contents. Redundancy analysis was used to investigate the relationships between vegetation dynamic and edaphic factors. The generalized linear method (GLM) was used to find the plant species response curves against edaphic factors. Results showed that plant species responded differently to edaphic factors, in which soluble sodium concentration, EC, SAR, gypsum content and soil texture were identified as the most discriminative edaphic factors. The studied plant species were also found to have different ecological requirements and tolerance to edaphic factors, in which Tamarix aphylla and Halocnemum strobilaceum were identified as the most salt-resistant species in the region. Furthermore, the presence of Artemisia sieberi was highly related to soil sand and gypsum contents. The results implied that exploring the plant species response curves against edaphic factors can assist managers to lay out more appropriate restoration plans in similar arid areas.

Salinity and sodicity problems are ubiquitous in dryland and irrigated systems, and research into possible amendments to remediate soils in these systems is needed. This study was conducted to investigate the effects of organic and inorganic amendments on spring wheat (Triticum aestivum UG99) yield and salts redistribution within the profile of a repacked saline–sodic silt loam soil (ECe = 12.9 dS m−1, exchangeable sodium percent (ESP) = 17.6% for control). The experimental design for greenhouse study was completely random with two factors (amendment and leaching fraction, LF). The amendments included biochar (2%) [B], biochar + manure (2%) [BM], zeolite modified with CaCl2 (2%) [ZC], super absorbent (1%) [SA], and a control (no amendment) considering two levels of LF (15 and 30%). All amendments, except ZC, decreased soil bulk density and electrical conductivity, and increased soil pH and water content at field capacity after 2 pore volumes leaching. There was positive effect (p + and Mg2+ concentration in straw, while K+ concentration increased; resulting in reductions in the Na+/K+ ratio. In general, the study showed that B, BM and SA are suitable amendments for increasing yield by improving soil conditions and reducing salts and Na+ accumulation in plants.

Near-saturated hydraulic properties are the key parameters for water transport models in the unsaturated zone and essential for management practices. This study was conducted to compare efficacy of multiple linear regression (MLR) and hybrid method of genetic algorithm with artificial neural network (GA-ANN) for prediction of near-saturated soil hydraulic properties in Moghan plain, north-western Iran. The results of MLR analysis indicated that this method had low potential to predict near-saturated soil hydraulic properties in the study area, which only could explain 14–38% of variability in the studied properties. Otherwise, GA-ANN was much higher powerful that could explain about 35–80% of total variability in the mentioned properties in the study area. The results of sensitivity analysis suggest that soil particle size distribution, organic matter, electrical conductivity and relative bulk density were the most crucial with variety of priorities for explaining variability of the near-saturated soil hydraulic properties in the study area in the semiarid region. In overall, it was concluded that application of intelligent system using the easily available soil properties as predictors could provide reliable estimates of near-saturated soil hydraulic properties at the filed scale.

Scarce and scattered precipitation in arid regions is detrimental for newly planted seedlings. It is essential to provide required water storage for seedlings in restoration projects in the first year of their establishment. The subsurface irrigation can be much more effective than the surface irrigation because of the regulation of water availability and reduction in water evaporation. We studied the effect of surface and subsurface irrigation methods on the growth and survival of four common tree species including heaven tree (Ailanthus altissima (Mill.) Swingle), China berry (Melia azedarach L.), white mulberry (Morus alba L.), and black locust (Robinia pseudoacacia L.) by installing underground clay reservoirs with different permeabilities in Isfahan City, Iran. Different amounts of animal manure and wheat straw were mixed with clay fraction and cooked in a pottery kiln at 900°C to produce reservoirs with different permeabilities. The experimental treatments consisting of irrigation and tree species were considered with a factorial arrangement in a completely randomized design with three replications in 2016 and 2017. Leaf water potential of seedlings, which is indirectly related to drought resistance, was measured by a portable pressure chamber. The results showed that saplings height, basal diameter, number of leaves, chlorophyll content and stomatal conductance were significantly (P 0.05) affected by the irrigation methods and different permeabilities of clay reservoirs. The clay reservoirs with low and medium permeabilities constantly provide better conditions for plant growth, and water with lower pressure and longer time intervals to the plant roots as compared with the reservoirs with high permeability. Analysis of variance of the data showed that year and interaction between year and permeability of reservoir had significant effects (P

In this study, wetting patterns around the reservoirs with different permeability (low, medium, and high) were assessed in the field and simulated using the HYDRUS-2D/3D software. The results showed that the highest soil water content was observed near the reservoir and it decreased with increasing distance from the reservoir. In the high permeability treatment, a large volume of water was released for almost three days, so that, more water was deep-percolated and lowered the soil water available to plant roots. In the low and medium permeability treatments, the water content slowly moved and observed that the maximum soil water content occurred in the 20-40 cm layer overtime. The HYDRUS-2D/3D software was able to simulate water flow and soil water content during the growth period of plants with a high correspondence between measured and simulated soil water contents (R2 = 0.90-0.95).

