Soil science
Tahmeineh Gheitasi Ranjbar; M. Nael
Abstract
IntroductionConventional cropping systems, dependent on heavy application of chemical fertilizers, are not ecologically and environmentally sustainable; they are a threat for soil and water quality and, in consequence, for plant and human health. Nitrogen fertilizers are heavily applied in conventional ...
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IntroductionConventional cropping systems, dependent on heavy application of chemical fertilizers, are not ecologically and environmentally sustainable; they are a threat for soil and water quality and, in consequence, for plant and human health. Nitrogen fertilizers are heavily applied in conventional leaf vegetable production systems to obtain maximum growth and yield. However, the excess nitrogen tends to accumulate in leaf vegetables in the form of nitrate, which pose serious human health hazards. Therefore, to supply nitrogen from non-chemical sources, such as organic amendments, is a sustainable practice for production of leaf vegetables. Spent mushroom substrate (SMS), which is the remaining material after the harvest of mushroom, is produced in large quantities (5 kg SMS for 1 kg of mushroom) and is enriched with organic carbon, N, P, K, and micronutrients. Therefore its reuse as a soil amendment not only provides essential elements for plants but also improves soil quality. Similarly, incorporation of green manures, especially legume green manures, into cropping systems is a sustainable practice for soil fertility and soil quality management. In this study, we aimed to investigate the short-term effects of two soil organic amendments (spent mushroom substrate and alfalfa residues) and their combination, in comparison to inorganic N fertilizer (urea), on soil fertility, and selected essential nutrients, and nitrate accumulation in a leaf vegetable, test plant (spinach). Materials and MethodA one-season pot experiment was led in a randomized complete block design with three replications in experimental greenhouse of Bu-Ali Sina University. Treatments were comprised of two levels of spent mushroom substrate (SMS-1: 2% SMS, and SMS-2: 5% SMS), two levels of alfalfa green manure (AGM-1: 1% AGM, and AGM-2: 3% AGM); two levels of the mixture of SMS and AGM (SMS+AGM-1: 1% SMS plus 0.5% AGM; and SMS+AGM-2: 2.5% SMS plus 1.5% AGM); two levels of urea fertilizer (U-1; 120 kg/ha, and U-2: 360 kg/ ha); and control. Selected properties of the initial soil and both organic amendments were determined. Spinach (Spinacea oleracea L.) was seeded as leaf vegetable, test plant in early autumn 2017. After ten weeks, spinach were harvested and the aboveground and root dry weights were determined. Moreover, the content of NO3-, P, Fe, Cu, Zn, and Mn in edible parts were measured. Soil samples were analyzed for EC, pH, total organic carbon, available P and K, and alkaline phosphatase activity.Results and DiscussionAll soil quality indicators were significantly affected by the treatments. TOC was significantly increased in all of the organic treatments compared to the chemical and control treatments. The maximum increase in TOC was observed in SMS-2, SMS+AGM-2, and AGM-2 treatments, compared to the control (134, 130 and 107%, respectively). A decreasing trend in TOC was detected in the high level of urea treatment (U-2) compared to the control which can be explained by the faster decomposition of soil organic matter in the presence of higher inorganic N inputs. Both organic amendments (in both levels) and the higher level of urea (U-2) decreased soil pH compared to the control. The initial low pH of SMS (5.6) and AGM (6.2), in the first case, and oxidation of urea to nitrate, in the latter, may justify this observation. In contrast, soil EC increased under the both organic amendments relative to the control and U-1 treatments. Moreover, the adverse effect of SMS on soil salinity was greater than AGM due to the initial differences in their corresponding source materials (5.8 vs. 3.0 ds/m). Available K was significantly increased in the second level of all organic treatments compared to the chemical and control treatments. As for available P, all organic treatments, except AGM-1, led to the significantly higher P than the chemical and control treatments. It is reported that organic materials compete with mineral particles for P adsorption and increase its availability. Moreover, all organic treatments, except SMS-1, significantly increased phosphatase activity compared to the chemical and control treatments. This could contribute to the mineralization of organic materials and increase available P. Spinach yield was affected by the experimental treatments. The highest increase in shoot dry weight occurred in SMS+AGM-2 and AGM-2 treatments by 235 and 230%, respectively, compared to the control. Moreover, the second level of all organic treatments as well as the first level of SMS plus AGM treatment significantly increased yield compared to the chemical treatments. Spinach P content was significantly higher in all organic treatments, except SMS-1 and AGM-1, compared to the chemical and control treatments. Organic amendments, by decreasing the surface adsorption of P and increasing soil microbial biomass, promote the availability of P for plants. Spinach nitrate content ranged from 265 (in control) to 7807 mg/kg (in U-2). According to the critical limit of nitrate in spinach (4000 mg/kg) presented by European Union, only U-2 treatment led to over-accumulation of NO3-. The two levels of AGM treatments and SMS+AGM-2 resulted in the comparable amounts of nitrate as the recommended amount of urea (U-1). A narrow variation in spinach Cu content (from 6.1 in SMS+AGM-2 to 9.8 mg/kg in AGM-2), all within the standard range reported for plants (5-20 mg/kg), was observed among the treatments. Spinach Fe content was increased under all organic treatments relative to the control, although some disparities were not significant. The lowest Fe was detected in U-2. It is reported that excessive N may diminish root growth and, in turn, reduce nutrient uptake. Spinach Zn content varied from 44.8 (in control) to 71.5 mg/kg (in SMS-2), which was close to the higher limit of standard range (20-50 mg/kg) reported for vegetables, but lower than toxic concentration range (200-400 mg/kg). Spinach Mn content varied from 17.4 (in control) to 32.1 mg/kg (in SMS-2), which was close to the lower limit of the standard range (40-400 mg/kg) reported for plants.ConclusionThe most appropriate treatments in view of improving yield and soil quality (i.e., optimum TOC, P, and K; and lower EC) as well as tolerable nitrate accumulation were SMA+AGM-1 and SMS-1 in decreasing order. These treatments are preferred over the chemical treatments (U-1 and U-2).
Soil science
H.R. Owliaie; E. Adhami; M. Najafi Ghiri
Abstract
IntroductionGlobal observations have confirmed that in recent decades, forests have been converted into agricultural land at a swift pace; this is a major global concern. Forests around the world have also experienced severe disturbances due to other anthropogenic activities. The conversion of forests ...
