Wykorzystując test NNI (indeks stanu odżywienia) określano deficyt i nadmiar azotu w czasie wegetacji roślin uprawianych w wazonach i w polu. Nadmiar azotu (NNI>1) zmniejszał współczynniki plonowania (HI). Mały deficyt azotu (1,0 > NNI > 0,7) zwiększał dystrybucję asymilatów do bulw. Duży deficyt azotu (NNI < 0,7) powodował drastyczne obniżenie nagromadzania biomasy oraz końcowego plonu bulw mimo stosunkowo dużej wartości HI. Okres wegetacji wilgotny i chłodny sprzyjał występowaniu deficytu azotu w roślinach ziemniaka.
Nitrogen nutrition index (NNI), harvest index (HI), dry matter accumulated by different organs were estimated several times during the vegetation period of potato plants grown in the both field and pot experiments at the Experimental Station in Jadwisin, Poland. Nitrogen fertilizer as NH4N03 was applied at three doses (40, 120, and 200 kg ha-1 N) in the field experiment and 2.7 g N in 1996 and 4g N in 1997 and 1998 per each plant in the pot experiment. Results showed that the values of NNI both in field and pot experiments increased from emergence till the about closing rows and then they gradually decreased. The NNI values were dependent on N rates. The higher were N doses, the higher were values of NNI. These differences were especially present during the first half of vegetation periods. The excess of N in potato plants (NNI values above 1.0) was recorded in the greater part of vegetation periods in plants grown at the dose 200 kg ha-1 N and for short length of time at the rate 120 kg . ha-1 N. The excess of nitrogen was associated with the highest values of total biomass accumulation and with decreasing of the harvest index ; (average NNI = 0.53). Unsufficient level of nitrogen nutrition (NNI values below 1.0) was found for the whole vegetation periods in all plants grown in pots and in the field at the dose 40 kg ha-1 N. These plants produced less total biomass but more of it was distributed to the tubers with average values of HI: 0.68 in field and 0.78 in pot experiments. Plants grown in the field under warmer weather conditions had better nitrogen nutrition status than those grown under cooler and wetter ones.