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

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

Investigation of the role of Mn in olive trees' mineral nutrition

The present investigation was divided into two groups: a) The hydroponics investigation and b) the investigation about the plant-soil relationships. The primary objective of this thesis was to produce and present numerous results concerning the influence of Mn on plant growth, absorption and use efficiency of different nutrient elements, as well as on some physiological and biochemical functions (chlorophyll fluorescence, stomatal conductance, transpiration, photosynthesis and PPO activity) of four olive cultivars. The secondary aims of this thesis were to compare values of the Mn absorption effectiveness of each olive cultivar between the different soil micronutrient extractive solutions, as well as to investigate the possible existence of different fungus genus which colonize the root system of each cultivar, keeping in mind that there were differences in the Mn status of each one of them. The Mn status did not influence the plant growth of 3 of the 4 olive cultivars used, with the exception of the cultivar Picual. The increase of Mn concentration in the nutrient solution significantly increased Mn absorption from the plants but decreased the absorption of most of the other nutrients. Furthermore, the increase of Mn in the nutrient solution significantly reduced Mn use efficiency in all the olive cultivars of the experiment and influenced the use efficiency of the other nutrient elements. Neither Mn absence from the nutrient solution, nor Mn excess in it influenced the function of PSII. Under Mn excess conditions, all the olive cultivars had significantly greater stomatal conductance values, compared with that of control (without Mn) and, consequently, had also greater transpiration rate. In contrast to that, two of the 4 olive cultivars (Picual and Manaki) did not have greater photosynthetic rate under Mn excess conditions, while the other two (FS-17 and Koroneiki) followed the tendency of their stomata opening and increased significantly their photosynthesis. Under Mn excess conditions, PPO activity in the leaves of the olive cultivars Picual and FS-17 was continuously increasing with time and this increase preceded the appearance of Mn toxicity conditions. In contrast to that, under Mn deficiency or Mn-limited conditions PPO activity was not increased with time. Apart from Mn, other nutrient elements, such as Ca, Mg, Fe and Zn were correlated (positively or negatively) with PPO activity. Between the 3 micronutrient extraction solutions, Mehlich-3 extracted significantly greater quantities of Mn, Fe and Zn, compared with that extracted by the other two solutions. Talking about the Mn and Zn absorption effectiveness, in all olive cultivars DTPA extraction solution gave the best results, in all soil types. In contrast to the above, in the case of Fe, DTPA extracted much smaller quantities of Fe than that really could be taken by plants. Mehlich-3 extraction solution extracted much greater quantities of Mn, Fe and Zn than that really could be taken by plants, so the values of Mn, Fe and Zn absorption effectiveness were very low. Between the 3 olive cultivars tested, the cultivar Manaki had the greatest values of Mn, Fe and Zn absorption effectiveness, because it absorbed significantly greater quantities of Mn, Fe and Zn from all soils. Although the cultivar Manaki had the greatest values of Mn, Fe and Zn absorption effectiveness, it also had significantly smaller Mn and Fe use efficiency, compared with the other two cultivars, in all soil types. Two different genus of mycorrhiza fungus (Glomus and Gigaspora) colonized the root system of the olive cultivars studied, when differed in their Mn status. The genus Glomus colonized only the root system of cultivar Koroneiki and not that of the other two cultivars. Finally, in all soil types, the cultivar Chondrolia Chalkidikis had the greatest percentage of root colonization by mycorrhiza fungus.