Traditional summer pastures in the Alps have been shaped by centuries of grazing by domestic livestock. To understand the effects of this land use on nutrient cycling, we quantified phosphorus (P) fluxes on a summer farm in southeastern Switzerland. We used high-frequency GPS tracking to record the spatial distribution of animal activities over an entire grazing season, and used these data to model spatial patterns of P depletion and accumulation at various spatial scales (the entire farm, four vegetation groups, 900 m2 sampling plots and 10 × 10 m2 grid cells). Since the model depended on parameter values obtained from diverse sources, we tested its robustness using Monte Carlo simulations based upon varying parameter values. The model indicated very small net P fluxes (between − 0.05 and + 0.05 kg P ha−1 yr−1) over nearly half (49%) of the pasture, mostly in dwarf-shrub vegetation. In a further 44% of the area, P depletion exceeded ‐0.05 kg P ha−1 yr−1, representing a total loss of 39.4 kg P yr−1 (2.1 kg P ha−1). A positive P balance of over 0.05 kg P ha−1 yr−1 was indicated for 6.6% of the area, representing a total annual accumulation of 16.4 kg P (1.8 kg P ha−1). The overall P balance for the entire summer farm was thus negative. The patches of substantial depletion or accumulation formed a mosaic in the areas most used by cattle. More active management of cattle and stable manure is recommended to maintain the delivery of ecosystem services.