اثر تغییر کاربری اراضی بر برخی ویژگی های فیزیکوشیمیایی و زیستی خاک منطقه‌ سروک، شهرستان یاسوج

تغییر کاربری اراضی از قبیل تغییر جنگل به اراضی تحت کشت به طور معنی‌د‌اری می‌تواند بر خصوصیات خاک تاثیر گذاشته و فرآیندهای تشکیل خاک را تحت تاثیر قرار دهد. از آن‏جایی که تغییر کاربری جنگل‌های زاگرس روند رو به رشدی دارد، به منظور بررسی اثرات این تغییر کاربری‌ها بر ویژگی های فیزیکوشیمیایی و زیستی خاک در منطقه سروک شهرستان یاسوج، از سه کاربری جنگل متراکم، جنگل تخریب شده و زراعت دیم، 5 نمونه خاک سطحی (20-0 سانتی‌متر) برداشت و پژوهش در قالب طرح کاملاً تصادفی انجام شد. آزمایش‌های فیزیکی، شیمیایی و زیستی بر روی نمونه های خاک انجام شد. نتایج تجزیه واریانس و مقایسه میانگین داده‌های به دست آمده از سه کاربری نشان داد که به دنبال تغییر کاربری اراضی جنگلی، مقادیر هدایت الکتریکی (40 درصد)، ماده‌ آلی (74 درصد)، نیتروژن کل (75 درصد)، پتاسیم قابل دسترس (49 درصد)، تنفس پایه (76 درصد)، تنفس برانگیخته (74 درصد)، جمعیت قارچ (11 درصد)، آنزیم های اسید فسفاتاز (55 درصد) و آلکالین فسفاتاز (47 درصد) در کاربری زراعی کاهش یافتند. این در حالی است که جمعیت باکتری در کاربری زراعی افزایش یافت (8 درصد). مقدار فسفر قابل جذب تفاوت معنی‌داری را نشان نداد. به طور کلی می‌توان چنین نتیجه گرفت که در پی تخریب جنگل و تغییر کاربری، ماده آلی خاک و شاخص های مرتبط با آن به خصوص ویژگی‌های زیستی به میزان بیشتری تحت تاثیر قرار گرفته اند.

Effect of Land Use Change on some Physicochemical and Biological Properties of the Soils of Servak Plain, Yasouj Region

Introduction: Land use changes such as conversion of forest to cultivated lands, significantly affect soil properties and modify soil forming processes. Land use changes can drastically affect the soil environment, which in turn markedly affect soils and soil processes. Human activities that are not associated with proper planning have undesirable effects on natural resources such as soil, including land use change. The results of the investigations in different parts of the world show that changing the use of natural ecosystems to managed ecosystems has destructive effects on soil properties. Cutting off the forest trees and converting pastures into agricultural lands will destroy or disrupt natural ecosystems and reduce the current or future production capacity of the soil. One of the important issues in the world is the destructive effects of agriculture on soil quality. These destructive effects can include a wide range of soil changes including physical properties such as soil compaction, soil water depletion, soil structure destruction and soil texture change, chemical properties such as accumulation of some elements such as N, P, K, and soil salinity, and soil biological properties such as soil microbial population and soil fauna activity changes, soil organic matter reduction and also effect on useful soil enzymes. Land use change from forest to agriculture does not necessarily lead to soil degradation. Land use changes and forest destruction in Yasouj region has increased in last decades. In this study, we investigated the effects of land use change on some soil characteristics in Servak plain, Yasouj region. Materials and Methods: Servak region is located in 4 km south of Yasouj city. Three main land uses of dense forest, degraded forest, and dry farming were chosen to study the role of land use change on some soil properties.. The elevation of the region varies from 1833 to 1869 m above sea level. Five soil samples (020 cm) were taken from each land use. Samples from each land use were taken from almost similar elevation and slope to minimize the effect of topography. Soil samples were transferred to the laboratory, air dried and passed through a 2mm sieve. The chemical and biological analyses were carried out. The determination of soil organic carbon was carried out based on the WalkleyBlack chromic acid wet oxidation method. Available K was extracted with 1N ammonium acetate at pH=7 and was determined by flame photometry. The Olsen method was used for the determination of available phosphorus. Total nitrogen was measured using the Kjeldahl method. Soil bacterial communities were counted using culture medium (Nutrient agar. The basal respiration rate was estimated by backtitration of the unreacted NaOH to determine CO2 evolved over 10 h. The substrateinduced respiration was measured by adding 2 ml of 1% glucose to soil samples over 6 h. Soil suspensions were prepared by 10fold serial dilutions with 1g soil. Counting the soil fungal community was done using a culture medium (Potato dextrose agar) and was prepared by 10fold serial dilutions. The activity of alkaline and acid phosphate enzymes was measured based on a colorimetric method using pnitrophenol. Results and Discussion: The land use change from a dense forest to dry farming has modified many chemical and biological soil properties. The results of analysis of variance and comparison of the means of data obtained from this study showed that as a result of land use change from dense forest to dry farming, Organic matter, total nitrogen, exchangeable potassium, basal and substrateinduced respiration, fungal community, acid phosphatase and alkaline phosphatase enzymes contents were decreased. Also, soil bacterial communities were increased at 1% level in dry farming land use. The amounts of phosphorus did not show any significant difference. In general, it can be concluded that following the degradation of the forest and land use change, the soil organic matter and relevant properties, especially biological indices, are more affected compared to the other properties. Soil organic matter plays a key role in ensuring agroecosystem productivity and the longterm conservation of soil resources. Conclusions: Largescale conversion of indigenous forests to cultivated land, driven by longterm agricultural development in the Servak region, has greatly affected the physicochemical and biological properties of the soils. Generally, the conversion of the natural ecosystem to agroecosystems decreased organic carbon content and relevant indices such as basal and substrateinduced respiration, fungal community, acid phosphatase and alkaline phosphatase enzymes contents in the topsoils at depth of 0 to 20 cm. The decrease of organic carbon in cropped farms could be attributed to the enhanced oxidation of soil organic C caused by cultivation. The results of this study showed that any management and type of land use that decreases soil capabilities can reduce soil quality and increase the susceptibility to degradation. So, in order to maintain soil quality, appropriate management practices should be done.