No abstract

Understanding topography effects and assessing the soil properties in different land use is an essential first step for sustainable soil management. Hence, land use type and altitudinal gradient on selected soil parameters were studied in Ayiba watershed, northern Ethiopia. Thirty composite soil samples were collected from 0 to 30 cm of soil depth under four land use types across three altitudinal gradients and were analyzed for selected soil parameters following the standard procedures. A significant main effect of land use and altitudinal gradient on the content of the soil particles was noted. Results also indicated that the bulk density (BD), total porosity (TP), and Pav of the soil are significantly different ( p  < 0.05) in the watershed because of land use type and altitudinal gradient. Barren land and higher altitude landscapes have the highest BD, and the lowest TP, and grassland and lower altitude landscapes have the lowest BD and high TP. Intensive cultivation accompanied by natural land conversion and erosion due to the rugged landscape nature caused high BD and low TP. Analysis of variance results also shows the significant interaction effect of land use type and altitudinal gradient on EC, SOM, SOC ( p  < 0.001), and pH-water (1:2.5), and TN ( p  < 0.01). The Pearson correlation of SOM with TP, TN, MC, and clay content showed a strong positive relationship. But, SOC, TN, and clay content were negatively correlated with BD. Soils of the study watershed are found in low to optimum rating levels in their selected physicochemical properties. Overall, the results show that land use and topography gradient significantly affected soil physicochemical properties in the study watershed. Therefore, soil management options should focus on scenarios that could improve the soil conditions to enhance crop production on a sustainable basis.

Soil quality is the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation. This definition of soil quality encompasses physical, chemical and biological characteristics, and it is related to fertility and soil health. Soil quality, which can be viewed in two ways [1] as inherent properties of a soil and [2] as the dynamic nature of soils as influenced by climate, and human use and management, often is related to soil degradation, which can be defined as the time rate of change in soil quality. Soil quality should not be limited to soil productivity but should encompass environmental quality, human and animal health, and food safety and quality. In characterizing soil quality, biological properties have received less emphasis than chemical and physical properties, because their effects are difficult to measure, predict, or quantify particularly in developing countries like Ethiopia is totally ignored science of the soil department but is very important than the physical and chemical indicators. Improved soil quality often is indicated by increased infiltration, aeration, macropores, aggregate size, aggregate stability, and soil organic Review Article, the highest in Sub-Saharan Africa), OM depletion(crop residue removal, intensive tillage, dung burning and deforestation) , Biological deterioration (Loss of SOM and decline in the biotic activity of soil fauna but the ignored part due to measurement facility), Chemical degradation (Salinity, sodicity, and Acidity) and Physical land degradation (deterioration of soil structure, crusting, compaction, erosion, and desertification). Thus, in the way forward, ways of soil monitoring are in need on a reasonably regular basis, the quality of soils at all levels from global, through to continental, national, regional and landscape/ catchment areas is getting due attention through the SDG framework; SDG 15 specifically calls for halting and reversing land degradation by 2030. It is only in this way which shall be able to evaluate the sustainability of the use to which people are putting the land. In line with this in Ethiopia, responsible governmental bodies and stakeholders are working on priority areas for action to improve soil fertility.

Understanding the role of soils in the soil organic carbon (SOC) and total nitrogen (TN) cycle is essential, assumed that these parameters are among the key soil quality indicators in a given landscape. Nothing but their status is in a state of continual flux due to land-use, soil management practices, and nature of topographic features. Thus, this study has evaluated the effect of land-use types and altitudinal gradient on SOC and TN concentrations and stocks at a watershed scale in northern Ethiopia. A total of 450 topsoil samples (0-30 cm depth) were collected from four different land-use types (Fig. 3) across three elevational categories (Fig. 1(b)), and their SOC and TN distributions were studied using descriptive statistics and geostatistical methods. Results revealed significant (p < 0.05) differences in SOC and TN concentrations and stocks by land-use type, elevation, and their interactions. The highest SOC stock was recorded at the lower elevation in GL (7.24 Mg C ha À1 ), followed by PF (4.65 Mg C ha À1 ) in the middle and GL (4.61 Mg C ha À1 ) in the upper elevations, respectively. On the other hand, the lowest SOC stock was observed in the BL areas of the upper (2.34 Mg C ha À1 ) and middle (2.75 Mg C ha À1 ) elevations. Spatially, the mean SOC stocks of the different land-uses were in the following order: GL > PF > CL > BL in upper elevation, PF > GL > CL > BL in middle elevation, and GL˃CL in lower elevation, respectively. The estimated total SOC and TN stocks of the study watershed were about 46,868.66 AE 7747.38 Mg C and 7,008.02 AE 441.25 Mg N, respectively. The notable difference is attributable to lack of vegetation cover, unsustainable land-use system, and land degradation via water erosion. Hence, these physical landscape disturbances result in disruption of SOC and TN's storage and stability. The SOC and TN stocks have shown a significant (p < 0.05) negative correlation with soil bulk density in the study watershed. The study concludes that variations in the land-use along topographic gradients drive the soils' SOC and TN storage. Therefore, land suitability planning, soil and water conservation measures, and reforestation practices are needed and practical worth increasing SOC and TN storage in the watershed.