Nutrient budgets in short rotation black wattle (Acacia mearnsii) stands for charcoal production as compared with teff (Eragrostis tef) cultivation

A rapid land use change from cropland to short-rotation forestry (SRF) with black wattle ( Acacia mearnsii De Wild.) has taken place in northwest Ethiopia. The market demand for charcoal in urban areas is the main driver of the SRF expansion. Farmers grow A. mearnsii in 5–6 years rotations and they use the wood for charcoal production and fuel wood. We investigated the sustainability of the land use change through comparing nutrient budgets for the A. mearnsii plantations with teff ( Eragrostis tef (Zucc.) Trotter) cultivation. We considered two harvest scenarios for A. mearnsii : whole biomass harvest and leaves retained on site. The average symbiotic nitrogen (N) fixation in the A. mearnsii stands was 175 kg N ha −1 y −1 . However, we did not observe any net accumulation of total N in the soil. The results suggest that the A. mearnsii cultivation depends on soil organic matter mineralization to mobilize organically bound phosphorus (P) and sulfur (S), in order to sustain the biomass production. Furthermore, A. mearnsii cultivation increased the net excess export of base cations by 110 % compared to E. tef, even when leaves were retained on the site. This export further increased to 155 % under the whole biomass harvest scenario. Thus, the land use change to SRF will lead to an intensified soil acidification. The findings highlight the need for improved nutrient management practices. These include the recycling of biomass residues and ash and potentially P and S fertilization to ensure the long-term sustainability of A. mearnsii cultivation in the region. • A. mearnsii fixed 175 kg N ha −1 y −1 but no net soil N increase was observed. • A. mearnsii depletes soil P and S stocks to sustain growth. • Base cation export was more than double in A. mearnsii stands compared to E. tef. • A. mearnsii cultivation needs external nutrient input for long-term sustainability.