Interrill and rill erodibility in the northern Andean Highlands
Introduction
More than 10 million rural inhabitants reside in the Mountainous region of the major Andean countries where moderate and severe soil erosion occurs (Zimmerer, 1993) However, quantitative studies on soil erosion as well as the knowledge on water and erosion processes are scarce in the Andes (Stroosnijder, 1997) compared with other areas in the world, especially those related to soil erodibility (Víctora et al., 2001, Zehetner and Miller, 2006). Published erosion rates are around 48 Mg ha− 1 year− 1 in Colombia (Ashby, 1985); 0 to 836 Mg ha− 1 year− 1 in Ecuador (Harden, 1988); 10 to 70 Mg ha− 1 year− 1 in Peru (Low, 1967) and 114 to 173 Mg ha− 1 year− 1 in Bolivia (Zimmerer, 1991). Current studies try to give a better approximation of the estimated erosion rates, because time- and scale-dependent aspects of soil loss and sediment transfer make comprehensive measurements difficult.
Inbar and Llerena (2000) determined sediment yield quantitatively from abandoned terrace areas in Central Andes of Peru. However, no calculation of erodibility values has been done in these plot studies. Sánchez et al. (2002) made a comparative study of soil erosion in the Venezuelan Andes. Soil losses were quantified by using erosion plots in areas covered by four types of vegetation (apple trees, pasture, natural forest, and horticultural crop in rotation). The lowest soil loss rated was associated to the natural forest, with an average value of 0.43 mg ha− 1 year− 1 and the highest occurred with horticultural crops in rotation, with an average value of 15 Mg ha− 1 year− 1. They calculated the soil erodibility factor (K) of the Universal Soil Loss Equation (USLE—Wischmeier and Smith, 1978) based on the relation between aggregation, textural class and organic matter content of the topsoil. The K factor values were 0.030, 0.045, 0.032 and 0.038 Mg ha− 1/MJ ha− 1 mm h− 1 for natural forest, horticultural crops, pastures and apple plantation treatments, respectively. Zehetner and Miller (2006) studied the erodibility and runoff-infiltration characteristics along an altitudinal Entisols–Inceptisols–Andisols sequence in the Andes of northern Ecuador. Using disturbed soil samples packed into small pans and placed on a 9% slope, simulated rainstorm with varying intensities was applied for a duration of 30 min. During the simulated event, runoff and eroded sediment were collected in 5-min intervals and measured by weight before and after drying. They calculated the interrill erodibility with the original WEPP interrill equation (Flanagan and Nearing, 1995). Ki ranged from 0.5 to 7.9 × 105 kg s m− 4.
Natural rainfall represents natural conditions at a given place; however, data acquisition is difficult due to the lack of control of the spatial and temporal distribution of rainfall intensity (Moore et al., 1983). A more cost-effective alternative is to use rainfall simulators to apply controlled rainstorms to small plots (Kamphorst, 1987, Esteves et al., 2000). Portable rainfall simulators used on small plots give sufficient flexibility to study a variety of processes (e.g. infiltration, irrigation, interrill erosion and water quality) on different soils and slopes and different land uses (Sharply et al., 1999, de Lima et al., 2002) and can be used to collect data in a relatively short period, providing maximum control over plot conditions and rainfall characteristics (Wilcox et al., 1986). Performing experiments with a rainfall simulator make possible to compare runoff rates and soil detachment by raindrop impact between sites at which the same experimental procedure was used, thus providing a basis from which to understand spatial patterns of vulnerability to soil erosion over a broad area. However, splash detachment rates from very small plots can exceed soil erosion rates determined in large, conventional plots for comparable natural rainstorms because conventional measure require entrained particles to be transported to the lower edge of the plot (Harden, 2001).
The main disadvantages of using rainfall simulators are related to scale. First, it is cheap and simple to use a small simulator which rains onto a test plot of only a few square meters, but simulators to cover field plots are large, expensive and cumbersome, and secondly, measurements of runoff and erosion from simulator tests on small plots cannot be extrapolated to field conditions. They are best restricted to comparisons, such as which of three cropping treatments suffers least erosion under the specific conditions of the simulator test, or the comparison of relative values of erodibility of different soil types (Hudson, 1993).
With the development of USLE (Wischmeier and Smith, 1978) — the identification of the soil erodibility K factor became a central issue in erosion studies (Bryan et al., 1989). USLE continues being applied all over the world and provides a practical alternative to estimate K. Different studies show different results of applying USLE in the tropics (Vanelslande et al., 1984, Mati et al., 2000, Mati and Veihe, 2001, Baumann et al., 2002, Kim et al., 2005, Weill et al., 2006, Millington, 2006). Problems with the use of USLE in this environment appeared to be: (1) rainfall intensities are higher than those occurring in eastern USA, where it was developed; (2) different methods of soil aggregation that are found in tropical soils — particularly bonding by iron, aluminium and organic acids; (3) farming occurring on more ecologically and topographically marginal areas; and (4) cropping and management factor which are radically different (Millington, 2006).