The Tigris-Euphrates River Basin (TERB) is one of the key transboundary basins among the developing countries in the Middle East which has been significantly damaged by mismanagement, exploitation for energy production and unsustainable water use. This study aimed to evaluate the water and soil resources in the lower parts of this basin. More specifically, how the area of the Shatt al-Arab River (SAR) formed at the confluence of the Tigris and Euphrates rivers is affected in terms of quality by upstream activities. Four mathematical models of hydrodynamics, advection-dispersion in the river, and convection-dispersion in soil were used in conjunction with assessment of soil salinization by irrigation water. The soil salinization based on direct saltwater infiltration from riverbanks and soil salinization by irrigation with river water were predicted after simulating the intrusion of saline seawater by considering the tidal conditions of the SAR. The results showed that by applying six optimistic and probable scenarios of freshwater inflows for the future, changes in the water and soil quality in downstream riparian countries (Iran and Iraq) reflect this basin's developments and water allocation upstream. Regarding the possible scenario of maximum inflow reduction in the future, the findings of this study can be used to create a comprehensive view of the current condition and development challenges. This emphasizes the need for participatory crisis mitigation strategies between the upstream and downstream countries.

This study was conducted to determine critical values of soil physical quality indicators according to vegetative growth of spring wheat in a range of degrees of soil compactness. A non-saline loam soil was used to produce a range of degrees of soil compactness in 10 mini-lysimeters. The mini-lysimeters were put outdoors and received similar amounts of water after sowing of spring wheat (Triticum aestivum L., cv. Pishtaz). Shoot dry weight (SDW) was measured, and relative SDW (RSDW) values of 0.9 and 0.8 were assumed to be the starting and end points of soil physical quality indicator limitation for wheat growth, respectively. Critical integral water capacity (IWC) values of 0.136 and 0.104 cm3 cm−3 were obtained for the start- and end-point limitations, respectively. This means that in the studied soil, the IWC values greater than 0.136 cm3 cm−3 represent good soil physical conditions for wheat growth. In the IWC range of 0.136–0.104 cm3 cm−3, there were slight physical limitations for wheat growth. In the IWC values smaller than 0.104 cm3 cm−3, unsuitable soil physical conditions (i.e., poor aeration and high mechanical impedance) strongly restricted the wheat growth. Start- and end-point limitations for Dexter’s index of soil physical quality (S) were found to be 0.051 and 0.038, respectively. Corresponding values for relative bulk density (RBD) were 0.805 and 0.846, respectively.

Water quality, particularly pH, is one of the most important factors that may significantly influence soil physical and mechanical properties leading to damage of structures. This study aimed to investigate the effect of pore water pH on engineering properties of a natural clay soil. The soil was exposed to solutions with different pH values (4, 5, 6, 6.5, 9, 10, and 11) as buffered by acetate and carbonate-bicarbonate. Atterberg consistency limits, unconfined compressive strength, and shear strength parameters of the soil were measured after 90 days of exposure to the solutions. The results indicated that the unconfined compressive strength, shear strength parameters, and liquid limit of the soil increased considerably when the pore fluid had a high pH or a low pH. Thus, the results obviously showed that engineering properties of the soil greatly depend on the pH of pore water.

Saline-sodic soils commonly display a poor soil structure which is associated with the reduction in soil quality. Therefore, optimal management of soil and water salinity in saline-sodic soils shou...

Long-term use of treated wastewaters for irrigation adds compounds and/or ions to soils which might alter the soil physical, hydraulic and mechanical properties. Soil mechanical properties are closely linked with the plant growth. This study was conducted to investigate the effect of short-, mid- and long-term applications of the treated wastewater of Mobarake Steel Company in Isfahan on the soil penetration resistance and shear strength in the company green space. Soil penetration resistance and shear strength were measured using a pocket penetrometer and in situ shear box, respectively. The results showed that soil penetration resistance (i.e. soil hardness) at both dry and wet conditions significantly was increased upon short-, mid- and long-term applications of wastewater; 19 years of the application of wastewater resulted in the highest soil penetration resistance at wet condition, but the well water did not significantly affect it. Surface crust in the non-irrigated locations increased the soil penetration resistance, but the irrigated sealed soils were not significantly different from the virgin soil in terms of dry and wet penetration resistances. For the soil shear strength parameters, wastewater, well water and surface crust did not significantly affect soil cohesion (c), they but significantly affected the angle of internal friction (φ). Overall, soil shear strength parameters were not greatly affected by the irrigation water treatments because of the dominant effect of the soil fractions (texture and gravel content) and the microstructure.