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IntroductionGlobal observations have confirmed that in recent decades, forests have been converted into agricultural land at a swift pace; this is a major global concern. Forests around the world have also experienced severe disturbances due to other anthropogenic activities. The conversion of forests to cropland often results in soil degradation. Slope gradient and land use change are known to influence soil quality; therefore, the assessment of soil quality is important in determining sustainable land-use and soil-management practices. Magnetic susceptibility (χlf) measurements are widely used to study soil-forming processes. Many efforts have been made to correlate soil magnetic susceptibility with different soil properties, such as topography, parent material, Fe oxide forms, etc. The Yasouj area of Kohgilouye Province is one of the most densely forested areas in Zagros mountainous region. Parts of the area have been cultivated to feed the growing population, which has led to forest degradation. The objectives of this study were to assess some soil properties focusing on soil χlf and Fe- oxides forms in different land uses and slope positions.Materials and Methods Forty soil samples were taken from dense forest, sparse forest, eroded lands and dryland farming from different slops (0-15 and 15-30 percent) in Mokhtar Plain, west of Yasouj city. Soil samples were taken from the depth of 0–15 cm in a completely randomized design with five replications. Soil moisture and temperature regimes in the study area are xeric and thermic, respectively. Particle size distribution was determined by the hydrometer method and soil organic matter, CaCO3 equivalent and bulk density were determined using standard procedures. Fe (Feo) were extracted by acid ammonium oxalate, using a single 4-h extraction at pH 3 in the dark. Total free iron (Fed) was extracted with the CBD method. The total Fe contents (Fet) in the soil samples were determined after extraction with 5 mol L-1 HNO3. Magnetic susceptibility of the soils was measured at low (0.46 kHz; χlf) and high (4.6 kHz; χhf) frequencies, respectively; using a Bartington MS2 dual-frequency sensor, with approximately 10 g of air-dry soil in polyethylene vials. The percentage of frequency-dependent magnetic susceptibility (χfd%) was calculated to study the size of magnetic crystals in soils and the abundance of pedogenic ferrimagnetic in SP-SSD (~0.03 μm) boundary.Results and DiscussionThe results of this study showed that the land use and slope positions were among the important factors affecting the change of soil properties in this area. Land use change along with the reduction of organic matter reduced the stability of aggregates and increased land erosion. This process caused the loss of clay particles and magnetic minerals and affected many soil properties. Organic matter as an important indicator of soil quality, showed a decrease of about 3 times as a result of land use change from dense forest to eroded lands following by an increase in bulk density and a decrease in soil permeability and other soil quality indicators. Long-term afforestation and agricultural activities on sloping lands changed the soil texture from a class of silty loam in the forest to a lighter class of silty loam in agricultural use. Soil magnetic susceptibility, which is a function of soil magnetic particles was greatly affected by land use change and to a lesser extent by slope position. Due to the fact that magnetic susceptibility is influenced by factors such as soil texture, drainage class, erosion conditions, magnetic mineral contents, soil evolution conditions, land use changes from forest to other uses had significant effects (about 2 times) on χlf. Significant decrease in the amount of calcium carbonate in low slope positions was another reason for the increase in magnetic susceptibility in these positions. According to the measured values of χfd (ranged from 1.9 to 7.2%), the magnetic particles of the soils had low to moderate amounts of superparamagnetic (SP) particles, which indicates the combined effect of pedogenic superparamagnetic ultrafine particles and lithogenic (inherited) magnetic particles in χlf of the soils. The effect of slope on Fe forms (Feo, Fed and Fet) has been significant (p < 0.01) in almost all land uses. Due to the relatively high correlation of χlf with some soil properties such as Fe forms, soil clay, the amount of diamagnetic compounds including calcium carbonate in the studied soils, it is possible to estimate the value of these soil properties using χlf, which is a quick and cost-effective approach. Overall, it seems that magnetic susceptibility could be applied successfully to estimate some soil properties in hilly regions of Zagros Mountains of southwestern Iran, especially for monitoring the consequences of land use changes. It should also be noted that any change in the use of the area should be defined in accordance with the potential of the land in the long term to prevent a reduction in soil quality.
M. Molaei Arpnahi; M.H. Salehi; M. Karimian Egbal; Z. Mosleh
Abstract
Introduction: The most important factor in environmental degradation and pressure on ecological resources is rapid population growth combined with unsustainable exploitation of resources. Soil is one of the most important and worthful natural resources of environment. Land use change and deforestation ...
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Introduction: The most important factor in environmental degradation and pressure on ecological resources is rapid population growth combined with unsustainable exploitation of resources. Soil is one of the most important and worthful natural resources of environment. Land use change and deforestation decrease soil quality. Land use change also causes destruction of the evolved soils and decrease soil quality which result in permanent destruction of land fertility. Therefore, studying land use management effects on the soil quality has got an attention in recent years. Destroying the vegetation especially in the last 50 years resulted in important problems like soil erosion, land slide as well as increasing flood in the Bazoft area. In this area, degradation of the forests and their convert to other land uses like pasture, agriculture and urban or rural land use, occurs annually at high extent, in which make high damages to natural resources. In this study, the effect of land use change on soil quality indices in this area located at Chaharmahal-Va-Bakhtiari province was investigated.
Materials and Methods: In this research, four different managements with relatively similar conditions in terms of the influence of soil producing processes were chosen. Then, 10 composite samples from 0-30 cm depth of each land use (40 samples in total) were taken and different soil properties including soil texture, mean weight diameter of aggregates (MWD), porosity, bulk density, soil acidity, electrical conductivity and calcium carbonate equivalent were determined. One-way ANOVA was used to analyze the dataset. Tukey HSD test was applied to compare the means at the probability level of 5%. The first land use includes the natural forest with predominant cover of Iranian oak and the highest density and cover with the least human interference. Another land use is the degraded forest, caused by deforestation over the last 50 years. The third land use is the agricultural land which transformed from forest land use by deforestation in the last 50 years. The fourth land use is the walnut garden which established from agricultural land about 20 years ago.
Results and Discussion: The results showed that land use change from natural forest to other uses had a significant effect on most of the studied parameters. The percentage of particle size distribution was affected by different land uses, so that the percentage of clay was significantly higher in the land use of natural forest and walnut orchard than other land uses. The results also showed that the mean weight diameter of aggregates was influenced by the land use change (P <0.001). Factors like soil compaction due to livestock grazing and machinery traffic, agricultural operations and reduced biological activity increased the bulk density in all land uses compared with the forest land use. Deforestation also resulted in 6.92%, 12.05% and 14.16% porosity reduction in walnut orchard, agricultural land and deforestation, respectively. Changing management from farmland to walnut orchards also improved soil porosity by 6 percent. In the study area, the problem of changing vegetation, grazing, planting and other mismanagement increased soil pH in other land uses compared with the forest land use. The comparison of means showed that degraded forest and agriculture land uses had the highest rate of electrical conductivity which showed significant difference with natural forest land use and walnut orchard. Analysis of variance indicated that the land use had a significant effect on calcium carbonate equivalent at the probability level of 0.001. The comparisons also showed that the equivalent calcium carbonate content in agricultural land was higher than the other land uses, and there was no significant difference between walnut orchard and natural forest.
Conclusion: The results of the present study showed that the soil physical and chemical properties were significantly affected by land use change. Overall, it can be stated that the rate of changes in soil quality under human management and different utilization systems indicates failure in sustainable management of soil resources in the study area. Some characteristics such as soil particle size distribution percentage, soil porosity and calcium carbonate equivalent shows that there is no significant difference between walnut orchard and natural forest. However, the walnut orchards can be selected as the best management in areas where it is impossible to restore natural forests. Also, the need for stopping deforestation in Zagros ecosystem is highly recommended.
