Maintaining Acacia polyacantha trees in farmlands enhances soil fertility and income of farmers in North Western Tigray, Northern Ethiopia Emiru Birhane . Roman Teklay . Kindeya Gebrehiwet . Negasi Solomon . Tewodros Tadesse Received: 22 March 2018 / Accepted: 19 November 2018 Ó Springer Nature B.V. 2018 Abstract Acacia polyacantha is a fast growing indigenous tree legume that can be integrated with crops as parkland agroforestry system. Farmers keep Acacia polyacantha on their farmlands mainly for fuel wood, animal fodder, farm tools and construction. However, quantitative information on the effect of Acacia polyacantha on soil fertility improvement and socioeconomic benefits is lacking. The effect of Acacia polyacantha on soil fertility and its contribu- tion to household income was evaluated in La’ilay Adiyabo district, northern Ethiopia. At three radii distances, 36 soil samples were collected from two soil depths from 24 trees in cultivated and uncultivated land using a 3 9 2 9 2 9 3 factorial arrangement in randomized complete block design (RCBD) replicated three times. The effect of planting Acacia polyacantha trees on household income was estimated using Ordinary Least Squares based on data collected from a sample of 120 randomly selected farm households. Total N, OC, OM, CEC and exchangeable K levels were significantly higher under the canopies of Acacia polyacantha than outside (p \ 0.05). The nutrient levels decreased significantly with increasing soil depth. Planting Acacia polyacantha trees was found to positively and significantly influence household income, in which case the aggregated monetary value of the different products from Acacia polyacantha contributed 13.7% to total household income, which is significant. However, land size was also found to be crucial; and the role that Acacia polyacantha trees play can be further increased through efficient use and management of agroforestry land. Keywords Acacia polyacantha Á SOIL FERTILITY Á Income Á Agroforestry Á OLS Introduction In the face of climate and environmental change, adoption of land use options that increase livelihood security and reduce vulnerability is crucial (Pandey 2007). Agroforestry system is one of the promising land use types that can improve livelihoods directly or indirectly (Pandey 2007). Various agroforestry sys- tems have been widely used across different parts of the world for different purposes (Nair 1991). For E. Birhane (&) Á R. Teklay Á K. Gebrehiwet Á N. Solomon Department of Land Resources Management and Environmental Protection, Mekelle University, P.O. Box 231, Mekelle, Ethiopia e-mail: emiru.birhane@mu.edu.et E. Birhane Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, 1432 A ˚ s, Norway T. Tadesse Department of Agricultural and Resource Economics, Mekelle University, P.O. Box 231, Mekelle, Ethiopia 123 Agroforest Syst https://doi.org/10.1007/s10457-018-0328-1