Soil science
Niloofar Koosha; Kyumars Mohammadi Samani; Vahid Hosseini
Abstract
IntroductionA large part of forest and woodland ecosystems in Iran have been located in arid and semi-arid areas which low level of soil organic carbon (SOC) is considered as one of the main problems. Millions of trees together that make forest ecosystems, play a major role in carbon sequestration and ...
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IntroductionA large part of forest and woodland ecosystems in Iran have been located in arid and semi-arid areas which low level of soil organic carbon (SOC) is considered as one of the main problems. Millions of trees together that make forest ecosystems, play a major role in carbon sequestration and can sequester it in the form of biomass, above ground in plants and also underground in plants root or in the soil. Forest ecosystems play a significant role in absorbing and reducing greenhouse gases and therefore, can play a crucial role in decreasing global warming. Soil is one of the great sources of carbon storage, which plays a significant role in the atmospheric carbon deposition and dioxide gas. The carbon stored in the soil changes under some important driving factors such as: land use change, animal grazing, pollarding, exploitation (included forest harvesting), topography and forest trees, and types. One of the main sources of income for forest stakeholders in Zagros area is the Zagros oak forest. These people livelihoods are heavily dependent on natural resources, especially forest, known as a kind of traditional land use system called “Galazani”. Each family, in this system, has its own common ownership and manages their proprietorships called “Gallajar” which is a part of the woodlands and use some kind of traditional silvopastoral techniques to use these areas. Dominant livestock in the most part of theses area are goats and sheep. In the growing season, they usually feed on ground vegetation and in the winter time, they use dried oak leaves (leaf hay) that is stored before on some special trees call “Daar-Galla”. In the northern part of Zagros oak forest (Kurdistan province), there are some very special stands that are found around every village called sacred groves and are totally intact because of some spiritual values and taboos. There are no exploitation and grazing and even land use changing in these areas, and they show the real undisturbed forest lands in Zagros. The aim of this research was to study and compare soil carbon stock and some essential soil properties in sacred groves and pollarded forests (Gallajar) of northern Zagros forests in order to obtain more precise data in soil after high exploitation and pollarding.Materials and MethodsThe average annual rainfall in 25 recent years in the study is 690 mm and the average annual temperature is 14.2 degrees Celsius. The dominant trees species in the region are Lebanon oak, Aleppo oak and Persian oak. To conduct this investigation, three study areas included both sacred groves and Gallajars, in three main slope aspects including north, east and south facing aspects, were chosen. Then six plots (10 a) were randomly selected in each area and tree canopy (%) and litter percentage were determined in the field. Soil samples took in two depths (0-15 and 15-30 cm) in the center of each plots and then bulk density (BD) and some chemical soil properties included soil organic carbon, soil carbon stock, total nitrogen (N), phosphorus (P), potassium (K), electrical conductivity (EC) and pH were measured in the soil laboratory. A factorial randomized complete block design was used to analysis soil data.Results and DiscussionThe results showed that there were significant differences between soil depths for studied soil properties except BD, N and K and also there were significant differences in various slope aspects in studied parameters. However, no such a trend was observed in soil N and EC. The results also revealed that pollarding had significant effects on all studied soil properties. In addition, all studied soil properties including SOC stock, N, P, K and EC in sacred groves was higher than Gallajars while pH and BD were increased in pollarded areas. The amount of SOC stock, N, P and EC were greater at depth 0-15 compared to depth of 0-15 cm while, pH showed lower amount in the surface soil layer and K and BD had no significant differences in the two studied soil layers. SOC stock in northern, eastern and southern slope aspect were 72.6, 48.2 and 45 tons/ha, respectively. Pollarding and livestock grazing in Gallajars caused a significant decrease in tree canopy and, as a result, the litters on the grounds also reduced. Therefore, it seems that the reduction of trees and canopy cover affected soil properties significantly and reduced SOC stock meaningfully in the long term. Other essential chemical soil properties were also lower in Galajars compared to sacred groves.ConclusionFinally, we can claim that, some factors including pollarding and grazing can significantly reduce SOC stock and other studied soil properties in this research. On the one hand, people are using these forest areas as grazing pastures and also for pollarding trees to fed their livestock and the government could not have convinced them not to pollard the trees and, on the other hand, the results in this study showed that these pollarding operations are affecting forest stands and forest soil chemical properties and SOC stock significantly and reduce their quality considerably. It can be suggested that some new management treatments should be done in these forest areas through the training of local people, preparing sufficient fodder resources and providing enough facilities by the government to reduce pollarding by stakeholders. As a result, the natural process of production and decomposition of organic matter may be controlled in a better way, so that, the soil quality and carbon storage in these forests to be improved in the long term.