Roghayeh Vahedi; Mirhasan Rasouli-Sadaghiani; mohsen barin
Abstract
Introduction: Trees pruning wastes by turning into compost and adding to soil improves the physical, chemical and biological properties of the soil. Soil biological indices are important aspects of soil quality, so soil quality is measured using different biological properties. The organic compounds ...
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Introduction: Trees pruning wastes by turning into compost and adding to soil improves the physical, chemical and biological properties of the soil. Soil biological indices are important aspects of soil quality, so soil quality is measured using different biological properties. The organic compounds are regularly released from plants into the rhizosphere, which increase the activity of the soil microbial community and improve the health of the soil. The organic matter such as compost, stimulates microbial activity like the enzymatic activity and microbial biomass in the soil. Another method to improve soil quality is the use of the microorganisms potential. The arbuscular mycorrhizal fungi (AMF) in soil can stimulate and increase soil microbial activity and also improve the activity of enzymes and microbial biomass in soil. The application of microorganisms and the addition of the organic matter to the rhizosphere can change the microbial communication composition of the rhizosphere. The Limiting roots to investigate the biological and chemical changes and the extent of these properties in the rhizosphere are challenges that have been less addressed. The rhizobox is one of the used tools to study the rhizosphere changes. The main objective of the present study was to investigate the effects of the compost prepared from pruning wastes of apples and grapes trees and also pruning wastes of apples and grapes trees on soil quality, in the presence of arbuscular mycorrhizal fungi, in rhizosphere of the wheat under the rhizobox conditions.
Materials and Methods; The present study was carried out in a completely randomized factorial design with three replications in rhizobox under greenhouse condition. The factors included the organic matter (compost of trees pruning wastes, trees pruning wastes and control) and soil (the rhizosphere and non-rhizosphere soil) in mycorrhizal inoculation conditions. The soil sample with light texture and low available phosphorus was prepared. The pruning wastes of apple and grape trees were collected from urmia orchards. Also, the compost of trees pruning wastes was prepared from the research greenhouse of Urmia University. The compost and pruning wastes were ground and crushed and then passed through a 0.5 mm sieve for the greenhouse experiment. The plants were planted in the rhizobox with the dimensions of 20 × 15 × 20 cm (length × width × height). The compost and pruning wastes were added to the boxes based on 1.5% pure organic carbon (each box contained 5.799 kg of soil). Glomus fasciulatum as mycorrhizal inoculation was used. The control treatments contained sterile soil with mycorrhizal inoculation and without organic matter. The wheat seeds (Triticumae stivum L.) of Pishtaz cultivar were grown in rhizoboxes. At the end of the growth period, organic carbon (OC) by Walkley-Black method, microbial biomass carbon (MBC) and microbial biomass phosphorus (MBP) by fumigation extraction method, metabolic quotient index (qCO2) (microbial respiration per unit of biomass), microbial quotient index (microbial biomass carbon per unit of organic carbon), carbon availability index (CAI) (substrate-induced respiration/microbial biomass ratio), colonization Percentage of arbuscular mycorrhizal fungi, and acid (ACP) and alkaline (ALP) phosphomonoesterase enzymes activities by spectrophotometry method, were determined.
Results and Discussion: The results showed that the application of compost significantly increased organic carbon, microbial biomass carbon, microbial biomass phosphorus and decreased MBC/MBP compared with the control treatment. Furthermore, compost increased the organic carbon, microbial biomass carbon and microbial biomass phosphorus in the rhizosphere soil by 8.08, 45.79 and 37.18 % compared with the non-rhizosphere soil, respectively. The pruning wastes increased 1.45, 1.26 and 1.30 fold metabolic quotient, carbon availability and acid phosphomonoesterase activity in the rhizosphere compared with non-rhizosphere soil, respectively.The highest activity of the alkaline phosphomonoesterase enzyme and the percentage of mycorrhizal root colonization were also related to pruning waste treatments in rhizosphere soils.
Conclusions: Different characteristics of the organic matter and the microbial inoculation led to an increase in the biological indices in the rhizosphere zone compared with non-rhizosphere soils. The application of organic matter in the soil, along with microbial inoculation, will accelerate the biological activity of the soil and thus contributes to a better cycle of nutrients in the soil. Following the application of organic matter, microorganisms rapidly grew and led to an increase in biological activity, such as increase activity of phosphomonoesterase enzymes, carbon and phosphorus of microbial biomass in the rhizosphere. It could be argued that increased activity of phosphomonoesterases and the microbial biomass and decreased metabolic quotient in the soil were influenced by the application of the organic materials and mycorrhizal inoculation. The findings of this study have a number of important implications for future practice. Therefore, the use of the organic materials and biological potential of the microorganisms are one of the most important tools to maintain organic carbon balance of the soil, contributing to the stimulation of soil microbiological activities.
mohsen barin; Ehsan Ehsan-Malahat; Farrokh Asadzadeh
Abstract
Introduction: Soil is a complex and dynamic biological system, and it still is difficult to determine the composition of microbial communities in soil. Most soil microorganisms are dormant, so their rate of respiration is low. However, their respiration can be stimulated by adding an easily decomposable ...
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Introduction: Soil is a complex and dynamic biological system, and it still is difficult to determine the composition of microbial communities in soil. Most soil microorganisms are dormant, so their rate of respiration is low. However, their respiration can be stimulated by adding an easily decomposable substrate. Also, by adding a simple organic matter, respiration may rapidly increase to a maximum and remains at a constant rate for more than 4 h. Glucose is commonly used as a substrate because most soil microorganisms can readily utilize it as a carbon source. The substrate-induced respiration (SIR) method was modified and adapted to measure fungal, bacterial and total microbial contributions to glucose-induced respiration and the potentially active microbial biomass on decaying plant residues of different composition. Decomposing residues from natural and agricultural ecosystems were chopped and sieved to include the >1 mm fraction for routine SIR analyses on a continuous flow-through respiration system. Substrate induced respiration is a main factor for the assessment of the soil microbial activity. This technique is already used widely in soil microbial studies. Different factors such as the source of carbon, temperature and incubation may play a significant role in the amount of SIR. Therefore, optimizing the test conditions is one of the important criteria for SIR determination. For this purpose, statistical methods such as central composite design (CCD) and response surface method can be used as a useful tool for determining optimal conditions. This study was carried out to model and compare the effect of carbon source (glucose), temperature and incubation time on the SIR of forest and agricultural soils.
Materials and Methods: In this research, 40 experiments were conducted for two soil types including agricultural soil (with relatively low organic matter content) and forest soil (with relatively high organic matter content). Soil samples were collected from the topsoil (0-20 cm) layer. In the laboratory, all visible roots were removed and the soil samples were divided into two parts. One part was kept in plastic bottles at 4°C for SIR analysis. And the rest was air dried in the shade at laboratory temperature for chemical and physical analysis. Electrical conductivity (EC) and pH were determined in saturated soil extract and organic carbon persent (%OC) was determined by di-chromate oxidation. Soil texture was determined using a Bouyoucos hydrometer in a soil suspension. Response surface methodology based on the central composite design was applied in modeling procedure. Different ranges of the independent variables including glucose (0.5-10 mg g-1), incubation time (1-10 hr), and temperature (15-30˚C) were used in central composite design experiments. Totally, 40 experiments based on the coded values of the independent variables were conducted for two soils.
