Soil science
Yahya Kooch; Mahin Fooladi Doghazlo; Katayoun Haghverdi
Abstract
Abstract
Vegetation, as a key factor in ecosystems, has significant impacts on soil properties through multiple ecological processes. Vegetative covers contribute to soil structure and composition by stabilizing organic matter, controlling erosion, regulating moisture, facilitating nutrient cycling, ...
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Abstract
Vegetation, as a key factor in ecosystems, has significant impacts on soil properties through multiple ecological processes. Vegetative covers contribute to soil structure and composition by stabilizing organic matter, controlling erosion, regulating moisture, facilitating nutrient cycling, and fostering microbial activity. While extensive research has elucidated the effects of various vegetation types on the physical and chemical properties of soil, the biological attributes of soil under different vegetation covers, particularly tree and shrub species, remain underexplored. This study aims to comprehensively evaluate the characteristics of the organic and mineral soil layers in areas dominated by Quercus macranthera tree cover, Crataegus microphylla shrub cover, Berberis integerrima shrub cover, and a mixed Crataegus microphylla and Berberis integerrima shrub cover in Rudbar County, Guilan Province, Iran. By examining these diverse vegetation types, the study seeks to elucidate their differential impacts on soil health and ecosystem functionality, providing insights for sustainable land management.
Materials and Methods
To investigate the influence of vegetation cover on soil properties, a rigorous site selection process was employed. Following preliminary field assessments, study areas were chosen to ensure continuity of vegetation cover and minimal variations in topographic factors, including elevation above sea level, slope gradient, and aspect. This approach minimized confounding variables, allowing for accurate comparisons across vegetation types. In each habitat, two 100 m × 100 m plots were implemented, with a minimum separation of 500 meters to account for spatial variability. Within each one-hectare plot, five soil samples (30 cm × 30 cm surface area, 10 cm depth) were collected from the organic and mineral layers at the four corners and the center of the plot. In total, 10 litter samples and 10 soil samples were collected from each vegetation type and transported to the laboratory for detailed analysis. Laboratory assays evaluated a suite of physical, chemical, and biological parameters, including soil aggregate stability, nutrient content, enzymatic activities, and microbial community dynamics, to provide a comprehensive understanding of soil responses to vegetation cover.
Results and Discussion
The findings revealed marked differences in soil properties across the studied vegetation types. The Q. macranthera tree cover exhibited the highest amount of essential nutrients in the organic layer, including nitrogen, phosphorus, potassium, calcium, and magnesium, reflecting its capacity to enhance nutrient cycling. In contrast, the B. integerrima shrub cover consistently showed the lowest nutrient amounts, suggesting limited contributions to soil fertility. Analysis of physical and chemical soil properties further underscored these disparities. The Q. macranthera cover demonstrated superior soil aggregate stability, higher clay content, increased coarse and fine aggregate percentages, optimal pH, and elevated levels of total nitrogen, ammonium, nitrate, phosphorus, potassium, calcium, and fine root biomass. Enzymatic activities, including urease, acid phosphatase, arylsulfatase, and invertase, were also significantly higher under Q. macranthera, indicating robust microbial and biochemical processes. Conversely, B. integerrima cover recorded the lowest values for these parameters, highlighting its limited impact on soil structure and function. Particulate and dissolved organic nitrogen levels were similarly highest under Q. macranthera, reinforcing its role in organic matter dynamics. Biological soil properties mirrored these trends. The Q. macranthera cover supported the highest densities of soil microfauna, including Acarina, Collembola, and nematodes, as well as abundant protozoa, fungal, and bacterial populations. Metrics of microbial activity, such as basal respiration, substrate-induced respiration, microbial biomass nitrogen, and microbial biomass phosphorus, were also maximized under this tree cover, reflecting a thriving soil microbial community. In contrast, B. integerrima cover exhibited the lowest values for these biological indicators, suggesting a less supportive environment for soil biota. Temporal analysis of carbon mineralization revealed significant variations at weeks 2, 4, 5, 8, and 12, with no notable changes at weeks 1 and 17. The highest carbon mineralization rates were observed under Q. macranthera, while B. integerrima showed the lowest. Nitrogen mineralization followed a similar pattern, with significant changes on days 7, 14, 21, 28, and 35, and the highest rates under Q. macranthera. These results collectively indicate that vegetation type, combined with topographic factors like elevation, significantly shapes the physical, chemical, and biological characteristics of soil in Rudbar County.
