كليدواژه :
فرسايش , انرژي جنبشي باران , كاسه پاشمان , پاشمان , شهركرد
چكيده فارسي :
فرسايش پاشماني اولين مرحله پديده فرسايش و عامل اصلي از دست رفتن حاصلخيزي خاك است كه ارتباط مستقيمي با بافت خاك دارد. هدف از پژوهش حاضر مطالعه آزمايشگاهي فرسايش پاشماني در كلاسهاي بافتي مختلف تحت شدتهاي بارش متفاوت با استفاده از دستگاه شبيهساز باران است. براي اين منظور 83 نمونه خاك از سه كلاس بافتي سبك، متوسط و سنگين خاكهاي منطقه شهركرد استان چهارمحال و بختياري استفاده شد. برخي ويژگيهاي فيزيكوشيمايي خاك شامل اسيديته ، شوري، بافت خاك، ماده آلي، كربنات كلسيم در نمونه ها اندازه گيري شد. شدتهاي 65، 95 و 120 ميليمتر در ساعات با دستگاه بارانساز موجود در پژوهشكده ي حفاظت خاك و آبخيزداري بر كلاسهاي بافتي خاك اعمال شد. قطر قطرات باران با روش گلوله ي آردي و فرسايش پاشماني با استفاده كاسه هاي پاشمان طراحي مورگان (1978) اندازه گيري شد. نتايج نشان داد كه بين نرخ پاشمان در كلاسهاي بافتي در شدت هاي 65 و 120 ميليمتر در ساعت تفاوت معنيداري وجود داشت درحاليكه در شدت 95 ميليمتر بر ساعت تفاوت معنيداري بين نرخ پاشمان در كلاسهاي بافتي ديده نشد. درصد رس خاك با ضريب همبستگي 0/388- بيشترين ارتباط را با نرخ پاشمان در شدت هاي مختلف داشت. ماده آلي با شدتهاي 65 و 95 ميليمتر همبستگي معنيدار بترتيب 0/375- و 0/255- داشت درحاليكه با شدت 120 ميليمتر در ساعت همبستگي نشان نداد كه مي تواند بدليل انرژي جنبشي زياد و قطرات سنگين باران در شدت 120 ميليمتر در ساعت باشد.
چكيده لاتين :
Introduction: Soil erosion is one the most serious environmental problems that causes great soil losses and threatens sustainable agriculture. Erosion cause severe land degradation and soil productivity loss, and generally consider as hazard of health society. For these reasons, preventing soil erosion is very important for managing and conserving the natural resources. Splash erosion is the first stage of the erosion process. It occurs when raindrops hit bare soil. The explosive impact breaks up soil aggregates so that individual soil particles are 'splashed' onto the soil surface. A rainfall simulator is an important tool for the study of runoff generation and soil loss because it can be used either under laboratory conditions, or in disturbed or natural soil. Splash cups have long been successfully used for both the quantification of kinetic energy of rainfall and the detachability of soil particles by rainfall impact, the so-called “splash erosion”. Splash erosion is highly affected by type of soil texture due to different particle size. The purpose of the present study was to investigate the effects of different soil texture on splash erosion under different rainfall intensity using rainfall simulator.
Methodology: The Shahrekord watershed, which mainly has calcareous soil with more than 40% lime (total carbonates), is located in the central of Chahrmal-va-Bakhtiyari province, between 458365 and 515623 N and 3550972 and 3603532 E according to UTM (WGS′ 1984, zone 39°N) with an area of about 1248 km2. For this study, 83 soil samples from different soil texture (light, moderate and heavy texture) were collected from 0-10 cm of soil surface. Rainfall simulator (Model FEL3) was used to simulate the rainfall with different intensity (65 mm-1 h-1 , 95 mm-1 h-1 and 120 mm-1 h-1). Splash cup designed by Morgan (1978) was used to measure the splash erosion. Some physicochemical properties including soil texture, organic matter, water aggregate stability, pH, EC were analyzed. The diameter of the rain drops were measured by Bullet Meal Method under different rainfall intensity. The normal distribution of data was tested using Kolmogorov-Smirnov test, Duncan's mean comparison at 95% level, and the correlation between erosion erosion and soil variables was performed using Pearson test in SPSS 15 software.
Results and discussion: Soil samples were classified to 3 classes including light texture (% clay < 30), moderate class ( % clay between 30 – 40) and heavy class (% clay > 40). Results showed that there were significant differences between splash erosion under different soil textures under rainfall intensity of 65 mm-1 h-1 and 120 mm-1 h-1, while there was no significant differences between splash erosion under different soil textures under rainfall intensity of 95 mm-1 h-1. % clay with correlation coefficient of -0.388 was the most effective parameter on splash erosion. The average amount of spraying in the intensity of 120 mm h-1 and light texture with 11.13 is the highest and has the lowest mean intensity at 65 mm / h and average texture. In heavy texture, with a change in rainfall intensity of 65 to 95 and 120 mph, the rate of spraying increased by 1.4 and 1.7 times, respectively.The second and third were % OM and % sand with correlation coefficient of -0.375 and 0.375, respectively. Organic matter had a significant correlation of -375.0 and -255.0 with intensity of 65 mm-1 h-1 and 95 mm-1 h-1, respectively, while it did not show significant correlation with intensity of 120 mm-1 h-1, which can be due to high movement of energy and heavy droplets of 120 mm-1 h-1. The average diameter of simulated rain drops at 65, 95 and 120 mm-1 h-1 were 1.2, 1.48 and 1. 57 mm using mean weighted method, , with all three severities having a significant difference with each other they had.
Conclusion: based on the results, % clay with r= -0.388, organic matter with r = -0.37 and % sand r= -0.375 had high significant correlation with splash erosion. Although the content of lime had a significant correlation of -0.273 with intensity rainfall of 95 mm-1 h-1, there was no significant correlation between splash erosion with 65 mm-1 h-1 and 120 mm-1 h-1. A significant negative correlation of -0.375) between soil % organic matter and splash erosion indicates that the effects of rain drops erosion can be attributed to the application of vegetation regeneration and strengthening methods that increase the % organic matter content of the soil. The splash erosion was significantly reduced with using increasing % organic matter. It is recommended that in future studies, in addition to assessing the different rainfall intensities and different types of tissue types, investigate the different types of vegetation cover in preventing erosion spraying.
