Two field experiments were conducted during Autumn 1982–83 and 1983–84 on a sandy loam oil to detemine the critical concentrations of nitrogen in leaves and petioles of potato (Solanum tuberosum L.) at different periods of plant growth and predict yield potential. Nitrogen was applied at the rates of 0, 50, 100, 150, 200 and 250 kg N/ha, alone and in combination with farmyard manure (FYM) at the rate of 30 t/ha. Maximum N concentration in the leaves and petioles was found to be, respectively, 6.18% and 3.48% with the application of 250kg N/ha in presence of 30 tons FYM/ha at 30 days after planting and minimum 3.41% and 1.23% in absence of nitrogen and FYM application at 60 days after planting. The critical N concentrations decreased from 5.31 to 3.83% N in leaves and 3.03 to 1.70% N in petioles between 30 and 60 days after planting. Highest significant correlation between N concentration and tuber yield (r=0.94**) was given by third petiole sampled at 30 days after planting. The regression model for predicting the tuber yield potential, based on concentration of third petioles sample at 30 days after planting was Y =−659.7899 + 511.8423 x − 69.0177 x2. Predicted yield and observed yield rankings agreed relatively well in magnitude.
