Sustainable Management of Olive Groves Can Tackle Effects of Climate Change

Very hot and dry sum­mer is pos­ing a chal­lenge to European farm­ers, who have had to imple­ment irri­ga­tion sys­tems almost every­where to give olive trees some relief from the heat.

With a view to mit­i­gate and pre­vent cli­mate change impacts on crops, var­i­ous and dif­fer­ent meth­ods and approaches are cur­rently being researched by experts at a global level. Among these, Cristos Xiloyannis has for years been com­mit­ted to devel­op­ing sus­tain­able and rel­e­vant olive grow­ing man­age­ment prac­tices.

“We have to assume that Italian and world olive cul­ti­va­tion, in gen­eral, are mostly non-irri­gated,” the pro­fes­sor of fruit tree phys­i­ol­ogy, gen­eral fruit grow­ing and nurs­ery tech­niques at the University of Basilicata told Olive Oil Times. ​“In view of increas­ingly dry peri­ods, there is a need to hoard as much water as pos­si­ble in the soil dur­ing the rainy sea­sons.”

In this con­text, it would be use­ful to deepen the knowl­edge and tech­nolo­gies of ​‘dry-farm­ing,’ since the rise in spring and sum­mer tem­per­a­tures affect water con­sump­tion due to a greater tran­spi­ra­tion in leaves and evap­o­ra­tion from the soil.

Xiloyannis pointed out that at this rate, over the next few years, we could increas­ingly expe­ri­ence water stress espe­cially with regard to tra­di­tion­ally non-irri­gated crops such as olive trees.

Moreover, the rise in tem­per­a­tures dur­ing win­ters will affect the needs of dif­fer­ent olive vari­eties at low tem­per­a­tures, namely their chill­ing require­ment. Considering that each vari­ety needs to spend a period below 6°C (42.8°F) dur­ing the cold sea­son in order to pre­pare flower buds and pro­duce fruits the fol­low­ing year, milder win­ters could lead to low pro­duc­tiv­ity.

Furthermore, a gen­eral global rise in aver­age tem­per­a­ture can cause a higher total annual pre­cip­i­ta­tion. Our expert in eco-phys­i­ol­ogy sug­gested rely­ing on the processes of the water cycle to cope with these issues, start­ing from the assump­tion that the greater inten­sity and grow­ing num­ber of thun­der­storms not only can cause dam­age but also make it dif­fi­cult to ensure water reserves in the sub­soil.

“With the aim to ensure a water sup­ply in the ground, we should improve the tex­ture of soil in terms of macro­p­oros­ity, enhanc­ing its hydraulic con­duc­tiv­ity,” he explained. ​“Our aim is that even intense rain water may be retained in the soil to reach deep lay­ers, up to 3 – 4 meters (10 – 13 ft.).”

“In my opin­ion, the best way to improve macro­p­oros­ity and water infil­tra­tion is to fol­low an almost zero tillage sys­tem,” Xiloyannis sug­gested. ​“A deep tillage should be car­ried out every once in a while, only in the sec­tors of plots with prob­lems of soil com­paction and there­fore water­log­ging, while in mid-March when the rainy sea­son is over. A light tillage of about 5 cen­time­ters (1.9 inches) is use­ful to ​‘dam­age’ the herba­ceous plants that com­pete with olive trees in terms of water and min­eral ele­ments.”

Undersowing with vol­un­teer plants of sev­eral vari­eties improve the struc­ture of soil thanks to the roots which run deep mak­ing room. ​“When the old roots die, they pro­mote the devel­op­ment of new roots thanks to the activ­ity of microor­gan­isms,” he explained. Moreover, if we cut the cover crop and left it to lay on the ground twice a year, we enrich the soil with car­bon, pro­mot­ing chem­i­cal and micro­bi­o­log­i­cal fer­til­ity thanks to the organic mat­ter and will help the soil absorb more water dur­ing the rainy sea­son. Reducing leaves in favor of a root sys­tem is also help­ful to bet­ter tackle drought and the olive trees’ increas­ing need of water.

“Just to give an idea, if rain­fall from September to March reaches 300 mil­lime­ters (11.8 inches), our goal is to col­lect at least 200 mil­lime­ters (7.8 inches) in the soil, which equals 2,000 cubic meters of water per hectare (28,582 cubic feet per acre),” Xiloyannis observed.

These mea­sures also help to pre­vent floods, as rain water will not remain in top­soil fill­ing in canals and rivers; more­over, they will limit soil ero­sion, while pre­vent­ing fer­til­iz­ers and her­bi­cides from reach­ing water in sur­face lay­ers.

Xiloyannis and his group of researchers are pro­mot­ing the use of treated urban waste­water for irri­ga­tion of olive trees. ​“Purified waste­water con­tains nitro­gen, phos­pho­rus, potas­sium, cal­cium, and other fun­da­men­tal ele­ments for the devel­op­ment of plants, and we can already rely on the exam­ple of Israel, where 50 per­cent of the water used in the agri­cul­tural sec­tor comes from urban waste­water,” he said, adding that in Apulia alone, 1.2 mil­lion cubic meters (42.4 mil­lion cubic feet) of treated waste­water per day could be reused.

With the University of Basilicata, they car­ried out tri­als for 15 years in a mature olive grove in Ferrandina, in the province of Matera, con­sist­ing of plants of the autochtho­nous dual-pur­pose vari­ety Maiatica di Ferrandina’ planted with an 8 x 8‑meter (26 x 26-feet) spac­ing.

The choice of the exper­i­men­tal site has been relo­cated to the Lucanian town, as it has a sewage sys­tem with a rel­a­tive irri­ga­tion net­work with­out the need for a pump­ing sys­tem, and this has made it easy and afford­able to carry urban waste treated from the munic­i­pal waste­water col­lec­tion tank to exper­i­men­tal olive grove.

The waste­water used in the exper­i­ment was puri­fied using sim­pli­fied treat­ment schemes that recov­ered part of the organic sub­stance and min­eral ele­ments con­tained in the waste­water, sig­nif­i­cantly reduc­ing purifi­ca­tion costs. It was dis­trib­uted by drip irri­ga­tion in part of the orchard. A nearby non-irri­gated and tilled plot, hav­ing plants with sim­i­lar fea­tures, was used as a con­trol.

This kind of irri­ga­tion increased the pro­duc­tiv­ity of olive trees and lim­ited the phe­nom­e­non of alter­nate bear­ing, while the extra vir­gin olive oil obtained was found to be excel­lent.

“Over the next few years, the imple­men­ta­tion of envi­ron­men­tally friendly man­age­ment tech­niques and sus­tain­able farm­ing approaches could be part of the solu­tion in pre­vent­ing the effects of cli­mate change,” Xiloyannis con­cluded.

• University of Basilicata


• ResearchGate


• ResearchGate