Results and Discussion: Experimental results indicated that the SIR in forest soil is two times greater than the agricultural soil, which may be related to the higher organic matter content and more microbial activity in this soil. Results also revealed the efficiency of the central composite design in predicting the SIR of forest (R2= 0.823) and agricultural (R2=0.919) soils. Among the three independent variables, the linear effect of temperature on the SIR were significant for both soils. However, the substrate (glucose) content has more significant effect in forest soil in comparison with agricultural soil which may be associated with the higher decomposable organic matter content of the forest soil. Glucose enhancement didn’t have significant effect on SIR alteration rate which can be attributed to low organic matter content in agricultural soil. Totally, with increasing time and temperature, the amount of SIR was significantly increased, however with increasing glucose, SIR amount was not significantly increased especially in the agricultural soil. In the forest soil, the process of SIR changes is clearly distinct in response to independent variables compared to agricultural soil. Maximum levels of the SIR in forest soil is clearly associated to the highest time and glucose levels. This indicates that increasing glucose and sufficient time in the forest soil, which contains high amounts of digestible organic matter, can stimulate microorganisms to decompose more organic matter and it outcome is increasing SIR.
Conclusion: This study indicated the high efficiency of response surface methodology in SIR modeling for both forest and agricultural soils. However, the quantitative amounts of SIR were very different in two soils. The amounts of SIR in the forest soil were almost twice relative to agricultural soil. In the forest soil, the amounts of glucose and temperature were as the main variables in increasing SIR, while the temperature and time variables were more determinant in agricultural soil on it.
Zahra Habibi; Mehdi Rahmati; Ali Asghar Alilou; Esmaeil Karimi
Abstract
Introduction: The use of soil amendments more specifically bio-polymers is increasing nowadays. Arabic Gum is also one of the hydrogels that are capable for soil modification. It seems that the main usage of amendments in soils is to improve the structure of intended soils. Saline-sodic soils are among ...
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Introduction: The use of soil amendments more specifically bio-polymers is increasing nowadays. Arabic Gum is also one of the hydrogels that are capable for soil modification. It seems that the main usage of amendments in soils is to improve the structure of intended soils. Saline-sodic soils are among the poorly structured soils. The use of soil amendments in these soils may be of the most concern. The different conditions of saline-sodic soils in terms of microbial activity and sodium concentration imply that there should be differences in effects of different soil amendments in saline-alkaline and non-saline-alkaline soils. There is no report (up to our knowledge) about the application of Arabic gum in saline soils. However, it seems that the effects of Arabic gum in saline-sodic soils may differ from what in non-saline-alkaline soils due to the interactions between Arabic gum, salinity, and sodium. Therefore, the current research was aimed to investigate the effects of Arabic gum as an analogue of exopolysaccharides on several soil characteristics of saline-sodic and non-saline-sodic soils collected from Lake Urmia catchment, northwest of Iran.
Materials and Methods: The current research was carried out using loam soil samples collected from Qareh Chopogh village located on the southeastern border of Lake Urmia, Bonab plain, Northwest of Iran. In order to evaluate the effects of Arabic gum on properties of salin-sodic and non-saline-sodic soils, a factorial experiment based on completely randomized design (CRD) with two factors (salinity - sodicity levels and Arabic gum) and three replications was carried out. Salinity - sodicity levels, as first factor, included EC = 1 dSm-1 and SAR = 1.3 (non-saline-sodic soil), EC = 6 dSm-1 and SAR = 16 (saline - sodic soil), and EC = 30 dSm-1 and SAR = 58 (severely saline-sodic soil). When soils were sampled from each salinity-sodicity classe and transformed to laboratory, pots were prepared and treated with different levels of Arabic gum including 0, 5, and 10 g kg-1 and incubated for one month with varying soil water content between around 0.5FC and FC. After incubation time, disturbed and undisturbed soil samples were collected from pots and were prepared for further analysis. Undisturbed soil samples were used to determine bulk density of pots (Db), volumetric (θv) and gravimetric (θm) saturated soil water contents, and saturated hydraulic conductivity (Ks). Disturbed soil samples were also used to determine wet-aggregate stability (WAS), mean weight diameter (MWD), and mass fractal dimension (Dm) of soil aggregates, soil pH, soil organic carbon (OC), soil cation exchange capacity (CEC), and soil respiration. Finally, results were subjected to analysis of variance in SAS software based on applied design.
Results and Discussion: The interaction of Arabic gum and soil salinity-sodicity was significant for organic carbon, microbial activity and soil structural characteristics (MWD, WAS, and mass fractal dimension). Arabic Gum improved biological soil properties even in saline-sodic soils. The higher microbial activity (16 to 443 mg CO2 kg-1 soil day-1 in higher amount of Arabic gum vs. 3 to 109 mg CO2 kg-1 soil day-1 in blank soil) and organic carbon content (0.31 to 0.36 % in higher amount of Arabic gum vs. 0.14 to 0.22 % in blank soil) were obtained in higher amount of Arabic gum in saline-sodic and non-saline soils. While, the stability (0.88 to 60 vs. 0.9 to 13 %), mean weight diameter (0.06 to 2.53 vs. 0.009 to 0.46 mm), and mass fractal dimensions (0.935 to 2.09 vs. 0.75 to 2.45) of soil aggregates were affected by Arabic gum in non-saline-sodic soils rather than saline-sodic soils. The main effect of soil salinity-sodicity was significant for soil cation exchange capacity, soil pH, gravimetric and volumetric soil water contents, and pots bulk density. The higher amounts of CEC (21 vs. 9 Cmole+.kg-1), pH (8.0 vs. 7.4), volumetric (53 vs. 41 %) and gravimetric (43 vs. 30 %) water contents, and the lower pots bulk density (1.23 vs. 1.37 g.cm-3) were recorded in severely saline-sodic soil compared to non-saline-sodic soil. The main effect of Arabic gum was significant for soil saturated hydraulic conductivity and soil pH where the higher rate of saturated hydraulic conductivity (0.06 cm.min-1 in higher amount of Arabic gum vs. 0.04 cm.min-1 in blank soil) and the lower pH (7.9 in higher amount of Arabic gum vs. 8.2 in blank soil) were recorded in 10 g.kg-1 Arabic gum.