Assessing soil quality indicators is essential for ecosystem function evaluation. This study aimed to compare soil quality indicators of semi-arid forests and rangelands with different condition classes using direct soil quality indicators and landscape function analysis (LFA). Vegetation and soil properties were studied in three forest sites with different densities and 16 rangeland sites. A total of 72 soil samples were collected from various land use/cover types and their physical and chemical properties were measured. Eleven soil quality indicators were assessed from each patch and inter-patch zone along the established transects in each land use/cover type to obtain three functional indices including soil stability, infiltration, and nutrient cycling. The accuracy of the stability and infiltration indices of the LFA was verified by their correlations with some soil quality indicators. The results revealed a similar trend in soil quality indicators among the land use/cover types indicating that soil organic carbon (SOC), particulate soil organic matters (POM), mean weight diameter (MWD), soil stability index (SSI), and macronutrients had more appropriate conditions in rangelands with good conditions and dense forest sites compared to other land uses/covers. The soils in rangelands with poor conditions and sparse forests required substantial input of organic carbon to achieve an appropriate level of soil quality. The results highlighted the importance of SOC, POM, and soil texture for the prediction of aggregate stability in the region. The regression model showed a significant relationship between MWD and SSI. Moreover, nitrogen and SOC had significant relations with nutrient cycling and the relation between water dispersible clay and infiltration index was also significant (p

Fungal endophytes, by living entire or part of their life inside a plant, are potentially useful in natural ecosystems and agroecosystems to confer multiple benefits to their hosts. These include improvement of water and nutrientional status, higher tolerance against biotic/abiotic stresses. In this review, the consequences of infection by Epichloe spp., as an obligative symbiont, and Serendipita indica, as a facultative one, on plant-soil relations have been discussed. Colonization and infection by both Epichloe and S. indica results in better plant growth and productivity, including enhanced root proliferation by indole-3-acetic acid production which in turn leads to a better nutrient acquisition. Moreover, the symbionts can confer both local and systemic resistances to pathogens/diseases through signal transduction. Up-regulation of antioxidant defense system components and reprogramming of stress-related genes in the presence of endophytic fungus can enhance plant resistance against biotic/abiotic stresses. Individual mechanical or drought stresses may impair plant growth and functioning; however, under combined mechanical and drought stresses, drought has little impact on the plant responses and mechanical stress mainly controls physiological attributes including water status and leaf proline. Endophyte-infected hosts usually have higher ability to do osmotic adjustment due to higher proline content. The physical, chemical and biological properties of rhizosphere soil might be changed by the endophyte infection too, presumably resulted in improving soil quality. Altering microbial communication structure and diversity, higher organic carbon storage, enhanced soil fertility and increased aggregate stability due to induced sub-critical hydrophobicity are some important influences of endophyte-host symbiotic relations on soil environment.

Post-fire erosion is a main concern to society because it has inflicted serious damages in managed ecosystems. In this study, the impacts of fire and time after fire events on soil erosion (as predicted using 137Cs technique) and on some soil chemical and physical properties were investigated in steep rangelands of western Iran. Three sites in rangelands with similar slope gradients and parent materials were selected, and within each site, the burnt (1, 5, and 10 years after the fire events) and the unburnt treatments were studied and soil samples were collected from five depths (0–2.5, 2.5–5, 5–10, 10–20, and 20–40 cm) with three replicates. The results indicated that soil organic matter (SOM), total nitrogen (TN), available phosphorus (Pava), available potassium (Kava), electrical conductivity (EC), and bulk density (BD) were significantly different between burnt and unburnt treatments for two times (1 and 5 years) after fire events. No significant difference by Duncan’s test was obtained for these properties between the 10 and 5 years after fire events. In addition, clay and sand contents and magnetic measures (χlf, χhf) were significantly different between burnt and unburnt treatments for all the three times after fire. The results of soil erosion by the 137Cs technique showed that profile distribution model (PDM) estimated the mean soil erosion rate of 38.9 and 23.02 Mg ha−1 year−1 in the three studied years in the burnt and the unburnt rangelands, respectively. Fire events increased soil erosion rate and altered soil physical, chemical, and magnetic properties in the studied steep rangelands. Overall, the results confirmed that the 137Cs technique could be used as a rapid and efficient model to determine soil degradation in the rangelands. The fire diminished soil organic matter and, subsequently, reduced aggregate stability, and increased soil erosion and degradation in the burnt rangelands. Hence, understanding historical contexts of fire occurrences is paramount to increase our capacity for ecological transformations and management in the face of the critical situation.

