مقايسه توليد رواناب سطحي، ‌هدررفت خاك و عناصر غذايي در آبخيز‌هاي نمونه و شاهد كاخك، استان خراسان رضوي

Comparison of Surface Runoff Generation, and Soil and Nutrient Loss in Kakhk Treated and Representative Watersheds, Khorasan Razavi Province

مهار تخریب اراضی به‌منظور حفظ ثروت‌های ارزشمند طبیعی، امری حیاتی به‌شمار می‌رود. در همین راستا، یكی از موارد مدیریت های علمی و بهینه كشاورزی و منابع طبیعی به عنوان اصولی‌ترین مؤلفه های مهم توسعه پایدار، كمّی‌سازی رواناب تولیدی، هدرفت خاك و عناصر غذایی از عرصه های منابع طبیعی و در شرایط سخت مدیریتی است. با این وجود، پژوهش‌های جامع و مقایسه‌ای ارزیابی میزان تولید رواناب سطحی و هدررفت خاك و نیز عناصر غذایی در اثر الگوهای مختلف مدیریتی بسیار محدود مورد توجه قرار گرفته است. لذا پژوهش حاضر با هدف مقایسه تولید روان‌آب سطحی، هدررفت خاك و عناصر غذایی در دو آبخیز حفاظت ‌شده (نمونه) و حفاظت نشده (شاهد) در حوزه آبخیز كاخك گناباد برنامه‌ریزی شد. بدین منظور پژوهش حاضر در كرت‌هایی با ابعاد استاندارد 1/22× 8/1 متر در هر یك از آبخیزهای نمونه و شاهد، در سه دامنه‌ شرقی، غربی و شمالی و با سه تكرار و در مقیاس رگبارهای طبیعی اتفاق‌ افتاده از سال 1390 تا اوایل سال 1393 صورت پذیرفت. نتایج پژوهش صورت گرفته نشان داد كه اختلاف هدررفت خاك، غلظت نیتروژن، غلظت پتاسیم و غلظت رسوب در آبخیزهای نمونه و شاهد معنی‌دار (05/0p <) بوده، بدین صورت كه مقادیر هدررفت خاك، غلظت نیتروژن، غلظت پتاسیم و غلظت رسوب در آبخیز شاهد به‌ترتیب 35/1، 23/0، 25/257 و 9/7 و در آبخیز نمونه به‌ترتیب 17/0، 17/0، 9/402 و 41/4 بود. علاوه‌ بر آن، نتایج به‌دست آمده نشان داد كه اختلاف حجم رواناب و غلظت فسفر در دو آبخیز نمونه و شاهد معنی‌دار (05/0p >) نبود، بدین صورت كه مقادیر آن‌ها در آبخیز شاهد به‌ترتیب 6/238 و 28/20 و در آبخیز نمونه به‌ترتیب 6/169 و 04/15 بوده است. مطالعه صورت گرفته نشان داد كه تداوم الگوی حفاظتی برای حفظ كمیت و كیفیت منابع آب و خاك ضروری است.

Introduction: It is vital to control land degradation, for conserving precious natural treasures. Quantification of runoff production and soil and nutrient loss from wild lands under different managerial systems is one of the scientific and optimal management in agriculture and natural resources, as a major component of sustainable development. Many researches have been conducted to assess the effects of different land uses on soil erosion and runoff generation throughout the globe. Most of which, mainly verified the detrimental effects of human intervention on land degradation. However, limited comprehensive and comparative studies have been conducted to consider the amount of surface runoff generation, and soil and nutrient loss from watersheds with different management patterns viz. untreated and treated small watersheds. Materials and Methods: The present study aimed to compare surface runoff generation,soil and nutrient loss in Kakhk treated and untreated watersheds with an area ca. 222 ha and precipitation of some 243 mm per annum. Other physical and geological characteristics of the paired watersheds were also similar to allow assessing the effects of study measures on soil, water and nutrient losses. The area under consideration has been located in Khorasan Razavi Province in northeastern Iran. The present study was performed in plots with standard size of 22.1 × 1.8 m in treating and representative areas, with three replicates and on the storm basis occurred during early 2011 and mid-2014. The treated plots were covered by biological measures viz. seeding, bunching and exclusre. The study plots have been situated on eastern,western and northern aspects with respective slope of 55, 40 and 40 %. The entire runoff from study plots were collected in a container in 0.5×1×1 m. The sediment concentration was also measured in 2-liter samples taken from the container after a complete mixing of the entire collected runoff. The sample was treated by decantation technique, oven dried and weighted by high precision scale. The transported elements, i.e. potassium, phosphorous and nitrogen were also measured in solute and particulate forms. Ultimately, the data bank was developed in Excel 2010 and got ready to be processed in SPSS 19.0 software package and statistically compared with the help of analysis of variance (ANOVA) test. Results and Discussion: The results showed that the soil loss, nitrogen concentration, potassium concentration and sediment concentration had significant difference (p <0.05) in treating and representative watersheds. So that, the amount of soil loss, nitrogen concentration and sediment concentration in representative sub-watershed were 7.9, 1.3 and 1.8 times more than those measured in treating sub-watershed, respectively. The amount of potassium concentration in treated sub-watershed was 1.5 times more than that measured in a representative sub-watershed. In addition, the results showed that runoff volume and phosphorus concentration of 95% of confidence level were not significant in treating and representative sub-watershed. It therefore showed that there was no significant effect of watershed management measures on runoff in treating plots compared to that recorded for untreated plots. However, the difference between sediment concentrations was statistically significant which clearly verified more effectiveness of the controlling measures on the study variable. So that, the sediment concentration was almost 1.8 times more in plots located in representative sub-watershed in comparison with that measured in a treated sub-watershed. It ultimately led to differences in the study chemical elements, mainly transported in particulate. Whilst, the nitrogen concentration in un-treated plots were almost 1.3 times more than that obtained for treated plots. It was incorporated to more breakage and crashing of plants residues by cattle and also more animal disposals containing high level of nitrogen into top soil. Likewise, significant positive effect of soil erosion treatments on potassium content was proved in treating plots led to an incremental rate of 1.5. No difference could be distinguished between phosphorous contents in treated and un-treated plots, since the phosphorous is almost evenly distributed in the soil profile and therefore was not controlled by anthropogenic activities. Conclusion: The results of the study verified that, despite of different effects of soil and water conservation measures on the study variables, they were often got influenced from the measures. It therefore proved that the governing conservation approach should be continued in the study area in order to preserve the quality and quantity of soil and water resources in the study area. Though further insight studies with longer periods of data collection, more hydrological variables, other temporal and spatial scales and even broad extension in different parts of the country are recommended to allow drawing final conclusion.