Conclusion
This study demonstrates that Q. macranthera tree cover significantly enhances soil quality compared to C. microphylla, B. integerrima, and their mixed shrub covers. The superior physical, chemical, and biological properties observed under Q. macranthera highlight its critical role in fostering soil microbial communities, improving nutrient cycling, and maintaining soil fertility. Enhanced carbon and nitrogen mineralization rates further underscore the importance of this tree species in driving biogeochemical processes essential for ecosystem health. These findings have important implications for land-use planning, forest management, and ecological restoration in Rudbar County. By prioritizing Q. macranthera in reforestation and conservation strategies, land managers can optimize soil productivity and ecosystem resilience. Future research should focus on long-term monitoring of these soil-vegetation interactions and explore additional environmental factors, such as climate and land-use history, to further refine management practices. The integration of such data will support the development of sustainable strategies that balance ecological health with agricultural and forestry objectives, ensuring the long-term vitality of Rudbar County’s ecosystems.
Soil science
Yahya Kooch; Mahmood Tavakoli Feizabadi; Katayoun Haghverdi
Abstract
IntroductionSoil, as habitat substrate, helps to regulate important ecosystem processes, including nutrient absorption, organic matter decomposition. Water availability and the well-being of humanity are directly linked to soil functions. On the other hand, vegetation with different species and ages ...
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IntroductionSoil, as habitat substrate, helps to regulate important ecosystem processes, including nutrient absorption, organic matter decomposition. Water availability and the well-being of humanity are directly linked to soil functions. On the other hand, vegetation with different species and ages have significant effects on the status of the surface soil layer through the creation of diverse environmental conditions and the production of different organic substances. However, few studies have been conducted in relation to the effect of the age of afforestation and the type of vegetation on the soil status. Considering that a practical, complete and effective assessment of soil condition should be the result of simultaneous measurement of physical, chemical and biological indicators, hereupon, the present study aimed to investigate the effect of 20-year old poplar stand, 20-year old maple stand, 10-year old poplar stand, 10-year old maple stand and rangeland cover, in plot 3 of Delak-Khil series of wood and paper forests in Mazandaran province, on the organic layer properties and physical, chemical and biological (including microbial activities, enzyme activity, earthworm population and biomass, the number of soil nematodes and root biomass) properties of the surface soil layer. Materials and MethodsFor this purpose, some parts of the study area were selected which are continuous with each other and have minimum height difference from the sea level, minimum change in percentage and direction of slope. Then, in order to take samples from the organic and surface layer of the soil, three one-hectare plots with distances of at least 600 meters were selected in each study habitats. From each of the one-hectare plots, 5 leaf litter samples and 5 soil samples (30 cm × 30 cm by 10 cm depth) were taken to the laboratory for analysis . In total, 15 litter samples and 15 soil samples were collected from each of the habitats under study. One part of the soil samples was passed through a 2 mm sieve after air-drying to perform physical and chemical tests, and the second part of the samples was kept at 4 °C for biological tests. One-way analysis of variance tests was used to compare the characteristics of organic layer and soil between the studied habitats. In the following, Duncan's test (P>0.05) was used to compare the average parameters that had significant differences among different habitats.Results and DiscussionThe results of this research showed that afforested stands with different ages and pasture cover had a significant effect on the characteristics of the organic and surface soil layers. The results indicated the improvement of most of the characteristics of the organic and surface soil layer in the afforested stands, especially the 20-year old afforestation compared to the rangeland cover. The organic matter produced in 20-year old afforestation, especially with poplar species, had a higher quality (high nitrogen and carbon content and low carbon-to-nitrogen ratio) compared to organic matter produced in 10-year old afforestation and pasture cover. Most of the physicochemical characteristics of the soil under 20-year old afforestation were in a better condition than the other studied habitats. Also, according to the results of this research, the highest values of biological characteristics such as microbial activity, enzyme activity, and the population of earthworms and nematodes were observed in the subsoil of 20-year old afforestation especially with poplar species. Based on the results obtained from the principal component analysis, the higher values of nitrogen, phosphorus, calcium, magnesium and potassium content of the organic layer led to the improvement of soil fertility characteristics, microbial activities, enzyme activity, earthworm population, the number of soil nematodes and root biomass, respectively, under poplar and maple plantation for 20 years, meanwhile, 10-year old plantation, especially with maple species, and rangeland with the production of organic materials with high carbon content and carbon to nitrogen ratio, resulted in the reduction of organic matter decomposition (greater thickness of organic layer), and consequently the reduction of the mentioned properties of the surface soil layer. ConclusionAccording to the findings of this research, it can be concluded that plantation with poplar species, especially after 20 years, had a higher ability to improve the soil condition compared to maple, which can be considered by managers in future afforestation. Also, with the passage of time, the presence of tree covers (poplar and maple) had a higher priority than rangeland cover in improving the fertility status and suitable edaphological conditions of the soil.