Η παρούσα έρευνα χωρίστηκε σε δύο μέρη: α) Την υδροπονική έρευνα και β) την έρευνα γύρω από τις σχέσεις εδάφους-φυτού. Πρωταρχικός σκοπός της παρούσας διατριβής ήταν να συγκεντρώσει και να παρουσιάσει ένα σύνολο ερευνητικών δεδομένων που σχετίζονται με την επίδραση του Mn στην αύξηση, την απορρόφηση και την αποτελεσματική χρήση διαφόρων θρεπτικών στοιχείων, καθώς και σε διάφορες φυσιολογικές και βιοχημικές λειτουργίες (φθορισμός χλωροφύλλης, στοματική αγωγιμότητα, φωτοσύνθεση, διαπνοή, δράση PPO) τεσσάρων ποικιλιών ελιάς. Στους σκοπούς ακόμα της παρούσας διατριβής ήταν να συγκρίνει τιμές της αποτελεσματικότητας πρόσληψης Mn της κάθε ποικιλίας ελιάς μεταξύ διαφορετικών διαλυμάτων εκχύλισης ιχνοστοιχείων εδάφους, καθώς και να διερευνήσει ύπαρξη τυχόν διαφορών στο γένος του μύκητα που αποικίζει το ριζικό σύστημα τριών ποικιλιών ελιάς, δεδομένου ότι υπήρχαν διαφορές στη θρεπτική κατάσταση του Mn μεταξύ αυτών. Η θρεπτική κατάσταση των φυτών σε Mn δεν επηρέασε την αύξηση τριών από τις 4 ποικιλίες ελιάς. Εξαίρεση αποτέλεσε η ποικιλία Picual, η οποία ελάττωσε την αύξησή της σε συνθήκες περίσσειας Mn. Κατά τα άλλα, η αύξηση του Mn στο θρεπτικό διάλυμα αύξησε την απορρόφηση του Mn από τα φυτά και των τεσσάρων ποικιλιών ελιάς και μείωσε την απορρόφηση των περισσοτέρων από τα υπόλοιπα θρεπτικά στοιχεία, αν και όχι σε όλες τις ποικιλίες. Επίσης, η αύξηση του Mn στο θρεπτικό διάλυμα μείωσε την αποτελεσματική χρήση του Mn και επηρέασε την αποτελεσματική χρήση των υπόλοιπων στοιχείων. Από τα αποτελέσματα φθορισμού της χλωροφύλλης προέκυψε ότι τόσο σε συνθήκες έλλειψης, όσο και σε συνθήκες περίσσειας Mn, η λειτουργία του PSII δεν επηρεάστηκε. Αντιθέτως, υπό συνθήκες περίσσειας Mn και οι 4 ποικιλίες ελιάς είχαν σημαντικά μεγαλύτερη στοματική αγωγιμότητα, συγκριτικά με την περίπτωση όπου τα φυτά δεν λάμβαναν Mn κατά τη θρέψη τους. Αντίστοιχα μεγαλύτερη σε αυτές τις συνθήκες ήταν και η διαπνοή, ακολουθώντας την τάση της στοματικής αγωγιμότητας. Αντίθετα, η φωτοσύνθεση, ενώ στις ποικιλίες FS-17 και Κορωνέϊκη αυξήθηκε με το περαιτέρω άνοιγμα των στοματίων σε συνθήκες περίσσειας Mn, στις ‘Picual’ και ‘Μανάκι’ δεν συνέβη κάτι τέτοιο. Η δράση της PPO στα φύλλα των ποικιλιών ελιάς Picual και FS-17 υπό συνθήκες περίσσειας Mn ήταν σε συνεχή αυξητική πορεία από πολύ νωρίς και η αύξηση αυτή προηγήθηκε χρονικά κατά πολύ της εμφάνισης συμπτωμάτων τοξικότητας Mn. Αντίθετα, υπό συνθήκες έλλειψης ή χαμηλής διαθεσιμότητας Mn, η δράση της PPO αυξομειώνονταν με το χρόνο. Εκτός από το Mn του οποίου οι συγκεντρώσεις τόσο στα φύλλα, όσο και στη ρίζα, συσχετίστηκαν θετικά με τη δράση της PPO, και άλλα θρεπτικά στοιχεία συσχετίστηκαν (θετικά ή αρνητικά, αναλόγως και με την ποικιλία) με τη δράση του ενζύμου, όπως το Ca, το Mg, ο Fe και ο Zn. Τα 3 εκχυλιστικά διαλύματα που δοκιμάστηκαν (DTPA, Mehlich-3 και Soltanpour & Schawk) είχαν διαφορετική ικανότητα εκχύλισης ιχνοστοιχείων στο έδαφος, με το Mehlich-3 να εκχυλίζει σημαντικά μεγαλύτερες ποσότητες Mn, Fe και Zn από τα άλλα δύο. Εξετάζοντας τα 3 εκχυλιστικά διαλύματα ως προς την αποτελεσματικότητα πρόσληψης των ιχνοστοιχείων, το διάλυμα DTPA έδωσε, συγκριτικά με τα άλλα δύο διαλύματα, τις καλύτερες τιμές της αποτελεσματικότητας πρόσληψης Mn και Zn από τις ποικιλίες Κορωνέϊκη, Μανάκι και Χονδρολιά Χαλκιδικής, και στα 3 εδάφη. Αντιθέτως, το ίδιο εκχυλιστικό διάλυμα στο Fe δεν έδωσε καλά αποτελέσματα, κυρίως στα εδάφη της Μάργας και του Περιδοτίτη, αφού υποεκτίμησε τις ποσότητες του Fe στο έδαφος που μπορούν να προσληφθούν άμεσα από τα φυτά. Το διάλυμα Mehlich-3, αντιθέτως, υπερεκτίμησε κατά πολύ την πραγματικά διαθέσιμη για τα φυτά ποσότητα και των τριών ιχνοστοιχείων, δίνοντας έτσι πολύ χαμηλές τιμές αποτελεσματικότητας πρόσληψης και από τις 3 ποικιλίες ελιάς. Μεταξύ των τριών ποικιλιών ελιάς που μελετήθηκαν και ανεξαρτήτως του διαλύματος εκχύλισης που χρησιμοποιήθηκε, τη μεγαλύτερη αποτελεσματικότητα πρόσληψης Mn, Fe και Zn είχε η ποικιλία Μανάκι, αφού προσέλαβε και από τα 3 εδάφη σημαντικά μεγαλύτερες ποσότητες των ιχνοστοιχείων αυτών. Αντίθετα, η ίδια ποικιλία (Μανάκι) είχε σημαντικά μικρότερη αποτελεσματικότητα χρήσης Mn και Fe και στα 3 εδάφη, σε σύγκριση με τις άλλες δύο ποικιλίες. Μεταξύ των τριών ποικιλιών ελιάς με τη διαφορετική θρεπτική κατάσταση του Mn, που αναπτύχθηκαν στα εδάφη της Μάργας και του Περιδοτίτη, διαφορετικά γένη μυκήτων αποίκισαν το ριζικό τους σύστημα. Τα γένη αυτά ήταν το Glomus και το Gigaspora.Το γένος Glomus αποίκισε μόνο το ριζικό σύστημα της ποικιλίας Κορωνέϊκη και όχι των άλλων δύο ποικιλιών, και στα 3 εδάφη. Τέλος, και στα 3 εδάφη, το μεγαλύτερο ποσοστό αποίκισης του ριζικού συστήματος μεταξύ των τριών ποικιλιών από το μυκορριζικό μύκητα το είχε η ποικιλία Χονδρολιά Χαλκιδικής

