Abstract :
In order to study the effect of water deficit stress at different growth reproductive stages
and N fertilizer rates on sterility of umbel, yield and nitrogen use efficiency of fennel, an experiment
was conducted as a split-plot based on a Randomized Complete Block Design with three replications
in research field of Islamic Azad University, Birjand branch, Birjand, Iran in 2009. The main plot
included irrigation at three levels (irrigation stop at start flowering, fruit-filling stages and complete
irrigation) and the sub-plot was N fertilizer at four rates (0, 60, 120 and 180 kg N ha-1). The results
showed that irrigation significantly affected number of sterile umbel, fruit number per umbellet, total
number of umbel per plant, fruit yield and nitrogen agronomical efficiency. Also, the rate of nitrogen
application significantly affected fruit number per umbellet,total number of umbel per plant, fruit yield
and agronomical nitrogen use efficiency. Interaction of irrigation and nitrogen rate affect only on the
total number of umbel per plant and fruit yield of fennel was significant. Means comparison showed
that the highest negative effect on yield, umbel fertilization and agronomical nitrogen use efficiency
was related to treatment irrigation stop at the start of flowering. Also, increasing nitrogen application
from 0 to 120 kg N ha-1 had a positive effect on yield, but agronomical nitrogen use efficiency declined
significantly with increasing of nitrogen from 60 to 180 kg N ha-1. According to the results, the
treatment of complete irrigation with N rate of 120 kg N ha-1 is recommended for realizing high fennel
yield in Birjand, Iran.
