نوع مقاله : مقالات پژوهشی
نویسندگان
1 دانشگاه گنبد کاووس
2 دانشگاه کردستان
چکیده
کربن آلی خاک بر توان بالقوه خاک، امنیت غذایی، تخریب خاک و گرمایش جهانی تأثیر زیادی دارد. بنابراین، شناخت توزیع مکانی و زمانی کربن آلی خاک در ارزیابی کیفیت خاک، مدیریت کشاورزی، مدل سازی حوزه های آبخیز و ترسیب کربن خاک ضروری است. در این پژوهش، برای تعیین تغییرپذیری کربن آلی خاک حوزه آبخیز الیگودرز استان لرستان از روش های آماری و زمین آماری استفاده گردید. افزون بر این، اثر ارتفاع، درجه شیب و نوع کاربری اراضی بر غلظت کربن آلی خاک نیز بررسی شد. نتایج نشان داد که ریشه مربعات غلظت کربن آلی خاک از توزیع نرمال پیروی کرده، میانگین حسابی و هندسی داده های اندازه گیری شده نیز به ترتیب معادل 81/0 و 73/0 درصد می باشد. مناسب ترین مدل برازش شده بر نیم-تغییرنمای تجربی کربن آلی خاک مدل نمایی بود. بررسی نسبت اثر قطعه‌ای به آستانه نشان داد که کربن آلی خاک در حوزه آبخیز مورد مطالعه دارای وابستگی مکانی متوسطی است. ارزیابی توزیع مکانی غلظت کربن آلی خاک با روش کریجینگ نشان داد که بیشتر سطح حوزه آبخیز الیگودرز (حدود 87 درصد) دارای مقدار کربن آلی خاک کمتر از 1 درصد می‌باشد. همچنین نتایج نشان داد که کربن آلی خاک به صورت معنی داری با ارتفاع و درصد شیب دارای همبستگی منفی است (به ترتیب r = -0.265** و r= -0.217**). افزون بر این، نتایج نشان داد که در کاربری های مختلف اراضی مقدار کربن آلی خاک متفاوت است. بیشترین مقدار کربن آلی خاک در اراضی آبی و کمترین مقدار آن در اراضی مرتعی مشاهده گردید.
کلیدواژه‌ها
عنوان مقاله [English]
Geostatistical Analyses of Soil Organic Carbon Concentrations in Aligodarz Watershed, Lorestan Province
نویسندگان [English]
- hojjat ghorbani vaghei 1
- M. Davari 2
1
2 University of Kurdistan
چکیده [English]
Introduction: Soil organic carbon (SOC) has great impacts on soil properties, soil productivity, food security, land degradation and global warming. Similar to other soil properties, SOC has a strong spatial heterogeneity as a result of dynamic interactions between parent material, climate and geological history, at both regional and continental scales. However, landscape attributes including slope, aspect, altitude, and land use types are dominant factors influencing on SOC in areas with the same parent materials and climate regime. Understanding and identifying the spatial and temporal distribution of SOC is essential to evaluate soil quality, agricultural management, watershed modeling and soil carbon sequestration budgets. Therefore, the objectives of this study was to estimate soil organic carbon content in the Aligodarz watershed, and to investigate the effects of altitude, slope, and land use type on SOC.
Materials and Methods: The research was carried out in the Aligodraz watershed in Lorestan province of Iran. The study area is located between latitudes N 33° 10' 51.72"to N 33° 34' 28.22" and longitudes E 49° 27' 17.99"to E 49° 58' 40.84" 14 that covers an area of 1078.9 km2. It has an altitude between 1866.3 and 3200 m above sea-level. The primary land uses within the watershed include pasture, dryland and irrigated farming. In this study, soil samples were randomly collected from 206 sites at depth of 0– 15 cm during June and August 2003. The mean distance between samples was about 5 km. Soil samples were air-dried in the shade for about 7 days and then passed through a 0.25 mm prior to determination of SOC. Soil organic carbon content was determined in triplicate for each sample using the Walkey-Black method. Basic statistical analyses for frequency distribution, normality tests, Pearson's correlation and analysis of variance were conducted using SPSS (version 18.0). Calculation of experimental variograms and modeling of spatial distribution of SOC were carried out with the geostatistical software GS+ (version 5. 1). Maps were generated by using ILWIS (version 3.3) GIS software.
Results and Discussion: The results revealed that the raw SOC data have a long tail towards higher concentrations, whereas that squareroot transformed data can be satisfactorily modelled by a normal distribution. The probability distribution of SOC appeared to be positively skewed and have a positive kurtosis. The square root transformed data showed small skewness and kurtosis, and passed the K–S normality test at a significance level of higher than 0.05. Therefore, the square root transformed data of SOC was used for analyses. The SOC concentration varied from 0.08 to 2.39%, with an arithmetic mean of 0.81% and geometric mean of 0.73%. The coefficient of variation (CV), as an index of overall variability of SOC, was 44.49%. According to the classification system presented by Nielson and Bouma (1985), a variable is moderately varying if the CV is between 10% and 100%. Therefore, the content of SOC in the Aligodarz watershed can be considered to be in moderate variability. The experimental variogram of SOC was fitted by an exponential model. The values of the range, nugget, sill, and nugget/sill ratio of the best-fitted model were 6.80 km, 0.058, 0.133, and 43.6%, respectively. The positive nugget value can be explained by sampling error, short range variability, and unexplained and inherent variability. The nugget/sill ratio of 43.6% showed a moderate spatial dependence of SOC in the study area. The parameters of the exponential smivariogram model were used for kriging method to produce a spatial distribution map of SOC in the study area. The interpolated values ranged between 0.30 and 1.40%. Southern and central parts of this study area have the highest SOC concentrations, while the northern parts have the lowest concentrations of SOC. Kriging results also showed that the major parts of the Aligodarz watershed (about 87%) have statistically SOC content less than 1%. Lower SOC concentrations were associated with high altitude (r = −0.265**). The results of Pearson correlation analysis showed that soil organic carbon content has a significantly negative correlatiton with slope gradient (r = −0.217**). The results also indicated that the SOC content was variable for the different land use types. The irrigated lands had the highest SOC concentrations, while the pasture lands had the lowest SOC values.
Conclusion: The square-root transformed data of SOC in Aligodarz watershed of Lorestan province, Iran, followed a normal distribution, with an arithmetic mean of 0.81%, and geometric mean of 0.73%. The coefficient of variation and nugget/sill ratio revealed a moderate spatial dependence of SOC in the study area. The results indicated that the major parts of the Aligodarz watershed have SOC content less than 1%. The land use type had a significant effect on the spatial variability of SOC and that lower SOC concentrations were associated with higher altitude and slope gradients. The irrigated and pasture lands had the highest and lowest SOC concentrations, respectively.
کلیدواژه‌ها [English]
- Exponential model
- Kriging
- Semivariogram
- Spatial variability
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