نوع مقاله : مقاله پژوهشی
نویسندگان
1 علوم و مهندسی خاک، دانشکده کشاورزی، دانشگاه تهران، کرج، ایران
2 علوم و مهندسی خاک، دانشکده کشاورزی، داشگاه تهران، کرج، ایران
3 پژوهشکده حفاظت خاک و آبخیزداری ، سازمان تحقیقات، آموزش و ترویج کشاورزی ، تهران، ایران
4 مرکز تحقیقات و آموزش کشاورزی خراسان رضوی، سازمان تحقیقات، آموزش و ترویج کشاورزی (AREEO)، مشهد، ایران
5 گروه احیاء مناطق خشک و کوهستانی، دانشکده منابع طبیعی، دانشگاه تهران، کرج، ایران
چکیده
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
This research aimed to determine the soil erodibility factor (K) of the Universal Soil Loss Equation (USLE) by direct measurement of soil loss at natural runoff plots (), and to compare it with the estimated K by the USLE-nomograph (). The research carried out at the Sanganeh Soil Conservation Research Site located in the northeast of Iran, in dry rangelands. The soil loss data were obtained from 19 plots with lengths of 20 and 25 m, and different conditions in terms of soil, slope, vegetation cover, and rock fragments under 20 natural rainfall events. The results showed that average intensity and the maximum 30-minute intensity had a greater correlation with soil loss compared to the . Based on the results obtained, is at least 24, 7, and 6 times of , obtained using the soil loss data of the long-term average, the year with the largest share, and the most intense event (), respectively. The main reasons likely for this overestimation are the low intensity of erosive events and the resulting uncertainties in the measurement of soil loss and other USLE model factors in dry rangelands. Therefore, based on the overestimation of the USLE nomograph, more research, especially with a longer statistical period or using a rainfall simulator with an intensity of 63 mm h-1 in field, is needed to develop appropriate relationships to estimate the K factor in rangelands in dry regions.
کلیدواژه‌ها [English]
EXTENDED ABSTRACT
Erodibility represents the inherent susceptibility of the soil to detachment and transportation by rainfall and surface runoff, which was introduced as K factor in the Universal Soil Loss Equation (USLE). Assuming that the methods of determining the other USLE factors (i.e. R, LS, C, and P) are appropriate, it was hypothesized that the USLE nomograph or its derived classical equation is the best available prediction tool for the K factor. This research aimed to determine the K factor by direct measurement of soil loss at natural runoff plots (K_obs), and to compare it with the estimated K by the USLE nomograph (K_est). The research was carried out at the Sanganeh Soil Conservation Research site with an area of 20 ha located in the northeast of Iran, in dry rangelands.
To consider different conditions in terms of slope steepness, soil, vegetation cover, surface rock fragments, and soil depth, 19 plots were installed throughout the site. The plots had lengths of 20 and 25 m and a fixed width of 2 m. Unlike the USLE unit plot, the plots were not disturbed and were in natural conditions. After installing the plots, the most important soil attributes and surface characteristics were measured in each hillslope. They include vegetation cover, primary soil particle size distribution and surface rock fragments, structural stability index, electrical conductivity, pH, organic carbon, cation exchange capacity, and carbonate calcium equivalent.
A recording gauge meteorological station with a measurement precision of 0.2 mm has been established to collect the characteristics of each rainfall event in the vicinity of the site. To perform calculations related to the rainfall erosivity index, the data of each event was converted to a time step of 5 minutes and then the relevant calculations were performed. During the research (1997-2000 and 2006-2009), 20 erosive rainfall-runoff events were recorded. The erosive events were defined based on Renard et al. (1997)’s conditions. To determine the concentration of sediment resulting from each rainfall event, after thoroughly mixing the runoff and sediment, a two-liter sample was taken using the valve at the bottom of the tank and transferred to the laboratory. Sediment samples were transferred to the laboratory and placed in an oven at 105 for 24 hours. The concentration of each sample was determined in terms of and finally, it was converted into using the volume of the tank and the dimensions of the plot. Then, calculated by for three cases: 1) the long-term average of soil loss during the research period. 2) the year with the highest annual soil loss, and 3) events with the highest contribution to annual soil loss (high-intensity events), Finally, was estimated by applying silt + very fine sand correction () by the classic equation of the USLE nomograph. and comparing to .
The average intensity () of the 20 measured rainfall events during the seven years was 11.6 . The average maximum 30-minute intensity () was 16.7 . The annual rainfall erosivity index () was 45.8 . Based on the erosive events (20 events) in the 7-year research period, the average annual soil loss was about in the whole site. While the minimum average annual soil loss was (Plot no. 4), its maximum for was about (Plot no. 15).
In general, no relationship () was observed between and . The values of long-term varied in the range of 0.00004 (plot no. 4) to 0.00293 (plot no. 1) , while the values of were in the range of 0.056 (plot no. 18 and 19) to 0.077 (plot no. 5 and 6) . Using the seven-year average soil loss, the year with the highest contribution to the total soil loss, and soil loss induced by the event with the highest intensity (), was at least 24, 7, and 6 times of , respectively.
The results showed that the value of obtained from the USLE nomograph significantly overestimated the value, leading to the rejection of the research hypothesis. The main reasons for this overestimation would be the low intensity of erosive events and the resulting uncertainties in the measurement of soil loss, in on hand, and determination uncertainty of the other USLE model factors (R, LS, C and P) in dry rangelands, on the other hand. The intensity of the rains used to develop the USLE nomograph was 63 . Events of this intensity rarely occur in arid regions. On the other hand, due to the variable duration of the drought period and fear in arid regions, the periods of 1-3 years, and even 7 years of measuring the K factor are associated with a high uncertainty and errors. Therefore, based on the overestimation of the USLE nomograph, further research is needed, especially with a longer statistical period or using a rainfall simulator with an intensity of >63 in the field conditions, to develop appropriate relationships for estimating the K factor in rangelands in arid regions.
Ayoub Avizhgan: Design, Analysis, and Interpretation of data Writing- Original draft preparation, Visualization. Hossein Asadi: Conceptualization, Methodology, Design, Revision of the manuscript and Editing. Mahmood Arabkhedri: Design, Revision of the manuscript and Editing. Hamzeh Noor: Revision of the manuscript and Editing. Aliakbar Nazari Samani: Revision of the manuscript and Editing.
Data can be sent from the corresponding author by email upon request.
We are grateful to the Soil Conservation and Watershed Management Research Institute of Tehran for for measurement and data collection.
The authors avoided data fabrication, falsification, plagiarism, and misconduct.
The author declares no conflict of interest.
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