Soil science
Z. Sohrabzadeh; Y. Kooch
Abstract
Introduction Shrub covers play a pivotal role in pasture ecosystems, exerting considerable influence on various biochemical processes that occur within the habitat and surface layers of the soil. Despite their significance, there is a scarcity of research exploring the impact of different ...
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Introduction Shrub covers play a pivotal role in pasture ecosystems, exerting considerable influence on various biochemical processes that occur within the habitat and surface layers of the soil. Despite their significance, there is a scarcity of research exploring the impact of different types of shrubs covers on soil properties within pasture ecosystems. Consequently, this present study was undertaken to address this gap in knowledge and investigate the effects of shrub cover on soil characteristics specifically within a semi-arid climate, which is known for its delicate and vulnerable habitats. Materials and MethodsThe implementation of this research involved the consideration of the mountainous region of Kiakola, Nowshahr city. The current investigation focused on assessing the impact of various shrubs, namely Carpinus orientalis Miller, Crataegus microphylla C. Koch, Berberis integerrima Bunge, Prunus spinosa L., and Rhamnus pallasii Fisch. and C. A. Mey, on specific soil properies within the mountainous area of Kiakla, Nowshahr city. To carry out this research, 15 sites were selected for each of the aforementioned shrub species. Soil samples were collected from under the canopy of these species, specifically at a depth of 0-10 cm and a surface area of 30 cm × 30 cm. A total of 75 soil samples were then taken to the laboratory for analysis. The samples were divided into two parts: one part underwent physical and chemical tests after air-drying and passing through a 2 mm sieve, while the other part was stored at 4 degrees Celsius for biological tests. The presence or absence of significant differences in soil properties related to the type of shrub cover under investigation was determined using a one-way analysis of variance test. Principal component analysis (PCA) was utilized to establish the relationship between different soil characteristics within the studied shrub covers. Results and DiscussionAccording to the findings of this investigation, alterations in the shrub species present in the examined pasture habitat resulted in modifications to the majority of soil quality properties. Nevertheless, no statistically significant disparity was observed in the quantity of soil organic matter. However, it is worth noting that the quantity of organic matter in the subsoil of Carpinus species exceeded that of the other examined shrubs. Carpinus and Crataegus shrubs were associated with the lowest values of bulk density, while the shrubs under investigation had no significant impact on soil particle density. Furthermore, the subsoil of the Carpinus shrub cover exhibited the highest values of soil porosity. In the studied area, the most stable soil aggregates were observed beneath the Carpinus and Rhamnus shrubs. The subsoil of Rhamnus and Carpinus shrubs exhibited the highest and lowest quantities of sand, respectively. Similarly, the subsoil of Carpinus and Rhamnus displayed the highest and lowest quantities of clay, respectively. The soil under Rhamnus displayed the highest ratio of CR and MCR indices, whereas the subsoil of Carpinus exhibited the lowest values of these indices. Fulvic and humic acids demonstrated the greatest values beneath the Carpinus, Crataegus, Berberis, Prunus, and Rhamnus shrubs, respectively, following a comparable pattern. Additionally, the subsoil of Carpinus exhibited the greatest quantity of microbial ratio, while the soil under Rhamnus displayed the lowest quantity of this characteristic. The outcomes of the principal component analysis (PCA) revealed that the quantity of organic matter, clay content, fulvic and humic acids, porosity, and stability of soil aggregate in the soil beneath Carpinus played a significant role in enhancing the soil microbial ratio of this shrub in comparison to the other shrubs. Conclusion The findings of this investigation validate the capability of Carpinus foliage to ensure the conservation of soil quality indicators on the hilly grasslands of northern Iran. Therefore, it is proposed that restoration efforts be conducted in the designated region and other areas with similar ecological conditions. Additionally, it is recommended that special attention be given to the implementation of Carpinus and other indigenous shrub species to protect soil integrity.