Hard-setting soils become hard and compact during drying, and are therefore difficult or impossible to cultivate unless they are re-wetted. This study was done to quantify the hard-setting behavior on nine soils with a wide range of texture (from sandy loam to silty clay). Repacked soil cores were prepared with least disturbance of soil aggregates (05‒4 mm). Water retention curves of the soils were measured in the matric suction range 10–15,000 hPa in different bulk densities (1.20–1.70 Mg m−3). Single-porosity van Genuchten-Mualem and dual-porosity Dexter models were fitted to the water retention data. Dexter's indices of soil physical quality (S) and hard-setting (HDexter) were calculated using the van Genuchten-Mualem parameters. Soil physical quality indices S1 and S2 (slopes of water retention curve at first and second inflection points, related to matrix and structural pore spaces, respectively) and new hard-setting indices (H1 and H2 related to matrix and structural pore spaces, respectively) were also calculated from the parameters of dual-porosity model. Tensile strength (Y) of the soil samples prepared at different bulk densities was also measured from near-saturation to oven-dry. Slopes of relationships between Y and water content were used as soil strength-based hard-setting indices. A larger slope means that the soil is more susceptible to hard-setting. The HDexter, H1 and H2 increased with an increment in the bulk density, whereas the S, S1 and S2 decreased. Significant positive relationships between hard-setting indices (HDexter and H1) and calcium carbonate content were observed. Negative linear relations were derived between S, S1 and S2, and bulk density and positive linear relations were obtained between HDexter, H1 and H2, and bulk density. Soil hard-setting and physical quality indices were significantly correlated with relative bulk density. Positive relationships were observed between soil strength-based hard-setting indices and relative bulk density, and the correlations between these indices and H2 and S1 were significantly positive and negative, respectively. These findings confirmed that the new proposed indices enable prediction of soil hard-setting behavior using only water retention data with no need to measure soil mechanical strength.

This study was conducted to examine feasibility of using some agricultural residues and their biochars as substitutes for commercial horticultural growing media as cocopeat, sand, perlite, zeolite, pumice, vermiculite and rockwool. Biochars of wheat straw, sawdust, rice hull, sugarcane bagasse and date palm bunches were produced at 300 and 500 °C. Following substrate properties were determined: easily available water (EAW) defined by the difference between water contents (θ) at absolute matric potentials (h) of 10 and 50 hPa (EAW = θ10 − θ50), air after irrigation (AIR = θ0 − θ10), water holding capacity (WHC = θ10), water buffering capacity (WBC = θ50 − θ100), saturated water content (θs), bulk density (BD), total porosity (TP), water drop penetration time (WDPT), pH and electrical conductivity (EC). A classification system was developed to evaluate the substrates as horticultural growing media. Higher pyrolysis temperature produced biochars with higher pH, EC, TP, θs, WHC, EAW, and WBC and lower biochar yield, AIR, BD and WDPT. Sugarcane bagasse biochars had higher θs, TP and WBC and lower BD than other biochars. Comparison among organic residues and inorganic substrates showed that highest TP, θs and EAW were observed in rockwool, whereas, among organic residues, maximum values of these properties were achieved for sugarcane bagasse, wheat straw and sawdust, respectively. Considering pH, EC, BD, TP, EAW, AIR, WBC and WDPT, wheat straw and sawdust were classified as very good substrates similar to cocopeat and rockwool. Other organic residues were placed in good class. Wheat straw and date palm bunches biochars produced at 500 °C and sugarcane bagasse and rice hull biochars were good growing media and can be suitable candidates for amendments or replacements of commercial growing media.

We aimed to determine the effect of Piriformospora indica inoculation on maize maximum root growth pressure (σmax) and root elongation rate (ER) over a wide range of water potentials. The maximum axial force (Fmax) exerted by the P. indica-inoculated and non-inoculated roots of maize (Zea mays L. cv. Maxima) seedlings were measured under control (osmotic potential of zero) and PEG-induced water stress (i.e., osmotic potentials of −0.1, −0.2, −0.3 and − 0.4 MPa) conditions. After measuring root diameter (d), σmax was calculated by dividing the Fmax by the corresponding root cross-sectional area. To test the toxicity of PEG-6000 on root growth, the effect of osmotic potentials induced by PEG-6000 on ER was compared with the corresponding matric potentials in two soils. The establishment of a mutualistic relationship between maize roots and P. indica exerted a temporary stress on plants leading to greater lag time for force development (Tlag) and the time to reach Fmax (Tmax) in inoculated plants. However, root colonization resulted in greater Fmax, σmax and ER especially under moderate and severe water stresses. Severe water stress decreased σmax, Fmax, d, Tmax and ER. P. indica inoculation can moderate adverse influences of stressful conditions on growth and elongation of plant roots especially during the initial growth stages by enhancing osmotic adjustment and/or by changing cell wall mechanical characteristics.

