Soil erosion in the northwestern Amhara region, Ethiopia has been a subject of anxiety, resulting in a major environmental threat to the sustainability and productive capacity of agricultural areas. ...This study tried to estimate soil erodibility factor (K-factor) using Universal Soil Loss Equation (USLE) nomograph, and evaluate the spatial distribution of the predicted K-factor in a mountainous agricultural watershed. To investigate the K-factor, the 54km2 study watershed was divided into a 500m by 500m square grid and approximately at the center of each grid, topsoil samples (roughly 10 to 20cm depth) were collected over 234 locations. Sand, silt, clay and organic matter (OM) percentage were analyzed, while soil permeability and structure class codes were obtained using the United States Department of Agriculture (USDA) document. The resulting coefficient of variation (CV) of the estimated K-factor was 0.31, suggesting a moderate variability. Meanwhile, the value of nugget to sill ratio of K-factor was 0.32, which categorized as moderate spatial autocorrelation. Prediction accuracy and model fitting effect of the Gaussian semivariogram approach was best, suggesting that the Gaussian ordinary Kriging model was more appropriate for predicting K-factor. The resulting value of the mean error (ME) was 0 and the mean squared deviation ratio (MSDR) was nearly 1, which indicates the Gaussian model was unbiased and reproduced the experimental variance sufficiently. The values of K-factor were smaller (0.0217 to 0.0188) in the northern part and gradually increased (0.0273 to 0.033MghMJ−1mm−1) towards the central and south of the study watershed.
In 1994 a field study started at three sites in eastern Austria to investigate the impacts of mulch till and no-till on soil erosion, surface runoff, nutrient and pesticide losses. The aim of this ...paper is to show long-term impacts of reduced tillage on runoff, erosion and related processes.
The experiments were carried out on fields of agricultural schools in Lower Austria about 100 km north and west of Vienna. Soil textures range from silt loam to silty clay loam. Average annual rainfall at the sites ranges from 621 to 916 mm with average annual air temperatures between 9.4 and 10.4 °C. The following soil tillage treatments were investigated: (1) conventional tillage system with ploughing in fall (CT), (2) mulch tillage with cover crops during winter (MT) and (3) no-till with cover crops during winter (NT).
Throughout growing season event based measurements of soil erosion, surface runoff, and nutrient and carbon losses were conducted for all sites and tillage systems. Data on losses of pesticide residues are only available for a few years. The crop rotation at the sites was mainly small grains-root crop but included also other field crops.
On a long-term basis reduced tillage practices decreased surface runoff from silt loam by 25–55 % (MT) and 49–60 % (NT). For the not well drained silty clay loam soil an increase by 12–21 % was observed which is related to significantly higher soil bulk densities of MT and NT in the 0−20 cm depth. Mean long-term annual erosion rates for CT ranged between 8.6 and 33.2 t ha−1, for MT between 3.6 and 5.3 t ha−1and for NT between 1.9 and 3.0 t ha−1. Compared to conventional tillage MT and NT reduced soil loss from a silty clay loam by 38 and 65 %, and from silt loam by 70–88 % and 84–93 %, respectively. 10−30% fewer erosion events occurred from MT plots and about 20 % fewer events from NT plots. Higher aggregate stabilities of MT and NT due to higher soil organic carbon contents in the 0−10 cm soil depth, higher soil cover as well as lower flow velocities are responsible for this reduction in soil loss from reduced tillage treatments.
Low erosion rates from the reduced tilled plots correlated with low runoff losses of nitrogen and phosphorus. Total nitrogen losses ranged from 13.3–48.1 kg ha−1 for CT, from 4.5–18.7 kg ha−1 for MT and from 1.6–9.4 for NT. Total nitrogen losses ranged from 13.3–48.1 kg ha−1 for CT, from 4.5–18.7 kg ha−1 for MT and from 1.6–9.4 for NT. Corresponding total P losses ranged from 6.7–29.4 kg ha−1 for CT, 2.1 to 3.7 kg ha−1 for MT and from 0.7 to 2.4 kg ha−1 for NT. Low erosion rates from the reduced tilled plots correlated with low runoff losses of nitrogen and phosphorus even though N and P concentrations in runoff were greater than from CT and sediments were enriched severalfold in N and P. Conservation tillage methods reduced the SOC losses by 34–86 % for MT and by 58–89 % for NT. Other studies show that these results are not only obtained in central Europe but also in other regions worldwide.
The long-term results of this study show that the use of mulch and no tillage in well-drained soils is beneficial for the farmers under central European conditions by improving soil´s aggregate stability and soil water contents and for the environment by reducing soil and nutrient losses.
Purpose
Land degradation due to soil erosion is a serious threat to the highlands of Ethiopia. Various soil and water conservation (SWC) strategies have been in use to tackle soil erosion. However, ...the effectiveness of SWC measures on runoff dynamics and sediment load in terms of their medium- and short-term effects has not been sufficiently studied.
Materials and methods
A study was conducted in 2011 to 2015 in the Gumara-Maksegnit watershed to study the impacts of SWC structures on runoff and soil erosion processes using the soil and water analysis tool (SWAT) model. The study was conducted in two adjacent watersheds where in one of the watersheds, SWC structures were constructed (treated watershed (TW)) in 2011, while the other watershed was a reference watershed without SWC structures (untreated watershed (UW)). For both watersheds, separate SWAT and SWAT-CUP (SWAT calibration and uncertainty procedure) projects were set up for daily runoff and sediment yield. The SWAT-CUP program was applied to optimize the parameters of the SWAT using daily observed runoff and sediment yield data.
