Croatian Farmers Turn to Foliar Analysis to Improve Yields and Quality

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.

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.

“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.