سينتيك اكسايش آمونيوم در حضور بازدارنده نيترات سازي دي سيانو دي آميد در برخي از خاك هاي آهكي استان چهارمحال و بختياري

Ammonium Oxidation Kinetics in the Presence of Nitrification Inhibitor Dicyandiamide (DCD) in some Calcareous Soils of Chaharmahal va Bakhtiari Province

مطالعه سینتیك اكسایش آمونیوم در حضور بازدارنده نیترات سازی دی سیانو دی آمید (DCD) می تواند اطلاعات مفیدی را در اختیار كارشناسان بخش كشاورزی در رابطه با مدت زمان ماندگاری آمونیوم در خاك های مختلف قرار دهد. این تحقیق به منظور بررسی تاثیر كاربرد بازدارنده نیترات-سازی دی سیانودی آمید بر سینتیك اكسایش میكروبی آمونیوم انجام شد. این تحقیق به صورت فاكتوریل در قالب طرح كاملا تصادفی با دو عامل نوع كود نیتروژنه و نوع خاك در سه تكرار در شرایط آزمایشگاهی انجام شد. در این آزمایش نوع كود نیتروژنه شامل سه سطح بود كه عبارتند از: (1) عدم مصرف نیتروژن به عنوان شاهد، (2) مصرف نیتروژن از منبع اوره و (3) مصرف نیتروژن از منبع اوره با بازدارنده نیترات سازی دی سیانو دی آمید (DCD). عامل نوع خاك نیز شامل 5 نوع با ویژگی های فیزیكی و شیمیایی متفاوت بود. نتایج نشان داد معادله مرتبه اول در تمام تیمارهای آزمایشی قادر به توصیف سینتیك اكسایش آمونیوم بود. این بدین معنی است كه سرعت اكسایش آمونیوم در خاك تابع غلظت آن در خاك می باشد. همچنین در تمامی خاك های مورد مطالعه، شیب معادله مرتبه اول در تیمار اوره به همراه DCD در مقایسه با كاربرد اوره بدون بازدارنده كمتر بود. این بدین مفهوم است كه كاربرد بازدارنده نیترات سازی DCD روند اكسایش آمونیوم به نیترات را كند كرده است. كاربرد اوره به همراه DCD منجر به افزایش نیمه عمر آمونیوم در خاك در مقایسه با كاربرد این كود بدون بازدارنده در تمام خاك های مورد مطالعه شد. مقدار این افزایش در حضور DCD 8/34، 6/31، 1/31، 1/25 و 4/40 روز به ترتیب در خاك های شماره 1، 2، 3، 4 و 5 بود. بر اساس نتایج این پژوهش، كاربرد بازدارنده نیترات-سازی (DCD) با افزایش ماندگاری آمونیوم در خاك و بالعكس كاهش غلظت نیترات می تواند از نظر جنبه های كشاورزی و زیست محیطی قابل توجه باشد.

Introduction: Nitrification inhibitors (NIs) are compounds that retard the biological oxidation of ammonium to nitrite by depressing the activity of Nitrosomonas bacteria in the soil. Many popular NIs such as nitrapyrine (NP), dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) are produced and used in agricultural soils. Dicyandiamide is a very popular NI in some of the world countries. It delays nitrification process in the soil through its bacterial static property. It is easy to blend with commercial fertilizers such as urea, due to its low volatile nature. Application of urea in combination with nitrification inhibitor DCD lengthens nitrogen presence in soil as ammonium form. It has several beneficial effects for agriculture and enhances environmental protection. Studying the ammonium oxidation kinetics in the presence of nitrification inhibitor DCD can provide the experts in agriculture with very useful information regarding the ammoniumdurability in different soils. This research has been done to study the effect of using NI dicyandiamide on the kinetics of ammoniumloss in some calcareous soils of Chaharmahal Va Bakhtiari province, Iran. Materials and Methods: This research was conducted as factorial using completely randomized design with two factors of nitrogen fertilizer type and soil type with three replications at laboratory conditions. In this experiment, nitrogen fertilizer type included 2 levels of: 1- urea 2- urea plus nitrification inhibitor DCD (3.2%). A no added nitrogen fertilizer was considered as control treatment.The soil factor also consisted of 5different soils with a wide variation in soil physical and chemical characteristics. Five selected soils were non-saline (EC1:2=0.14-0.76 dS m-1) and alkaline (pH1:2=7.5-8.2). Organic carbon and cation exchange capacity (CEC) ranged from 0.48 to 2.34% and 10 to 30 cmolc kg-1, respectively. The dose of applied nitrogen in all experimental treatments was 50 mg kg-1 N as urea. Forty-five containers containing different soils were incubated at 20°C for 105 days. At 1, 7, 14, 21, 28, 35, 49, 63, 77, 91 and 105 days after adding urea and urea+DCD, soil subsamples were extracted to determine ammonium content. The ammonium concentration (extracted with 0.5 M K2SO4) was determined colourimetrically using a spectrophotometer at a wavelength of 667 nm. Then zero, first and second order equations were calibrated on the residual ammonium in the soil using SAS 8.02 and the best equation was seleted on the basis of coefficients of determination (R2) and standard error of the estimate (SE). In addition, ammonium half-time and nitrification inhibitor index were calculated. Results and Discussion: The results indicated that the first order equation was able to describe ammonium oxidation kinetics of the soil in all of the experimental treatments (control, urea and urea+DCD). The average values of R2 and SE of first order equationwere 0.915 and 1.51 in control, 0.903 and 4.98 in urea treatment and 0.863 and 4.92 in urea+DCD treatment, respectively. It means that ammonium oxidation kinetics is dependent on the ammonium concentration in soil. In all study soils, the slope of the first order equation in the urea treatment with DCD has been less in comparison to similar treatment but without NI. This may be explained by the fact that application of DCD has slowed down the process of ammonium oxidation to nitrite. The application of urea with DCD resulted in increase of ammonium half-life (calculated with first order equation) in the soil comparing to urea fertilizer without NI in all of the studied soils. The amount of this increase for DCD was 34.8, 31.6, 31.1, 25.1 and 40.4 days for the soils number of 1 2, 3, 4, and 5, respectively. Increasing the presence of ammonium in soil can be considerable for agricultural and environmental purposes. The maximum nitrification inhibitor indexes were 11.3% and 28.1% after 28 days of incubation in soils number 1 and 3, respectively. These nitrification inhibitor index values are in agreement with observations by other researchers. Conclusion: The results showed that nitrification inhibitor DCD is compound with a high capacity for extending ammonium presence in studying soils under conditions of this experiment. However, its efficiency was dependent to physical and chemical properties of soil.According to the results, first order equation was the best equation for describing ammonium oxidation kinetics in tested soils fertilized with urea and urea+DCD.