This study was designed and conducted to investigate on physiological growth indices and photosynthetic pigments in three maturing corn (Zea mays L.) hybrids (SC704, SC500, and SC260) using four nitrogen (N) levels (0, 80, 160, and 240 kg N ha^-1, from Urea, N= 45%). The experiments were conducted in Zabol and Isfahan in 2014 and 2015, respectively, using the split-plot arrangement in a randomized complete block design with three replications. Results revealed that LAI, CGR, RGR and NAR were affected by nitrogen. Increasing the nitrogen application rate from 80 to 240 kg ha^-1 increased the LAI, RGR and CGR from 35 days after planting, which was significant after fertility. Among the physiological growth indices, NAR was lower by nitrogen fertilizer. Increasing the amount of nitrogen fertilizer increased the amount of photosynthetic pigments. The results of the experiment showed that the maximum yield of corn in Isfahan and Zabol were obtained in SC704 and SC500 at 160 kg.ha^-1, respectively, and the lowest grain yield in both areas was obtained in control treatment. The threshold level of nitrogen fertilizer requirement based on a 50% maize yield loss were determined to be 178 and 200 kg ha^-1, respectively, in SC704 grown in Isfahan and Zabol while these same values were 164 and 192 kg ha^-1 for SC500, and 150 and 186 kg ha^-1 for SC260. SC704 compared to the other two hybrids also the Isfahan region, in comparison with Zabul, were superior in terms of measured traits. The results of this experiment can be used in the sustainable production of corn in similar climatic conditions.

Keywords: Growth Indices, Maturity groups, Threshold level

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