Towards sustainable watershed-based landscape restoration in degraded drylands: Perceived benefits and innovative pathways learnt from project-based interventions in Ethiopia.

Land degradation is one of the contemporary environmental challenges affecting regions inhabited by over one-third of the global population. In response to land degradation, restoration of degraded landscapes through area closure has been implemented through government and bilateral organizations for the last three decades in Ethiopia. Objectives of this study were to: i) explore the effects of landscape restoration on vegetation cover; ii) identify the perceived benefits to local communities; and 3) synthesize the lessons learnt on communities' willingness to sustain the restored landscapes. The study was conducted in project-supported restoration areas including the Dimitu and Kelisa watersheds representing the central rift valley dry lands and the Gola Gagura watershed representing the eastern dry land areas around Dire Dawa. The temporal changes in land use and land cover due to area closure integrated with physical and biological soil and water conservation measures were detected using GIS/Remote sensing techniques. Moreover, eighty-eight rural households were interviewed. The results of the study revealed that landscape restoration activities such as area closure integrated with physical soil and water conservation, and planting of trees and shrubs contributed to the significant changes in land covers of the watersheds in 3-5 years. Hence, barren lands were reduced by 35-100% while there were significant increases in forest lands (15%), woody grasslands (247-785%), and bushlands (78-140%). More than 90% of the respondents in the Dimitu and Gola Gagura watersheds verified that the landscape restoration activities improved vegetation cover and ecosystem services, reduced erosion, and increased incomes. A great majority of farm households (63-100%) expressed their willingness to contribute to different forms of landscape restoration interventions. Encroachment of livestock to closed area, shortage of finance, and the growing number of wild animals in closed area were the perceived challenges. Proper planning and implementation of integrated interventions, creating local watershed user associations, ensuring appropriate benefit-sharing and implementing innovative pathways to reconcile the tradeoffs could be considered to scale up interventions and address potential conflicts of interest.

Soil and water conservation management on hill slopes in southwest Ethiopia. II. Modeling effects of soil bunds on surface runoff and maize yield using AquaCrop.

On the cultivated slopes of the highlands of southwest Ethiopia, soil degradation due to water erosion is a challenge for crop production. To limit surface runoff and soil erosion, soil bunds often in combination with trenches, constructed along contour lines, are common. In addition to the interception of surface runoff, soil bunds may affect crop yield. Here, we evaluate effect of soil bunds on surface runoff and maize yield, using FAO's AquaCrop model, calibrated based on field experiments in the Bokole-Karetha watershed, in SW Ethiopia. Experiments were conducted in 2018 and 2019 on three neighboring fields, each comprising plots in triplicate without and with soil bunds. Experimental data from 2018 to 2019, which were average and above average with respect to rainfall, indicate that water availability was sufficient or even in excess for maize production. Soil bunds significantly (p < 0.05) reduced surface runoff, but maize yield did not differ significantly. In plots without soil bunds, the AquaCrop model described surface runoff satisfactorily after slight adjustment of the curve number (related to infiltration capacity) in one of the three fields. Maize yields were reproduced adequately after calibrating soil fertility and adjusting water productivity. After calibration and validation, the AquaCrop model was used to hindcast surface runoff and grain yield from 1999 to 2017, given available climatic data for the region. Hindcasts show that maize yield in the Bokole-Karetha watershed, with its relatively high rainfall, is not significantly affected by rainfall in two of the three fields. In the third field maize yield decreases slightly, but significantly (p < 0.05) with rainfall. In the short run, yield differences between plots with and without soil bunds are not significant. However, eventually high surface runoff from plots without soil bunds are expected to result in unsustainable crop production, due to significant erosion and degradation of the often nutrient-poor soils. Implementation of soil and water management techniques, combined with fertilization, are important to prevent soil degradation and nutrient stress on sloping land.

Soil and water conservation management on hill slopes in Southwest Ethiopia. I. Effects of soil bunds on surface runoff, erosion and loss of nutrients.

On the steep hill slopes of southwest Ethiopia, soil erosion may cause significant declines in soil organic carbon (SOC) and nutrients, negatively affecting cropland productivity. Soil bunds are advised as an effective means to reduce surface runoff and soil erosion. However, the effects on SOC and nutrients are rarely quantified. The objective of this study was to assess the quantitative effect of soil bunds on surface runoff as well as soil and nutrients losses from cropland in the region. Data was collected from experimental fields on three farms (fields 1, 2 and 3) in the Omo-Gibe River basin in southwest Ethiopia. On each farm, effects of soil bunds on runoff and erosion were investigated and compared with adjacent plots without soil bunds in the 2018 and 2019 growing seasons. Soil bunds effectively reduced surface runoff (by 80-92%). Without soil bunds, soil losses in the growing season were 5-22 t ha-1 in 2018 and 15-43 t ha-1 in 2019, on average removing 1.3-4 mm soil per year. Soil bunds decreased soil losses by about 96%. Observed soil losses from fields without soil bunds were well described by the Universal Soil Loss Equation (USLE; R2 = 0.92; p < 0.01). Of the total soil loss, 47-69% was removed in suspended form. Suspended material had significantly larger (p < 0.05) SOC, and plant available potassium (K) and phosphorus (P) concentrations than coarser, rapidly settling sediment and bulk soil. In 2019, up to 733 kg SOC ha-1, 77 kg total nitrogen ha-1 and 21 kg K ha-1 were lost per season from plots without soil bunds. For SOC this amounts to 6% of its stocks in the topsoil. Soil bunds are important controls on surface runoff, strongly limiting losses of SOC and nutrients in sloping croplands of southwest Ethiopia.