This study aimed to evaluate the application of landscape function analysis (LFA) and some soil quality indicators for the assessment of the structure and function of Steppe rangelands in arid regions of Ghamishloo National Park, Isfahan, central Iran. Three zones with different protection levels/grazing intensities, including a national park with wild herbivores, a peripheral protected area where both livestock and wild herbivores were present, and an adjacent grazing-free area where wild herbivores were absent, were selected. Eleven soil surface indicators were assessed to measure soil stability, infiltration, and nutrient cycling indices in various zones. Eighty-seven soil samples were collected in the study area and their characteristics, including pH, electrical conductivity (EC), total nitrogen, phosphate, soil organic carbon (SOC), particulate organic matter (POM), microbial respiration, and mean weight diameter (MWD), were measured. The results showed that although structural attributes (patch area index and landscape organization index) and LFA functional attributes varied significantly between the sites with various management histories (P

The pulp and paper wastewater contains various organic and inorganic compounds in considerable amounts. Membrane bioreactor (MBR) technology has been used extensively for various industrial wastewater treatments due to its ability to produce appropriate effluent according to water quality regulations. Pulp and paper wastewater can be successfully treated by MBR in different conditions according to the wastewater and MBR characteristics. However, a major drawback in the use of MBR is membrane fouling, which leads to the reduction of effluent permeate flux. Fouling factors need to be considered because they are the major problems affecting the MBR performance. Besides, the performance of MBR can be increased by wastewater pretreatment methods and addition of a fouling reducer. In this paper, the application of aerobic and anaerobic MBR for pulp and paper wastewater treatment and membrane fouling has been reviewed. It has been found that the advantages of MBR over conventional biological treatment processes have made this technology popular for pulp and paper wastewater treatment.

Carbon (C) sequestration in soil is recognized as a possible solution for climate change mitigation. Different land uses may alter carbon sequestration in soil. In the semiarid regions of central Iran, during the last decades, land use changes from native cover to farmlands have altered the C sink role of soil to a source of CO2 emission to the atmosphere. This study was conducted to evaluate and compare changes and the potential of soil organic carbon (SOC) sequestration from 1988 to 2014, under different land uses, in western central Iran (Lordegan). The land uses included pasture, forest, rain-fed, and irrigated farmlands. Soil (450 samples) from 50 points across the study basin (390 km2) was collected in three depth increments (0–5, 5–15 and 15–30 cm) during three sampling times (June and November 2014, and June 2015). Mean SOC concentrations in the pasture, forest, rain-fed and irrigated farmlands were 10.3, 20.2, 9.2 and 10.1 g kg−1, respectively. The SOC concentration in the forest soil was significantly greater than the other land uses, and any reduction in forestland area would lead to the SOC stock decline. About 1390 Gg organic carbon was found to be stored in the top 0–30 cm depth of the study area. Comparing land use maps between 1988 and 2014 indicated an alteration in the relative contribution of each land use across the study area leading to SOC stock reduction by 100 Gg carbon during this period. The results showed that all studied soils comprised non-complexed clay, suggesting a considerable potential capacity for sequestering carbon. The results also indicated that the SOC controlling factors varied considerably among different land uses and soil depths. Mean weight diameter of aggregates (MWD), bulk density, clay and sand content, and altitude were identified as the important controlling variables by the stepwise multiple linear regression analysis.

Unsaturated soil shear strength is an important parameter in soil erosion and management. Measurement of unsaturated shear strength at field scale is difficult, time-consuming, and very costly. This study was conducted to investigate the relationship between unsaturated shear strength parameters and soil properties, and to predict the unsaturated shear strength parameters (effective cohesion, c', angle of effective internal friction, φ' and angle of internal friction related to matric suction, φb) using multiple-linear regression (MLR). Direct shear tests were performed at combinations of three normal stresses of 25, 50 and 100 kPa, and four matric suctions of 0, 10, 30 and 50 kPa (i.e., 12 tests per each soil) to determine the shear strength parameters in 14 soils. Soil properties including particle size distribution (sand, silt, and clay percentages or geometric mean diameter, dg and geometric standard deviation, σg), organic matter content (OM), calcium carbonate content (CaCO3), compactness indices (bulk density, ρb and, relative bulk density, ρb-rel), and mean weight diameter of aggregates (MWDdry, MWDwet), structural stability indices (aggregate stability, AS, stability index, SI and index of crusting, Ic) were determined and used as predictors in MLR models. Strong negative correlations were found between c' and φ'. The c' positively correlated with clay content. Significant negative correlation was observed between c' and sand fractions and dg. Significant positive correlation was obtained between φ' and fractions of sand and dg. The φ' negatively correlated with clay, fine silt content (FSi), MWDdry, and AS. The φb had no significant correlation with soil properties, indicating that φb is independent of soil properties and basically is affected by matric suction. Clay, coarse sand (CS) and very fine sand (VFS) were applied in the model for predicting c'. Clay had a positive and, CS and VFS had negative effects on c'. Pedotransfer functions (PTFs) using the fine sand (FS) and VFS as predictor could estimate the φ' accurately, so that they entered to PTFs with positive signs. In addition, the φb was predicted by parameter Ic only, so that it had negative effect on φb. Overall, better prediction models were developed for φ' than for c' and φb.

