Croatian Farmers Turn to Foliar Analysis to Improve Yields and Quality

By analyzing leaves, agronomists can determine which elements and compounds the olive tree may be missing or have in excess.
Feb. 17, 2022
Nedjeljko Jusup

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When some­one around here exag­ger­ates or says some­thing that’s untrue, they risk being told, you lie like an olive flower,” whose appear­ance often fail to fore­tell har­vest results.

An olive leaf, on the other hand, does not lie. Leaves can tell grow­ers exactly what the olives are miss­ing through foliar analy­sis.

See Also:As the Harvest Gets Underway in Croatia, Officials Provide Safety Tips to Farmers

Two years ago, at an olive pro­duc­tion event in Zadar, Dalmatia, Mirjana Herak Ćustić, an agron­o­mist from Zagreb, aroused great inter­est among the gath­ered grow­ers.

Analysis of olive leaves is the only true indi­ca­tor of the nutri­tional sta­tus of olives,” she said.

Many dif­fer­ent fac­tors in the soil and envi­ron­ment can lead to nutri­ent block­age and soil uptake of recently planted olive trees. The most promi­nent of these include mois­ture, tem­per­a­ture and microor­gan­isms.


These fac­tors affect the yield and qual­ity of oil, said Herak Ćustić. She pointed out that par­tic­u­lar prob­lems occur in alka­line soils (those with a high pH) with a lack or excess of water expe­ri­enc­ing tem­per­a­tures that are either too high or low.

The expe­ri­ences of olive grow­ers have con­firmed Herak Ćustić’s claims.

Olives don’t like any­thing too much and noth­ing too lit­tle,” says Ante Vulin, an award-win­ning Dalmatian olive grower.

Foliar analy­sis, which will reveal what olives are miss­ing, can be done ear­lier in the spring to deter­mine the nutri­tional sta­tus when the veg­e­ta­tion starts (before flow­er­ing).

It may also be done after har­vest in the autumn to see what is left behind in the plant to be stored as a reserve for spring.

Thus, by deter­min­ing the actual sta­tus of the nutri­ents in the leaf, it is pos­si­ble to inter­vene and pro­vide the tree with those it is miss­ing or reduce what it does not need.

To con­duct the analy­sis, leaf sam­ples should be taken from sev­eral trees (prefer­ably of the same vari­ety) and the same agroe­co­log­i­cal con­di­tions.

According to Herak Ćustić, the aver­age sam­ple should com­prise about 200 grams of olive leaves from the mid­dle of the canopy from branches with at least five to 10 olives.

Leaf analy­ses most often include the fol­low­ing ele­ments: nitro­gen, phos­pho­rus, potas­sium, mag­ne­sium, cal­cium, iron, man­ganese, zinc, cop­per and boron. If nec­es­sary, heavy met­als and other ele­ments are also iden­ti­fied. A com­plete fer­til­iza­tion rec­om­men­da­tion fol­lows the analy­sis.

Mladen Dušević is one of the most well-known grow­ers in Zadar, with 350 trees spread around the region. His son, Mato, is also an award-win­ning pro­ducer. However, the two were not sat­is­fied with their Oblica yields in the past cou­ple of years and decided to do a foliar analy­sis.


The Dušević family

I sent leaf sam­ples for analy­sis to the depart­ment of plant nutri­tion at the fac­ulty of agri­cul­ture in Zagreb,” Dušević said. After a week, the results of the analy­sis and rec­om­men­da­tions for fer­til­iza­tion arrived by e‑mail.”

Based on the analy­sis, Herak Ćustić told the father-and-son duo that the trees lacked phos­pho­rus, potas­sium, zinc and boron. However, the amounts of nitro­gen, cal­cium, mag­ne­sium, iron, man­ganese and cop­per were ade­quate.

We, there­fore, sug­gested apply­ing foliar fer­til­iza­tion of these ele­ments as soon as pos­si­ble, and repeat it two to three times dur­ing the grow­ing sea­son for flow­er­ing, fer­til­iza­tion, ger­mi­na­tion and fruit devel­op­ment (for which phos­pho­rus and boron are essen­tial) and alle­vi­ate stress due to pos­si­ble high tem­per­a­tures and lack of water,” Herak Ćustić told the grower and pro­ducer.

She also com­posed the appro­pri­ate cock­tail” for foliar fer­til­iza­tion for the trees.

Dissolve in 100 liters of water and mix well:

  • 300 grams of Hascon Ad M 10, which con­tains phos­pho­rus, potas­sium, boron, man­ganese and molyb­de­num;
  • 100 grams of Borogreen, which con­tains more boron;
  • 100 grams of Drin, a nat­ural bios­tim­u­la­tor that con­tains a high con­tent of free amino acids, which are eas­ily digestible and acti­vate bio­chem­i­cal and enzy­matic processes in the plant;
  • 150 grams of Zinc 25, which is essen­tial for enzy­matic activ­ity and alle­vi­ates stress.

Foliar spray­ing should be done early in the morn­ing (in the shade) so it does­n’t burn the leaf,” Herak Ćustić added.

She fur­ther clar­i­fied how foliar analy­sis deter­mines the actual state of nutri­ents in the plant, whether there is a defi­ciency, excess or imbal­ance. She also warned that every farm is dif­fer­ent, and treat­ments are likely to vary between them as a result.


So the find­ing in Dušević’s olives indi­cates some­thing that some­one else may have, but most likely not,” Herak Ćustić said.

In this spe­cific exam­ple, the find­ing revealed an insuf­fi­cient sup­ply of phos­pho­rus and boron, both of which are very impor­tant for flow­er­ing, fer­til­iza­tion and translo­ca­tion of assim­i­lates, and potas­sium and zinc affect­ing the enzy­matic activ­ity and plant resis­tance to stress, espe­cially from high and low tem­per­a­tures,” she added.

That’s why this time I put together a cock­tail with an empha­sis on these ele­ments,” Herak Ćustić said, which accel­er­ates absorp­tion, translo­ca­tion and incor­po­ra­tion of the organic com­pounds upon which oil qual­ity and yield depend.

However, she also warned that these treat­ments are only tem­po­rary solu­tions. Since the nutri­ents in the soil and tree can change each year, so too does the recipe of the cock­tail.”

She advised grow­ers to do foliar analy­ses as soon as pos­si­ble to see what their trees are miss­ing and find the appro­pri­ate solu­tions, whether those are chang­ing the type of fer­til­izer or cul­ti­va­tion method to direct inter­ven­tion, such as the one done by Dušević.


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