تأثير كاربري اراضي بر جمعيت ميكروبي خاك و تغييرپذيري مكاني آنها در اراضي ميرآباد، نقده

Effect of Land Uses on Soil Microbial Community and Spatial Variability in Mirabad Lands, Naghadeh

فهم بیولوژی و اكولوژی خاك به¬طور فزاینده¬ای برای تجدید و پایداری اكوسیستم مهم است. در تمام اكوسیستم¬ها، میكروب¬های خاك نقش مهمی در تجزیه مواد آلی، چرخه مواد غذایی و فراهمی عناصر غذایی قابل جذب گیاه ایفا می¬كنند. هدف از این تحقیق، بررسی تغییرپذیری مكانی و پهنه‌بندی جمعیت میكروبی خاك، كربن آلی و كربنات كلسیم معادل خاك متأثر از كاربری‌های اراضی شامل باغ سیب، مرتع و زراعت می‌باشد. بدین منظور، از منطقه میرآباد مابین شهرهای نقده و اشنویه (استان آذربایجان غربی) 65 نمونه خاك سطحی (30-0 سانتی‌متری) برداشته شد. آزمون نرمال بودن توزیع داده‌ها توسط برنامه آماری SPSS انجام گرفت. مقادیر نقاط نمونه‌برداری نشده با استفاده از روش‌های كریجینگ و وزن‌دهی معكوس فاصله‌ها در نرم‌افزار زمین‌آمار (+GS) میان‌یابی شد. نتایج نشان داد روش كریجینگ بهترین روش میان‌یابی نقاط نمونه‌برداری نشده می‌باشد. وابستگی مكانی جمعیت میكروبی خاك متوسط بوده و این امر نشان‌دهنده تأثیر كاربری بر توزیع مكانی ویژگی‌های‌ مذكور می‌باشد. نتایج به‌دست آمده از تحلیل آماری توسط برنامه MSTATC در قالب طرح بلوك‌های كامل تصادفی (RCBD) نیز بیان كننده تفاوت معنی‌دار در بین سه كاربری از نظر ویژگی‌های مطالعه شده است. نقشه‌های توزیع مكانی با تلفیق نتایج حاصل از زمین‌آمار و GIS تهیه شدند.

Introduction: Understanding soil biology and ecology is increasingly important for renewing and sustainability of ecosystems. In all ecosystems, soil microbes play an important role in organic matter turnover, nutrient cycling and availability of nutrients for plants. Different scenarios of land use may affect soil biological properties. Advanced information technologies in modern software tools such as spatial geostatistics and geographical information system (GIS) enable the integration of large and complex databases, models, tools and techniques, and are proposed to improve the process of soil quality and sustainability. Spatial distribution of chemical and biological properties under three scenarios of land use was assessed. Materials and Methods: This study was carried out in Mirabad area located in the western part of Souldoz plain surrounded by Urmieh, Miandoab, Piranshahr and Naghadeh cities in the west Azerbaijan province with latitude and longitude of 36°59′N and 45°18′E, respectively. The altitude varies from 1310 to 1345 with average of 1325 m above sea level. The monthly average temperature ranges from -1.4 °C in January to 24.6 °C in July and monthly precipitation ranges from 0.9 mm in July to 106.6 mm in March. Apple orchard, crop production field and rich pasture are three selected scenarios in this research work. Soil samples were systematically collected at 65 sampling points (0-30 cm) on mid July 2010. Soil chemical and biological properties i.e. microbial community, organic carbon and calcium carbonate equivalent were determined. The ArcGIS Geostatistical Analyst tool was applied for assessing and mapping the spatial variability of measured properties. The experimental design was randomized complete blocks design (RCBD) with five replications. Two widely applied methods i.e. Kriging and Inverse Distance Weighed (IDW) were employed for interpolation. According to the ratio of nugget variance to sill of the best variogram model three following spatial dependence conditions for the soil properties can be considered: (I) if this ratio is less than 25%, then the variable has strong spatial dependence; (II) if the ratio is between 25% and 75%, the variable has moderate spatial dependence; and (III) otherwise, the variable has weak spatial dependence. Data were also integrated with GIS for creating digital soil biological maps after testing analysis and interpolating the mentioned properties. Results and Discussion: Spherical model was the best isotropic model fitted to variograms of all examined properties. The value of statistics (R2 and reduced sum of squares (RSS)) revealed that IDW method estimated calcium carbonate equivalent more reliably while organic carbon and microbial community was estimated more accurately by Kriging method. The minimum effective range (6110 m) was found for microbial community which had the strong spatial dependence [(Co/Co+C) <25]. The highest amount of estimated microbial community was scattered in the north-east of study area. On contrary, organic carbon and calcium carbonate equivalent was mainly mapped in the center of study area mostly with land use of rich pasture. Land use change from pasture to crop production and apple orchard increases soil aeration and also decreases organic matter content. Therefore, it may be involved in climate change challenge. As soil management in particular at harvest stage influences other soil biological properties especially enzyme activities, assessing enzymes activity under different scenarios of land use is hence recommended. Conclusion: The geostatistical results showed that the management practices may have relevantly effects on microbial community, but the statistical analysis revealed significant differences between pasture and two other land uses. The created maps were classified to five subdivisions, while for better explanation of land use effects on soil biological indices and their spatial variability, the digital maps must be classified to many subdivisions.