تعیین حدود بهینه شاخص‌های منحنی توزیع اندازه منافذ خاک

نوع مقاله : مقالات پژوهشی

نویسنده

• مهدی زنگی آبادی

بخش تحقیقات خاک و آب، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی خراسان‌رضوی، سازمان تحقیقات، آموزش و ترویج کشاورزی، مشهد، ایران

10.22067/jsw.2023.83150.1300

چکیده

منحنی توزیع اندازه منافذ خاک و استفاده از حدود بهینه شاخص­های موقعیت و شکل این منحنی می­تواند به‌عنوان ابزاری برای بررسی و ارزیابی کیفیت فیزیکی خاک استفاده گردد. پژوهش حاضر در اراضی ایستگاه تحقیقات کشاورزی و منابع طبیعی طرق واقع در جنوب شرقی شهر مشهد با هدف تعیین حدود بهینه شاخص­های منحنی توزیع اندازه منافذ با استفاده از شاخص کیفیت فیزیکی خاک انجام شد. از 30 نقطه در قسمت­های مختلف ایستگاه با بافت و ساختمان متفاوت نمونه خاک تهیه و آزمایشات صحرایی و آزمایشگاهی لازم برای تعیین و محاسبه 35 ویژگی فیزیکی خاک انجام شد. شاخص عددی کیفیت فیزیکی خاک در قالب انتخاب مهم­ترین ویژگی­ها با استفاده از تجزیه مؤلفه­های اصلی، وزن­دهی و امتیازدهی آنها محاسبه و از آن به‌عنوان معیاری جهت دسته­بندی خاک­های مورد مطالعه در چهار کلاس کیفیت خاک استفاده شد. خاک­های کلاس یک با بیشترین کیفیت فیزیکی ملاک تعیین حدود بهینه شاخص­های موقعیت و شکل منحنی توزیع اندازه منافذ خاک قرار گرفت. نتایج نشان داد که خاک­های با بیشترین کیفیت فیزیکی نسبی، دارای منافذ با میانگین اندازه بزرگتر و تنوع اندازه کمتر از مقادیر بهینه ارائه شده در منابع می­باشند. در این مطالعه حدود بهینه شاخص­های موقعیت منحنی توزیع اندازه منافذ شامل میانگین، میانه و مد اندازه منافذ به‌ترتیب 7-2، 16-5 و 92-29 میکرومتر و شاخص­های شکل شامل انحراف معیار، کشیدگی و افراشتگی منحنی به‌ترتیب 81-22 میکرومتر، (33/0-)-(38/0-) و 15/1-14/1 تعیین گردید. استفاده از نتایج این مطالعه به‌منظور ارزیابی و مقایسه کیفیت فیزیکی خاک­های با بافت متوسط و سبک در مناطق با اقلیم نیمه­خشک ایران توصیه می­گردد.

کلیدواژه‌ها

• شاخص های شکل
• شاخص های موقعیت
• کیفیت فیزیکی خاک

موضوعات

• علوم خاک

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عنوان مقاله [English]

Determination of the Optimal Ranges for Soil Pore Size Distribution Curve Parameters

نویسنده [English]

• Mehdi Zangiabadi

Soil and Water Research Department, Khorasan-Razavi Agricultural and Natural Resources Research and Education Center, AREEO, Mashhad, Iran

چکیده [English]

Introduction
Soil pore size distribution curve and using the optimal ranges of the location and shape parameters of this curve can be used to evaluate the soil physical quality. This research was carried out in an area of about 220 hectares of Torogh Agricultural and Natural Resources Research and Education Station, to determine the optimal ranges for soil pore size distribution curve parameters using the soil physical quality index. Different soil textures and the diversity in soil properties are the distinct features of this research station.
 
