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The Argentinean Pampa is an important grain production region in which nitrogen (N) availability restricts wheat (Triticum aestivum L.) yield. We performed 46 experiments in the Semi-arid Pampa for evaluating soil N supplying capacity using a mass balance approach. The information generated was combined with published results from 58 experiments performed in the Humid Pampa. Average rainfall was 50% lower under semi-arid conditions and soils had half of the clay+silt and total N contents than those of humid environments. Wheat yield under humid scenarios doubled the yield attained under semi-arid ones, and N and rainfall use efficiencies were also higher. A model could be fitted with good performance for estimating N-supplying capacity from mineral and organic soil pools (R-2=0.53-0.93), absorbed N (R-2=0.70) and yield (R-2=0.57). This methodology can be used for estimating fertilizer needs under defined climate- and site-specific scenarios. For the average yields, rainfall and soil conditions of the experimental networks, targeted N supply (soil mineral+fertilizer N) was estimated as 160kgNha(-1) in the Humid Pampa and 50kgNha(-1) in the Semi-arid Pampa. Current N rates applied by farmers need to be increased under humid conditions and overfertilization occurs under semi-arid ones.