hossein dehghani; Hamidreza Haji Agha Bozorgi; ali asghar ghaemi
Abstract
Introduction: Creating a uniform and adequate moisture in the root zone is one of the most challenging issues in irrigated lands. Use of irrigation systems with high water efficiency, such as sub-surface drip irrigation is recommended as a solution to reduce water losses. Information on soil ...
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Introduction: Creating a uniform and adequate moisture in the root zone is one of the most challenging issues in irrigated lands. Use of irrigation systems with high water efficiency, such as sub-surface drip irrigation is recommended as a solution to reduce water losses. Information on soil moisture variation is an important factor for managing and designing a subsurface drip irrigation system. This study was conducted to evaluate the soil moisture variation for different irrigation regimes in a pistachio orchards equipped by a subsurface drip irrigation system (SDI).
Materials and Methods: This study was carried out in a two-hectare of 10 years old pistachio orchard located in Semnan province, Iran ( located at 35°28ˊ N, 53°12ˊE and elevation of 1160 m above sea level) during the 2012-2013 growing season. The climate of the studied area is hot desert having an average annual precipitation of approximately 110 mm. Daily meteorological data such as the temperature, relative humidity, wind speed, rainfall, and solar radiation were collected from a meteorology station in farm. The soil was sandy loam textured with average field capacity and permanent wilting point of 12.23 and 5.01%, respectively. Subsurface drip irrigation system was equipped by EuroDrip Company emitters (PC2), inline, to a distance of 80 cm and with a discharge of 26.2 Lit/ hr installed at a depth of 40 cm. In this study, a factorial experiment in split plot design was used with three replications. Three irrigation treatments i.e. control (I1), Irrigation based on irrigation requirement (I2) and I2 plus leaching requirement (I3), and changes in the moisture front were investigated by weight sampling between two drip lines, between the trees rows, on the drip line and out of the drip line of each row, before and after irrigation and in development, middle and late season.
Results and Discussion: For the evaluated irrigation systems, increased levels of irrigation regime resulted in increased moisture content in the root zone. The higher average soil moisture (16.6 %) was measured after irrigation under I3. The I1 irrigation regime did not significantly change the soil moisture content in upper part of emitters before and after irrigation event. Average soil moisture content at different depths showed that the soil moisture content in 75 soil depth was significantly higher than that in 25 and 50 cm soil depth, which can be attributed to higher root water uptake by root in 0-50 cm soil depth. Bilateral impact of irrigation regimes and soil depth showed higher soil moisture content (19.3%) under I3 and 75 cm soil depth which may lead to deep percolation. Bilateral impact of irrigation regimes, soil depth, and time before and after irrigation event also resulted in higher soil moisture content (22.5 %) in 75 cm soil depth after irrigation under I3. The lowest soil water content (10.5 %) was measured in 25 soil depth before irrigation under I1.
Conclusion: The results of this study showed that I2 and I3 irrigation regimes did not show water shortage during growth season (before and after irrigation), but the I1 irrigation regime caused water scarcity. Therefore, the formation of continuous moisture profiles with low moisture in I1 irrigation regime was caused as a result of low irrigation during this period. Accumulation of moisture at depth of 50-75 cm from the soil surface, even under low irrigation conditions I1 irrigation regime, implies that irrigation time is not suitable for irrigation regimes. In general, in order to improve the irrigation management, it is necessary to reduce the irrigation intervals and have a more appropriate distribution of moisture in the soil profile.
A. Mehnatkesh; S. Ayoubi; A. Jalalian
Abstract
Introduction: Soil depth is defined as the depth from the surface to more-or-less consolidated material and can be considered as the most crucial soil indicator, affecting desertification and degradation in disturbed ecosystems. Soil depth varies as a function of many different factors, including slope, ...