Effects of Chromium Toxicity on Physiological Performance and Nutrient Uptake in Two Grapevine Cultivars (Vitis vinifera L.) Growing on Own Roots or Grafted onto Different Rootstocks

Chromium toxicity is considered within the most severe and dangerous nutritional disorders, and it can often be observed in crops grown in industrial areas. The present study aims to determine the effects of Cr(VI) toxicity on the growth, nutrition, and physiological performance of grapevines. In a pot hydroponic experiment, own-rooted Merlot and Cabernet Franc grapevine cultivars or cultivars grafted onto 1103P and 101-14 Mgt rootstocks were exposed to 120 μM Cr(VI). Leaf interveinal chlorosis appeared after forty-five days of treatment. Overall leaf chlorosis and brown root coloration after sixty days was reported. A significant effect on the majority of the measured parameters due to the Cr(VI) treatment was observed. Chromium stress increased the total Cr concentrations in all parts of the vines, i.e., leaves, shoots, roots, and trunks. When comparing between the studied plant sections, the roots presented the highest Cr concentrations, ranging from 396 to 868 mg kg−1 d. w., and then, in descending order, the Cr concentrations ranged from 41 to 102 mg kg−1 d. w. in the trunks, from 2.0 to 3.3 mg kg−1 d. w. in the leaves, and from 1.9 to 3.0 mg kg−1 d. w. in the shoots. Between the assessed rootstocks, 1103P was identified to be a better excluder of Cr concentration in the roots and other aerial parts of the vines. Additionally, chromium toxicity negatively affected the concentrations and compartmentalization of the most important nutrients. Leaf chlorophyll (Chl) concentration decreased down to approximately 53% after sixty days of Cr stress. Chromium toxicity significantly reduced the stem water potential (SWP), net CO2 assimilation rate (A), stomatal conductance (gs), and PSII maximum quantum yield in all the cases of grafted or own-rooted vines. At this stage, chromium stress increased the leaf total phenolic content from 46.14% in Merlot vines to 75.91% in Cabernet Franc vines

