Chemical characteristics of the soilIt seems that N application increased umbel number per plant in fennel through extending shoots,
expanding carbon-absorbing surface and increasing the number of auxiliary branches per plant. Although
Tuncturk et al. (2008) reported the decrease in reproductive unit number of fennel per plant with the increase in
N fertilization level over 40 kg.ha-1, in their study on dill, Rassam et al. (2007) found that the increase in N level
up to 120 kg.ha-1 increased umbel number per plant which is in agreement with the results of the current study.
Although according to the findings of Koucheki et al. (2006) about fennel and Kafi (1990) about cumin, the
increase in density decreases umber bearing potential per plant due to decreasing the space for each plant and
increasing inter-plant competition which causes the plants to have lower share of the available light, nutrients
and other resources, the increase in the density from 10 to 15 plants per m2 in this study resulted in the
increase in umbel number per plant which can be related to the production of more lateral branches due to the
competition-caused increase in plant height which resulted in the production of reproductive umbels; whereas,
there was no significant difference in umbel number per plant between the densities of 15 and 20 plants per m2.
It is likely that the maximized inter-plant competition at the densities of 15-20 plants per m2 neutralized the
effect of density on the potential of umbel production per plant. The production of reproductive umbels per plant
is expected to decrease at the densities of more than 20 plants per m2 owing to less available space for the
plants and higher inter-plant adverse competition.