تاثیر افزودن ماده آلی بر انتخابگری تبادل کاتیونی پتاسیم-کلسیم در خاک آهکی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 ﮔﺮوه ﻋﻠﻮم و ﻣﻬﻨﺪﺳﯽ ﺧﺎک، داﻧﺸﮑﺪه علوم ﮐﺸﺎورزی، داﻧﺸﮕﺎه ﮔﯿﻼن، رﺷﺖ، اﯾﺮان

2 ﮔﺮوه ﻋﻠﻮم و ﻣﻬﻨﺪﺳﯽ ﺧﺎک، داﻧﺸﮑﺪه علوم ﮐﺸﺎورزی، داﻧﺸﮕﺎه ﮔﯿﻼن، رشت، ایران

چکیده

ماده آلی ‌از مهم‌ترین عوامل موثر بر ویژگی‌های خاک بوده و درک تاثیر آن بر انتخاب­گری کاتیون‌های پتاسیم و کلسیم می‌تواند به مدیریت این دو عنصر ضروری کمک نماید. در این پژوهش تاثیر افزودن ماده آلی بر انتخابگری کاتیون‌های پتاسیم و کلسیم در خاک با کانی‌شناسی غالب ایلایت در سیستم تبادلی دوتایی بررسی شد. کود دامی به میزان 2 درصد به خاک افزوده و سپس خاک برای مدت 10 ماه در آزمایشگاه نگهداری شد. آزمایش در قدرت یونی 1/0 مولار و با استفاده از محلول‌هایی با اجزای هم‌ ارز پتاسیم (ẼK) و کلسیم (ẼCa) بین 0 و 1 انجام شد. سپس ضرایب انتخابگری ونسلو (KV)، گاپون (KG) و دیویس (KD, n=2, 4, 6) و پارامترهای ترمودینامیکی با استفاده از داده‌های تبادلی در دو حالت با و بدون در نظر گرفتن اثر انحلال کربنات کلسیم بر مقدار کلسیم تبادلی محاسبه شدند. مقایسه همدماهای تبادلی  K-Caبا همدمای عدم ترجیح (NP) نشان داد که در خاک اولیه و تیمار شده تا 8/0ẼK≃، پتاسیم به کلسیم و سپس در ẼK‌ های بالاتر کلسیم به پتاسیم ترجیح داده می‌شود. با افزایش جزء هم‌ارز پتاسیم در فاز تبادلی (EK) تمامی ضرایب انتخابگری افزایش یافت که نشان‌دهنده این است که این ضرایب ثابت‌های تعادلی واقعی واکنش نیستند. ثابت تعادل (Kex) کوچک‌تر از 1 و تغییرات انرژی آزاد استاندارد واکنش (ΔG°ex) مثبت بود که نشان‌دهنده ترجیح خاک برای پتاسیم نسبت به کلسیم بود. همچنین، پس از افزودن ماده آلی، Kex افزایش و ΔG°ex کاهش یافت که گویای کاهش ترجیح خاک برای پتاسیم پس از افزودن ماده آلی است. علاوه ‌بر ‌‌این، نتایج این پژوهش نشان داد که اصلاح اثر انحلال کربنات کلسیم بر مقدار کلسیم تبادلی در خاک‌های آهکی اثر قابل توجهی بر ضرایب انتخابگری و پارامترهای ترمودینامیکی تبادل دارد که این امر لزوم توجه به انحلال کانی‌های کلسیم‌دار خاک را در حین مطالعات تبادلی آشکار می‌نماید.

کلیدواژه‌ها


عنوان مقاله [English]

The Effect of Organic Matter on Potassium-Calcium Cation Exchange Selectivity in a Calcareous Soil

نویسندگان [English]

  • Narjes Babaei Kasmaei 1
  • Maryam Khalili Rad 1
  • Mahmood Fazeli Sangani 2
1 Department of Soil Science, Faculty of Agriculture, University of Guilan, Rasht, Iran
2 Department of Soil Science, Faculty of Agriculture, University of Guilan, Rasht, Iran
چکیده [English]

Organic matter is one of the most important factors affecting soil properties, and understanding its effect on potassium and calcium selectivity can help the management of these two essential nutrients. This study examined the effect of organic matter on potassium and calcium selectivity in a binary exchange system in soil with dominant illite mineralogy. Organic matter was added to soil at a rate of 2%, and then the soil was incubated for ten months. The experiment was performed at an ionic strength of 0.1 M using solutions with a different equivalent fractions of potassium (ẼK) and calcium (ẼCa) between 0 and 1. Then Vanselow (KV), Gapon (KG) and Davis (KD, n = 2, 4, 6) selectivity coefficients and thermodynamic parameters including exchange equilibrium constant (Kex) and free energy changes of the exchange reaction (ΔG°ex) were calculated using exchange data with and without considering the effect of calcium carbonate dissolution on exchangeable calcium values. Comparison of K-Ca exchange isotherms with non-preference isotherm (NP) showed that potassium was preferred over calcium up to ẼK≃0.8, before and after adding organic matter, however at higher ẼK, calcium was preferentially selected. All selectivity coefficients increased with increasing equivalent fraction of potassium in the exchange phase (EK), which indicates that these selectivity coefficients are not true equilibrium constants. Moreover, Kex was less than 1, and ΔG°ex was positive, indicating a preference for potassium over calcium by soil. Also, after the addition of organic matter Kex, increased, and ΔG°ex decreased, indicating a decrease in soil preference for potassium. In addition, results showed that considering the effect of calcium carbonate dissolution on exchangeable calcium value has a significant impact on selectivity coefficients and thermodynamic parameters of exchange in calcareous soil. This highlights the need to pay attention to the dissolution of calcium-containing minerals in the soil during exchange studies.

کلیدواژه‌ها [English]

  • Illite
  • Thermodynamic equilibrium constant
  • Selectivity coefficients
  • organic matter
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