UPTAKE AND NITROGEN EFFICIENCY IN FORAGE MAIZE: EFFECTS OF NITROGEN AND PLANT DENSITY

Efficient nitrogen (N) fertilizer management is critical for the economic production of maize (Zea mays L.) and the long-term protection of environmental quality. To study the effects of N doses and plant density on the N uptake and efficiency on forage maize cv. SC 704, an experiment was conducted in the Shahrekord region (32 degrees 21' N, 50 degrees 49' E; altitude 2050 m), Iran, at the Agricultural Research Station of Shahrekord University, during the 2007 growing season. The experiment was arranged with four plant densities (92 600, 104 200, 119 000 and 138 900 plants ha(-1)) and four nitrogen doses (200, 240, 280 and 320 kg ha(-1)) in a randomized complete block design with four replications. Increases of the plant density led to a significant N uptake in stalk, grain and whole plant. Also, N use efficiency, N uptake efficiency and N harvest index were significantly higher with increasing plant population. However, plant population showed no significant effect on leaf N uptake and N consumption efficiency. Increasing the N doses resulted in a significant higher leaf, stalk, grain and whole plant N uptake. However, N use, uptake and utilization efficiency were significantly decreased. The N harvest index showed different response to the N doses and there was no significant effect. It may be concluded that the optimum plant density for silage maize production can be beyond 138 900 plants ha(-1) and utilization of a N dose higher than 240 kg ha(-1) should be avoided, in order to minimize N losses.