بررسی اثر کیفیت بقایای گیاهی بر روند معدنی شدن نیتروژن در خاک در شرایط رطوبتی متفاوت

نوع مقاله : علمی - پژوهشی

نویسندگان

دانشگاه فردوسی مشهد

چکیده

به‌منظور بررسی روند تغییرات نیتروژن معدنی در خاک و چگونگی تأثیرپذیری آن از میزان رطوبت خاک و کیفیت بقایای گیاهی اضافه شده، تحقیقی در دانشکده کشاورزی دانشگاه فردوسی مشهد در قالب طرح اسپلیت پلات در زمان بر پایه طرح کاملاً تصادفی با سه تکرار به اجراء درآمد. بقایای گیاهی شامل گندم (Triticum aestivum L.)، کلزا (Brassica napus L.)، ذرت (Zea mays L.)، سویا (Glycin max L.) و پنبه (Gossypium hirsutum L.) بود و از خاک بدون بقایا نیز به عنوان شاهد استفاده شد. رطوبت خاک شامل سه سطح30، 60 و 100 درصد ظرفیت زراعی بود. در این مطالعه از روش کیسه لاشبرگ استفاده شد و نمونه‌برداری در طی زمان با فواصل 10، 20، 50، 90، 140، 190، 240، 290، 340 و 390 روز پس از شروع آزمایش صورت گرفت. نتایج نشان داد که کیفیت بقایا تأثیر به‌سزایی بر میزان نیتروژن معدنی خاک داشت و افزودن بقایای گیاهی سبب غیرمتحرک شدن آن شد. همچنین نیتروژن معدنی در خاک دارای بقایای گیاهی در ابتدای آزمایش (50-10 روز اول بسته به نوع بقایا) کاهش و سپس افزایش یافت. میزان غیرمتحرک شدن نیتروژن در خاک دارای بقایای گندم و پنبه (با نسبت کربن به نیتروژن بالاتر) بیش از بقایای سایر گیاهان بود. در هیچ یک از خاک‌های دارای بقایای گیاهی، معدنی شدن خالص نیتروژن مشاهده نگردید و بالاترین میزان نیتروژن معدنی مربوط به خاک شاهد بدون بقایا بود. رطوبت خاک نیز به عنوان یکی از عوامل مهم تعیین‌کننده میزان تجزیه بقایا و فعالیت زیست‌توده میکروبی، معدنی شدن نیتروژن را تحت تأثیر قرار داد، به نحوی‌که با افزایش رطوبت خاک میزان نیتروژن معدنی نیز افزایش نشان داد.

کلیدواژه‌ها


عنوان مقاله [English]

Net Nitrogen Mineralization as Affected by Residue Quality and Soil Moisture

نویسندگان [English]

  • z Boroumand Rezazadeh
  • A Koocheki
  • P Rezvani Moghaddam
  • M Nassiri Mahallati
  • A Lakzian
چکیده [English]

Introduction
Soil organic matter is one of the main sources of carbon, nitrogen, phosphorus and sulfur and the agronomic value of organic materials depends on their nitrogen release. Nitrogen dynamics varies considerably depending on soil properties (e.g. soil texture and moisture content), residue location (incorporation or surface placement residues) and intrinsic characteristics of residues, especially carbon to nitrogen ratio. The presence of carbonaceous compounds easily accessible by microorganisms increases organic nitrogen mineralization whereas more recalcitrant organic residues with large amounts of lignin reduce nitrogen release. Nitrogen content of residue which is rich in N releases and accumulates in soil during decomposition. Considerable portion of nitrogen content of non-leguminous residues harvested at green stage, with C/N ratio lower than 25, might be also released when the residues are incorporated into the soil.
Material and Methods
In order to study the nitrogen mineralization patterns of residues with different qualities and soil moisture contents, an experiment was conducted at Faculty of Agriculture, Ferdowsi university of Mashhad as slit-plot in time arrangement based on a completely randomized design with three replications. Five mature plant residues including wheat (Triticum aestivum L.), oilseed rape (Brassica napus L.), maize (Zea mays L.), soybean (Glycine max L.) and cotton (Gossypium hirsutum L.) were used. Un-amended soil was considered as control. Soil moisture consisted of three levels of 30, 60 and 100 percentage of field capacity. Litterbag method was used and sampling was conducted in 10, 20, 50, 90, 140, 190, 240, 290, 340 and 390 days after incubation (25°C and darkness) to measure mineral nitrogen. Net cumulative N mineralized was calculated as the difference between mineral nitrogen in each sampling and at day 0 and net N mineralization rate was defined as mineralized nitrogen divided by incubation period. Data analysis was performed using Minitab 16. Means were compared by Duncansʼ test at a significance level of 0.05.
Results and Discussion
Results indicated that soil mineral nitrogen was almost the same in all three levels of soil moisture in early day of the experiment and increased during incubation period. Mineral nitrogen was significantly affected by residue quality and soil moisture content. Soil moisture as a key factor in residue decomposition and microbial biomass activity affected nitrogen mineralization as the highest (59.9 mg.kg-1) and lowest (26.9 mg.kg-1) mineral nitrogen was found in soil moisture content of 100 and 30% FC, respectively. Net cumulative N mineralized was increased in un-amended control soil during the incubation period and reached to 61 mg.kg-1 in day 390 but a different trend was observed in amended soils. In these treatments mineral nitrogen changes had two distinct phases: the first phase included mineral nitrogen immobilization and the intensity and duration of this phase was related to residue type and especially their initial nitrogen content. The second phase lasted to the end of the incubation period, included nitrogen mineralization. Soil amendment with plant residue led to soil nitrogen immobilization. The highest immobilization was observed in soils containing wheat (-7 mg.kg-1) and cotton (-5.2 mg.kg-1) residues (containing high carbon to nitrogen ratio). No net N mineralization was found in amended soils. The highest net N mineralization rate was found in control followed by soils amended with soybean residues (0.14 mg.kg-1.d-1) and the lowest in soils amended with wheat and cotton.
Conclusion
Results of the present study indicated that the net N mineralization rate and soil mineral nitrogen was significantly affected by residue quality and residues with higher nitrogen content led to nitrogen immobilization. Soil moisture also played an important role in nitrogen mineralization as higher mineral nitrogen was found in soils with higher moisture content.

کلیدواژه‌ها [English]

  • C:N Ratio
  • Field capacity
  • Immobilization
  • Litterbag
  • Net Cumulative-N Mineralized
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