Nutrient balances in small upland catchments of the Gumara River, northwestern Ethiopia

Abstract Nutrient balance analysis is a robust tool for evaluating soil fertility and identifying constraints to sustainable crop production. This study quantified nutrient flows and balances in the Enqulal watershed, Dera district, northwestern Ethiopia, during the cropping season to evaluate nutrient depletion across major land uses. Inputs from mineral fertilizer, manure, atmospheric deposition, and biological N fixation, and outputs through crop harvest, residue removal, gaseous losses, leaching, and erosion were estimated using field measurements and empirical models. Partial nutrient balances indicated negative N and K balances in teff ( Eragrostis tef ) cropland, whereas wheat cropland showed a positive balance only for N. When all loss pathways were included, full nutrient balances were consistently negative for N and K across both cultivated and non‐cultivated land uses. Teff cropland exhibited deficits of −20.9 kg N ha − 1 year − 1 , −0.7 kg P ha − 1 year − 1 , and −37.8 kg K ha − 1 year − 1 , while wheat cropland showed severe N depletion (−61.4 kg N ha − 1 year − 1 ) despite a positive P balance (+11.0 kg P ha − 1 year − 1 ). Nutrient depletion were primarily driven by erosion, followed by crop harvest and residue removal, with dissolved losses in runoff exceeding sediment‐associated losses. Forested land maintained relatively stable nutrient balances, highlighting the role of vegetation cover in reducing nutrient export. Overall, mineral fertilizer inputs alone were insufficient to offset nutrient losses under current management. Integrated nutrient management combining mineral and organic inputs with erosion control and residue retention is required to sustain soil fertility and reduce land degradation in the watershed.