تأثیر مقدار و زمان مصرف کود نیتروژن بر عملکرد و برخی شاخص‌های فیزیولوژیکی رشد ذرت

In order to investigate the effects of rates and nitrogen fertilizer application timing on yield and some growth physiological indices of corn ( Zea mays L.), an experiment was conducted as split plot based on randomized complete block design with three replications at the Research Farm of University of Mohaghegh Ardabili during 2009 cropping season. Nitrogen fertilizer levels were arranged in main plot with four levels including: 0, 75, 150 and 225 Kg N.ha-1 and nitrogen application timing in sub plots by three levels including : (1/3 in planting + 1/3 in 8-10 leaf stages + 1/3 in tasseling initation), (½ planting + ½ in tasseling initiation) and (½ in planting+¼ in 8-10 leaf stages + ¼ in tasseling initation). Investigation of dry matter accumulation indicated that in all of treatment combinations, it increased slowly until 300-400 growth degree days after sowing and then increased rapidly till 850-900 growth degree days. From 900 growth degree days till harvest time, it decreased due to increasing aging of leaves and decreasing of leaf area index. Maximum of dry matter accumulation was observed in the plotes which 225 Kg N.ha-1 was applied as 1/3 in planting + 1/3 in 8-10 leaf stages + 1/3 in tasseling initation. Similar results were obtained in crop growth rate and relative crop growth. With increasing rates of nitrogen fertilizer application, leaf area index was significantly increased. The highest leaf area index was belonged to 225 Kg N.ha-1 when was applied as 1/3 in planting + 1/3 in 8-10 leaf stages + 1/3 in tasseling initation with 850-900 growth degree days, while the least value of it was obtained in application of 75 Kg N.ha-1 as ½ planting + ½ in tasseling initiation. Grain yield and yield components were significantly affected by rate, nitrogen application timing and interaction of rates × nitrogen application timing. The highest grain yield (7928.6 Kg.ha-1) resulted from treatment combination of 225 Kg N.ha-1 as 1/3 in planting + 1/3 in 8-10 leaf stages + 1/3 in tasseling initation. Thus, it could be suggested that in order to increasing the grain yield and the other growth indices such as dry matter accumulation and crop growth rate should be applied 225 Kg N.ha-1 as 1/3 in planting + 1/3 in 8-10 leaf stages + 1/3 in tasseling initation in Ardabil climaste conditions.