Conclusion: Based on the results, we conclude that although the effectiveness of the Arabic gum is decreased in saline-sodic soils, it significantly affects different soil characteristics. However, it seems that we need to apply higher amount of Arabic gum (higher than 10 g.kg-1) to gain the considerable effects of Arabic gum in saline – sodic soils. Since gradual drying of Urmia Lake, located in northwest of Iran, is leaving behind wide areas of saline and saline-sodic soils which is threatening habitant’s health, modification of these salt-affected areas using Arabic gum can be a useful strategy. Although, improving vegetation density seems to be main key for this aim, application of soil amendments (more specifically Arabic gum) may support the establishment of vegetation in area. Our objective observation also points to this fact that Arabic gum (specifically in higher amount of 10 g.kg-1) resulted in a crust like layer in soil surface specially in dry state that can prevent the removal of salt particles by the wind. However, the effectivity of Arabic gum in preventing the removal of salt particle by the wind (which is a common issue in area) needs to be evaluated through wind tunnel experiments.
vahid alah jahandideh mahjan abadi; alidad karami; sayed roholla mousavi; H. Asadi Rahmani
Abstract
Introduction:Soil quality as an important part from soil resource sustainability, consistently isinfluenced by human activities.Today, the presence of accurate information about variability of soil quality properties is considered more than ever to apply this information in economic modeling, environmental ...
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Introduction:Soil quality as an important part from soil resource sustainability, consistently isinfluenced by human activities.Today, the presence of accurate information about variability of soil quality properties is considered more than ever to apply this information in economic modeling, environmental predictions, accurate farming and natural resources management. Soil quality is defined as: “capacity of the soil to function, within the ecosystem and land-use boundaries, to sustain biological productivity, maintain environmental quality, and promote plant and animal health”; therefore, it is one of the most important factors in developing sustainable land management and sustaining the global biosphere. The definition of soil quality encompasses physical, chemical and biological characteristics, and it is related to fertility and soil health. Many indicators can be used to describe soil quality, but it is important to take into account sensitivity, required time, and related properties, than can be explained. Properties related to organic matter content, such as microbial respiration, microbial biomass carbon (MBC) and enzymatic activity (urease and phosphatases) can be used as soil quality indicators. They provide early information about mineralization processes, nutrient availability and fertility, as well as effects resulting from changes in land use or agricultural practices (e.g. tillage or application of different types of organic matter). In this context, biological properties have been used as soil quality indicators, because of their relationship with organic matter content, terrestrial arthropofauna, lichen, microbial community (biomass or functional groups), metabolic products as ergosterol or glomalin and soil activities as microbial respiration and enzyme production. This study was carried out for evaluation the spatial variability of biological soil quality indicators in wheat farms of Pasargad plain.
Materials and Methods: After reviewing the initial map of Pasargad, a total of 60 samples were provided using a systematic grid square sampling pattern with 500×500 m over the 1200 ha area of Pasargad at surface soil depth (0-30 cm). The characteristics of soil including organic carbon, pH, EC, microbial respiration, microbial biomass carbon , soil alkaline phosphatase and urease enzymes activity, ratio of microbial biomass carbon to organic carbon (MBC/OC) andmicrobial metabolic quotient(qCO2) were measured and calculated. Results were analysed with SPSS, Excel, GS+, and ArcGIS sotwares. Summary statistics were calculated for the 60 samples including mean, maximum and minimum, coefficient of variation (CV), kurtosis and skewness. In addition, Pearson correlation coefficients were calculated for untransformed data. For evaluation of different interpolation methods of soil characteristics in Pasargad plain root mean square error (RMSE), mean bias error (MBE) and mean absolute error (MAE) were used. We also constructed maps of the spatial distributions for each individual variable using best interpolators including kriging, inverse distance weighting (IDW) and cokriging methods.
Results and Discussion; The results showed that in the most cases the studied properties had too much variation. Based on the coefficient of variation, pHand qCO2had the lowest and highest variations, respectively. There was significant linear correlation between most of soil properties. From lognormal transformation was used for normalization of EC and qCO2. Best model for single semivariogram of organic carbon, microbial respiration, urease enzyme activity, microbial biomass carbon, qCO2 and MBC/OC in the soil was spherical model, for pH in the soilwas exponential model and for EC and phosphatase enzyme activity was gaussian model. Also, the best interpolator for pH, EC, organic carbon, microbial biomass carbon, urease activity, qCO2and MBC/OC was kriging, for alkaline phosphatase activity was inverse distance weight, and for microbial respiration was cokriging method. Amount of pH increased from north to south of Pasargad plain, but amounts of EC and organic carbon were inverse of pH.The higher amounts of microbial respiration and urease activity were observed at the south and east, respectively. The amount of phosphatase activity in the soil of Pasargad plain was scattered, and wide area in the plain had the activity between 215-275 µg PNP/g.hr. The higher amount of MBC and MBC/OCand lower amount of qCO2were observed at the west.
Conclusions: The biological soil properties were sensitive and rapid indicators of effects of soil management. Generally, according to the spatial variabilitymap, the areas in the region are critical situations in terms of biological indicators of soil. So the management techniques that are applied by farmers in these areas have to be changed. The results of this study used in the improvement of regional planning for sustainable management of soil.
maryam tajbakhshian; Mohamad Hosien Mahmudy Gharaie; Asadollah Mahboubi; Reza Moussavi Harami; Iraj Ejlali
Abstract
Introduction: Elemental sulfur is byproduct of natural gas refining which during this process, H2S is removed from sour gas and after changes to solid sulfur, it is stored in large block forms. Continuous precipitation of sulfur and its oxidation causes soil acidification and as a result, nutrient cations ...
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Introduction: Elemental sulfur is byproduct of natural gas refining which during this process, H2S is removed from sour gas and after changes to solid sulfur, it is stored in large block forms. Continuous precipitation of sulfur and its oxidation causes soil acidification and as a result, nutrient cations such as Ca2+, Mg2+, Na+ and K+ will leach from the soil profile. Also, sulfate accumulation led to soil acidification and accelerates the silicates weathering in upper layer of the soil profile. Accumulation of water soluble sulfate in the soil and increase the nutrient cations leaching from the soil depend on sulfate resistance rate. Also, addition of sulfur to the soil for a long time can cause calcium sulfate formation that will cause problems such as increase in soil salinity. Shahid Hashemi Nezhad gas refinery is located about 35 km south of Sarakhs city and about165 km east north of Mashhad. In addition to exploiting, refining and producing 50 × 106 m3.day-1 natural gas, recovered sulfur with %99/9 purity and 2000 tons per day production capacity is one of the byproducts of this gas complex.
Materials and Methods: 22 soil samples were collected from surface soil in Shahid Hashemi Nezhad gas refinery (3 samples) and nearby areas (19 samples) (Fig.1). Soil extracts pH was measured in equilibrium with pure water and with KCl 1M solution in 1:2.5 soil solution ratio. EC of the soil samples was measured in different soil water ratios to obtain the EC 1:1 (Fig.2). Total sulfate content was measured by gravimetry method at geochemistry laboratory of Faculty of Sciences at Ferdowsi University of Mashhad. To get the digestion extract, a mixture of 2 ml concentrated HF, 5 ml HCl and 8 ml HNO3was added to 0.5 gr soil in a teflon vessel, then heated for 60 min at 170° C. After cooling, the solution was evaporated at 130 °C to dry it. Then, the dried salt was dissolved in a mixture of 2 ml HNO3 and 2 ml HCl and diluted with deionized water up to 25 ml. Ca2+ and Mg2+contentswere measured through titration of the soil extract with EDTA 0.01 N and in EBT reagent at the first stage, and titration of the soil extract by EDTA 0.01 N and in Moroxide reagent at the second stage. Na+ and K+ contents were determined using AAS method at geochemistry laboratory at Ferdowsi university of Mashhad after extraction with CaCl2 0.01 M.
