Stefan Strohmeier

Linking selected soil properties to land use and hillslope – A watershed case study in the Ethiopian Highlands

Addis H., Klik A., Oweis T., Strohmeier S. (2016): Linking selected soil properties to land use and hillslope – A watershed case study in the Ethiopian Highlands. Soil & Water Res., 11: 163−171. Deforestation of native forests for crop production in the Gumara-Maksegnit watershed, located in the Lake Tana basin, Ethiopia, dramatically increases the vulnerability of the soil for rainfall driven erosion. Hence, the central task of the study is to investigate general links of land-use and topography related to selected soil properties. The 53.7 km2 watershed was divided into a 500 × 500 m square grid to sample bulk density (ρd), pH, soil organic carbon (SOC), total nitrogen (TN), available phosphorus (AP), and texture of topsoil. Such properties were investigated with respect to the two main land-uses, forest and agriculture, and three different slope steepness classes, 0–10%, 10–30%, > 30%. Descriptive statistics and correlation analyses were undertaken to explore potential dependencies of the obtained soil parameters according to land-use and slope steepness. The study indicates higher SOC, TN, silt and sand content in forest soils compared to agricultural soils, while solely ρd is lower in the forest soil. Overall increases of SOC, TN, silt, and sand content from the gentle to the steep slopes have been observed for both land-uses. In contrast, clay content and ρd seem to increase from steep to gentle slopes on agricultural areas, which might be due to accumulation of particularly fine soil particles eroded from the steep areas. Basic correlations valid for all land-uses and slope steepness classes have not been detected. Nevertheless, the study suggests slope steepness as a tool to assess the potential drivers of soil depletion in the Ethiopian Highlands.

Effect of nitrogen fertilizer rate and timing on sorghum productivity in Ethiopian highland Vertisols

ABSTRACT Sorghum is cultivated on Vertisols in the Ethiopian Highlands. An experiment was conducted in the Gumara-Maksegnit watershed in 2013 and 2014 to assess the effect of rate and timing of nitrogen fertilizer application on the possibility to shorten the maturity period and to improve the productivity of sorghum. The experiment was laid out as Randomized Complete Block Design with three replications. Treatments were nitrogen doses between 0 and 87 kg N ha−1 as urea applied at planting, at knee-height stage or in split doses at both stages. Results showed that application of 23, 41, 64 and 87 kg ha−1 N gave a yield increase of 40, 53, 62 and 69% over the control (0 kg N ha−1), respectively. In addition, split application of 41 kg ha−1, 64 kg ha−1 and 87 kg ha−1 of nitrogen fertilizer, half at planting and half at knee height stage, gave 19%, 15% and 18% increase in sorghum grain yield over a single dose application, respectively. Applying 87 kg ha−1 nitrogen fertilizer with split application half at planting and half at knee height stage, along with 46 kg ha−1 of P2O5, gave the highest grain yield and income.

Prediction of soil and water conservation structure impacts on runoff and erosion processes using SWAT model in the northern Ethiopian highlands

PurposeLand 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 methodsA 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 discussionThe 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 (R2 = 0.78 for the TW and R2 = 0.77 for the UW). The validation (2014–2015) results also showed good correlation with R2 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 R2 values of 0.65 and 0.69 for the TW and UW for the calibration and R2 values of 0.55 and 0.65 for the TW and UW for the validation, respectively.ConclusionsThe 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.

Assessment of gully erosion using conventional field measurements: A case study from northern Ethiopia

In Ethiopia, one of the poorest countries in the world, soil erosion by water contributes significantly to food insecurity of rural households and represents a real threat to sustainability of the existing subsistence agriculture (Hurni 1993; Sutcliffe 1993; Sonneveld 2002). Ethiopia has a total surface area of 111.8 million ha (276.3 million ac); 24% of the land area, and 45% of the area used for agriculture, is significantly affected by erosion. Studies by Fikru (1990) and Sertsu (2000) estimate an annual total soil loss of 2 billion m3 (71 billion ft3), which corresponds to an overall mean annual soil loss of 18 t ha−1 (8.0 tn ac−1). Other studies suggest erosion rates ranging from 16 to 300 t ha−1 y−1 (7.1 to 133.8 tn ac−1 yr−1) (Hurni 1993; Hawando 1989, 1995). In the Ethiopian highlands, annual soil loss reaches rates up to 200 to 300 t ha−1 (89.2 to 133.8 tn ac−1), while global soil loss can reach up to 23,400 million t y−1 (25,787 million tn yr−1) (FAO 1986). Compared to rill and interrill erosion rates measured in Europe (Cerdan et al. 2010), these soil losses are much higher. Occurrence of wide and deep gullies is a common observation…

Erosion Plot Monitoring: Impact of Different Tillage Systems on Average Annual Soil Erosion and the Significance of Extreme Rainfall Events

Based on the Lower Austrian erosion plot monitoring program, general behavior of surface runoff and soil loss on agricultural fields in the north-eastern alpine uplands has been analyzed since 1994.