رفتار ویژگی‌های فیزیکی و شیمیایی خاک در برابر تغییر کاربری جنگل (مطالعه موردی: شهرستان خلخال در استان اردبیل)

تغییر کاربری جنگل‌ها و مراتع به کشاورزی، یکی از نگرانی‌های بزرگ جهانی در زمینه ی تخریب محیط‌زیست و تغییر اقلیم محسوب می‌شود و تغییرات غیرعلمی و ناآگاهانه ی کاربری اراضی اثرات منفی زیادی بر ویژگی‌های فیزیکی وشیمیایی خاک دارد؛ از این رو، در این پژوهش تاثیر تغییر کاربری اراضی بر برخی ویژگی‌های فیزیکی و شیمیایی خاک در اراضی جنگلی شمال شرق شهرستان خلخال با مساحت 270 هکتار ارزیابی شد. در هر کدام از سه کاربری جنگل، مرتع و زراعی، به‌طور تصادفی 30 محل نمونه (در مجموع 90 نمونه) تعیین و نمونه‌برداری سطحی از عمق 30 0 سانتی‌متر انجام شد. ویژگی‌های بافت، جرم ویژه ظاهری، کربن آلی، ازت کل، کربنات کلسیم معادل، هدایت الکتریکی، واکنش خاک اندازه‌گیری شده، تجزیه ی واریانس یک طرفه و مقایسه ی میانگین داده‌ها به روش دانکن صورت گرفت. میانگین شن، سیلت، کربن آلی، ازت کل و هدایت الکتریکی از کاربری جنگل به ترتیب81.30، 10.49، 6.32، 0.83 درصد و 1.34 دسی زیمنس بر متر بود که در مرتع به ترتیب به مقادیر 73.75، 16.88، 3.96، 0.64 درصد و 0.64 دسی زیمنس بر متر و در کاربری زراعی به ترتیب به 52.78، 21.07، 1.52، 0.31 درصد و 0.72 دسی زیمنس بر متر) کاهش معنی داری یافت. همچنین بین میانگین رس، جرم ویژه ظاهری، کربنات کلسیم معادل و واکنش خاک در دو کاربری جنگل و مرتع تفاوت معنی داری وجود نداشت، ولی با تغییر کاربری از جنگل به زراعی، میانگین این ویژگی‌ها افزایش معنی داری یافت. میانگین رس از مقدار 8.19 درصد در جنگل به 26.14 درصد در کاربری زراعی و میانگین جرم ویژه ظاهری از 1.36 گرم بر سانتی متر مکعب در جنگل به 1.59 گرم بر سانتی متر مکعب درکاربری زراعی تغییر یافت. پایین بودن جرم ویژه ظاهری در کاربری جنگل نسبت به زراعی را می‌توان به ماده آلی بالا در کاربری جنگل نسبت داد.

Behavior of Soil Physical and Chemical Properties against Forest landuse Change (Case Study: Khalkhal County, Ardabil Province)

Extended abstract1 IntroductionChanging the forests and pasture landuses to agricultural lands is one of the major global concerns about environmental degradation and climate change. As a result of the rangeland and forest changes into agricultural land and also tillage operations, about 430 million hectares, representing 30% of the world's total plowed land, are annually eroded and leaving the optimal production cycle at different countries. Nonscientific and unknowingly land use changes have negative effects on desirable physical and chemical properties of soil. However, these lands have low production potential on one hand and high erodibility potential on the other hand. In the past four centuries, about 30 percent of the world's forests and natural grasslands have changed to pastures of livestock and agricultural land. Such activities reduce the input of fresh plant residues into soil and result in significant changes in physical and chemical properties of the soil (Haghighi et al., 2010). Landuse changing leads to loss of soil organic carbon, reducing nutrient availability and maintenance, changing soil biological community, degradation of soil structure, decreasing soil permeability and hydraulic conductivity and increasing soil bulk density (Golchin Asghari, 2008). In addition, land use change and deforestation have increasingly increased CO2 that resulted in global warming and climate change in recent years.2 MethodologyThe study area is located in the forest lands of Andebil village, 5 km northeast of Khalkhal city. Khalkhal city is a suburb of Ardabil province and is about 110 kilometers far from Ardabil city. The study area covers an area of ​​about 270 hectares and includes three types of forest, pasture and agricultural land uses. The geological structure of the area is uniformly composed of sandy limestone from the Upper Mesozoic period. 30 samples were randomly taken from each landuse (90 sampling sites in total) and surface sampling from the depth 030 cm was performed. The geographical location of each sample was also recorded by GPS. Undisturbed (clod) and disturbed (with shovel) samples were prepared. The experimental design was completely randomized with forest, pasture and agricultural treatments and 30 replications (in total 90 samples). Analysis of variance and Duncan's post hoc test were performed using SPSS 16.0 software after normality test of data.3 ResultsThe effect of landuse on all the studied characteristics was significant (p <0.01). The percentage of sand in the three forest, pasture and agricultural landuses was significantly different. The highest average of sand was obtained in forest and the lowest amount was in agricultural use. A similar trend is observed for the significant decrease in silt mean in agricultural compared to the other two landuses. The mean of clay also shows the effect of landuse changes with a significant increase compared to other two landuses. forest and pasture samples mainly belong to the two texture classes of loamy sand and sandy loam, while agricultural samples include sandy loam, sandy clay loam and clay loam classes which are finer than the others. Bulk density was significantly increased in agricultural (1.59 g / cm3) compared to forest and pasture and there was no significant difference between forest and pasture landuse. The effect of landuse change on soil organic carbon content was significant. Comparison of the mean of this parameter in three landuses shows that the highest average of soil organic carbon was obtained in forestuse (6.32%) and the lowest (1.49%) in agricultural landuse. The amount of total soil nitrogen was significantly different at between different landuses. The highest amount of calcium carbonate (11.31%) was for agricultural use and the least (7.36%) was for forestuse. Soil EC in forest was significantly higher than pastures and agricultural landuse. The highest soil reaction (7.38) was related to agricultural use and the lowest (5.88) to forest use. The reason for the increase in soil pH in agricultural use should be the application of fertilizers and pesticides.4 Discussion ConclusionsThe result of this study showed that the landuse change affected the soil properties significantly. Changing the landuse of forest significantly resulted in increasing of silt, clay, bulk density, soil reaction and equivalent calcium carbonate) and a decreasing in the amount of sand, organic carbon, total nitrogen and electrical conductivity of the soil.Along with properties changing, soil qualities (which are a combination of two or more properties) are also affected by landuse changing. In most cases, landuse change has the same effects at different locations that are baring the soil surface, reducing soil permeability and ultimately speeding up surface water movement. The result of all this will be an increase in erosion in lands that once served as forest conservationists. Therefore attention to this issue can prevent the great risk of erosion threat.