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A greenhouse experiment was conducted, in order to study the effect of nitrogen (N) form (NO 3 − , NH 4 + , urea, NH 4 + + NO 3 − ) and concentration (1, 8 and 16 mM) on growth, mineral nutrition and photosynthetic performance of olive plants ( Olea europaea L., cv. ‘Kalamon’). Our data indicate that when plants at high supply (16 mM) received urea as N source better growth performance was recorded, compared to the cases olive plants received other N forms; however, at low to medium N supply (1 or 8 mM) better plant growth performance observed when they were fertilized with NO 3 − –N. Total N uptake at 16 mM was significantly lower when plants received NO 3 − –N, in comparison to the other N forms. NO 3 − form at 16 mM resulted in lower total uptake of P, Fe, Mn and Zn, compared to the other treatments. On the other hand, NH 4 + -N at high N supply (16 mM) resulted in lower total uptake of Ca and Mg. However, significantly higher K uptake was found when plants were treated with NH 4 + , at high N rate (16 mM). High N supply in the form of NH 4 + -N significantly inhibited net photosynthetic rate (A), although the chlorophyll fluorescence (as an indicator of the function of PSII) did not significantly differ among the N treatments. In conclusion, urea-N proved to be the most appropriate N form for the mineral nutrition of the olive cultivar ‘Kalamon’; thus, it should be preferred as a source of N in olive groves receiving high N fertilizations. [ABSTRACT FROM AUTHOR]

Two sustainable management models were studied, in order to investigate if they were successful in satisfying the nutritional needs of mature olive groves (20 year-old olive trees- Olea europaea , cv. ‘Koroneiki’), situated in two geographical regions of Greece (Thessaloniki, Central Macedonia, Northern Greece, and Corfu, Ionian Islands, Western Greece). Nutrient supply in both olive orchards was based, during the last 20 years, on pruning material recycling, as well as on cow manure (8 t/ha/year, in the grove of Corfu) and patent kali (5 kg/tree/year, in the grove of Thessaloniki) application. Soil analysis revealed that pH was slightly alkaline in the olive grove of Thessaloniki and acidic (6.00–6.34) in the olive orchard of Corfu; organic matter content was approximately two times greater in the grove of Corfu. Exchangeable Ca concentrations in deeper soil layers (20–40 and 40–60 cm) of the olive orchard of Thessaloniki were approximately two times greater, compared to those found in the grove of Corfu. In contrast, 2–14.5 times greater K exchangeable concentrations, but only in deeper layers (20–40 and 40–60 cm), were found in the grove of Corfu. DTPA extractable Fe, Mn and Zn concentrations were 9–14, 3–5, and 3–5.5 times greater (depending on soil layer) in the olive orchard of Corfu, compared to those found in Thessaloniki. Leaf K concentrations were significantly greater in the grove of Corfu (1.2–1.4% d.w.), while Fe concentrations in the same olive orchard exceeded 120 ppm. Generally, most of the leaf nutrient concentrations for both groves were within the normal levels of sufficiency, or within the over-sufficiency range (e.g. those of N and K in the grove of Corfu, and P in both olive orchards). Only leaf B concentrations in January (17–19 p.p.m.), in both orchards, and leaf Mn levels in the grove of Corfu were slightly (but not seriously) deficient to marginal. Consequently, it can be concluded that both studied sustainable management models for mature olive groves (no soil tillage, pruning material and weed cuts recycling, in addition to: (i) patent kali, or (ii) manure supply) were successful. Thus, the two models are commercially and environmentally sustainable for olive cultivation, especially in marginal, degraded, and/or hilly Mediterranean areas. Finally, they are of great socioeconomic importance in specific rural areas (where olive-growers combine olive oil production with domestic animal breeding). [ABSTRACT FROM AUTHOR]

