Increased in soil total nitrogen (TN) as influenced by Faidherbia albida here after F. albida have been explored for decades. However, changes in ammonium (NH 4 +) to nitrate (NO 3 -) ratios as influenced by the tree and the relationships with other soil physicochemical and biological properties were not explored. Thus, the present study was carried out in 2023 to investigate changes in soil NH 4 +/ NO 3 - ratios and the relationships with biotic and abiotic factors across different stand age of F. albida in a semi-arid Arenosols at Abraha we Atsbeha, northern Ethiopia. Soil NH 4 + and NO 3 - were extracted using analytical grade potassium chloride solution and their concentrations were determined by colorimetric method using UV-VIS spectrophotometer (Model: UV-VIS Spectrophotometer, Series No.: AE1605020). One-way analysis of variance (ANOVA) was done to compare means and Pearson correlations using IBM SPSS Statistics Version 20, and redundancy analysis (RDA) using CANOCO software to understand the relationships among soil physicochemical and biological variables. Our results indicated that TN, NH 4 +, NO 3 - and NH 4 +/ NO 3 - ratios significantly (P < 0.05) increased with F. albida stand age. The most important thing here was that the proportion of NH 4 + has been succeeding over NO 3 - and this could have profound effect on both below and above ground features of the Arenosol agro-ecosystem. Moreover, redundancy analysis (RDA) showed that NH 4 + concentration strongly associated with soil moisture content (MC), cation exchange capacity (CEC), TN, extractable base cations (K, Ca, Mg), extractable phosphorus (EP), soil organic Carbon (SOC), organic matter (OM) microbial biomass carbon (MBC), clay texture, abundance of nematodes, density of fibrous rooted weeds while it was found to have negative relationships with soil bulk density, sandy texture and pH. Our findings enabled us to accept the hypothesis that NH 4 +/ NO 3 - ratios would increase with increasing F. albida stand age. In conclusion, increased F. albida stand age in agro ecosystems would increase NH 4 +/ NO 3 - ratios. Consequently, this triggered below and above ground communities successions and ultimately surpasses production and productivity of arid and semi-arid Arenosols.

Conservation agriculture (CA) systems represent a set of three soil management principles that include minimal soil disturbance, permanent soil cover and crop rotations whereas the CA-based systems in this study add the bed and furrow tillage structures as integral elements of CA. This study aimed at investigating the long-term (2005-2013) influence of CA-based systems on soil health and crop productivity in northern Ethiopia. The treatments include two types of CA-based systems (permanent raised bed PRB and contour furrowing CF) and conventional tillage (CT). The experimental layout was arranged in a randomized complete block design. Soil samples were collected at 0-10 cm soil depth to assess soil health. Wheat root samples were used to measure arbuscular mycorrhizal fungi (AMF) colonization percentage using grid line intersect method. Piecewise structural equation modeling (PSEM) was used to understand linkages between management practices, soil health and crop productivity. Higher soil microbial biomass carbon (SMBC), AMF spore abundance and root colonization were recorded in PRB followed by CF as compared to CT (P < 0.05). Carbon sequestration rate, nutrient availability, plant available water capacity and air capacity were significantly higher in PRB and CF compared to CT. Outputs of the PSEM highlighted two pathways in which CA-based systems contributed to improved productivity: (1) via higher density of bacteria and improved hydraulic conductivity, and (2) via higher density of fungi and increase soil organic carbon content in the topsoil. The study concludes that CA-based systems have the potential to improve crop productivity through improved soil health.

Afforestation of degraded lands using both exotic and indigenous species is used to reduce land degradation and to reforest degraded areas. Acacia saligna is one of the common exotic plantation species planted in Ethiopia. This study analyzed the existing carbon stock and some soil physico-chemical properties of A. saligna plantation at two districts in Tigray, northern Ethiopia. Soil samples were collected from 204 samples at three soil depths from plantation site and adjacent grazing lands. Paired t-test was used to analyze data. Soil organic carbon (SOC) stock was higher at lower depth (40-60cm) than middle and upper depths at plantation sites while the second depth (20-40cm) was found higher SOC at grazing lands. Furthermore, in Mai-Brazio, soil properties except Total nitrogen(TN) and Available Phosphorus (Av,P), Cation Exchange Capacity (CEC), Available Potassium (Av,K) and soil pH were significantly (P<0.05) higher than adjacent grazing lands While CEC and Av.K were non-significant in Barka-Adisbha site (p>0.05). Area converted to plantation site showed lower soil bulk density than the open grazing land. Further, CEC is negatively correlated (P < 0.001) with soil pH, this may shows that CEC is affected by the variation of soil pH.