Soil erosion changes nitrogen balance estimates across a management gradient in Mediterranean olive groves

Introduction Nitrogen balances are widely used to assess nutrient management in perennial cropping systems, but in Mediterranean olive groves their interpretation may be biased when soil erosion and internal biomass recycling are not considered. Methods We quantified annual N inputs, outputs, internal recycling flows, and N balances in 12 olive groves in Andalusia (southern Spain) spanning a management gradient from conventional to agroecological systems. The analysis integrated mineral and organic fertilization, atmospheric deposition, biological N fixation, crop and biomass exports, internal returns from pruning residues, leaf litter, cover crops, and grazing, as well as erosion-driven N losses. Results Nitrogen acquisition and cycling showed consistent trends across the management gradient. Conventional and early-transition systems relied mainly on external mineral fertilization (74–88% of total N inputs), whereas agroecological systems obtained a greater share of N from natural sources (about 67%) and showed the highest internal recycling rates (about 96 kg N ha -1 y -1 ). When soil erosion was excluded, all systems showed positive or near-neutral N balances, with an average surplus of 40 kg N ha -1 y -1 . However, including erosion frequently shifted these balances towards neutrality or deficit, especially in farms with limited ground cover. Non-erosive losses, including volatilization, denitrification, and leaching, were of similar magnitude to crop N export and were strongly associated with N input rates. Discussion These results show that N balance assessments in Mediterranean olive groves can be substantially altered when erosion is ignored. Management strategies that promote biomass retention and ground cover enhance internal N recycling, but improved recycling alone does not offset erosion-related N losses in sloping orchards. Accounting simultaneously for internal recycling and soil erosion provides a more realistic basis for evaluating nitrogen management and soil–plant functioning in Mediterranean olive systems.