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Introduction: Soil depth is defined as the depth from the surface to more-or-less consolidated material and can be considered as the most crucial soil indicator, affecting desertification and degradation in disturbed ecosystems. Soil depth varies as a function of many different factors, including slope, land use, curvature, parent material, weathering rate, climate, vegetation cover, upslope contributing area, and lithology. Topography, one of the major soil forming factors, controls various soil properties. Thus, quantitative information on the topographic attributes has been applied in the form of digital terrain models (DTMs). The prediction of soil depth by topographic attributes depends mainly on: i) the spatial scale of topographic variation in the area, ii) the nature of the processes that are responsible for spatial variation in soil depth, and iii) the degree to which terrain-soil relationships have been disturbed by human activities. This study was conducted to explore the relationships of soil depth with topographic attributes in a hilly region of western Iran.
Materials and Methods: The study area is located at Koohrang district between 32°20′ to 32°30′ N latitudes and 50°14′ to 50°24′ E longitudes, in Charmahal and Bakhtiari province, western Iran. The field sites with an area of 30,000 ha are located on the hillslopes at about 20% transversal slope. The soils at the site are classified as Typic Calcixerepts, Typic Xerorthents and Calcic Haploxerepts for the representative excavated profiles in summit, shoulder and backslope, respectively. The soils located at footslope and toeslope were classified as Chromic Calcixererts. Measurements were made in twenty representative hillslopes of the studied area. At the selected site, one hundred points were selected using randomly stratified methodology, considering all geomorphic surfaces including summit, shoulder, backslope, footslope and toeslope during sampling. Overall, 100 profiles were dug and described; and the solum thickness was measured for each profile. DEM data were created by using a 1:2,5000 topographic map. Topographical indices were generated from the DEM using TAS software. Terrain attributes in two categories, primary and secondary (compound) attributes; primary attributes are included elevation, slope, aspect, catchment area, dispersal area, plan curvature, profile curvature, tangential curvature, shaded relief. Secondary or compound attributes such as soil water content or the potential for sheet erosion, stream power index, wetness index, and sediment transport index. Correlation coefficients to define relationships between soil depth and terrain attributes, and analysis of variance by Duncan test were done using the SPSS software. The statistical software SPSS was used for developing multiple linear regression models. Terrain attributes were selected as the independent variables and soil depth was employed as dependent variable in the model. Thirty sampling sites were used to validate the developed soil-landscape model. In testing soil-landscape model, we calculated two indices from the observed and predicted values included mean error (ME) and root mean square error (RMSE).
Results and Discussion: The soil depth in the studied profiles varied from 30 cm to 150 cm with an average of 108.6 cm. Relatively high variability (CV = 76%) was obtained for soil depth in the study area. The linear correlation analysis of the 12 topographic attributes and one soil property (soil depth), showed that there was a significant correlation among 36 of the 77 attribute pairs. Soil depth showed high positive significant correlations with catchment area, plan curvature, and wetness index, and showed high negative correlation with sediment transport index, sediment power index and slope. Low positive significant correlations of soil depth were identified with tangential curvature, and profile curvature. Moreover, soil depth was negatively correlated with elevation. The rest of the topographic attributes including aspect, shaded relief, and dispersal area were not significantly correlated with soil depth. Many of these relationships are similar to those found in other landscapes. The results of analysis of variance showed that there are significant differences for soil depth among the selected slope positions in the studied area. The highest values of soil depth were observed in the downslope positions including footslope and toeslope. The lowest soil depth was observed in shoulder position with the highest rate of soil erosion.
Conclusions: It seems that the high variability for soil depth depends on topography of the field, and the landscape position, causing differential accumulation of water at different positions on the landscape; and moreover the soil erosion and deposition processes, resulting in high variability in the soil depth. We found relatively high correlation coefficients of soil depth with two groups of topographic attributes (erosional processes and water accumulation). Empirical model (MLR) using selected terrain attributes explains 76% of the variation of soil depth in the studied area. The terrain attributes that best predicted soil depth variability in the selected site were mainly the attributes that had significant relationships with soil depth. The dominant attributes in the MLR model included slope, wetness index, catchment area and sediment transport index.
