Comparative Study between Urea and Biogas Digestate Application towards Enhancing Sustainable Fertilization Management in Olive (Olea europaea L., cv. ‘Koroneiki’) Plants

Abstract

Organic fertilization is a promising strategy to decrease N mineralization rates and high N losses via leaching and denitrification, thus synchronizing N application with N uptake for crops. A 230-day experiment with olive plants was realized under greenhouse conditions to compare urea and biogas digestate (BD) application on the growth, nutrient uptake, and physiological performance of Olea europaea L. plants. The following treatments were applied: (i) UREA, (ii) UREA + DCD (nitrification inhibitor), (iii) BD, (iv) BD + DCD, (v) acidified BD, (vi) acidified BD + DCD, (vii) CONTROL (typical native Marl soil type, without fertilizer application). Under BD application, significantly higher levels of organic matter, Olsen P, and exchangeable K compared to UREA were found. Significantly lower main shoot length and total plant biomass were recorded in the CONTROL soil compared to BD. Foliar N was lower in the ACID.BD and ACID.BD + DCD treatments, while leaf P was lower in UREA. The highest PSII activity was recorded in UREA + DCD, while the highest photosynthetic rate and intercellular CO2 concentration were determined in UREA. It is expected that these data will constitute a first comparative approach between urea and BD application in olive plants, which should be carefully considered, towards boosting sustainable fertilization in the frame of circular economy strategy.

Seasonal Variation of Leaf Ca, Fe, and Mn Concentration in Six Olive Varieties

“…Additionally, Ca concentration fluctuations upon element absorption by the trees were observed due to temperature changes and rainfall events during the winter when compared to the dry period of the summer. Ca concentration was higher in basal compared to the apical leaves in young 'Koroneiki' plants [10].…”

“…Leaf Fe concentration showed a general tendency to oscillate around a value. Fe concentration was higher in basal compared to the apical leaves in young 'Koroneiki' plants [10]. Stateras and Moustakas [8] also reported a low fluctuation of Fe leaf concentration.…”

“…Available information on the nutritional requirements of olive varieties is limited. Several studies have been realized using one variety [8,[10][11][12][13][14], although few studies have compared the seasonal variation of nutrients in a range of varieties [15,16]. However, the relationship between leaf seasonal variation and availability of nutrients supplied from the soil have indicated that nutrient uptake during the cold winter months is reduced due to low tree activity under Mediterranean conditions.…”