Page 18 - Volume 4, Issue 1, January 2011

© Benaki Phytopathological Institute
Troyanos & Roukounaki 16
2), whereas the DWT of shoots, stems and
roots did not (data not shown). The leaf DWT
of the plants grown with treatment N f was
less than that of the plants grown with N1, N2,
N3 and N4, treatments whereas that of young
olive trees grown with no N fertilization (N 0)
had a intermediate value. The response of
olive cv. ‘Koroneiki’ to increased soil N fertil-
ization rate has been reported to be differ-
ent than that of other cultivars, such as Naba-
li, Manzanillo, etc. (8). More specifically, in the
latter cultivars, the increased N availability in-
creased the shoot DWT and length, but it did
not have any effect on the leaf DWT (8). These
results show that varietal differences to N fer-
tilization response could be expected.
In the present study, the root length was
the greatest in the non-fertilized (N0) olive
trees and it was reduced with increasing soil
N fertilization rate (Fig. 3). The root length
of young olives treated with leaf applica-
tion of N (treatment Nf) did not differ signif-
icantly (P<0.05) from that of the trees treat-
ed with N3 and N 4. The increased root length
with diminishing soil N external supply has
been recorded in other plants too and it is
probably one of the mechanisms by which
plants adjust to shortage of exogenous re-
sources (15). The results of the present study
are in agreement with field empirical obser-
vations made by growers according to which,
olive trees grown without nitrogen fertilizer
produced longer roots. However, in the cur-
rent experiment the increased root length,
observed in the N-deficient young olive trees
(Fig. 3), was accompanied by a reduction in
the leaf+stems+shoots DWT: root length ratio
(Fig. 4) which is undesirable, especially during
the establishment of young olive trees.
The leaf [N] increased (P<0.01) with in-
creasing N soil supply (Fig. 5). Leaf [N] was
relatively stable during time in treatments
N2, N3 and N4, whereas in treatments N0 and
N f it decreased considerably from 65 DAF
showing that soil and foliar fertilization did
not satisfy the N requirements of young ol-
ive trees. Response of leaf [N] of young ol-
ive trees to N fertilization has been reported
elsewhere (3, 8, 13, 19). At 201 DAF, when the
leaf DWT of the experimental plants grown
without fertilization (N 0) was affected by the
soil N fertilizer treatments, the leaf [N] was
approximately <2%, indicating that this leaf
[N] was not sufficient for the growth of the
young olive trees. Nevertheless, this concen-
tration has been reported to be sufficient for
Leaf DWT (g)
N fertilizer treatments
Figure 2. Effects of N fertilization on olive leaf dry weight
(DWT), 201 days after first fertilization (DAF). Soil N fertiliza-
tion rates: N0: 0, N1: 0.95, N 2: 1.90, N3: 3.80, N4: 6.25 g N at three
monthly applications. Foliar treatment Nf: 0.3 g/l of 21-21-21
(N-P-K) soluble fertilizer at sixmonthly applications. Means fol-
lowed by a different letter are significantly different at P<0.05
level. Means separation calculated by the Duncan test.
Root length (m)
N fertilizer treatments
Figure 3. Effects of N fertilization on root length (m) of one-
year-old olive trees. Soil N fertilization rates: N0: 0, N1: 0.95, N2:
1.90, N3: 3.80, N4: 6.25 g N at three monthly applications. Foli-
ar treatment Nf : 0.3 g/lof 21-21-21 (N-P-K) soluble fertilizer at
six monthly applications. Means followed by a different letter
are significantly different at P<0.05 level. Means separation
calculated by the Duncan test.