اثر كاربرد پلي‌آكريل‌آميد در مهار فرسايش پاشماني از خاك تحت تأثير پديده انجماد- ذوب

Effects of Polyacrylamide in Controlling of Splash Erosion from a Soil induced Freeze-Thaw Cycle

بررسی اثرات پدیده انجماد و انجماد- ذوب در مباحث فرسایش و تولید رسوب حائز اهمیت است. با این‌حال، حفاظت خاك‌های تحت تاثیر این پدیده‌ها با شیوه‌های مختلف و از جمله استفاده از افزودنی‌ها هنوز مورد توجه قرار نگرفته است. از این‌رو پژوهش حاضر برای ارزیابی عملكرد پلی‌آكریل‌آمید (PAM) در مهار تأثیر چرخه انجماد- ذوب روی فرسایش پاشمانی از یك خاك لوم سیلتی انجام پذیرفت. در این راستا، فرسایش پاشمانی با استفاده از فنجان‌های پاشمان در دو تیمار شاهد بدون استفاده از PAM روی خاك با شرایط انجماد و دیگری با انجماد- ذوب و دو تیمار با شرایط انجماد و دیگری با انجماد- ذوب بعد از كاربرد PAM به ‌میزان 20 كیلوگرم در هكتار اندازه‌گیری شد. میانگین میزان فرسایش پاشمانی خالص، در بالادست و پایین‌دست فنجان‌های پاشمان در كلیه تیمارهای آزمایش با آزمون t جفتی مقایسه شد. مقایسه میانگین‌های مقادیر رسوب مشاهداتی و برآوردی نشان‌دهنده اختلاف معنی‌دار (018/0P <) میزان فرسایش پاشمانی خالص به‌دست آمده در قبل و بعد از كاربرد PAM در تیمارهای مطالعاتی بود. هم‌چنین، نتایج مؤید وجود اختلاف معنی‌دار (003/0P <) بین میزان فرسایش پاشمانی بالادست در تیمار انجماد و عدم وجود اختلاف معنی‌دار (365/0P >) در تیمار انجماد- ذوب در قبل و بعد از كاربرد PAM بود. وجود اختلاف معنی‌دار (041/0P <) بین میزان فرسایش پاشمانی در پایین‌دست فنجان‌های پاشمان در كلیه تیمارهای مطالعاتی نیز مشاهده شد. در مجموع، كاربرد PAM باعث كاهش میزان فرسایش پاشمانی خالص، فرسایش پاشمانی بالادست و پایین‌دست فنجان‌های پاشمان در تیمارهای مطالعاتی شد.

Introduction: The capability of a soil to resist erosion depends on soil-particle size and distribution, soil structure and structural stability, soil permeability, water content, organic matter content, and mineral and chemical constituents. Among many affecting factors on aforesaid characteristics, the freezing-thawing processes may considerably affects. Freeze–thaw fluctuation is a natural phenomenon that is frequently encountered by soils in the higher latitude and altitude regions in late autumn and early spring. Effects of freezing and freezing-thawing phenomena on soil erosion and sediment yield are important. Nevertheless, soil conservation under these phenomena by using different methods as well as soil amendments has not been yet considered. Surface application of anionic polyacrylamide (PAM) in solution has been found to be very effective in decreasing seal formation, runoff, and erosion.PAM stabilizes soil structure due to the ability of the polymer chains to adsorb onto clay particles and bridge them together forming stable domains. This adsorption can be a result of interactions between the negatively-charged functional groups of the PAM molecules and the positively-charged edges of clay minerals, orexchangeable polycations (mainly Ca2+) acting as ‘bridges’ between the negative charges of the PAM 's functional groups and the negatively- charged planar surfaces of the clay. The PAM is adsorbed on the external surfaces of the aggregates and binds soil particles far apart together, thereby were shorter and evidently less effective in enhancing increasing their resistance to splash by raindrop impact and detachment by runoff. A lot of research work focused on freezing effects in soils on aggregation or increase aggregate stability and emphasis corresponding effects. But the effects of application of soil amendments on soil induced freeze and thaw cycle have not been studied yet. Materials and Methods: The present study evaluated the performance of PAM in controlling freeze-thaw cycle effects on splash erosion from a silty loam soil. A freeze-thaw cycle was simulated in Soil Erosion and Rainfall Simulation Laboratory of TarbiatModares University. The present study was conducted under controlled laboratory conditions with a simulated rainfall. The maximum efforts were made to mimic natural conditions to get access to results with high level of fidelity. Towards this attempt, air and different soil depth temperatures were analyzed in natural condition and 10 cm soil depth was targeted for the soil laboratory experiments. The rainfall storm with 72 mm h-1 and 30 min duration was simulated and conducted for the study treatments. The soil was poured in small erosion box with 0.25 m2 surface area in three replicates. A thick filter, draining the lower 20 cm of the soil profile was generated using mineral pumices.The prepared soil sample was evenly packed into the soil plots at a bulk density of 1.3 Mg m−3 similar to that measured under natural conditions. The plots were then placed in saturated pool for 24 h and then left to be drained to achieve an average moisture content of 35% similar to that recorded for the realities in the study area. So, splash erosion rates were measured using splash cups in two control treatments without PAM subjected to freezing and freezing-thawing processes, and two other plots treated by freezing and freezing-thawing processesplus application of 20 kg ha-1 of PAM. After securing thenormality ofdata, the average net splash erosionand the average upward and downward rates of splash erosion in allexperimental treatmentswere comparedby paired sampled T-test. Results and Discussion: According to the results of statistical analyses, the PAM application had a significant effect (p <0.018) on net splash erosion. The collected data on upward segments of cups treated with freeze phenomena showed that PAM played an effective and a significant role (P <0.003) in splash and no significant effect (P >0.365) on freezing-thawing processes. The significant difference (P <0.041) between downward segments of cups were also observed in all treated plots. In overall, PAM application reduced the amount of net splash erosion, upward and downward splash erosion in study treatments. The study revealed that the PAM can be successfully used in the silty loam soil to improve soil structure and control splash erosion. Though, further studies with deeper insights to different conditions and under various rainfall intensities and conservation measures are essentially needed to draw more reliable conclusion about affectability of splash erosion induced freeze-thaw cycle.