Results and discussion
The runoff simulations indicated that SWAT can reproduce the hydrological regime for both watersheds. The daily runoff calibration (2011–2013) results for the TW and UW showed good correlation between the predicted and the observed data (
R
2
= 0.78 for the TW and
R
2
= 0.77 for the UW). The validation (2014–2015) results also showed good correlation with
R
2
values of 0.72 and 0.70 for the TW and UW, respectively. However, sediment yield calibration and validation results showed modest correlation between the predicted and observed sediment yields with
R
2
values of 0.65 and 0.69 for the TW and UW for the calibration and
R
2
values of 0.55 and 0.65 for the TW and UW for the validation, respectively.
Conclusions
The model results indicated that SWC structures considerably reduced soil loss by as much as 25–38% in the TW. The study demonstrated that SWAT performed well for both watersheds and can be a potential instrument for upscaling and assessing the impact of SWC structures on sediment loads in the highlands of Ethiopia.
Soil erosion and runoff data are collected at three sites in eastern Austria using field erosion plots. Observed treatments include 1) conventional tillage with plough (CT), 2) mulch tillage with ...winter cover crop (MT), and 3) no-till with winter cover crop (NT). Data cover a time span from 1994 to 2018. They include data about surface runoff, soil loss, nitrogen, phosphorus and soil organic carbon losses as well as cop yields associated with the erosion processes. Interpretation of the data will be found in “Long-term experience with conservation tillage practices in Austria: impacts on soil erosion processes” 1.
Rift Valley-Awash River Basin, Ethiopia
Irrigation schemes in Awash Basin, Ethiopia, are severely affected by the buildup of soil salinity. The main source of the salinity is shallow groundwater ...heightened by improper irrigation practices and management. However, salinity predictions have not been developed based on direct measured data for the basin. Therefore, this study aims predicting topsoil salinity in irrigated land from basic hydrological parameters using two approaches: Artificial neural networks (ANNs) and Partial least squares regression (PLSR). Irrigation water amount, water table depth, precipitation and estimated canal seepage were considered for variable inputs.
Our results showed that ANNs were superior over PLSR in predicting soil salinity, explaining 77% vs. 45% of the variance in soil salinity with root mean square error (RMSE) of 0.12 vs. 0.94 dS/m. In both models, groundwater depth is the most influential variable for soil salinity prediction, with relative contributions of 63% and 65% for PLSR and ANNs, respectively. Though, irrigation water is non-saline river water, it contributes to the rising groundwater table which contains high salinity. Our study demonstrates that proper irrigation management, use of drainage system, and reducing high seepage from the irrigation canal system will sustain the depth of the water table, and simultaneously reduces top-soil salinity accumulation and productivity loss in the Rift Valley Region of Awash Basin.
Display omitted
•The study uses artificial neural networks and partial least square regression to predict soil salinity of irrigated fields.•Prediction of soil salinity was better when using artificial neural networks compared to partial least square regression.•Groundwater table depth was the most influential variable for soil salinity prediction.•Irrigation and canal seepage contributed to rising groundwater.
Besides the importance of dissolved organic matter (DOM) in soil biogeochemical processes, there is still a debate on how agricultural intensification affects the leaching of terrestrial DOM into ...adjacent aquatic ecosystems. In order to close this linkage, we conducted a short-term (45 day) lysimeter experiment with silt loam and sandy loam undisturbed/intact soil cores. Mineral (calcium ammonium nitrate) or organic (pig slurry) fertilizer was applied on the soil surface with a concentration equivalent to 130 kg N ha.sup.-1. On average, amounts of leached DOC over 45 days ranged between 20.4 mg (silt loam, mineral fertilizer) and 34.4 mg (sandy loam, organic fertilizer). Both, mineral and organic fertilization of a silt loam reduced concentration of dissolved organic carbon (DOC) in the leachate and shifted its composition towards a microbial-like signature (BIX) with a higher aromaticity (Fi) and a lower molecular size (E2:E3). However, in sandy loam only mineral fertilization affected organic matter leaching. There, lowered DOC concentrations with a smaller molecular size (E2:E3) could be detected. The overall effect of fertilization on DOC leaching and DOM composition was interrelated with soil texture and limited to first 12 days. Our results highlight the need for management measures, which prevent or reduce fast flow paths leading soil water directly into aquatic systems, such as surface flow, fast subsurface flow, or drainage water. Keywords: Absorbance spectra; agricultural management; dissolved organic carbon (DOC); dissolved organic matter (DOM); fluorescence spectra; lysimeter; mineral; organic; soil pore water
The interaction between rainfall erosivity parameters and splash erosion is crucial for describing the soil erosion process; however, it is rarely investigated under natural rainfall conditions. In ...this study, we conducted splash erosion experiments under natural rainfall on three sites in Central Europe. The main goal was to obtain the relationship between splash erosion of the bare soil in seedbed condition and commonly used rainfall erosivity parameters (kinetic energy, intensity, and rainfall erosivity (EI30)). All sites were equipped with a rain gauge and an optical laser disdrometer where the splash erosion was measured, with modified Morgan splash cups. In order to investigate which parameter best describes the splash erosion process for all sites, a regression analysis was performed. In total, 80 splash erosion events were evaluated. Splash erosion can be described as a linear function of total kinetic energy and a non-linear function of EI30. However, the use of the total kinetic energy led to underestimation of the splash erosion rates for highly intensive rainfalls. Therefore, better results were obtained when using average rainfall intensity as the splash erosion predictor or the kinetic energy divided by the rainfall duration. Minor differences between the replicates during splash erosion measurements indicate that the modified Morgan splash cup provides a good tool for soil erosion assessment.
PDF
