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In arid Africa, it is unclear how the transition from grassland to cropland affects CO2 fluxes and whether these effects are climate-dependent. From November 2019 to March 2020 (dry season), we studied autotrophic (Ra) and heterotrophic (Rh) soil respiration. At highlands, grazing land (1.18 ± 0.13 µmol m−2 s−1) and teff croplands (1.36 ± 0.14 µmol m−2 s−1) had the lowest Rh, while acacia decurrens plantations (1.94 ± 0.19 µmol m−2 s−1) were the largest. When compared to teff (2.08 ± 0.20 µmol m−2 s−1) and khat (1.73 ± 0.24 µmol m−2 s−1), grazing land in the midland had a lower Rh (1.18 ± 0.13 µmol m−2 s−1). Ra on teff (1.51 ± 0.27 µmol m−2 s−1) was substantially (P < 0.05) greater than on grazing land (1.08 ± 0.32 µmol m−2 s−1) in the highlands. Grazing lands (1.54 ± 0.21 µmol m−2 s−1) have a considerably (P < 0.05) greater Ra than farmlands (teff, 0.20 ± 0.07 µmol m−2 s−1; groundnut, 0.09 ± 0.03 µmol m−2 s−1) in lowlands. Growing teff in the highlands and midlands will result in higher CO2 fluxes into the atmosphere. However, in-depth research is needed to implement effective land management that reduces CO2 emissions.

In arid Africa, it is unclear how the transition from grassland to cropland affects CO2 fluxes and whether these effects are climate-dependent. From November 2019 to March 2020 (dry season), we studied autotrophic (Ra) and heterotrophic (Rh) soil respiration. At highlands, grazing land (1.18 ± 0.13 µmol m−2 s−1) and teff croplands (1.36 ± 0.14 µmol m−2 s−1) had the lowest Rh, while acacia decurrens plantations (1.94 ± 0.19 µmol m−2 s−1) were the largest. When compared to teff (2.08 ± 0.20 µmol m−2 s−1) and khat (1.73 ± 0.24 µmol m−2 s−1), grazing land in the midland had a lower Rh (1.18 ± 0.13 µmol m−2 s−1). Ra on teff (1.51 ± 0.27 µmol m−2 s−1) was substantially (P < 0.05) greater than on grazing land (1.08 ± 0.32 µmol m−2 s−1) in the highlands. Grazing lands (1.54 ± 0.21 µmol m−2 s−1) have a considerably (P < 0.05) greater Ra than farmlands (teff, 0.20 ± 0.07 µmol m−2 s−1; groundnut, 0.09 ± 0.03 µmol m−2 s−1) in lowlands. Growing teff in the highlands and midlands will result in higher CO2 fluxes into the atmosphere. However, in-depth research is needed to implement effective land management that reduces CO2 emissions. [ABSTRACT FROM AUTHOR]

In the drought-prone Upper Blue Nile River (UBNR) basin of Ethiopia, soil erosion by water results in significant consequences that also affect downstream countries. However, there have been limited comprehensive studies of this and other basins with diverse agroecologies. We analyzed the variability of gross soil loss and sediment yield rates under present and expected future conditions using a newly devised methodological framework. The results showed that the basin generates an average soil loss rate of 27.5 t ha − 1 yr − 1 and a gross soil loss of ca. 473 Mt yr − 1 , of which, at least 10% comes from gully erosion and 26.7% leaves Ethiopia. In a factor analysis, variation in agroecology (average factor score = 1.32) and slope (1.28) were the two factors most responsible for this high spatial variability. About 39% of the basin area is experiencing severe to very severe (> 30 t ha − 1 yr − 1 ) soil erosion risk, which is strongly linked to population density. Severe or very severe soil erosion affects the largest proportion of land in three subbasins of the UBNR basin: Blue Nile 4 (53.9%), Blue Nile 3 (45.1%), and Jema Shet (42.5%). If appropriate soil and water conservation practices targeted ca. 77.3% of the area with moderate to severe erosion (> 15 t ha − 1 yr − 1 ), the total soil loss from the basin could be reduced by ca. 52%. Our methodological framework identified the potential risk for soil erosion in large-scale zones, and with a more sophisticated model and input data of higher spatial and temporal resolution, results could be specified locally within these risk zones. Accurate assessment of soil erosion in the UBNR basin would support sustainable use of the basin's land resources and possibly open up prospects for cooperation in the Eastern Nile region. [ABSTRACT FROM AUTHOR]

