Page 17 - Volume 4, Issue 1, January 2011
Basic HTML Version
© Benaki Phytopathological Institute
Response of young olive trees to nitrogen
15
and N
4,
whereas in pots of treatment N
f
no
soil fertilizer was applied. The following day
(16 April 2007), 0.45 g N, derived fromNH
4
NO
3
and dissolved in 1 l tapwater, were applied to
each pot of the treatments N
1
, N
2
, N
3
and N
4,
whereas no N was applied to pots of treat-
ment N
0
(Control). On the same day, the ol-
ive trees of treatment N
f
were sprayed with
0.3 g/l of 21-21-21 (N-P-K) soluble fertilizer.
The rest of the soil N fertilizer was gradual-
ly applied according to Table 1, whereas the
olive trees of treatment N
f
received a total of
six monthly foliar applications.
Statistical analyses
The statistical analyses were carried out
using Genstat (10th Edition). ANOVA was
applied and when the F-test was statisti-
cally significant (P<0.05) the comparisons
of means were performed using the Dun-
can and the LSD (Least significant differ-
ences) tests. Non-linear regression analysis
was performed between the leaf dry weight
(DWT) and the soil [NO
3
-N].
Harvests - Measurements
One week prior to each harvest, 36 soil
samples (6 treatments x 6 replications) were
taken from the pots using a soil auger. The
samples were stored in a refrigerator and
the following day the soil NO
3
-N was extract-
ed using a 1:10 w/w soil to deionized water
ratio. NO
3
-N was determined using a modi-
fied hydrazine nitrate reduction method (21).
Each soil sample was extracted and analy-
sed twice and if the results differ more than
10%, a third sub-sample was analysed and
the mean of the three measurements was
estimated. The dry weight (DWT) of the soil
samples was determined after drying at 105
o
C
until constant weight and the soil [NO
3
-N] was
expressed on a dry weight basis.
At each harvest, the above ground plant
parts, i.e. leaves, stems and shoots, were cut,
placed separately into plastic bags to reduce
moisture loss and weighted (fresh weight).
The length of the shoots and the diameter
of the stems were also measured. The fol-
lowing day, the roots were removed from
each pot and washed from the soil using a
sieve mesh; then they were placed into plas-
tic bags and put in a refrigerator until the
root length was measured. The root length
was measured according to the method of
Tennant (20) using square grids of 1 cm (for
the first harvest) and 2 cm (for the rest 5 har-
vests). All plant parts were washed using de-
ionised water and dried by placing them
into an air-forced oven at 80
o
C until con-
stant weight.
After drying, the plant samples were
ground and 100 mg of each sample were di-
gested with 2 ml H
2
SO
4
containing 1 g/l Se
and 1 ml 30% H
2
O
2
. The digests were made
up to 25 ml with deionized water and the
concentration of ammonium-N was deter-
mined using the indophenol blue method
(22). There were two digestions per treat-
ment and replication and if the results dif-
fer more than 10%, a third sub-sample was
analysed and the mean of the three mea-
surements was taken.
Results and Discussion
At 201 DAF (last harvest), the DWT of leaves
responded to N fertilization treatments (Fig.
Table 1.
Soil N fertilization rates applied monthly to one-year-old olive trees.
Treatments
Soil N fertilization rates (g/pot)
16 April 2007
15 May 2007
15 June 2007
Total
N
0
0
0
0
0
N
1
0.45
0.50
0
0.95
N
2
0.45
0.45
1
1.90
N
3
0.45
1.35
2
3.80
N
4
0.45
1.80
4
6.25
