پديد آورندگان :
پادياب، جواد دانشگاه محقق اردبيلي - دانشكده ي كشاورزي و منابع طبيعي - گروه علوم و مهندسي خاك، اردبيل , عباسي كلو، آيدا دانشگاه محقق اردبيلي - دانشكده ي كشاورزي و منابع طبيعي - گروه علوم و مهندسي خاك، اردبيل , كيوان بهجو، فرشاد دانشگاه محقق اردبيلي - دانشكده ي كشاورزي و منابع طبيعي - گروه منابع طبيعي، اردبيل
كليدواژه :
كاربري جنگل , خلخال , كاربري زراعي , كاربري مرتع , كيفيات خاك
چكيده فارسي :
تغيير كاربري جنگل‌ها و مراتع به كشاورزي، يكي از نگراني‌هاي بزرگ جهاني در زمينه ي تخريب محيط‌زيست و تغيير اقليم محسوب مي‌شود و تغييرات غيرعلمي و ناآگاهانه ي كاربري اراضي اثرات منفي زيادي بر ويژگي‌هاي فيزيكي و شيميايي خاك دارد؛ از اين رو، در اين پژوهش تأثير تغيير كاربري اراضي بر برخي ويژگي‌هاي فيزيكي و شيميايي خاك در اراضي جنگلي شمال شرق شهرستان خلخال با مساحت 270 هكتار ارزيابي شد. در هر كدام از سه كاربري جنگل، مرتع و زراعي، به‌طور تصادفي 30 محل نمونه (در مجموع 90 نمونه) تعيين و نمونه‌برداري سطحي از عمق 30 -0 سانتيمتر انجام شد. ويژگي‌هاي بافت، جرم ويژه ظاهري، كربن آلي، ازت كل، كربنات كلسيم معادل، هدايت الكتريكي، واكنش خاك اندازه‌گيري شده، تجزيه ي واريانس يكطرفه و مقايسه ي ميانگين داده‌ها به روش دانكن صورت گرفت. ميانگين شن، سيلت، كربن آلي، ازت كل و هدايت الكتريكي از كاربري جنگل به ترتيب 81/30، 10/49، 6/32، 0/83 درصد و 1/34 دسي زيمنس بر متر بود كه در مرتع به ترتيب به مقادير 73/57، 16/88، 3/96، 0/64 درصد و 0/64 دسي زيمنس بر متر و در كاربري زراعي به ترتيب به 52/78، 21/07، 1/52، 0/31 درصد و 0/72 دسي زيمنس بر متر) كاهش معني داري يافت. همچنين بين ميانگين رس، جرم ويژه ظاهري، كربنات كلسيم معادل و واكنش خاك در دو كاربري جنگل و مرتع تفاوت معنيداري وجود نداشت، ولي با تغيير كاربري از جنگل به زراعي، ميانگين اين ويژگي‌ها افزايش معني داري يافت. ميانگين رس از مقدار 8/19 درصد در جنگل به 26/14 درصد در كاربري زراعي و ميانگين جرم ويژه ظاهري از 1/36 گرم بر سانتيمتر مكعب در جنگل به 1/59 گرم بر سانتيمتر مكعب دركاربري زراعي تغيير يافت. پايين بودن جرم ويژه ظاهري در كاربري جنگل نسبت به زراعي را مي‌توان به ماده آلي بالا در كاربري جنگل نسبت داد.
چكيده لاتين :
1- Introduction
Changing 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. Non-scientific 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- Methodology
The 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 0-30
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- Results
The 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 & Conclusions
The 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.