• A P-fertilization experiment (+P or –P) was conducted in two olive groves. • P fertilization influenced soil properties, P fractions and its mineralization. • Acid and alkaline phosphatase activities were significantly higher in the –P plots. • P fertilization did not significantly influence trees' foliar P nutrition. • It is useless for the olive growers to provide P every year in their groves. Often, from soil and plant tissue analyses, over-sufficient foliar P levels in olive trees, grown under low Olsen P availability, are determined. In order to deepen our knowledge in this topic, a field P fertilization experiment (with or without supply of the fertilizer 0-46-0) with 25-year-old olive trees was conducted, in order to investigate if: i) soil organic P was a sufficient 'pool' to satisfy the P nutritional needs of mature, fully productive, olive trees under low Olsen P availability and sufficient organic matter content, ii) the activities of acid and alkaline phosphatase were enhanced under low Olsen P availability, iii) soil chemical properties were significantly influenced by P fertilization, iv) significant differences in foliar nutrition of olive trees existed between P-fertilized (+P) and unfertilized (-P) trees. Our results indicated that in the -P plots 48 % of the total soil P was in organic fraction, while in the + P ones approximately 23 % of the total P was in organic form. In contrast, Olsen, inorganic and total P fractions were significantly higher in the + P plots. In addition, in the + P plots significantly lower: i) soil Fe, Mn and Zn, and ii) foliar Ca, Mg and Mn concentrations were determined, while, in contrast, iii) higher leaf K concentration was found. Foliar P was not influenced by P fertilization, while at the same time, both the activities of alkaline and acid phosphatase were significantly higher in the –P plots, compared to those received P fertilization. Overall, the kind of management of olive groves (sufficient organic matter levels, with or without inorganic P fertilization inputs) significantly influences P dynamics and modifies its fractions in soils, while it also affects organic P mineralization and supports P nutrition for olive trees. It is believed that these data reveal the crucial role of organic matter to sustain P uptake and contribute towards a sustainable management of olive groves to support and sufficiently satisfy the P nutritional needs of olive trees, by also significantly reducing the unnecessary annual P fertilizer inputs. [ABSTRACT FROM AUTHOR]

• Olive plants were fertilized with manures or a controlled release fertilizer (CRF). • The highest biomass, macronutrient content and PSII activity were found in the CRF. • Significantly lower photosynthetic rate and stomata opening were recorded in the CRF. • The lowest foliar P, K, Mg, Zn and Cu concentrations were found in the CRF. • The higher macronutrient accumulation in the CRF was owed to the higher biomass. Organic fertilization has been proposed as an alternative method, in the frame of sustainable agriculture, to enhance soil fertility and satisfy the nutritional needs of crops, without the input of chemical fertilizers. A six-month pot experiment, with 3 soil amendments, used as organic fertilizers (cow manure-CM, goat manure-GM, and their mixture, i.e. CM + GM) and a controlled release fertilizer (CRF) was conducted, in order to investigate if the growth, nutrient uptake, photosystem II (PSII) activity, photosynthetic rate and total sugars of Olea europaea L. (cv. 'Koroneiki') plants were influenced by the kind of fertilization. The highest plant biomass, macronutrient content and PSII activity were found in the CRF treatment. In contrast, significantly lower photosynthetic and transpiration rates were recorded in the CRF due to the lower stomatal conductance. Translocated sugars were higher in the CM + GM treatment, while total sugar concentration did not significantly differ among the treatments. Despite the highest content of all macronutrients, Fe and Mn recorded in the CRF, the lowest foliar P, K, Mg, Zn and Cu concentrations revealed that the higher nutrient accumulation, compared to the organic treatments, should be ascribed to the higher plant biomass, rather than to higher nutrient uptake. From the above data, it is clear that the kind of organic/inorganic fertilization significantly influenced soil organic C content, fertility, growth, nutrient uptake and the physiology of olive plants. Thus, the kind of manure(s) used to enhance soil fertility and support crop production should be seriously taken into consideration by the olive growers before its/their use. [ABSTRACT FROM AUTHOR]