Due to the heavy costs of wind erosion control measures, the correct selection of technical methods is indispensable for a sustainable land management in arid and semiarid regions. Thus, th...

Temperature is a key factor that can affect soil properties and processes. Surface tension-viscous flow (STVF) theory is widely used to explain the temperature effects on soil hydraulic properties. We hypothesized that one of the reasons for deviation of measured soil water retention data from the STVF theory predictions is due to the temperature effects on soil structural stability (i.e., near-saturated pore size distribution [PSD]). Therefore, the objective of this study was to evaluate the effect of temperature on soil structural stability as characterized using the high energy moisture characteristic (HEMC) method in a wide range of arid and semi-arid soils of Iran. Aggregates of 28 soil samples were fast-wetted to mimic the natural conditions of soils during rainfall and irrigation. Four ambient temperatures (5, 10, 15 and 30 °C) were applied using an incubator during the wetting of aggregates, and after that HEMCs in the matric suction (h) range of 2 to 50 hPa were measured. Both van Genuchten (VG) and modified van Genuchten (MVG) models were fitted to the HEMC data and structural stability indices were calculated. The results generally showed that ambient temperature significantly altered soil PSD and structural stability, and as temperature increased: (i) an expansion of entrapped air initiated by the formation of microbubbles, was enhanced, (ii) water content at near full saturation h = 2 hPa (θ2hPa) decreased, and at h = 50 hPa (θ50hPa) it increased, leading to a reduction in the volume of drainable pores [VDP], and thus (iii) the soil structural index [SI] and slope at the inflection point of HEMC [Si] decreased, and (iv) amount of macropores (h, 2–12 hPa) was markedly decreased, however, micropores (h, 12–50 hPa) were not notably affected or were increased at high temperature due to intensive shifting of macropores into micropores. These findings imply that soil structure was damaged due to loosening effects of high temperatures on inter-particles bonds and increased repulsive forces between clay particles. Cluster analysis showed that the effect of ambient temperature on the structural stability was greatest in carbonate-rich soils with low clay and organic carbon (OC) contents and was least in the soils rich in OC. The results of this study could be important for projecting the effect of global warming and climate change on soil structure and erosion.

The wastewater produced in a pulp and paper industry is one of the most polluted industrial wastewaters, and therefore its treatment requires complex processes. One of the simple and feasib...

This study was conducted to investigate the impact of water salinity (ECw) and sodicity (SARw) on saturated (Ks) and relative (Kr) hydraulic conductivities in two clay (C) and sandy clay loam (SCL) soils. The results showed that the Ks decreased with increasing SARw, and in all of water quality treatments, the Ks of SCL soil was higher than that of the C soil. Sodicity effect (even at high SARw) on the Kr of clay soil was minimized by high salinity. Although Kr of both soils similarly responded to ECw and SARw, microstructure of clay soil was more sensitive to water quality. Effect of ECw on soil structure was greater than that of SARw. In order to assess the applicability of artificial neural networks (ANNs) in estimating Ks and Kr, two types of FFBP and CFBP ANNs and two training algorithms, namely Levenberg–Marquardt (LM) and Bayesian regulation, were employed with two strategies of uniform threshold and different threshold functions. Multiple linear regressions were also used for Ks and Kr prediction. Based on the ANN results of second strategy, best topology (4–5–4–1) was belonged to CFBP network with LM algorithm, LOGSIG–LOGSIG–TANSIG threshold functions, and values of MAE and R2 are equal to 0.1761 and 0.9945, respectively. Overall, the efficacy of ANNs is much greater than regression method for Ks prediction.

Soil water repellency (SWR) is an important soil physical property that may restrict water infiltration and soil water retention. Common laboratory and field techniques for assessing SWR are laborious, time-consuming, and costly. Meanwhile, Visible–Near-Infrared (Vis-NIR) spectroscopy has been reported as a rapid, cost-effective, and alternative technique to estimate several soil properties. To investigate the efficacy of this technique for predicting SWR indices [soil water repellency index (RI) and soil–water contact angle (β)] at dry condition, 100 soil samples collected from farmlands, orchards, rangelands and forests of Zrebar lake watershed in Kurdistan province, Iran, were measured by Vis-NIR spectroscopy within the 350–2500 nm range. The Savitzky–Golay first derivative method was applied for denoising the spectral data. The RI and β were measured by the intrinsic sorptivity method (using water and ethanol as absorbing liquids). The other basic soil properties were also measured by standard laboratory methods. Stepwise multiple linear regression (SMLR) and partial least squares regression (PLSR) were utilized to establish pedo-transfer functions (PTFs) and spectro-transfer functions (STFs) using basic soil properties and spectral absorbance data, respectively, to estimate soil organic matter (SOM) content and SWR indices. We obtained good predictions for SOM with R2 = 0.67 and RPIQ (the ratio of performance to interquartile range) = 1.92 using the PLSR-based STF. The results also revealed that although the SMLR-based STFs achieved slightly better estimates of the SWR indices (RI and β) than the SMLR-based PTFs (R2 values of 0.28 to 0.39 vs. 0.19 to 0.23, respectively); but, overall, none of these transfer functions for estimating these indices showed acceptable predictive capability. However, the PLSR-based STFs could provide a reasonable prediction for the studied SWR indices (R2 > 0.52 and RPIQ > 2.27). The majority of important adsorption bands in the Vis-NIR PLSR models for the SWR prediction was related to both the quantity and quality of SOM. Overall, the results demonstrated that the Vis-NIR PLSR could be applied to predict SOM and SWR indices rapidly, non-destructively, and with fair accuracy.

