Page 15 - Volume 4, Issue 1, January 2011

Laboratory of Non-Parasitic Diseases, Deparatment of

Phytopathology, Benaki Phytopathological Institute,

8 St. Delta Str., GR-145 61 Kifissia, (Athens), Greece

Corresponding author:

y.troyanos@bpi.gr

Hellenic Plant Protection Journal

4:

13-19, 2011

Response of young olive trees to nitrogen fertilization

Y.E. Troyanos and E. Roukounaki

Summary

The response of young olive trees to soil nitrate nitrogen imposed by different N fertiliza-

tion rates and to a foliar N–P-K fertilizer was investigated in a pot experiment. The dry weight of leaves

increased with increasing soil N fertilization rate, whereas that of the whole plants sprayed with a foli-

ar N-P-K was not affected. The root length increased in N-deficient olives (e.g. olives grown without N

fertilization) indicating that the N-deficient olives produced a longer root system. However, this longer

root system was accompanied by a reduction in (stems+leaves+shoots) : root length ratio. When the

leaf N concentration was <2% and the soil nitrate nitrogen <25 mg/kg DWT, the plants had the low-

est leaf dry weight.

Additional Keywords:

leaf dry weight, nitrate,

Olea europaea

L., root length

Introduction

In Greece, farmers are investing to modern

olive growing by using drip-irrigation, fer-

tigation and no-tillage cropping system for

reducing soil erosion. However, fertiliza-

tion of olive trees is based mostly on tradi-

tion, i.e. few growers are following soil and

leaf analyses for the application of fertilizers,

whereas most of them use only their empiri-

cal knowledge as a guide. During the estab-

lishment of young olive trees, fertilization

practices applied by the growers are quite

diverse. Some growers apply large quanti-

ties of nitrogen (N) fertilizers, while others

none. The former may over-fertilize the ol-

ive trees causing potential growth reduction

and toxicities. The latter claim that, without

fertilization the young olive trees produce

a large root system that penetrates deep-

er into the soil, which is desirable especial-

ly when there is water shortage (e.g. in rain-

fed conditions). However, in that case, olive

trees are under-fertilized and growth reduc-

tion could be evident.

Response to N fertilization of young ol-

ive trees grown in soil (8) and nutrient solu-

tions (13) has been reported in the literature.

However, there is a discrepancy concerning

the effect of N fertilization on mature ol-

ive trees. Hartmann (14) reported that ma-

ture olive trees responded to N only when

grown in poor soil. Other researchers (5, 6)

have shown that the traditional fertilization

based on annual applications of N-P-K had

no effect on yield of mature olive trees com-

pared to the leaf analysis-based fertilization,

which had a positive effect on yield. Howev-

er, mature olive trees have been found to re-

spond to foliar application of urea (2, 5, 17,

19) and potassium (18). In recent years, foliar

feeding has been used extensively in olive

orchards, especially under rain-fed condi-

tions, where shortage of soil moisture re-

duces the availability of fertilizers (7).

In the present study, an experiment was

carried out to investigate the response of

young olive trees to N fertilization. Differ-

ent rates of soil N fertilization and a foliar

N-P-K fertilizer were applied to young olive

trees (cv. ‘Koroneiki’). The objectives were a)

to determine the minimum soil NO

3

-N con-

centration ([NO

3

-N]) and the minimum leaf

N concentration ([N]) for maximum growth,

b) to determine the minimum N, P and K

root absorption rates required for maximum

growth of young olive trees, and c) to test

if foliar feeding with a N-P-K fertilizer could

sustain the maximum growth of plants. The