Results and Discussion: Based on EC values, 77% of the soil samples were non-saline (EC < 2 dS m-1), 18% were slightly saline (EC= 2-4 dS m-1) and 5% were highly saline (EC=8-16 dS m-1) (Fig.3). In addition, low ΔpH values in the soil samples showed high salinity and similar results to EC. SAR index had the highest value in TS5 sample, and the cations content in this index can be attributed to evaporative sediments with carbonate and sulfate salts in the area (Shurijeh and Chehel-Kaman formations). Moreover, the halite bearing formations in the study area can be regarded as a source for Na+. Based on SAR and EC, majority of the samples (except TS5 in saline and non-sodic) were non-saline and non-sodic that were suitable for agriculture. ESP index of less than 15% in all samples indicated that Na+ concentration has no danger to crops. Relation between the total sulfate content to pH and EC was inverse and direct, respectively. This indicates that recovered sulfur affect in the soil acidification within the refinery site and increase the soluble salts content. These effects are very considerable in the soils inside the refinery site.
Conclusions: Salinity is the major factor affecting decrease of the samples quality for agriculture. Exposed formations in the area with highly soluble rocks causes to increase the soluble salts in the soil. The second factor is high temperature and low precipitation that led to increase the evaporation from the soil surface and accumulation of salts on the soil. Recovered sulfur from natural gas processing can reduce the soil pH and increases the soluble salts to some extent, especially in the inside refinery samples, and then decreases the soil quality for agricultural purposes. Except for one, all studied samples were classified as non-saline and non-sodic soils. Furthermore, the samples were classified in two classes of flocculated soils and potentially dispersive soils based on SAR and EC. ESP index indicates that there is no serious problem regarding sodium concentration in the soils. The pH values indicate that the samples were almost alkaline soils except for the samples inside the site, which are slightly acidic. Acidity of those few samples are attributed to the sulfur released from gas refinery process and its effect on the soil pH.
Hanye Jafari Vafa; Fayez Raiesi
Abstract
Introduction: Land application of organic wastes and biosolids such as municipal sewage sludge has been an important and attractive practice for improving different properties of agricultural soils with low organic matter content in semi-arid regions, due to an increase of soil organic matter level and ...
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Introduction: Land application of organic wastes and biosolids such as municipal sewage sludge has been an important and attractive practice for improving different properties of agricultural soils with low organic matter content in semi-arid regions, due to an increase of soil organic matter level and fertility. However, application of this organic waste may directly or indirectly affect soil bio-indicators such as microbial and enzymatic activities through a change in the activity of other soil organisms such as earthworms. Earthworms are the most important soil saprophagous fauna and much of the faunal biomass is attributed to the presence of these organisms in the soil. Therefore, it is crucial to evaluate the effect of earthworm activity on soil microbial and biochemical attributes, in particularly when soils are amended with urban sewage sludge. The purpose of this study was to evaluate the earthworm effects on biochemical and microbiological properties of a calcareous soil amended with municipal sewage sludge using Factor Analysis (FA).
Materials and Methods: In the present study, the experimental treatments were sewage sludge (without and with 1.5% sewage sludge) as the first factor and earthworm (no earthworm, Eiseniafoetida from epigeic group, Allolobophracaliginosa from endogeic group and a mixture of the two species) as the second factor. The study was setup as 2×4 full factorial experiment arranged in a completely randomized design with three replications for each treatment under greenhouse conditions over 90 days. A calcareous soil from the 0-30 cm layer with clay loam texture was obtained from a farmland field under fallow without cultivation history for ten years. The soil was air-dried and passed through a 2-mm sieve for the experiment. Sewage sludge as the soil organic amendment was collected from Wastewater Treatment Plant in Shahrekord. Sewage sludge was air-dried and grounded to pass through a 1-mm sieve for a uniform mixture with soil matrix.Heavy metals concentrations were found to be below the maximum permissible limits for municipal sewage sludge. After applying sewage sludge treatments, the pots were irrigated (70% soil field capacity) for three months to achieve a relative equilibrium condition in the soil. Eight adult earthworms with fully-developed clitellum were added to each pot. In the pots with both earthworm species, 4 specimen of each earthworm species was added. At the end of the experiment (90 days), soil samples were collected from treatments and were separately air-dried for chemical analysis or kept fresh and stored (4oC) for microbial analysis. Finally, data obtained from the study were analyzed using multivariate analysis.
Results and Discussion: Factor analysis led to the selection of three factors with eigen value greater than 1. The first, second and third factors were accounted for 62, 17.7 and 9.2% of the variability in soil data, respectively. The three factors together explained 89% of the original variability (i.e., variance) in the soil dataset. Consequently, three factors were retained to represent the original variability of the dataset. The first factor had 16 highly weighted variables with a negative loading for soil pH and positive loadings for other variables. The first factor, which included most soil indicators as input variables, clearly separated sewage sludge treatments. Most of the soil microbial characteristics were increased by sewage sludge application due to the high contents of organic matter and nutrients in sewage sludge, as well as low concentrations of heavy metals. Fungal respiration, bacterial respiration and microbial biomass carbon loaded heavily on the second factor with a negative loading for fungal respiration and positive loadings for bacterial respiration and microbial biomass carbon. The second factor, which included microbial biomass and community composition, noticeably discriminated earthworm treatments. In sewage sludge treatments, the dependence of E. foetidaspecies on soil microorganisms as a food source declined, because of the consumption of organic waste by this epigeic species. However, the activity and impact of A. caliginosa species from endogeic group was only related to soil microbial biomass probably due to selective feeding of soil microorganisms.
Conclusion: Factor analysis was used successfully in discriminating the effects of sewage sludge and earthworm either alone or in combination on soil microbial and biochemical parameters. A. caliginosa species in soils amended with sewage sludge had a positive effect on microbial community and biomass, while E. foetidaspecies had no such effect. A. caliginosa species indirectly benefited from sewage sludge application following the increase of soil microbial biomass. In summary, A. caliginosa species positively affected microbiological and biochemical properties in soils amended with sewage sludge due to its less dependence on this organic resource.
parvane mohaghegh; Mahdi Naderi; jahangard mohammadi
Abstract
Introduction: The mismanagement of natural resources has led to low soil quality and high vulnerability to soil erosion in most parts of Iran. To have a sustainable soil quality, the assessment of effective soil quality indicators are required. The soil quality is defined as the capacity of a soil to ...