Erosion can be divided into two components: rill and interrill erosion. Interrill erosion is caused by soil particles being detached by raindrops and transported by overland flow. Rill erosion, however, is the detachment and transport of soil particles by concentrated flow: it is a function of the shear of the water flowing in the rill (Lal and Elliot, 1994). Computer simulation models like the Water Erosion Prediction Project – WEPP (Nearing et al., 1989) – developed by the United States Department of Agriculture (USDA) require the input of two erodibility values for each soil type: interrill (Ki) and rill (Kr) erodibility. If the inputs are not available, WEPP includes two regression equations to calculate Ki and Kr, also based on soil properties like content of clay, silt, very fine sand, sand and organic matter (Flanagan and Nearing, 1995). The main objective of this study is to determine the interrill and rill erodibility values for a northern Andean highland watershed in Peru and to compare field measurements with existing models that describe erodibility.
Section snippets
The study area
The Northern Andean Cordillera in the district of La Encañada belongs to a transition zone between an inter-Andean valley and a highland plateau. It is a 160 km2 watershed located between 7°0′21″S and 7°8′2″S latitude and 78°11′22″W and 78°21′31″W longitude. The altitude ranges from 2950 to 4100 meters above the sea level. As a part of the Andean relief, this watershed presents a variety of geomorphic characteristics, resulting in a complex topography. Seventy four percent of the area presents
Results and discussion
Measured Ki values ranged from 1.9 to 56 × 105 kg s m− 4 that differed from the estimated Ki using Eq. (2), ranged from 20 to 110 × 105 kg s m− 4. Measured Ki values are comparable to those reported by Zehetner and Miller (2006) where data ranges from 0.5 to 25 × 105 kg s m− 4 for diverse Andean soils. As shown in Fig. 2, estimated values are higher than the observed ones. The distribution of the observed Ki values is shown in Fig. 3. The maximum Ki value (56 × 105 kg s m− 4) was measured in a soil with
Conclusions
Measured interrill (Ki) and rill (Kr) erodibility values were low in the evaluated Andean watershed. The most erodible soils were those with the greatest amount of silt and very fine sands and the most resistant were clayey soils. Silt and very fine sand were strongly correlated with the interrill erodibility values, whereas clay, very fine sand and organic matter were strongly correlated with rill erodibility. Two equations using these predictors were proposed. Ki values followed similar
Acknowledgments
This research was supported by the International Foundation for Science (IFS), Stockholm, Sweden, through a grant to C.C. Romero. The authors want to thank the USAID and Soil Management — CRSP project through the grant No. 291488 and the International Potato Center for administrative issues. Joy Burrough advised on the English. Reviewers of this paper are duly acknowledged for their comments.
References (46)
- et al.
Aggregate stability as an indicator of soil susceptibility to runoff and erosion; validation at several levels
Catena
(2002) - et al.
The concept of soil erodibility and some problems of assessment and application
Catena
(1989) - et al.
A mathematical model for evaluating the effect of wind on downward-spraying rainfall simulators
Catena
(2002) - et al.
Erodibility and runoff-infiltration characteristics of volcanic ash soils along an altitudinal climosequence in the Ecuadorian Andes
Catena
(2006) Soil erosion and labor shortages in the Andes with special reference to Bolivia, 1953–91: implications for “conservation-with-development”
World Development
(1993)The social ecology of soil erosion in a Colombian farming system
Rural Sociology
(1985)- Baigorria, G.A., 2005. Climate interpolation for land resource and land use studies in mountainous regions. Ph.D....
- Baigorria, G.A., Romero, C.C. and Olivares, M., 2002. La Encañada and Tambomayo watersheds, Cajamarca, Peru. In...
- et al.
Atmospheric transmissivity: distribution and empirical estimation around Central Andes
International Journal of Climatology
(2004) - et al.
Adaptation of the Universal Soil Loss Equation to the Tropical Pacific Coastal Region of the Chiapas State, Mexico
Particle fractionation and particle size analysis
A Compendium of Soil Erodibility Data from WEPP Cropland Soil Field Erodibility Experiments 1987 and 88
Erodibility of selected tropical soils in relation to structural and hydrologic parameters
The “EMIRE” large rainfall simulator: design and field testing
Earth Surface Processes and Landforms
USDA-Water Erosion Prediction Project (WEPP). WEPP Users Summary
Mesoscale estimation of soil erosion in the Rio Ambato drainage, Ecuadorian sierra
Mountain Research and Development
Soil erosion and sustainable mountain development. Experiments, observations and recommendations from the Ecuadorian Andes
Mountain Research and Development
Field Measurement of Soil Erosion and Runoff
A survey of soil erosion processes in tropical forest ecosystems on volcanic ash soils in the Central Andean Cordillera, Colombia
Geografiska Annaler
Erosion processes in high mountain agricultural terraces in Peru
Mountain Research and Development
Estudio integrado de caracterizacion de recursos naturales renovables en microcuencas altoandinas para el alivio a la pobreza en la sierra
Microcuenca La Encañada, Cajamarca
A small rainfall simulator for the determination of soil erodibility
Netherlands Journal of Agricultural Science
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