Spanish Researchers Pioneer Olive Fertilization with Silicon

Researchers from the María de Maeztu Unit of Excellence — Department of Agronomy of the University of Córdoba (DAUCO) have pub­lished the first major study exam­in­ing sil­i­con as a fer­til­izer for olive groves. They con­cluded that this abun­dant ele­ment could pro­tect against drought and a wide range of pests and dis­eases and can be applied to rain-fed and irri­gated olive groves with­out neg­a­tive envi­ron­men­tal impacts.

Numerous stud­ies have shown that sil­i­con, the sec­ond most abun­dant ele­ment in the soil after oxy­gen, improves plants’ abil­ity to resist the effects of key stres­sors, includ­ing drought, freez­ing, salin­ity and nutri­ent imbal­ance, pests and pathogens. The major­ity of these stud­ies, how­ever, have only researched ground crops such as wheat, rice, toma­toes and root veg­eta­bles.

To estab­lish a sci­en­tific basis for the effec­tive appli­ca­tion of sil­i­con fer­til­iza­tion in olive groves, the team con­ducted three exper­i­ments at the Experimental Farm of Rabanales, University of Córdoba, using Arbequina and Picual cul­ti­vars.

In each exper­i­ment, the researchers stud­ied the effec­tive­ness of two sil­i­con fer­til­iza­tion meth­ods: direct appli­ca­tion to the roots via irri­ga­tion water and to the leaves via a foliar spray. After 120 days of treat­ment, all plants con­tained major sil­i­con accu­mu­la­tion in the roots. Leaves and shoots also had sig­nif­i­cant lev­els of sil­i­con.

Furthermore, dif­fer­ences in leaf accu­mu­la­tion between treated and con­trol plants were evi­dent within 60 days of appli­ca­tion.

Leaf accu­mu­la­tion is of par­tic­u­lar sig­nif­i­cance. The sil­ica gel layer that forms between the outer lay­ers of the leaf acts as a phys­i­cal bar­rier, con­fer­ring pro­tec­tion against many pests and dis­eases and abi­otic stresses, such as drought. In addi­tion, pre­vi­ous stud­ies have shown an active increase in pho­to­syn­the­sis in this layer’s leaves.

Once the sil­ica gel layer is present, the sil­i­con is no longer mobile. Therefore, researchers rec­om­mend reg­u­lar treat­ment to ensure the ele­ment remains avail­able to new leaves as the plant grows.

In addi­tion to the phys­i­cal sil­ica gel bar­rier, biochemical/molecular mech­a­nisms are induced or rein­forced by sil­i­con. They allow the plant to uti­lize defen­sive com­pounds, such as phe­no­lics and phy­toalex­ins and acti­vate defen­sive enzymes, such as per­ox­i­dase and polyphe­nol oxi­dase.

Previous stud­ies have also demon­strated a link between sil­i­con and a plant’s abil­ity to pro­duce her­bi­vore-induced plant volatiles (HIPVs), which attract ben­e­fi­cial preda­tor species. One such HIPV is methyl sal­i­cy­late, which has been shown to attract the green lacewing, a nat­ural preda­tor of many olive pests, such as the olive lace bug.

At the end of their exper­i­ments, the researchers found that both appli­ca­tion meth­ods were equally effec­tive at increas­ing sil­i­con lev­els in the plants. This result led them to con­clude that the foliar spray method could deliver the same ben­e­fits to rain­fed olive groves as the irri­ga­tion method con­fers to irri­gated groves.

Researcher Ricardo Fernández Escobar high­lighted the sig­nif­i­cance of this find­ing, say­ing, ​“most olive groves are rain-fed, and it is [already] very com­mon to apply foliar treat­ments.”

“This study is a start­ing point that estab­lishes the basis for future research that will allow us to know the exact ben­e­fits of sil­i­con against dif­fer­ent types of stresses. Right now, we are study­ing it against salin­ity, water stress, and olive fruit fly,” said Fernández, not­ing that sil­i­con treat­ment has already proved suc­cess­ful against Spilocaea oleag­ina, the fun­gus respon­si­ble for olive pea­cock spot.

If fur­ther stud­ies con­firm sil­i­con fer­til­iza­tion as an effec­tive pest and dis­ease con­trol method, the results could have sig­nif­i­cant eco­nomic and envi­ron­men­tal impli­ca­tions. Due to its nat­ural abun­dance in the earth’s crust, includ­ing top­soil, sil­i­con is both read­ily avail­able and of lit­tle-to-no eco­log­i­cal con­cern.

Perhaps even more impor­tant is the element’s poten­tial for increas­ing drought resis­tance in com­mer­cial olive trees, as shown in other crops, such as rice and wheat. 2022 saw record olive har­vest losses across Europe and the Mediterranean due to extreme or unsea­sonal weather events, with drought being a dri­ving force in many regions.

• American Society for Horticultural Science
• Nature
• Frontiers in Plant Science