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Introduction: The mismanagement of natural resources has led to low soil quality and high vulnerability to soil erosion in most parts of Iran. To have a sustainable soil quality, the assessment of effective soil quality indicators are required. The soil quality is defined as the capacity of a soil to function within natural and/or managed ecosystem boundaries. Among approaches which are suggested for soil quality assessment like soil card design, test kits, geostatistical methods and soil quality indices (SQIs), SQIs are formed by combination of soil indicators which resulted from integration evaluation of soil physical, chemical and/or biological properties and processes complement by existing/measureable data, sensitive to land use changes, management practices and human activities and could be applied in different ecosystems. As the measurement and monitoring of all soil quality indicators is laborious and costly, many researchers focused on limited soil quality indicators. There are many methods for identification and determination of minimum data set that influence on soil quality such as linear and multiple regression analysis, pedotransfer functions, scoring functions, principle component analysis and discriminant analysis. Among these methods, principle component analysis is commonly used because it is able to group related soil properties into small set of independent factors and to reduce redundant information in original data set. The objective of this research was to investigate the effects of land use change on soil quality indicators and also the determination of minimum effective soil quality indicators for assessment of soil quality in Choghakhor Lake basin, Chaharmahal and Bakhtiari province, Iran.
Materials and Methods: To meet the goal, Latin hypercube sampling method was applied by using slope, land use and geological maps and 125 composite soil samples were collected from soil surface (0-20 cm). After pretreatments, 27 physical and chemical soil properties like clay, sand and silt content, bulk density (ρb), porosity, organic carbon (OC), particulate organic carbon in macro aggregate (POCmac), particulate organic carbon in micro aggregates (POCmic), proportion of particulate organic carbon in macro aggregates to micro aggregates (POCmac/mic), mean weight diameter (MWD), macro porosity (Mac pore), air content, available water content (AWC), relative water content (RWC), effective porosity (Feff), Dexter index (S), porosity, acidity (pH), electrical conductivity (EC), Nitrogen (N), Phosphorous (P), Iron (Fe), manganese (Mn), Zinc (Zn), Cadmium (Cd), lead (Pb), Copper (Cu) and Cobalt (Co) were measured using appropriate methods.
Results and Discussion: The impact of different land use types on soil quality was evaluated by measuring several soil properties that are sensitive to stress or disturbance and comparison of them. The results showed that measured values of OC, POCmac, POCmic, POCmac/mic, P, Fe, Zn, Mn, Cu, ρb, MWD, AWC, air content and S were in order orchards > crop land > good rangelands > dry lands > weak rangelands. In this region, land use changes have different effects on soil quality. The alternation of good pasture lands to orchard and crop lands caused to enhancement of soil quality parameters. The variation of good pasture to dry land and degradation of good pasture in this area led to decreasing of soil quality. The principle component analysis (PCA) was employed as a data reduction tool to select the most appropriate indicators of site potential for the study area from the list of indicators. Based on PCA, 8 components with eigenvalues ≥ 1 were selected that explained 99.96 percent of variance. The prominent eigenvectors in components were selected using Selection Criterion (SC). The results revealed that the most important component, was the first component with the most dominant measured soil property of Cu. 12 soil quality parameters base on SC were determined in the first component. Stepwise discriminate analysis also was applied for determination significant soil quality indicators from 12 soil parameters. Our result showed that the minimum data set influencing on soil quality were Zn followed by POCmac/mic, clay %, Cu, Mn and P, respectively.
Conclusion: The results suggested that the permanent crop management (Orchard and crop land) had generally a positive impact on soil quality, while dry land and degradation of good pasture had a negative impact on soil quality. Our study suggested that the PCA method and stepwise discriminant analysis for determination of minimum data set can be used in Chughakhur lake basin. In this study from27 of physical and chemical soil properties, the fertility factors such as the content of Zn, Cu, Mn and P and the proportion of particle organic carbon in macro aggregate to micro aggregate and also soil texture components can be used to the minimum data set that evaluates soil quality. These parameters mostly depend on soil management system.
rouhollaah vafaeezadeh; shamsollah Ayoubi; mohamamdreza mosaddeghi; maryam yousefifard
Abstract
Introduction: Land use changes are the most reasons which affect natural ecosystem protection. Forest soils have high organic matter and suitable structure, but their land use management change usually affects soil properties and decreases soil quality. There are several outcomes of such land use changes ...
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Introduction: Land use changes are the most reasons which affect natural ecosystem protection. Forest soils have high organic matter and suitable structure, but their land use management change usually affects soil properties and decreases soil quality. There are several outcomes of such land use changes and intensification: accelerated soil erosion and decline of soil nutrient conditions, change of hydrological regimes and sedimentation and loss of primary forests and their biodiversity. Establishing effects of land use and land cover changes on soil properties have implications for devising management strategies for sustainable use. Forest land use change in Yasouj caused soil losses and decreased soil quality. The objectives of this study were to assess some soil physical and chemical properties and soil magnetic susceptibility changes in different land uses and slope position.
Materials and Methods: Soil samples were taken from natural forest, degraded forest and dryland farm from different slops (0-10, 10-20 and 20-30 percent) in sout east of Yasouj. They were from 0–10 cm depth in a completely randomized design with five replications. Soil moisture and temperature regimes in the study area are xeric and mesic, respectively. Particle size distribution was determined by the hydrometer method and soil organic matter, CaCO3 equivalent and bulk density was determined using standard procedures described in Methods of Soil Analysis book. Magnetic susceptibility was measured at low and high frequency of 0.46 kHz (χlf) and 4.6 kHz (χHf) respectively with a Bartington MS2D meter using approximately 20 g of soil held in a four-dram clear plastic vial. Frequency dependent susceptibility (χfd) is expressed as the difference between the high and the low frequency measurements as a percentage of χ at low frequency.
Results and Discussion: Soil texture was affected by land use change from silty clay loam in forest to silty loam in dry land farm. Declining of organic matter and aggregate stability caused soil surface loss by erosion. The bulk density increased from 1.12 to 1.54 gcm-3 when forest changed to dry land farms. Soil compaction by tillage and lower amount of organic matter in farm lands are some of the reasons for increasing bulk density. Another possible reason could be decreasing of biological activity and parent material with greater calcite mixed with soil surface layer during land use change. Thus, the maximum and minimum amount of calcite was observed in dry land farm in 20-30 % slopes (57.46 %) and forest in 0-10 % slopes (13.37 %), respectively. In addition during soil formation calcite was translocated to lower horizons in natural forest. The greatest organic matter was 7.45 % and related to natural forest in 0-10 % slopes. Overall, the organic matter content was greater in all forest slopes than all other land use. In mineral soil, total organic carbon is not a proper factor in soil physical behavior. Complex and noncomplex organic carbon influence the soil physical behavior. Organic carbon in degraded forest and dry land farming was in complex form but in forest land use it was observed in two complex and noncomplex forms. Noncomplex organic matter was 53% and complex organic matter was 47%. It means that forest soil have better quality than degraded forest and dry land farm, respectively. Sedimentary rocks have rather low concentration of magnetic minerals with magnetic susceptibility from 0.1 (10-8 m3 kg-1) in the limestone to approximately 20 (10-8 m3 kg-1) in the siltstone. Low magnetite susceptibility in natural forest was more than degraded forest and dry land farm. Mean magnetite susceptibility values were 61.8, 48.6 and 42.4 10-8 m-3 kg-1, respectively which probably related to magnetic minerals formation during pedogenesis. Frequency magnetite susceptibility (χfd) was more than 3% in the most soils, significantly in forest soil (from 4.63-5 percent). Greater frequency magnetite susceptibility (χfd) values are suggested to be indicative of the dominance of super-paramagnetic grains and fiug single domain particles. χfd in soils reflects significant pedogenic magnetic minerals which formed during soil formation from calcitic parent materials.
