توزيع شكلهاي شيميايي منگنز و ارتباط آن با قابليت استفاده گياهان تحت تاثير لئونارديت (Leonardite)

Distribution of Manganese Chemical Forms and its Relationship to the Availability of Plants Affected by Leonardite

سابقه و هدف: تامين عناصر غذايي كم مصرف در بهبود فرايندهاي بيولوژيكي گياهان ضروري است. مقادير كل عناصر در خاك شاخص مناسبي از قابليت استفاده براي گياهان نمي باشد و اغلب بصورت شكل‌هاي غيرقابل جذب حضور دارند. مواد هوميكي مي تواند شكل‌هاي شيميايي عناصر در خاك را تغيير دهد. لذا اين تحقيق با هدف بررسي تاثير لئونارديت در تغيير شكل‌هاي شيميايي منگنز در خاك‌هاي زراعي انجام شد. مواد و روشها تعداد 20 نمونه خاك زراعي از عمق 30-0 سانتيمتري از مزارع شهرستان اروميه برداشت شد. برخي از ويژگي‌هاي فيزيكوشيميايي به روش‌هاي استاندارد، منگنز قابل استفاده به روش DTPA و كاني شناسي رس (20) اندازه گيري شدند (21). طيف FT-IR لئونارديت جهت تعيين گروههاي عاملي بررسي شد. بررسي هاي آزمايشگاهي بصورت فاكتوريل در قالب طرح پايه كاملا تصادفي در سه تكرار انجام شد. چهار نمونه خاك متفاوت انتخاب شده و با استفاده از MnSO4.H2O با غلظت 200 ميلي گرم در كيلوگرم منگنز تيمار شد و به مدت دو ماه در رطوبت ظرفيت مزرعه‌اي نگهداري شدند. بعد از انكوباسيون سطوح مختلفي از لئونارديت (0، 2 و 4 درصد) اضافه شد. منگنز قابل استفاده و شكلهاي شيميايي آن پس از گذشت 20، 90 و 120 روز با استفاده از روش DTPA و عصاره گيري متوالي (32) اندازه گيري شد. يافته ها نتايج نشان داد كه كميت و كيفيت كاني‌هاي رس متفاوت بود و كاني غالب خاك‌هاي مورد مطالعه ايليت بود. نتايج نشان داد كه لئونارديت داراي گروه‌هاي عاملي مختلف بوده و تاثير معني دار در افزايش ميزان منگنز قابل استفاده گياه داشت .

Background and Objectives: Supply of micronutrients is necessary for the improvement of plant biological processes. The total amount of elements in soil is not an appropriate indicator for plant availability, because main portion of nutrients are usually as unavailable forms. Humic substances can change the chemical forms of elements in soil. Therefore, this study was done to investigate the influence of humic substance on changes of chemical forms of manganese (Mn) in some cultivated soils of Urmia region. Materials and Methods: Twenty soil samples were collected of 0-30 cm from the fields of Urmia region. Some physicochemical properties of soils were measured by standard methods. DTPA extractable Mn and clay mineralogy of soils were also determined. FT-IR spectra were analyzed to determine the functional groups of leonardite. Laboratory evaluations were carried out as a factorial in a completely randomized design with three replications. Four different soil samples were selected and were treated by 200 mg kg-1 MnSO4.H2O and were incubated for two months at field capacity moisture. Different levels of leonardite (0, 2 and 4%) were added after incubation. Laboratory evaluations were carried out as a factorial in a completely randomized design with three replications. The concentration and chemical forms of the Mn were evaluated using DTPA and sequential extraction Tessier method respectively after 20, 60 and 120 days. Results: The results showed that the quality and quantity of the clay minerals were different and the illite mineral was dominant in the studied soils. Results showed that the leonardite have different functional groups and showed significant effect on increasing plant available Mn (P<0.001). Also, leonardite application increased the amount of Mn extractable with DTPA solution. The results showed that more than 76-85% of Mn (exchangeable, carbonate-, Fe-Mn oxides-, organic matter-bonded) was extracted in a sequences extraction method. In addition, a large part of Mn was absorbed in the oxide form (more than 50%) and lowest value in the exchange form (less than 0.1%). Effect of leonardite on increasing Mn availability was decreased as a calcium carbonate increased in soil. As, the highest Mn available (4.5 ppm) obtained in the Ordushahi soil with the least amount of calcium carbonate was observed. Analysis variance showed that the main effects of soil, leonardite and their interactions were significant in changing chemical forms of Mn (P<0.001). The exchangeable, carbonate and organic carbon forms of Mn increased significantly (0.01) as leonardite treatment. As well as a significant decrease (4.5-11.6%) in the section related to Fe-Mn oxides were observed. Conclusion: The results showed that the leonardite can to changes the chemical forms of elements to improve adsorption of nutrient for plants. In addition, a positive significant correlation was observed between the amount of Mn extractable with DTPA solution and chemical forms of Mn. The effect of contact time was significant on Mn availability and extracted of high Mnwith increasing the incubation time. The effect of 4% Leonardite treatment was more than 2%. Accordingly, the use of leonardite is suitable to increase of productivity and supply micronutrients and can be used as biodegradable materials in improving the quality and quantity of agricultural products.