RESUMEN

Soil erosion by water and wind is among the most crucial land degradation processes in Ethiopia. This is also the case for Alage watershed located in the cental Rift Valley system. This study aimed at assessment of soil erosion hazard and its relation to land use land cover change in the watershed during the period from 1984 to 2016 for a better land management. The study is based on application of Remote Sensing (RS) and Geographical Information System (GIS) to extract inputs factor values for the Revised Universal Soil Loss Equation (RUSLE). Time-series satellite imageries of Landsat TM 1984, ETM+ 2000 and OLI 2016 were used for land use land cover change detection and determination of cover management (C) factor of the RUSLE. Biophysical data such as rainfall, soil properties, land management practices including soil and water conservation measures within the watershed were collected using field survey and secondary data sources. Slope steepness and slope length factors were derived using Digital Elevaition Model (DEM). Long-term average annual soil loss rates were estimated by the RUSLE integrated with GIS for 1984, 2000 and 2016. Using satellite imageries, the land use land cover and changes within the watershed during the three periods were obtained through a supervised classification with maximum likelihood algorithim. The results of land use land cover change indicated that the proportion of rain-fed cropland, bare land and built up areas increased by 17.4%, 5.9% and 2.9% respectively over the three study period. In contrast the proportion of bush/shrub land, irrigated cropland, grass land, forested areas and waterbodies decresaed by 15.5%, 4.7%, 3.4%, 2.3% and 0.3% respectively during the same period. Estimated average annual soil loss rates showed an increasing trend from 24.3 ton ha-1 yr-1 in 1984 to 38 ton ha-1 yr-1 in 2016. Increasing trends of average annual soil loss rate is attributed to increased proportion of cropland, bare land and built up areas during those periods leading to decreased protective vegetation cover. Hotspot areas within the watershed require implementation of land management practices to prevent further degradation and expansion of gullies. This study is relevant to demonstrate environmental implication of land use land cover change for future land management practices and land use policy in the Rift Valley of central Ethiopia.

RESUMEN

Soil erosion by water is a major cause of land degradation in the highlands of Ethiopia and anywhere else in the world, but its magnitude and variability are rarely documented across land uses and climatological conditions. The purpose of this study was to examine runoff and soil loss responses under cropland (CL) and grazing land (GL) management practices in three climatic regions of the Ethiopian highlands: semi-arid (Mayleba), dry sub-humid (Gumara), and humid (Guder). We measured runoff and soil loss using runoff plots with and without soil and water conservation (SWC) measures (trenches, stone/soil bunds [embankments] with trenches on the upslope side, and exclosure) during the rainy season (July-September). The results revealed significant variation in runoff and soil loss amounts across land uses, SWC measures, and climatic regions. At Mayleba, seasonal runoff and soil loss in control plot were far higher from GL (280 mm, 26.5 t ha-1) than from CL (108 mm, 7.0 t ha-1) largely due to lack of protective vegetation cover and soil disruption because of intense grazing. In contrast, at Gumara and Guder, seasonal soil loss values were much higher from CL (21.4-71.2 t ha-1) than from GL (0.6-24.2 t ha-1) irrespective of runoff values. This was attributed to the excessive tillage/weeding operations involved in cultivation of teff (cereal crop) at Gumara and potato at Guder. Although SWC measures (practices) substantially reduced runoff and soil loss (decreased by 23%-86%) relative to control plot, seasonal soil loss under GL uses with trenches at Mayleba (12.6 t ha-1), CL with soil bunds and trenches at Gumara (22.1 t ha-1), and Guder (21.4 t ha-1) remained higher than the average tolerable soil loss rate (10 t ha-1 year-1) proposed for the Ethiopian highlands. This suggests that SWC measures should be carefully designed and evaluated specific to land use and climatic conditions. Overall, the results of this study can help improve SWC planning in regions where land use and climate impact on soil erosion vary across geographical areas, as they do in Ethiopia and anywhere else. However, further investigation is crucial with replication of measurements over years and locations to provide more accurate information on land use, management and climate controls on hydrological and soil erosion processes.

Asunto(s)

RESUMEN

Increasing costs of chemical fertilizers, environmental concerns of their application and demand for protein foods, placed an extensive interest in growing of legume crops for human nutrition, and soil fertility replenishment. This study was conducted to investigate the effects of nitrogen (N) and phosphorus (P) fertilizers on parameters of phenology, growth performance, grain yield, yield components, grain protein content of groundnut, and residual soil nitrogen content in the northern Ethiopia during the growing season of 2017. Three levels of N (0, 15 and 30 kg ha-1) and four levels of P2O5 (0, 23, 46 and 69 kg ha-1) were set in factorial combinations of randomized complete block design with three replications. Results showed that an average total biomass yield increased by 22.5% for separate individual application of 15 kg N ha-1 and by 16.6% for 46 kg P2O5 ha-1 compared to control plots. Haulm yield increased by 29.17% for plots treated with N fertilization compared to control plots. Average pod yield increased by 85.4% for a combined application of 15 kg N ha-1 and 46 kg P2O5 ha-1 fertilizers compared to the control plots. Plots fertilized with the highest combined rates of N and P have attained lower grain yield compared to the combined application of 15 kg N ha-1 and 46 kg P2O5 ha-1. The highest grain protein contents were obtained for a combined application of 30 kg N ha-1 and zero P, and 15 kg N ha-1 plus 46 kg P2O5 ha-1. The highest N harvest index was obtained for control treatments and for plots treated with combined application of 15 kg N ha-1 and 46 kg P2O5 ha-1. Residual soil N content increased by 119% on plots with combined application of 15 kg N ha-1 and 46 P2O5 ha-1 compared to control plots. Based on our results, combined application of 15 kg N ha-1 and 46 kg P2O5 ha-1 was recommended for increasing grain yield, grain protein content and residual soil nitrogen. The results of this study are crucial to improve groundnut productivity, grain protein content and also to provide implication on soil fertility management in a crop rotation system.