Khadije Salarinik; Mohsen Nael; Ghasem Asadian; Ali Akbar Safari Sinegani
Abstract
Introduction: Soil organic matter is influenced strongly by vegetation cover and management, therefore it is proposed as the main indicator of soil quality and health. The changes in soil organic matter status occur much more rapidly in the labile pools than in organic C. Thus, labile pools can be used ...
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Introduction: Soil organic matter is influenced strongly by vegetation cover and management, therefore it is proposed as the main indicator of soil quality and health. The changes in soil organic matter status occur much more rapidly in the labile pools than in organic C. Thus, labile pools can be used as early indicators of changes in total organic matter that will become more obvious in the longer term here. In addition, the labile fraction has a disproportionately large effect on nutrient-supplying capacity and structural stability of soils. Land management as well as soil and environmental conditions lead to the deployment of different plant communities in rangeland ecosystems, which in turn may have different effects on soil quality indicators. The main objective of this research was to investigate the influence of different vegetation covers on the quantity and quality of soil organic carbon fractions in Gonbad experimental watershed, Hamadan. Moreover, the seasonal changes of selected soil carbon fractions were investigated.
Materials and Methods: Paired Gonbad watershed in Hamedan consists of two sub-basins: in control sub-basin no grazing management is applied, while in protected sub-basin, grazing has been restricted to a very short period in late autumn since 2002. Average annual precipitation and average annual temperature in the area are 304.4 mm and 9.5 °C, respectively (5). The soil cover of the watershed consists of TypicCalcixerepts, TypicHaploxerepts and Lithic Xerorthents (9). Five different vegetation typesof which, grasses (G), Astragalus-Bromus (A-B), Astragalus-Artemisia (A-A), Astragalus-Lactuca (A-L) in protected sub-basin, and Astragalus-Euphorbia (A-E) in control sub-basin, were selected. In addition, a formerly cultivated hilly land outside the watershed, now under rainfed wheat farming (RW) was selected as a non-pasture vegetation type. All of the six vegetation types were similar in terms of soil parent materials and slope aspect.. Soil and plant sampling were conducted in mid-autumn 2012 (a), and late spring 2013 (s). Three plots (1*1 m2) were studied in each vegetation type. Total organic carbon (TOC), carbon stock (CS), carbon stock normalized with sand(CS/Sa), active carbon (AC), normalized active carbon (AC/TOC), soil carbohydrates (Ch), normalized carbohydrates (Ch/TOC), basal respiration (BR) and normalized basal respiration (BR/TOC) were measured in surface soils (0-15 cm). A factorial experimental design with two factors, vegetation type (6 levels) and time (2 levels), was conducted. Prior to statistical analysis, data were normalized, if required.
Results and Discussion: TOC and CS contentswere significantly different between vegetation types. A-B and A-A had highest canopy cover, litter cover and species diversity. Species diversity in the rangeland ecosystems has direct effect on fodder production and soil organic carbon content. A-E site, despite its low TOC content, hadhigher CS/Sa (51.9 Mg/ha) due to higher amount of clay content, compared to A-A (43.1Mg/ha) with higher TOC content. The amount of AC andAC/TOC in different vegetation types is proportional to the amount of TOC, CS, total canopy, and the canopy and production of herbaceous species. AC content was significantly highest in A-B (711.7 mg/kg), and lowest in RW site(262.6 mg/kg). A-B site is rich in grass species with high amounts of readily decomposable root residues and exudates. The variation of carbohydrate contents in different vegetation types wasvery similar to that of total organic carbon, in that A-B and A-A exhibited the highest (5843 and 5258 mg/kg, respectively) and RW showed the lowest (1937 mg/kg) carbohydrate contents. The woody, not easily decomposible litters in A-A explainedthe high content of Ch/TOC (38.12%) in this site; low rate of humification entails increased soil carbohydrates. Ch/TOC was significantly lower in A-E than other covers. The highest BR andBR/TOC, were observed in A-B and A-A sites, mainly due to the high canopy cover, species richness,and soil organic matter. The lowest BR andBR/TOC were observed in A-E.Thesoil texture in this site was clay.The recirculation of organic matter in fine-textured soils is low because of organic materials protection from microbial decomposition. Total organic matter and labile organic carbon inputs werelower in A-L, A-E and G sites; this may explain the reduction of microbial activity in these vegetation types. Except for AC/TOC, Ch, and BR, seasonal changes of all other indicators were significant. Unlike other indicators, the content of Ch/TOC was significantly higher in autumn than spring.
Conclusion: Vegetation types had significant effects on selected soil quality indicators, so that A-A and A-B sites exhibited the highest soil quality, mainly because of higher vegetation cover, litter, and plant diversity. RW, followed by A-E site, demonstrated the lowest soil quality due to the tillage practices and low plant residue inputs in the first case, and overgrazing of vegetation cover and litter in the second. Total soil organic carbon and active carbon were significantly higher in spring compared to autumn. Seasonal changes of basal microbial respiration and carbohydrates were not statistically significant.
H. Emami; A.R. Astaraei; A. Fotovat
Abstract
Soil quality is important for evaluating the soil fertility and physical condition. Soil physical and chemical indicators should be regarded for determining the soil quality. This research was conducted to study the effect of organic matter on quantitative value of soil quality. Three level (15, 30, ...
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Soil quality is important for evaluating the soil fertility and physical condition. Soil physical and chemical indicators should be regarded for determining the soil quality. This research was conducted to study the effect of organic matter on quantitative value of soil quality. Three level (15, 30, and 60 ton/ha) of different organic compounds including municipal waste compost, sewage sludge, cattle manure, and wheat straw to gether with control treatment in three replications were applied into loamy soil. The treated soils were kept for 6 months at 70% of field capacity moisture in greenhouse condition. Then soil quality determined based on non-linear score function by using of 14 physical and chemical indicators. The results showed that the score of control treatment was 52.7, which it belong to class 4, i.e. low quality. Addition of different organic matter into studied soil led to improve soil quality score and soil quality class was increased one to 2 degrees. Among the studied treatments, the highest score of soil quality was obtained in 60 ton/ha sewage sludge and 30 and 60 ton/ha compost. Also, addition the other organic treatments cause to increase the quantitative soil quality score in relation to control, and soil quality class increased one degree. Among the studied indicators, iron (Fe), Manganese (Mn), zinc (Zn) micro-nutrients, aeration porosity (AC), and mean weight diameter of aggregates (MWD) were the important limiting indictors in degrading the soil quality in control treatment, and applying the compost and sewage sludge increased their scores.
