The effects of four rates of N (0, 56, 112 and 168 kg/ha) as ammonium nitrate, with and without irrigation, on potato (Solanum tuberosumL.) leaf nutritional status at tuber initiation (t.i.) and midbloom (m.b.) were evaluated. Soil test parameters (pH, and extractable Ca, Mg, K, N) were not significantly altered by N rate. In general, leaf N concentration was increased, Ca concentration decreased, and P, K and Mg concentrations were unchanged as N rate increased. Greater changes in nutrient concentrations with time were noted as soil moisture stress was reduced. Under optimal soil moisture, concentrations of all nutrients either decreased or remained the same between t.i. and m.b. Nutrient ratios, employed by the Diagnosis and Recommendation Integrated System (DRIS) for evaluation of nutrient status, often exhibited significant changes between t.i. and m.b. across N rates, irrigation treatments and crop years. Diagnoses of the most limiting nutrients by DRIS indices were influenced by N rate, sampling period and crop year but were largely unaffected by irrigation treatment. Differential nutrient uptake and nutrient translocation during crop growth may have induced changes in elemental ratios and subsequent tissue diagnosis by DRIS between sampling periods.