Organic Fertilization and Tree Orchards

Organic fertilization has been proposed as an alternative approach to supply nutrients for crops, in the frame of organic and sustainable agriculture, with the aim to decrease high inorganic fertilization rates, protect the environment and decrease production costs for farmers. Since different types of organic fertilizers, such as manures, olive mill wastewater (OMW), sewage sludge (SS), crushed pruning wastes, composts and cover crops, exist as soil amendments to improve soil fertility, enhance plant nutrition and sustain the productivity of tree crops, their role as biofertilizers has been fully analyzed under the most important published papers. In addition, the benefits and drawbacks of organic fertilization, in a comparative approach with inorganic fertilization, are presented and discussed. Within the most important advantages of organic fertilizers, the enhancement of beneficial soil microorganisms and the improvement in soil physical properties and fertility should be included, while their most important disadvantage is their inability to directly satisfy the prompt N nutritional needs of tree crops, due to slow N mineralization rates. Finally, some novel aspects on the interrelation among innovative organic fertilizers for tree crops, sustainable field management, crop productivity and fruit quality are also included in this review, under the light of the most important and recent research data existing in the literature, with the aim to provide recommendations and future directions for organic fertilizers by tree growers

Colonization of Greek olive cultivars' root system by arbuscular mycorrhiza fungus: root morphology, growth, and mineral nutrition of olive plants

Rooted leafy cuttings of three Greek olive (Olea europaea L.) cultivars (Koroneiki, Kothreiki and Chondrolia Chalkidikis) were grown for six months in three soil types, in an experimental greenhouse, in order to investigate: i) if their root system was colonized by arbuscular mycorrhiza fungus (AMF) genus and, ii) if genotypic differences concerning growth and mineral nutrition of olive plants existed. Gigaspora sp. colonized the root system of the three cultivars studied, while Glomus sp. colonized only the root system of 'Koroneiki'. Furthermore, in most cases root colonization by AMF differed among cultivars and soil types. The maximum root colonization, in all soils, was found in 'Chondrolia Chalkidikis'. In the three soils studied, the ratio shoot dry weight (SDW)/ root dry weight (RDW) was higher in 'Chondrolia Chalkidikis' than in the other two cultivars. Furthermore, root system morphology of the three olive cultivars was completely different, irrespectively of soil type. Leaf Mn, Fe, Zn, Ca, Mg, K and P concentrations, as well as total per plant nutrient content and nutrient use efficiency, differed among cultivars under the same soil conditions. These differences concerning root morphology, SDW/RDW, as well as nutrient uptake and use efficiency, could be possibly ascribed to the differential AMF colonization by Glomus sp. and Gigaspora sp

Independent or Combinational Application of Sheep Manure and Litter from Indigenous Field Vegetation of <i>Quercus</i> sp. Influences Nutrient Uptake, Photosynthesis, Intrinsic Water Use Efficiency, and Foliar Sugar Concentrations in Olive Plants (<i>Olea europaea</i> L., cv. “Koroneiki”)

The recent energy crisis has increased the cost of fertilization for olive growers. This is why alternative nutrient sources, such as manures and other organic materials, could be used to sustain olive production within the framework of sustainable agriculture, by decreasing chemical fertilization inputs. A greenhouse pot experiment was established with a marl soil substrate that was modified with three amendments (sheep manure, or SM; litter from evergreen broadleaf species, or EBLS, such as Quercus sp.; their combination, i.e., SM + EBLS) and a control soil (no application of amendments) to investigate their influence on the nutrition, physiology, and leaf sugar concentrations of olive plants. Plant growth was not significantly affected by the amendments, while the lowest leaf N, K, and Zn concentrations were determined in the control soil. Significantly higher photosynthetic rate was determined in the SM + EBLS, compared to SM. Significantly higher intercellular CO2 was found in the EBLS and SM + EBLS, while significantly higher intrinsic water use efficiency (WUEi) was found in the SM + EBLS and the control. Significantly higher translocated sugar content was recorded in the SM + EBLS compared to the control. Overall, it was concluded that the optimum treatment was SM + EBLS, i.e., the combinational application of SM and EBLS. However, multi-year research under field conditions is necessary to draw more stable conclusions about the beneficial role of organic amendments on the nutrition and physiology of olive trees

Zeolite and Vermiculite as Inorganic Soil Amendments Modify Shoot-Root Allocation, Mineral Nutrition, Photosystem II Activity and Gas Exchange Parameters of Chestnut (<i>Castanea sativa</i> Mill) Plants