Under combined drought and mechanical stresses, mechanical stress primarily controlled physiological responses of maize. Piriformospora indica mitigated the adverse effects of stresses, and inoculated maize experienced less oxidative damage and had better adaptation to stressful conditions. The objective of this study was to investigate the effect of maize root colonization by an endophytic fungus P. indica on plant water status, physiological traits and root morphology under combined drought and mechanical stresses. Seedlings of inoculated and non-inoculated maize (Zea mays L., cv. single cross 704) were cultivated in growth chambers filled with moistened siliceous sand at a matric suction of 20 hPa. Drought stress was induced using PEG 6000 solution with osmotic potentials of 0, - 0.3 and - 0.5 MPa. Mechanical stress (i.e., penetration resistances of 1.05, 4.23 and 6.34 MPa) was exerted by placing weights on the surface of the sand medium. After 30 days, leaf water potential (LWP) and relative water content (RWC), root and shoot fresh weights, root volume (RV) and diameter (RD), leaf proline content, leaf area (LA) and catalase (CAT) and ascorbate peroxidase (APX) activities were measured. The results show that exposure to individual drought and mechanical stresses led to higher RD and proline content and lower plant biomass, RV and LA. Moreover, increasing drought and mechanical stress severity increased APX activity by about 1.9- and 3.1-fold compared with the control. When plants were exposed to combined stresses, mechanical stress played the dominant role in controlling plant responses. P. indica-inoculated plants are better adapted to individual and combined stresses. The inoculated plants had greater RV, LA, RWC, LWP and proline content under stressful conditions. In comparison with non-inoculated plants, inoculated plants showed lower CAT and APX activities which means that they experienced less oxidative stress induced by stressful conditions.

Plant-based methods such as rhizodegradation are very promising for the remediation of petroleum-contaminated soils. Associations of plants with endophytes can further enhance their phytoremediation potential. In this study, a rhizobox experiment was conducted to investigate whether inoculation with the root-colonizing fungus Piriformospora indica could further enhance the degradation of petroleum hydrocarbons in the root zone of maize (Zea mays L.). The rhizoboxes were subdivided into compartments in accordance with distance from the plants. After filling the boxes with soil from a petroleum-contaminated site, seedlings that had either been inoculated with P. indica or not were grown in the middle compartments of the rhizoboxes and grown for 64 days. A plant-free treatment was included for control. The presence of roots strongly increased the counts of total and petroleum-degrading soil bacteria, respiration, dehydrogenase activity, water-soluble phenols and petroleum degradation. All these effec...

Knowledge about the spatial variability of soil aggregate stability indices, soil organic carbon (SOC) in various aggregate sizes, and aggregation across the landscape is crucial for sustainable land use planning and management practices. Direct traditional measurements for the target variables, as mentioned above, are time-consuming and expensive. Thus, this study attempts to spatially predict the soil aggregate stability indices, including mean weight diameter-MWD, geometric mean diameter-GMD, water-stable aggregates-WSA, and SOC in various aggregate fractions using digital soil mapping and machine learning models using the environmental covariates as the time and cost-effective approaches. Thus, a total of 100 soil surface samples (0–10 cm depth) were collected from the natural forest, tea plantation, and paddy rice field land uses, and soil aggregate stability indices were determined following laboratory analyses. The machine learning models, including random forest (RF), k-nearest neighbors (kNN), support vector machine (SVM), artificial neural network (ANN), and the ensemble of four single models, were trained using the repeated 10-fold cross-validation method. The models were evaluated by the root mean square error (RMSE), mean absolute error (MAE), coefficient of determination (R2), and normalized RMSE (nRMSE). The modeling results demonstrated that the RF model outperformed for MWD (R2 = 0.74, nRMSE = 24.28), GMD (R2 = 0.75, nRMSE = 12.72), and WSA (R2 = 0.58, nRMSE = 10.40), while kNN and SVM models resulted in the best prediction of SOC in (meso and micro-aggregates (RMSE = 1.03 and 0.88)) and macroaggregates (RMSE = 1.49), respectively. However, the ensemble model increased the prediction accuracies for all soil targets (RI ≥ 15.78%). Moreover, the variable importance analysis showed that soil properties such as soil organic matter (SOM) and remote sense-data mainly explained the variation of soil aggregate stability indices and SOC in various aggregate fractions. Overall, the results revealed that the machine learning-based models could accurately predict the soil aggregate stability and associated SOC, and the produced maps can be a baseline map for land use planning and decision making.

