Site-specific nitrogen fertilizing is an important part of precision agriculture. Based on the positive results in use of a mechanical sensor (pendulum-meter) for the indirect measurement of the grown plant mass in grain crop stands, late nitrogen fertilization on farm-scale strip trials with winter wheat were arranged on three fields to analyse the ecological and economic effects of site-specific fertilization. The approaches are described and evaluated. Site-specific nitrogen balances are used for determining the nitrogen surplus as an indicator for nitrogen loss potential, and the nitrogen use rate as an indicator for nitrogen efficiency. The summarized results of the significance test reveal the significant advantages of a variable fertilization for the N-surplus in all fields. As regards nitrogen use rate, variable fertilizing produced significant advantages in one field only. The advantages are particularly evident on plots with low plant growth. Precise fertilizing had no negative effects on yield, grain quality and gross margins. Further test years with different crops are in preparation, along with improving the evaluation method in order to validate the assessment of the impact of nitrogen precision fertilizing on plant production.