Soil science
Y. Kooch; A. Shahpiri; K. Haghverdi
Abstract
Introduction
Forests, encompassing approximately 30% of the Earth's land area, hold significant ecological importance due to their rich biodiversity and the multitude of environmental services they provide. These ecosystems outperform other terrestrial habitats, making them invaluable to all life forms ...
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Introduction
Forests, encompassing approximately 30% of the Earth's land area, hold significant ecological importance due to their rich biodiversity and the multitude of environmental services they provide. These ecosystems outperform other terrestrial habitats, making them invaluable to all life forms on our planet. The destruction of forest habitats and changes in land use patterns exert significant impacts on the variability of soil quality indicators. The consequence of forest degradation encompass various adverse consequences, including the destruction of wildlife habitats, climate change, global warming, diminishing plant and animal biodiversity, and reduced water conservation capacity. Extensive research has been conducted to investigate soil quality in diverse land uses within temperate regions. However, there is a noticeable scarcity of studies focusing on semi-arid regions. It is imperative to note that a comprehensive and practical assessment of soil condition necessitates the simultaneous measurement of physical, chemical, and biological indicators. Such an integrated approach ensures a thorough and effective evaluation of soil quality. The primary objective of this study was to assess the impact of various land uses, namely natural forest (C. betulus - P. persica), plantation (Q. castaneifolia), garden, rangeland, and agricultural lands (rice), on the physical, chemical, and biological properties of the organic and mineral soil layers. Specifically, the investigation focused on the evaluation of fauna and flora, microbial communities, and enzyme activities. The study was conducted in the semi-arid region of Kajur Nowshahrmourd.
Materials and Methods
To achieve this objective, contiguous sections of the study area were carefully chosen, ensuring minimal variations in height above sea level, percentage and direction of slope. Subsequently, three slice of one-hectare dimension plots (100 × 100) were selected within each study habitat, with a minimum distance of 600 meters between them. From each one-hectare plot, four leaf litter samples and four soil samples (30 cm × 30 cm, 10 cm depth) were collected and transported to the laboratory for analysis. In total, 12 litter samples and 12 soil samples were collected from each of the habitats. The soil samples were divided into two parts: one part was air-dried and then passed through a 2 mm sieve for subsequent physical and chemical testing, while the other part was stored at 4 degrees Celsius for biological assessments. One-way analysis of variance tests were employed to compare the characteristics of the organic layer and soil among the studied habitats. Furthermore, Duncan's test (P>0.05) was utilized to compare the average parameters that exhibited significant differences among the different habitats.
Results and Discussion
The findings derived from this investigation underscore the substantial variability in organic layer characteristics across different vegetation types. Natural forests emerged as the most prominent in terms of thickness, nitrogen content, and calcium concentration, whereas agricultural areas exhibited the lowest values. Grassland areas displayed the highest carbon content and carbon-to-nitrogen ratio, while agricultural and natural forest areas demonstrated comparatively lower values. Agricultural lands demonstrated elevated bulk density and sand content, whereas natural forests exhibited the lowest values. Notably, natural forests showcased the highest porosity, aggregate stability, silt percentage, and macro- and micro-aggregate quantities, while agricultural areas presented the lowest values. Chemical analysis of the soil indicated that natural forests recorded the highest values for most chemical characteristics, while agricultural lands displayed the lowest values. Biological attributes generally exhibited the highest levels in natural forests and the lowest levels in agricultural areas. Specifically, the abundance and biomass of epigeic and endogeic fauna did not exhibit significant differences among different land uses during the summer season. Managed forests demonstrated the highest values for moisture content, basal respiration, substrate-induced respiration, and microbial biomass carbon. Conversely, agriculture exhibited the lowest values in these regards. The microbial biomass carbon-to-nitrogen ratio was highest in agricultural areas, while natural forests displayed the lowest value. Natural forests displayed the highest values for most nitrogen transformation characteristics, whereas agricultural areas exhibited the lowest values. Nitrogen nitrification and mineralization showed a decreasing trend across different land uses during the summer and autumn seasons. The type of vegetation cover also significantly influenced the variability of soil ammonium and nitrate levels.
Conclusion
Based on the results obtained from this study, it can be inferred that the preservation and conservation of natural forest cover should be given utmost importance. Additionally, in degraded areas, the establishment of woody vegetation can serve as a viable approach for the restoration of ecosystems with similar ecological conditions. Furthermore, the presence of tree covers, specifically C. betulus and P. persica, is of greater significance compared to rangeland and agricultural land uses in enhancing soil fertility and creating favorable biological conditions. As a result, this research provides valuable insights into the impact of different land uses on the characteristics of the organic and mineral soil layers in mountainous habitats. The information obtained can be instrumental in guiding natural resource managers and offering practical assistance in decision-making processes.
