بررسي تأثير پساب فاضلاب شهري بر برخي ويژگيهاي هيدروليکي خاک
محورهای موضوعی : مدیریت آب در مزرعه با هدف بهبود شاخص های مدیریتی آبیاری
محسن دهقانی
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پریسا مشایخی
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1 - استاديار، بخش تحقيقات خاک و آب مرکز تحقيقات و آموزش کشاورزي و منابع طبيعي استان اصفهان، سازمان تحقيقات آموزش و ترويج کشاورزي اصفهان، ايران.
2 - استاديار، بخش تحقيقات خاک و آب مرکز تحقيقات و آموزش کشاورزي و منابع طبيعي استان اصفهان، سازمان تحقيقات آموزش و ترويج کشاورزي اصفهان، ايران.
کلید واژه: آبياري سطحي, پساب, نفوذ,
چکیده مقاله :
زمينه و هدف: با توجه به کاهش کمّي و کيفي منابع آب کشور و خشکساليهاي چند سال اخير، استفاده از پساب‌ها و فاضلاب‌ها از سوي کشاورزان بهمنظور آبياري مزارع و باغات مورد توجه قرار گرفته است. اين پژوهش بهمنظور بررسي تأثير آبياري با پساب فاضلاب شهري بر برخي ويژگيهاي فيزيكي و هيدروليكي خاک در منطقه شمال اصفهان انجام گرديد. پارامترهاي هيدروليکي خاک از جمله سرعت نفوذ آب در خاک اهميت زيادي در مديريت بهينه آبياري جويچه‌اي دارد و اندازهگيري آن براي اين مزارع ضروري است.
روش پژوهش: اين پژوهش با استفاده از پساب فاضلاب شهري و بهصورت طرح آماري فاكتوريل با پايه بلوک كاملاً تصادفي با سه سطح تيمار آبياري (آبياري با پساب خروجي تصفيه‌خانه فاضلاب، آبياري بهصورت تناوبي با پساب و آب چاه و آبياري با آب چاه)، در منطقه شمال اصفهان، صورت گرديد.
يافته‌ها: تيمارهاي مختلف آبي تأثير معنيداري بر روي ميزان رطوبت خاک در ظرفيت زراعي (FC[1]) و نقطه پژمردگي دايم گياه (PWP[2]) نداشتند. مقدار وزن مخصوص ظاهري بهصورت معنيدار در سطح يک درصد، در تيمار آبياري با آب چاه افزايش و در تيمار آبياري با پساب کاهش يافت. ميزان هدايت هيدروليکي اندازهگيري شده در تيمار آبياري با پساب در حدود 20 درصد بيشتر از تيمار آبياري با آب چاه بود. همچنين بيشترين ميزان اختلاف بين زمان پيشروي و پسروي در تيمار آبياري با پساب (4/68 دقيقه) و کمترين آن مربوط به آبياري با آب چاه (8/50 دقيقه) بود. نشان داد فرصت نفوذ آب به خاک در تيمار پساب بيشتر از تيمار آبياري شده با آب چاه بوده است. روند كلي ضرايب معادله نفوذ کوستياکوف-لوييس در تيمار آب چاه نسبت به پساب كاهشي بود (به ترتيب حدود 58 و 60 درصد براي ضرايب k و a). بيشترين ميزان ميانگين نفوذ تجمعي مربوط به پساب و كمترين مقدار مربوط به تيمار تناوبي بود. ميزان سرعت نفوذ آب به خاک در تيمار آبياري با پساب در حدود 001/0 متر بر دقيقه و در تيمار آبياري با آب چاه در حدود 0008/0 متر بر دقيقه بود که تقريباً معادل 73 درصد کاهش در سرعت نفوذ ميباشد.
نتايج: براساس نتايج بهدست آمده از اين پژوهش، تاثير آبياري با پساب و آب چاه بر ويژگيهاي مختلف فيزيکي خاک، تا حد زيادي به ويژگيهاي شيميايي آب چاه و پساب و ماهيت اوليه پساب بستگي دارد. يون سديم موجود باعث تخريب ساختمان خاک و انسداد منافذ درشت شده و در کل باعث کم شدن حجم خلل و فرج موجود در خاک و متراکمتر شدن آن و در نهايت افزايش وزن مخصوص ظاهري در خاک شد. ميزان هدايت هيدروليکي اندازهگيريشده در تيمار آبياري با پساب بيشتر از تيمار آبياري با آب چاه بود. علت اين امر را ميتوان به افزايش مواد آلي خاك در اثر مصرف پساب و نيز افزايش غلظت کلسيم و منيزيم خاك، افزايش فعاليت ميکروبي خاك و بهبود ساختمان خاک نسبت داد.
[1] Field capacity
[2] Permanent wilting point
Background and Aim: Due to the quantitative and qualitative reduction of the country's water resources and the droughts of the last few years, the use of effluents and sewage by farmers to irrigate fields and gardens has been considered. This research was conducted in order to investigate the effect of irrigation with urban sewage effluent on some physical and hydraulic characteristics of soil in the northern region of Isfahan. Soil hydraulic parameters, such as infiltration is very important in the optimal management of furrow irrigation, and its measurement is necessary for these farms.
Method: This research using urban sewage effluent and in the form of a factorial statistical design based on a completely randomized block with three levels of irrigation treatment (irrigation with wastewater treatment plant effluent, intermittent irrigation with effluent and well water, and irrigation with well water) in the region North of Isfahan, was done.
Results:Different irrigation treatments had no significant effect on the amount of soil moisture in crop capacity (FC) and permanent wilting point (PWP). The amount of apparent specific gravity was significantly increased at the level of 1% in the irrigation treatment with well water and decreased in the irrigation treatment with wastewater. The hydraulic conductivity measured in the irrigation treatment with effluent was about 20% higher than the irrigation treatment with well water. Also, the greatest amount of difference between advance and retreat time was in the treatment of irrigation with wastewater (68.4 minutes) and the lowest was related to irrigation with well water (50.8 minutes). It showed that the chance of water infiltration into the soil was greater in the wastewater treatment than in the treatment irrigated with well water. The general trend of the coefficients of the Kostiakov-Lewis infiltration equation in the treatment of well water was a decrease (about 58 and 60% for k and a coefficients, respectively). The highest amount of average cumulative infiltration was related to wastewater and the lowest amount was related to periodic treatment. The rate of water infiltration into the soil in the effluent irrigation treatment was about 0.001 m/min and in the well water irrigation treatment was about 0.0008 m/min, which is approximately equivalent to a 73% decrease in infiltration rate.
Conclusion: Based on the results obtained from this research, the effect of irrigation with wastewater and well water on different physical characteristics of the soil depends to a large extent on the chemical characteristics of the well water and wastewater and the basic nature of the wastewater. The existing sodium ion caused the destruction of the soil structure and the blockage of coarse pores, and in general, it caused the volume of voids and pores in the soil to decrease and become denser, and finally, the apparent specific gravity of the soil increased. The reason for this can be attributed to the increase in soil organic matter as a result of wastewater consumption, as well as the increase in soil calcium and magnesium concentration, the increase in soil microbial activity and the improvement of soil structure.
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