One of the most challenging topics for the sustainable agriculture is how to decrease high fertilization rates. A pot experiment, exploring the effects of zeolite (ZEO) and/or vermiculite (VER) as soil amendments, comparing to the soil application of a controlled release fertilizer (CRF), was realized in chestnut plants. Various parameters related to soil fertility, and plant growth, nutrition, and physiology were investigated to gain knowledge towards more sustainable management. After ZEO application and in comparison to CRF, an impressive boost in soil K was achieved. Moreover, soil P and Zn levels were higher in the VER-treated soil, compared to CRF. Leaf K and Ca concentrations were significantly higher in ZEO, compared to the VER treatment; the highest foliar N and Zn concentrations were measured in CRF and VER, respectively. However, significantly lower foliar Mn and Cu were found in VER. The highest root biomass produced in the ZEO treated plants. For most nutrients, their total uptake per plant was higher in CRF and ZEO. Finally, photosynthetic rates were higher in VER (mainly due to non-stomatal factors) and CRF (mainly due to stomatal factors). Our data open a discussion towards the application of ZEO and/or VER as soil amendments in chestnut nurseries and orchards, aiming at partially decreasing fertilization rates and boosting sustainable nutrient management

Comparative Approach on the Effects of Soil Amendments and Controlled-Release Fertilizer Application on the Growth, Nutrient Uptake, Physiological Performance and Fruit Quality of Pepper (<i>Capsicum annuum</i> L.) Plants

Under the economic pressure from the increase of fertilizers’ prices due to the recent energy crisis, more efforts are needed to search for alternative and cheaper sources of nutrients for crops. The purpose of our study was to compare the effects of manure and inorganic amendments’ application to those derived from the application of a controlled-release fertilizer (CRF) on the growth, nutrition, physiology and fruit quality of pepper plants. For that reason, zeolite (ZEO) and vermiculite (VER) were applied either independently, or in combination between them, or with manure (MAN), in a pot experiment. Insignificant differences for plant growth among the treatments were recorded, while higher foliar N, Mg and Mn concentrations were determined in CRF. In contrast, a significantly higher K uptake was recorded in the ZEO and VER + ZEO treatments; the highest leaf P levels (0.47 and 0.44% D.W.) were recorded in the MAN + VER and ZEO treatments, respectively. The optimum photosynthetic II (PSII) performance was observed in the VER and in the MAN + ZEO (based on the performance index—PI) treatments. The highest stomata opening was found in the CRF treatment, while the photosynthetic rate of pepper plants showed its maximum values both in the CRF and VER treatments. Finally, fruit quality (as indicated by total soluble solids, total phenols and antioxidant activity—FRAP) was significantly influenced by treatment. In conclusion, significant differences in the growth, nutrition and physiological performance of pepper plants between soil amendments’ application (inorganic, such as zeolite and vermiculite, and organic, such as manures) and CRF application were recorded; thus, these amendments should be more thoroughly studied in future projects to investigate if they could partially decrease high inorganic fertilization rates in Capsicum annuum L

Comparative Approach on the Effects of Soil Amendments and Controlled-Release Fertilizer Application on the Growth, Nutrient Uptake, Physiological Performance and Fruit Quality of Pepper (Capsicum annuum L.) Plants

Under the economic pressure from the increase of fertilizers&rsquo; prices due to the recent energy crisis, more efforts are needed to search for alternative and cheaper sources of nutrients for crops. The purpose of our study was to compare the effects of manure and inorganic amendments&rsquo; application to those derived from the application of a controlled-release fertilizer (CRF) on the growth, nutrition, physiology and fruit quality of pepper plants. For that reason, zeolite (ZEO) and vermiculite (VER) were applied either independently, or in combination between them, or with manure (MAN), in a pot experiment. Insignificant differences for plant growth among the treatments were recorded, while higher foliar N, Mg and Mn concentrations were determined in CRF. In contrast, a significantly higher K uptake was recorded in the ZEO and VER + ZEO treatments; the highest leaf P levels (0.47 and 0.44% D.W.) were recorded in the MAN + VER and ZEO treatments, respectively. The optimum photosynthetic II (PSII) performance was observed in the VER and in the MAN + ZEO (based on the performance index&mdash;PI) treatments. The highest stomata opening was found in the CRF treatment, while the photosynthetic rate of pepper plants showed its maximum values both in the CRF and VER treatments. Finally, fruit quality (as indicated by total soluble solids, total phenols and antioxidant activity&mdash;FRAP) was significantly influenced by treatment. In conclusion, significant differences in the growth, nutrition and physiological performance of pepper plants between soil amendments&rsquo; application (inorganic, such as zeolite and vermiculite, and organic, such as manures) and CRF application were recorded; thus, these amendments should be more thoroughly studied in future projects to investigate if they could partially decrease high inorganic fertilization rates in Capsicum annuum L