This study was done to evaluate the effects of the root-colonizing endophytic fungus Piriformospora indica on wheat growth under combined drought and mechanical stresses. Inoculated (colonized) and non-inoculated (uncolonized) wheat ( Triticum aestivum L. cv. Chamran) seedlings were planted in growth chambers filled with moist sand (at a matric suction of 20 hPa). Slight, moderate and severe mechanical stresses (i.e., penetration resistance, Q p , of 1.17, 4.17 and 5.96 MPa, respectively) were produced by a dead-load technique (i.e., placing a weight on the sand surface) in the root medium. Slight, moderate and severe drought stresses were induced using PEG 6000 solutions with osmotic potentials of 0, –0.3 and −0.5 MPa, respectively. After 30 days, plant physiological characteristics and root morphology were measured. An increase in Q p from 1.17 to 5.96 MPa led to greater leaf proline concentration and root diameter, and lower relative water content (RWC), leaf water potential (LWP), chlorophyll contents and root volume. Moreover, severe drought stress decreased root and shoot fresh weights, root volume, leaf area, RWC, LWP and chlorophyll content compared to control. Catalase (CAT) and ascorbate peroxidase (APX) activities under severe drought stress were about 1.5 and 2.9 times greater than control. Interaction of the stresses showed that mechanical stress primarily controls plant water status and physiological responses. However, endophyte presence mitigated the adverse effects of individual and combined stresses on plant growth. Colonized plants were better adapted and had greater root length and volume, RWC, LWP and chlorophyll contents under stressful conditions due to higher absorption sites for water and nutrients. Compared with uncolonized plants, colonized plants showed lower CAT activity implying that wheat inoculated with P. indica was more tolerant and experienced less oxidative damage induced by drought and/or mechanical stress.

Soil wettability and water repellency are important physical properties which greatly affect soil-water relations. This study was conducted to investigate the effects of polyacrylamide (PAM) on soil water repellency and wettability in a pomegranate orchard drip irrigated with saline water in Isfahan Province, central Iran. The experiment was a randomized complete block design conducted within each “durations of drip irrigation” (considered as the environment) including control (uncultivated), and 8 and 15 years old trees under drip irrigation system (DIS). PAM concentrations were 0 (control), 10 and 20 mg l −1 arranged in each block at three replications. The PAM (solubilized in saline water with electrical conductivity of 6.2 dS m −1 ) with the mentioned concentrations was applied once during the irrigation time. A week after applying the PAM, soil samples were taken from 0 to 0.3, 0.3–0.6 and 0.6–0.9 m depths under the emitters. Water repellency index (WRI) and soil-water contact angle ( β ) were determined using intrinsic sorptivity method by measuring the water and ethanol sorptivities in all soil samples. Increasing the duration of irrigation with saline water increased electrical conductivity (EC e ), concentrations of (Ca 2+ + Mg 2+ ) and Na + , and sodium adsorption ratio (SAR) of the saturated extract in the 0–0.3 m soil layer under the emitters. Increasing the duration of irrigation also increased WRI and β , and decreased water infiltration, especially in the 0–0.3 m soil layer, presumably through enhancing effects of long-term use of saline water on surface tension of water, soil aggregate stability, physical protection of organic matter in soil and stability of hydrophobic coatings. PAM application significantly reduced soil water repellency and increased soil water sorptivity. In the 0–0.3 m, 8 and 15 years of drip irrigation increased the WRI by 56 and 134 percent, respectively, compared with the control. PAM application at rates of 10 and 20 mg l −1 decreased WRI by 27 and 40 percent, respectively, when compared with the control. Application of 20 mg l −1 of PAM could completely ameliorate the degradative effects of drip irrigation with saline water for 8 years, whereas amelioration in the 15-year treatment remained incomplete.

This study aimed to evaluate the soil aggregate stability and selected soil quality indicators in various land uses in a semiarid region in central Iran. Random soil sampling was used to collect soil samples from surface (0–5 cm) and subsurface (5–25 cm) soil layers in rangelands of different condition classes, dry farmland and abandoned land. The aggregate size distribution indices including mean weight diameter (MWD), geometric mean diameter (GMD) and median diameter (D50) of water-stable aggregates in the collected soil samples were measured. Our findings showed that percent of macroaggregates (>0.25 mm) of the surface and subsurface layers in rangelands of different condition classes were significantly higher than dry farmlands and abandoned lands (P rangeland with poor condition > abandoned land ...