This experiment was conducted at the Agricultural Research Station of Fars located in Zargan city in 2005 to evaluate the effects of the combination of rate and timing of nitrogen application on yield and yield components of corn (SC 704). Four nitrogen rates (0, 150, 200, and 250 kg ha -1 ) were used with different fractions being applied at planting, 6-7 leaf stage and tasseling. The experiment was laid out using a factorial arrangement in a randomized complete block design with three replications. The four combinations of splited nitrogen application were as; 100% nitrogen application at 6-7 leaf stage; 75% nitrogen application at 6-7 leaf stage + 25% at tasseling; 25% nitrogen application at planting + 75% at 6-7 leaf stage; 25% nitrogen application at planting + 50% at 6-7 leaf stage + 25% at tasseling. There was a significant increase in the plant height, leaf area index, stem and leaf dry weight, number of grains in ear, plant dry weight, grain yield, and also nitrogen use efficiency as the rate of nitrogen application was increased. Maximum plant dry weight, grain yield, and nitrogen use efficiency were achieved when 250 kg ha -1 nitrogen was applied as 25% at planting and 75% at 6-7 leaf stage. There was a high correlation between the concentration of leaf nitrogen measured at 6-7 leaf stage and the chlorophyll readings by chlorophyll meter (SPAD 502). These findings suggest that the level of nitrogen in corn plants can be assessed by using chlorophyll meter instead of the expensive and time consuming direct measurement of plant nitrogen. The results from this experiment show that under situation similar to that of this experiment, the application of the total amount of nitrogen up to 6-7 leaf stage may be more beneficial in term of grain yield production as compared with the other methods of nitrogen application in which a fraction of nitrogen is applied later at tasseling growth stage.