Y. Kooch; M. Azizi Mehr
Abstract
Introduction: Degradation of forest habitats and alteration of soil vegetation are efficient factors affecting the variability of ecological indices of organic and mineral layers of soils. In Iran, degradation of forest habitats and changes in habitat type, especially over the last century, affected ...
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Introduction: Degradation of forest habitats and alteration of soil vegetation are efficient factors affecting the variability of ecological indices of organic and mineral layers of soils. In Iran, degradation of forest habitats and changes in habitat type, especially over the last century, affected soil quality, plant biomass production and environmental sustainability. Hence, in this study, the effect of different forest and rangeland vegetation types on the ecological parameters of soil organic and mineral layer has been investigated. Materials and Methods: To study and evaluate the effects of forest degradation and site change on soil organic and mineral ecological indices, four types of vegetation were selected in Gorgpas areas, southwest of Chalus city, Mazandaran Province. The land cover is as follows in the study area: (1) Less-degraded forest dominated by Carpinus betulus L.- Parrotia persica C. A. May (2) Fourty year's old plantation of Pinea abies (L.) Karst - Pinus nigra Arnold (3) Deforested areas including Carpinus betulus L. - Parrotia persica C. A. May (4) Exclosure rangeland dominated by Coronilla varia L. Physiographically similar land covers, were selected during a field research in the studied areas. Eight litter and soil samples (0-15 cm in depth and 30 cm × 30 cm in depth) were collected from each area in summer. In order to reduce the boundary effects, sampling was performed in the center of each land cover. The collected samples of organic layer (litter) and soil mineral transferred to the laboratory for analysis. The collected data was stored as a database in Excel. Then, to analyze and compare the data, the normality distribution of observations was evaluated by Kolmogorov-Smirnov test and variance homogeneity by Levene test. Analysis of variance used to investigate the significant/non-significant differences of different soil organic and inorganic layer characteristics in relation to the studied areas. Duncan test used for multiple mean comparisons. All statistical analyzes were performed by SPSS software version 23. Principal component analysis (PCA) was employed to study the relationship between soil organic matter and soil mineral quality in the studied land cover. Results and Discussion: According to the results, in the soil organic layer the highest carbon/nitrogen ratio (%) assigned to the rangeland, while the nitrogen (%) content was highest in the natural forest. The highest amount of carbon and organic layer thickness were also observed in rangeland and degraded forest cover, respectively. In the mineral soil layer, the highest value of sand (%), moisture (%), carbon (%) and carbon to nitrogen ratios (%) belonged to the rangeland cover, while the highest amount of clay v (%), pH (1:2.5 H2O), electrical conductivity (ds m-1), nitrogen (%), phosphorus (%), potassium (mg kg-1), calcium (mg kg-1) and magnesium (mg kg-1) were observed in the forest cover. The highest number and biomass of earthworms (n m-2), nematode population (In 100-gram soil), nitrogen mineralization (mg kg-1l), ammonium (mg kg-1), nitrate (mg kg-1), basal respiration (mg CO2 g−1 day−1), substrate induced respiration (mg CO2 g−1 day−1), microbial nitrogen biomass (mg kg-1) and metabolic coefficient (μg CO2-C mg-1 MBC day-1) observed in forest cover. There was no significant difference between the studied vegetations for bulk density (g cm-3) characteristics, silt (%), microbial biomass of carbon (mg kg-1) and microbial coefficient (μg CO2-C mg-1 MBC day-1). Higher nitrate density in natural forest and under cultivated soils are due to the presence of litter species with low carbon/nitrogen ratio, high pH and calcium. Conversion of natural broadleaf covers to needle leaf plantation and rangeland reduces the biochemical processes of ammonium. Nitrogen mineralization rates are strongly influenced by area management and forest canopy cover, so that under the broadleaf stands, this rate was more than the needle leaf stands. This probably was due to the greater nitrogen of litter, the lower carbon to nitrogen ratio and the faster rate of decomposition of organic matter in broadleaves. Most of the time the increase in pH increases the rate of mineralization of nitrogen. Conclusion: The present study indicated that forest habitat had the highest number and biomass of earthworms, soil nematode population, ammonium, nitrate, metabolic coefficient, basal and substrate induced respiration, carbon availability index, microbial biomass and nitrogen mineralization, while, there was no significant difference between the studied forests and rangelands in carbon microbial biomass and microbial coefficient. In general, the results of this study showed that the physicochemical and biological characteristics of soil organic matter in the forest habitats were better than other studied vegetations and the forest degradation and land-use changes reduced soil fertility and microbial indices.
