Soil Fertility Mapping of Agamsa Watershed in Habru District, Northeastern Ethiopia

Declining soil fertility is the major challenge to boost crop production in Ethiopia. As a result, assessment of soil fertility status and mapping can help to design site specific soil fertility management techniques. Therefore, this study was conducted at Agamsa watershed in Habru District, Northeastern Ethiopia, with the objectives of assessing the soil fertility status of the watershed and mapping the spatial distribution of the selected soil fertility parameters. Field survey was conducted during the 2015/16 cropping season and nine composite soil samples were collected from top soil (0 to 20cm) for laboratory analysis following the standard procedures. Arc GIS software was used to prepare soil fertility maps and soil test values at other locations were interpolated using geostatistical technique of ordinary Kriging. The soil textural class was clay loam. The highest soil BD was 1.37 g cm-3 whereas the lowest was 1.22 g cm-3. Similarly, total porosity ranged from 42.92% to 52.49%. The water content at FC ranged from 33.64% to 42.17% while that of PWP ranged from 20.12% to 26.67% on the surface soil (0-20cm). AWHC values in the study area were between 13.19% and 17.23%. The soil pH (pH_H2O) ranged from 5.8 to 6.7 (moderately acidic to neutral range). The highest and lowest values of TN were 0.21% and 0.06%, respectively while that of OM ranged from 1.17% to 3.71%. Similarly, the highest and lowest values of AP were 9.65 mg kg-1 and 2.5 mg kg-1, respectively. The relative abundance of basic cations in the exchangeable complex of soil was dominated by Ca followed by Mg, K and Na and the values ranged from 20.38 to 31.72, 8.92 to 12.08, 0.29 to 0.59 and 0.27 to 0.45cmolc kg-1, respectively. The highest and lowest values of CEC were 53.10cmolc kg-1 and 36.94cmolc kg-1. On the other hand, the relative abundance of micronutrients in the soil was dominated by Fe followed by Mn, Zn and Cu, with the values ranged from 7.25 to 16.55, 5.62 to 15.47, 0.7 to 5.70 and 1.66 to 4.12mg kg-1, respectively. The soils of Agamsa Watershed had good physical fertility status and pH range. The soils had sufficient exchangeable bases, CEC, PBS and available micronutrients. However, SOM, TN and AP were ranged low to medium. The soil fertility management should focus on improving and maintaining OM, TN and AP level of the soils. In order to increase soil OM, AP and TN content, farmers should practice crop rotation like cereal-pulse crop based, minimize removal of crop residues and animal manures, and as combined applications of organic and inorganic fertilizers. Moreover, nutrient supplying powers of the soils and demanding levels of the plants need further correlation and calibration works to come up with site-soil-crop specific fertilizer recommendation