پديد آورندگان :
فرپور محمد هادي نويسنده دانشكده كشاورزي,گروه علوم و مهندسي خاك,دانشگاه شهيد باهنر كرمان,كرمان,ايران
كليدواژه :
پارامترهاي مغناطيسي , ايران مركزي , زمين زراعي , مرتع , مغناطيس خاك
چكيده فارسي :
ویژگی¬های مغناطیسی خاك¬ بازتابی از برهمكنش¬های پیچیده شیمیایی، زمین¬شناسی و زیستی موجود در آن می‌باشد. بنابراین، آگاهی از عوامل موثر بر پذیرفتاری مغناطیسی خاك به درك و تفسیر هرچه بهتر نتایج كمك می¬كند. هدف از انجام این مطالعه، بررسی اثر كاربری¬های مختلف و نوع پوشش گیاهی بر میزان پذیرفتاری مغناطیسی در خاك¬های سطحی و ارتباط بین مقادیر آنها با ویژگی¬های خاك بود. چهار نوع كاربری شامل زراعی، مرتع پوشش¬دار، مرتع تخریب¬شده و دیم¬رهاشده در منطقه مطالعاتی انتخاب شد كه دارای شرایط اقلیمی، توپوگرافی و مواد مادری مشابه و تا حد امكان نزدیك به یكدیگر بودند. در مجموع 60 نمونه مركب خاك سطحی (15-0 سانتی¬متر) برداشت گردید. میانگین میزان lfᵡ در نمونه¬های خاك سطحی m3 kg-110-8× 8/695 محاسبه گردید. تجزیه و تحلیل¬ آماری نتایج حاكی از وجود تفاوت معنی¬دار در سطح احتمال 5 درصد بین میانگین مقادیر lfᵡ در كاربری¬های مختلف بود. مقدار میانگین lfᵡ اندازه گیری شده به ترتیب در مرتع با پوشش مناسب، مرتع تخریب¬شده، دیم رهاشده و زراعی كاهش یافت. مقادیر محاسبه شده fdᵡ در محدوده (73/1-52/0 %) نشان¬دهنده حضور ذرات چند حوزه¬ای به ارث رسیده از مواد¬ مادری آذرین به عنوان منشاء اصلی پذیرفتاری مغناطیسی در منطقه مطالعاتی بود. تغییرات اكثر ویژگی¬های اندازه¬گیری شده خاك در كاربری¬های مختلف از لحاظ آماری معنی-دار گردید. همبستگی مثبت و معنی¬داری بین داده¬های پذیرفتاری مغناطیسی و درصد شن وجود داشت. در حالی كه میان داده¬های پذیرفتاری مغناطیسی، سیلت و كربنات¬كلسیم همبستگی منفی و معنی¬دار مشاهده گردید. نتایج نشان داد كه نوع كاربری و پوشش¬گیاهی با تاثیر بر ویژگی¬ها و فرآیندهای تشكیل خاك، می¬تواند تشكیل و تجمع كانی‌های مغناطیسی خاك را تحت تاثیر قرار دهد.
چكيده لاتين :
Introduction: Soil magnetic properties reflect the complex chemical, geological and biological interactions occur in the soil. Thus, knowledge about the factors affecting soil magnetic properties helps better understanding and interpreting the results.. The lithogenic magnetic minerals are often found in the coarse soil fractions (sand and silt) and they have inherited from parent rocks. Weathering and soil formation factors may lead increasing or decreasing of magnetic susceptibility. Climate and vegetation type are among the other factors affecting magnetic susceptibility too. Amount and distribution of magnetic susceptibility may also be affected by land use. The main objective of this research was to study the effect of different land uses and vegetation types on the magnetic susceptibility of topsoil related to soil properties.
Materials and methods: The study area was located in MahoonakeZiba around the Bardsir region, Kerman Province. The moisture and temperature regimes of the study area were sub aridic and mesic, respectively. The study area is located in the alluvial plain with igneous parent material originated from andesite, volcanic tuff, anddacite. Four land uses including farmland, well-covered pasture, disturbed pasture and degraded dryland farm with similar climate, topography, and parent material were selected. Overall, 60 complex surface samples were collected from the depth of 0-15 cm. The physicochemical analyses were done on the samples after that the soils were air dried, crushed, and passed through a 2 mm sieve. The soils magnetic susceptibility (ᵡ) in low (0.46 kHz) and high (4.6 kHz) frequencies were measured using the Bartington MS2 dual frequency sensor in two replications. The frequency depended magnetic susceptibility (ᵡfd %) was calculated as a development index of soil forming factors reflecting ferrimagnetic particle sizes.
Results and discussion: The pH of studied soils were in the range of neutral to alkaline and had the lowest coefficient of variance between measured parameters. The average of soil EC was 1.76 dS/m with a high coefficient of variance. The lowest amount of organic matter was in land use ofdegraded drylandfarm (0.26 %) and the highest was in farmland (2.15 %). The lowest amount of calcium carbonate with the coefficient of variance 12.37 % measured in the degraded pasture and its maximum was in the farmland. The loamy sand and sandy loam textural classes were found in the area under study. The minimum and maximum amounts ofᵡlf were determined in farmland (134.8× 10-8 m3 kg-1)and well-coveredpasture (1778.9 ×10-8 m3 kg-1 ), respectively and the relatively high mean value was 695.83 × 10-8 m3 kg-1. The topsoil of the study area was formed on alluvial deposits with a parent material originated from igneous andesite, tuff and dacite rocks. The high values of magnetic susceptibility of all soils under study could be attributed to the existence of initial magnetic minerals inherited from the parent material. The statistical analysis revealed a significant difference among ᵡlf values (p <0.05). The average measured ᵡlf values decreased in the order of well-covered pasture, disturbed pasture, degraded dryland farm, and farmland. The cultivated soils showed significantly lower magnetic susceptibility values compared to natural vegetative land uses. The type of irrigation water and fertilization could have affected calcium carbonate and salt contents of soils. The lower amounts of magnetic susceptibility observed in soils were attributed to the higher amounts of calcium carbonate and salts. It seems that irrigation has led to decrease of soil wetting-drying periods which in turn decreased transformation of nonmagnetic to magnetic forms of minerals. The calculated ᵡfd in the range of 0.52 to 1.73 percent indicated the presence of multidomain particles induced from igneous parent materials as the main source of magnetic susceptibility in the studied area. The variability of most measured soil properties determined in different land uses was statistically significant. There was a significant positive correlation between magnetic susceptibility and sand content. On the other hand, a significant negative correlation among magnetic susceptibility, silt and calcium carbonate contents were observed. Besides, the kind of vegetation cover affects the amount of soil magnetic susceptibility. In the well-covered pasture, the vegetation is usually C4 type. While, the farmland soils were usually covered by C3 plants including wheat, barley, and alfalfa. According to human-induced erosion and over grazing in degraded pasture and dryland, very scarce vegetation was found. Therefore, it seems that C4 plants present in soils of well-covered pasture played a role in increasing the topsoil magnetic susceptibility in this land use.
Conclusion: The results showed that, type of land use and vegetation cover have caused the formation and accumulation of soil magnetic minerals by affecting soil forming processes and changing the soil properties.
