Heat Wave Challenges Italian Olive Growers

In the last month Italy has been affected by a heat wave so intense that the Ministry of Health issued warn­ings for sev­eral cities includ­ing Ancona, Cagliari, Frosinone, Campobasso, Latina, Perugia, Pescara and Rieti where ​“high-risk con­di­tions last­ing three or more days” saw tem­per­a­tures up to 39°C (102.2°F).

In the coun­try­side, high tem­per­a­tures caused con­cern among farm­ers. ​“At present, Italy is affected by a high-pres­sure struc­ture of African ori­gin,” said the expert in mete­o­rol­ogy, Marco Giovani. ​“This was caused mainly by a neg­a­tive anom­aly of the sur­face waters of the mid-Atlantic, where tem­per­a­tures decreased below the sea­sonal aver­age.” He noted that due to this sit­u­a­tion, which prob­a­bly will per­sist through­out the sum­mer, depres­sions descended to low lat­i­tudes, and as a dynamic reac­tion, fur­ther to the east, the ascent of hot air masses involved the Mediterranean and a good part of Western Europe.

“In Maremma, drought has been going on for a year and a half, and already in the spring sev­eral olive trees showed poor veg­e­ta­tive devel­op­ment,” affirmed Giovani, who man­ages an olive grove in Porto Santo Stefano, in Southern Tuscany.

While the flow­er­ing was delayed but good, the set­ting was poor. Giovani said that in this area, since last December just 48 mil­lime­ters (1.9 inches) of rain fell, where a typ­i­cal annual pre­cip­i­ta­tion is about 500 mil­lime­ters (20 inches).

Olive trees can safely with­stand 35 – 36 °C (95°-96.8°F), said an agron­o­mist spe­cial­ized in olive grow­ing, Fiammetta Nizzi Griffi. ​“Beyond this limit and up to 48 – 49 °C (118.4°-120.2°F), the plant devel­ops defense mech­a­nisms, depend­ing on vari­ety,” she explained.

Some cul­ti­vars become sus­cep­ti­ble at 48 °C (118.4°F) and some can reach tem­per­a­tures of up to 50°C (122°F); then the plant starts show­ing signs of dam­age, which are sim­i­lar to those caused by Iron Chlorosis.

“We recently expe­ri­enced a cli­matic sit­u­a­tion with higher than annual aver­age tem­per­a­tures, and we already observed some man­i­fes­ta­tions of suf­fer­ing in the olive trees,” she said, observ­ing that first, part of flow­ers did not open because they dried up; then, parts of the flow­ers opened but did not reach set­ting because the pollen tube had been affected by hot wind.

“Flowers which were able to develop fruits are now the size of a pep­per­corn or peanut, depend­ing on the area, and we must pay atten­tion as some of them have been already affected by drought.”

“In my opin­ion, these issues are attrib­ut­able not only to cli­mate but also to agro­nomic man­age­ment,” she affirmed. ​“I think that now we should make choices with a wider vision.”

With regard to soil, in fear of ero­sion due to heavy rains, which are now increas­ingly con­cen­trated and inten­si­fied in short peri­ods, tillage has been grad­u­ally aban­doned in favor of under-sow­ing. ​“This approach is undoubt­edly cor­rect but it can­not be car­ried out in all ter­ri­to­ries,” the agron­o­mist affirmed. ​“In regions like the Chianti, with high clay con­tent and a nat­ural ten­dency to rad­i­cal asphyxia, it is nec­es­sary to deep till the soil to avoid its exces­sive hard­en­ing.”

If the ground hard­ens too much, rain­wa­ter is not able to pen­e­trate and water reserves can­not be cre­ated; fur­ther­more, the root appa­ra­tus of olive trees tends to develop just below the layer of herbs, com­pet­ing with their roots.

“One month ago, I super­vised a deep tillage in an olive grove of the inner Maremma char­ac­ter­ized by a clayey soil,” Nizzi Griffi told us. ​“The work­ers broke a great num­ber of roots which had devel­oped just under the veg­e­tal layer. Now, those olive trees will tol­er­ate high tem­per­a­tures much bet­ter because roots have been stim­u­lated to go deeper and they will no longer com­pete with the other plants.”

When we make our agro­nomic choices, we should con­sider all the rel­e­vant fac­tors, not just ero­sion. ​“Since the heat is a new issue, we must make sure that soil is able to absorb water and the roots are renewed,” she con­tin­ued, point­ing out that besides the biggest and sup­port­ive roots which no longer have absorb­ing func­tion, we must focus on the vital and cap­il­lary root which can absorb water and nutri­ents, stim­u­lat­ing their renewal.

We can count on two sys­tems: prun­ing and deep tillage. Because, ​“when a part of the tree is pruned, parts of the roots die and new ones develop along with the devel­op­ment of new veg­e­ta­tion; sim­i­larly, deep tillage breaks roots, renew­ing and mak­ing them more recep­tive to water and nutri­ents.” In this sense, we can re-eval­u­ate the use of plows and har­rows, Nizzi Griffi sug­gested.

In addi­tion, she rec­om­mended keep­ing as many leaves as pos­si­ble when prun­ing, because each leaf is a small water reserve to draw on. In this sense, the plant should be leafy, pro­por­tion­ally to expo­sure to day­light.

Moreover, we should reduce the height of the olive tree in order to decrease its effort to feed the veg­e­ta­tive parts and translo­cate nutri­ents.

“A good farmer will till the soil or let herbs grow accord­ing to cli­mate and other fac­tors, in view of a ​‘tai­lor-made’ olive grove,” she added. ​“I believe that the dif­fi­cul­ties of recent years may be seen not as a threat but as an incen­tive to improve the man­age­ment of olive groves. In fact, despite hard sea­sons, we obtained excep­tional pro­duc­tions.”

Now, the tem­per­a­ture is going back in the range of nor­mal and scat­tered show­ers finally refreshed some of the thirsti­est olive groves.

• Il Sole 24 Ore


• ANSA