In this paper are reported pot and field experiments with potatoes, comparing the application, in the presence of PK, of the total dose of nitrogen (urea) at planting time with treatments in which that dose was top-dressed or parceled out and added part at planting time and part afterwards. The results confirmed those of previously reported trials, indicating that large portion of the whole nitrogen requirement should be added at planting time, but in .such way as to avoid excessive concentration in the soil contacting the seed pieces. Top-dressing part of the total dose contributes to reduce that concentration; this application, however, should be made early enough to avoid nitrogen hunger during the period of active growing.