اثر كرم خاكي بر سرعت نيتريفيكاسيون و آمونيفيكاسيون آرژينين در يك خاك آهكي تيمار شده با لجن فاضلاب شهري

Earthworm Effects on Nitrification Rate and Arginine Amonification in a Calcareous Soil Amended with Urban Sewage Sludge

كرم های خاكی یكی از مهم ترین جانوران خاك بوده و فعالیت آنها از شاخص های كیفی خاك به شمار می رود. این جانداران ممكن است تحت تأثیر افزودن پسماندهای آلی قرار گیرند. یكی از روش های سریع و آسان برای پایش كیفیت خاك در هنگام كاربرد لجن فاضلاب، استفاده از شاخص های زیستی از جمله فعالیت های میكروبی است. هدف این پژوهش ارزیابی اثر كرم خاكی بر سرعت نیتریفیكاسیون و آمونیفیكاسیون آرژینین به عنوان فعالیت میكروبی در خاك های تیمارشده با لجن فاضلاب شهری بود. تیمارهای آزمایش شامل لجن فاضلاب (بدون لجن و دارای 5/1 درصد لجن شهری)، و كرم خاكی (بدون كرم، آیزنیافتیدا، آلولوبوفورا كالیژینوزا و مخلوط این دو گونه) به صورت فاكتوریل (4×2) در قالب طرح كاملاً تصادفی با سه تكرار بودند. لجن فاضلاب سرعت نیتریفیكاسیون و آمونیفیكاسیون آرژینین را به ترتیب به میزان 7/16 و 5/62 درصد افزایش داد كه دلیل آن بالا بودن میزان مواد آلی و عناصر غذایی و همچنین غلظت پایین فلزات سنگین در پسماند آلی به كار برده شده می‌باشد. تلقیح كرم خاكی نیز این دو شاخص را تحت تأثیر قرار داد (001/0 >p). به طور خلاصه، مصرف لجن فاضلاب شهری اثر تحریك كنندگی كرم خاكی را بر فعالیت میكروبی خاك كاهش داد كه این كاهش در حضور گونه ی آیزنیافتیدا (اپی ژئیك) به دلیل تغذیه از لجن فاضلاب محسوس تر بود. علاوه بر این، اثر متقابل دو گونه ی كرم خاكی اغلب جمع پذیر (بدون اثر متقابل) بود.

Introduction: Earthworms are among the most important organisms in soil and their activities can be an indicator of soil quality. These organisms may be influenced by organic wastes application such as sewage sludge and subsequently affect soil quality. One of the quick and easy methods for soil quality monitoring is the use of biological indicators such as microbial activity. It is due to their quick response to changes in the environment. The purpose of this study was to evaluate the effect of earthworms on nitrification rate and arginine ammonification as microbial activity in a calcareous soil amended with urban sewage sludge. Materials and Methods: The studied soil was sampled from Shahrekord University land and sewage sludge belonged to the refinery sludge ponds of shahrekord. Based on dry weight, this organic waste had carbon and nitrogen, approximately 67 and 110 times more than tested soil, respectively. The organic waste in terms of quality and heavy metal concentrations was in class A. Experimental treatments were sewage sludge (without and with 1.5% sewage sludge) and earthworm (no earthworm, Eiseniafoetida from epigeic group, Allolobophracaliginosa from endogeic group and a mixture of the two species) as 2×4 full factorial experiment arranged in a completely randomized design with three replications. After applying sewage sludge, the pots were irrigated three months to achieve a balance in the soil. An adult earthworm per kg of soil was added and in the mixed treatments comparison species were 1:1. To prevent the exit of earthworms, the pots was closed with a thin lace. At the end of the experiment, soil was completely mixed. Part of it was stored in the refrigerator to measure the microbiological parameters. Chemical properties were measured by the air-dried soil. The effectiveness of a factor in the observed changes is shown by partial effect size (Tabachnick and Fidell 2012). So, partial effect size (Eta2p) for each source of variation (SS, earthworm and SS×earthworm) was calculated. Results Discussion: According to Eta2p, the role of sewage sludge application to increase total nitrogen was almost twice the earthworm and had a greater effect on the property. Because of low concentrations of heavy metals and high nutrient in sewage sludge, it increased nitrification rate and arginine ammonification by 16.7 and 62.5 percent, respectively. Considering that the indices represent microbial biomass activity, so we can say sewage sludge application increased theri activities. Sewage sludge application increased total nitrogen, because provided the substrate for heterotrophic bacteria. Consequently, ammonium production improved and stimulated activity of Nitrosomonas and Nitrobacter. There was a positive and significant correlation between total nitrogen, arginine ammonification and nitrification rate, that confirmed the occurrence of this process. Earthworm inoculation affected these two indicators (p <0.001). In the earthworm gut, ammonificators and nitrificators increased. With application of sewage sludge, A. caliginosa has greater effect than E. foetida. Rising food source of microbial community in the presence of sewage sludge increased microbial biomass and subsequently the intensity of A. caliginosa feeding. So, microbial activity was more stimulated. For this reason, the effect of A. caliginosa on arginine ammonification was more impressive in soil treated with sewage sludge. Eiseniafoetida and A. caliginosa improved nitrification rate in soil un-treated sewage sludge to the 152 and 97.7 percent, respectively. However, increases in the soil treated sewage sludge were in order 57.7 and 95.8 percent, repectively. Sewage sludge application decreased earthworm effects on stimulation of the index. The reason for reducing the influence of earthworms in sewage sludge was the increase of available substrate. As a result, using the urban sewage sludge decreased the stimulatory effect of earthworms. Because of feeding from the sewage sludge, this decrease in the presence of Eiseniafoetida (Epigeic) was more tangible. In addition, the interaction of two species of earthworms was often additive (without interaction). Conclusion: According to the results, we can say that use of sewage sludge with a composition similar to what was used in this study, improve microbial activity such as ammonification and nitrification, and finally, soil nitrogen dynamics. Although earthworm activity also increased the indices, the stimulator of earthworms on biomarkers in the presence of sewage sludge decreased. This event was due to increasing availablability substrates. In addition, sewage sludge application during the study was not alarming of environmental pollution due to the low concentration of heavy metals. However, it seems that the implemention of a long-term research is necessary.