Materials and Methods
Torogh Agricultural and Natural Resources Research and Education Station of Khorasan-Razavi province, with a semiarid climate, is located in south-east of Mashhad city. For the field measurements and laboratory analysis to determine the soil physical properties and indices, 30 points with different soil textures and structures were selected. Intact soil cores (5 cm diameter by 5.3 cm length) and disturbed soil samples were collected from 0-30 cm depth of each point. After the laboratory analysis and field measurements, 35 soil physical properties were measured and calculated. Soil particle size distribution and five size classes of sand particles, soil bulk, and particle density, dry aggregates mean weight diameter (MWD) and stability index (SI), soil moisture release curve (SMRC) parameters, S-index, soil porosity (POR) and air capacity (AC), soil pore size distribution (SPSD) curves, relative field capacity (RFC), plant available water measured in matric pressure heads of 100 and 330 hPa for the field capacity (PAW₁₀₀ and PAW₃₃₀), least limiting water range measured in matric pressure heads of 100 and 330 hPa for the field capacity (LLWR₁₀₀ and LLWR₃₃₀), integral water capacity (IWC) and integral energy (EI) of different soil water ranges, were the soil physical properties and indices which were determined in this study. Three parameters of modal, median, and mean pore sizes of the SPSD curves were considered as the location (central tendency), and three parameters of standard deviation, skewness, and kurtosis of the SPSD curves were considered as the shape parameters. Selection of the most important soil physical characteristics using principal component analysis (PCA) method by JMP software (ver. 9.02), weighting and scoring of the selected characteristics using PCA and scoring functions, respectively, and the summation of multiplied characteristics weights by their scores for each soil sample, were the four steps of calculation of the 0-1 value of soil physical quality index (SPQI). Soil samples were classified into four soil physical quality classes by SPQI values. The soils of the first class with the highest SPQIs (> 0.78) were considered to determine the optimal ranges of SPSD curves location and shape parameters.
 
Results and Discussion
The texture of soil samples were loam (40 %), silt loam (23 %), silty clay loam (17 %), clay loam (13 %), and sandy loam (7 %). Soil organic carbon was between 0.26-1.05 (%), and the average soil bulk density was 1.45 (gr.cm^-3). The MWD values of studied soil samples were between 0.94-2.88 (mm), an average of 1.93 (mm). The average modal, median, and mean pore sizes as the location parameters of the SPSD curves were 60.3 (μm), 12.4 (μm), and 6.5 (μm), respectively. The average of standard deviation, skewness, and kurtosis as the shape parameters of the SPSD curves were 71.56 (μm), -0.36 and 1.15, respectively. The average modal pore sizes showed that the pores with a size of 60 (μm) had the highest frequency in soil samples. The range of calculated standard deviation of SPSD curves, along with the difference between the minimum and maximum mean pore sizes (24.6 μm), implied the diversity of pore sizes in the studied soils. The results of PCA showed that the four soil physical properties of PAW₃₃₀ (0.1-0.2 cm³.cm^-3), POR_t (0.40-0.51 cm³.cm^-3), LLWR₁₀₀ (0.12-0.22 cm³.cm^-3) and SI (0.76-2.61 %) accounted for about 88% of the variance between soil samples and were selected to calculate the SPQIs. The PAW₃₃₀, POR_t, LLWR₁₀₀, and SI were entered into the calculation of SPQIs with weights of 0.46, 0.31, 0.15, and 0.08, respectively. All the selected physical properties were scored using the scoring function of more is better. The maximum and minimum values of SPQIs for the studied soils were 0.84 and 0.14, respectively. Five soil samples with SPQIs greater than 0.78 were classified as class 1 with the highest physical quality. The ranges between the minimum and maximum values of the SPSD curves, location, and shape parameters of these five soils were proposed as the optimal ranges. In this regard, the ranges of 29-92 (μm), 5-16 (μm), and 2-7 (μm) were suggested for optimal ranges of modal, median, and mean pore sizes, respectively. The optimal ranges of standard deviation, skewness, and kurtosis of the SPSD curves were proposed as 22-81 (μm), (-0.38)-(-0.33), and 1.14-1.15, respectively.
 
Conclusion
The optimal ranges of SPSD curves location and shape parameters suggested in the literature may probably not apply to a wide range of agricultural soils. They must be evaluated in a more extensive range of land uses, soil management, and soil textures. In this research, the soils with the relatively higher physical quality had larger mean pore size and less SPSD curves standard deviation (less diversity of pore size) than the optimal ranges suggested in the literature. The optimal ranges of SPSD curves location and shape parameters proposed in this research are appropriate for medium to coarse-textured soils of regions with the semiarid climate in Iran.

کلیدواژه‌ها [English]

• Location parameters
• Shape parameters
• Soil physical quality

©2023 The author(s). This is an open access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source.

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