Agriculture & Food, Volume 11, 2023

Abstract: Konservolia and Kalamon olive orchards were tested for their vegetative and fruit growth after foliar urea applications served as nitrogen nutritional delivery scheme. Five urea aerial fertilizations (8-65 kg/m3/ha) from January to September with summer aerial supplement of buffered KNO3 replaced regular fertilization program for the above-mentioned olive orchards. Despite of different stem growth rates due to seasonal effect on tree physiology, throughout the experimental period no major changes in biomass productivity were observed for both varieties. Final size Konservolia fruits did not differ among conventional and foliar urea treatments. Although Kalamon olive fruits including pit data, differ in size among fertilization strategies with bigger size observed in foliar urea treated areas; their flesh firmness was found to be significantly lower to fruits received from soil fertilized orchards. Both varieties produced olives with increased pit weight and size and lower fruit flesh firmness when trees treated with urea. Konservolia decreases its fruit flesh/pit ratio as opposed to Kalamon where treated trees increased the weight of their commercial fruit flesh. Data suggest that each of tested olive varieties respond differently in foliar application of urea as a replacement of soil fertilization strategies. Results for Konservolia reveal that urea foliar applications can be approached as safe, conservative tactic nutritional replacement to soil fertilization for the orchard trees. For Kalamon variety, aerial treatments positively affect fruit size, increased pit size and flesh/pit ratio providing potentially faster harvest maturity times. This alternative nitrogen fertilization delivery strategy for Kalamon olive orchards can be considered as viable approach to restrict groundwater nitrate leaching and atmospheric pollution from previous fertilization conventional plans and increase fruit biomass for olive oil and olive waste byproducts useful in circular economy.