• Soil properties significantly varied across agro-ecologcal zones & land uses types. • Croplands exhibited low values of most soil quality property parameters. • Sustainable land management practices improved sensitive soil properties. • Exlcosure substantially improved soil organic carbon and total nitrogen contents. The knowledge of how soil properties vary over space and time is essential to better understand the potential of soils and their sensitivity to management interventions under different local conditions. The objective of this study was to analyze the variation in key soil properties as influenced by different land use types (cropland, grazing land, and bushland) and sustainable land management (SLM) practices (soil bund reinforced with grass, and fanya juu for croplands, and exclosures with and without trenches for grazing and bushlands) in the three contrasting agro-ecological zones of the drought-prone Upper Blue Nile basin, Ethiopia. Nine soil properties—texture, bulk density (BD), pH, electrical conductivity (EC), cation exchange capacity (CEC), total nitrogen (TN), soil organic carbon (SOC), available phosphorus (P av), and available potassium (K av)—were measured for topsoil (0–20 cm) samples collected from experimental plots established for monitoring runoff and soil loss rates. The results showed that seven of the nine studied soil properties significantly differed among the three land use types in the three agro-ecological zones (P < 0.05 to P < 0.001); pH, CEC, SOC, and TN values were generally lower in croplands than in others. These results imply that soil quality under crop production has been greatly deteriorated by unsustainable cropping systems practiced over centuries. Three years after the implementation of SLM practices, however, most soil parameters become within optimal ranges for supporting plant production. More particularly, sensitive soil properties (BD, SOC, TN, P av , and K av) showed remarkable improvement in plots where soil bunds reinforced with grass and exclosures were implemented. This improvement was primarily associated with the development of well-established vegetation cover owing to the favorable natural conditions maintained by fencing of plots and minimum tillage. These results therefore indicate that soil degradation can best be controlled through enhancing vegetation growth and reducing soil disturbance by tillage operations. We conclude that integrating land uses with suitable SLM practices is the most effective way to maintain and restore soil quality and sustain ecosystem functioning. [ABSTRACT FROM AUTHOR]

• LULC changes, drivers and implications were examined (1982-2016/2017) in contrasting agro-ecologies. • Cultivated land has progressively increased in the first three decades across all agro-ecologies. • After 2012, A. decurrence has increased by 400% at the expense of cultivated land in highland agroecology (Guder). • Population growth associated with changing farming practices were the major drivers for LULC changes. • The expansion of cultivated land had aggravated the soil erosion and surface runoff in the watersheds. This study examined the trends, driving factors, and implications of land use/land cover (LULC) dynamics over the past 35 years (1982–2017) in three watersheds of the drought-prone areas that represent different agro-ecologies of Upper Blue Nile basin, Ethiopia: Guder (highland), Aba Gerima (midland), and Debatie (lowland). The changes in LULC were analyzed by integrating field observations, remote-sensing data (aerial photographs [1: 50,000 scale] and very high resolution [0.5–3.2 m] satellite images), and geographic information systems. The drivers of LULC were explored using key informant interviews and relevant literature reviews. The implications of LULC change on soil erosion and surface runoff responses were also evaluated. A minimum of four and maximum of six LULC classes were identified in each watershed over the study period. The study revealed that forest land was the dominant LULC class accounting for 40.9% and 32.0% in Guder and Aba Gerima, respectively in 1982. While in the same period, bush land (36.6%) was the dominant LULC class in Debatie watershed. From 1982 to 2016/2017, forest land, bush land, and grazing land respectively decreased by about 70%, 50%, and 27% in Guder; 65%, 49%, and 63% in Aba Gerima; and 63%, 59%, and 38% in Debatie. During the same period, cultivated land increased by approximately 40%, 129%, and 704% in Guder, Aba Gerima and Debatie, respectively. In contrast, between 2012 and 2017, plantation cover increased by about 400% in the Guder, mainly at the expense of cultivated land, which decreased by 40% for the same period. Population growth and associated changes in the farming practices were the major driving forces for the observed LULC changes in the study watersheds. The traditionally deleterious impacts of human activities on the environment have been recently reversed at an unprecedented rate, particularly at Guder and to a lesser extent at Aba Gerima, following the shift from the traditional annual cropping to more economically attractive tree-based farming practices such as Acacia decurrens plantation in Guder and khat (Catha edulis) cultivation in Aba Gerima. The continued expansion of cultivated land combined with population growth positively linked to the increase of gully erosion and surface runoff potential in the study watersheds particularly, in Aba Gerima and Debatie watersheds. The Upper Blue Nile basin is currently experiencing both positive and negative socio-economic and environmental consequences of LULC dynamics. Hence, the present study can help form a basis for the appropriate development of land management policies and strategies in this and other basins experiencing similar problems. [ABSTRACT FROM AUTHOR]