Y. Kooch
Abstract
Introduction: Among the collection of natural resources in the world, soil is considered as one of the most important components of the environment. Protect and improve the properties of this precious resource, requires a comprehensive and coordinated action that only through a deep understanding of ...
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Introduction: Among the collection of natural resources in the world, soil is considered as one of the most important components of the environment. Protect and improve the properties of this precious resource, requires a comprehensive and coordinated action that only through a deep understanding of quantitative (not only recognition of the quality) the origin, distribution and functionality in a natural ecosystem is possible. Many researchers believe that due to the quick reactions of soil organisms to environmental changes, soil biological survey to estimate soil quality is more important than the chemical and physical properties. For this reason, in many studies the nitrogen mineralization and microbial respiration indices are regarded. The aim of the present study were to study the direct and indirect effects of soil physicochemical characteristics on the most important biological indicators (nitrogen mineralization and microbial respiration), which has not been carefully considered up to now. This research is the first study to provide evidence to the future planning and management of soil sciences.
Materials and Methods: For this, a limitation of 20 ha area of Experimental Forest Station of Tarbiat Modares University was considered. Fifty five soil samples, from the top 15 cm of soil, were taken, from which bulk density, texture, organic C, total N, cation exchange capacity (CEC), nitrogen mineralization and microbial respiration were determined at the laboratory. The data stored in Excel as a database. To determine the relationship between biological indices and soil physicochemical characteristics, correlation analysis and factor analysis using principal component analysis (PCA) were employed. To investigate all direct and indirect relationships between biological indices and different soil characteristics, path analysis (path analysis) was used.
Results and Discussion: Results showed significant positive relations between biological indices and clay, organic carbon and total nitrogen, whereas the correlations of the other soil properties (bulk density, silt, sand and CEC) were insignificant. Factor analysis using of principle component analysis showed that the behavior of these two biological indices in the same territory and controlled by the same factors. Path analysis was employed to study the relationship among soil biological indices and the other soil properties. According to results, soil nitrogen mineralization is more imposed by nitrogen (0.98) and organic carbon (0.91) properties as direct and indirect effects respectively. Whereas the values of soil microbial respiration were affected by organic carbon (0.89) and total nitrogen (0.81). It can be claimed that total nitrogen and organic carbon are the most important soil properties in relation to nitrogen mineralization and microbial respiration, respectively. Regarding to the strong relationship between soil organic carbon and nitrogen and also similarly strong relationship between nitrogen and organic carbon mineralization, enhancing nitrogen mineralization is expected by the increase in organic carbon. In this regard, Nourbakhsh, et al. (2002) claimed that nitrogen mineralization is depended to soil organic nitrogen and derived from total nitrogen. In addition, there is a strong relationship between total nitrogen and soil organic carbon. So, the greater amounts of nitrogen mineralization can be related to more accumulation of organic carbon and nitrogen in topsoil (23). This result is in accordance with Wood, et al. (1990) and Norton, et al. (2003) findings (21, 30). Ebrahimi, et al. (2005) stated that if the C/N ratio is more than 30, the process immobility or nitrogen mineralization stopwill be occurred. The ratios between 20 and 30 usually settle and release of mineral nitrogen does not take place, and the balance remains. If the C/N ratio is less than 20 net release of nitrogen in the soil will increase (9).In the present study, the values of soil C/N ratio were less than 20 (mean 15.80), so the process of nitrogen mineralization occurred in the study area. Suitable conditions for microbial activity of soil microorganism's especially adequate supply of organic carbon increased the microbial respiration in the study area. High correlation between the amount of organic carbon and microbial respiration confirmed this claim. However; it seems that the soil organic carbon is driver of microbial respiration rate. This finding is reported by different researchers (6, 7, 15, and 20).
Conclusion: Path analysis as a complementary method of regression analysis and factor analysis using principal component analysis showed that the biological activity of the soil characteristics are directly affected by soil nitrogen (for nitrogen mineralization index) and organic carbon (for microbial respiration index) and other useful features influence them indirectly through strong correlation with the characteristics of nitrogen and organic carbon in soil.
