Development and calibration of uptake models for the micronutrients mn and zn in cucumber cultivated in closed hydroponic systems

The aim of this thesis was to develop and calibrate uptake models for the micronutrients Mn and Zn in cucumber cultivated in closed hydroponic systems. A total of two experiments were carried out in which investigated the effect of Mn and Zn accumulation in the root environment and its influences on plants, the effect of Mn and Zn concentration in the supplied nutrient solution in their uptake by the cucumber plants and the development, calibration and validation of Mn and Zn uptake models based on cumulative water consumption (CWC).In order to establish critical Zn and Mn, a standard and a high Mn level (10 and 160 μM) were combined with a standard and a high Zn level (4 and 64 μM) in the nutrient solution supplied to cucumber in closed cycle hydroponic units to compensate for nutrient and water uptake (RNS). The first symptoms of Mn and Zn toxicity appeared when the concentrations of Mn and Zn in the leaves of cucumber reached 900 and 450 mg kg–1 in the dry weight, respectively. Excessively high Mn or/and Zn concentrations in the leaves reduced the fruit biomass production due to decreases in the number of fruits per plant, as well as the net assimilation rate.For the uptake estimation of Mn and Zn by cucumber at different Mn and Zn concentrations in the recirculating (NS) under Mediterranean climatic conditions, four Mn and four Zn levels at a standard Zn and Mn concentration respectively in the RNS were applied as experimental treatments. The actual uptake concentrations of Mn and Zn were estimated by applying two different methods who gave similar uptake concentrations for Mn in the low-Mn supply level and Zn in all Zn levels. However, in the three higher Mn supply levels, the values estimated on the basis of nutrient removal from the NS were significantly higher than those found by measuring the total Mn content in plant biomass. These discrepancies in the three high-Mn treatments were ascribed to partial immobilization of Mn by oxidizing bacteria in the NS.For the development of uptake models of Mn and Zn which are based on the CWC, used a differential equation that relates the rate of accumulation of Mn or Zn with the uptake rate of the nutrient solution used for the compensation of transpiration losses. As demonstrated by the validation of models, concentrations of Mn or Zn in the NS can be predicted with acceptable accuracy, based on the above models, only in case of high concentrations of these elements in the RNS.Σκοπός διατριβής ήταν η μελέτη των επιπτώσεων υψηλών συγκεντρώσεων Mn και Zn στην αγγουριά όταν καλλιεργείται σε κλειστά υδροπονικά συστήματα και η ανάπτυξη και βαθμονόμηση μοντέλων απορρόφησης των δύο αυτών ιχνοστοιχείων. Αρχικά, διερευνήθηκε η επίδραση της συσσώρευσης Mn και Zn στο ριζικό περιβάλλον στα φυτά. Κατόπιν διερευνήθηκε η επίδραση που ασκεί η συγκέντρωση του Mn και του Zn στο παρεχόμενο θρεπτικό διάλυμα (ΘΔ) στην απορρόφησή τους από την αγγουριά. Στη συνέχεια τα δεδομένα αυτών των πειραμάτων χρησιμοποιήθηκαν σε μία μετα-ανάλυση με στόχο την ανάπτυξη-βαθμονόμηση μοντέλων απορρόφησης Mn και Zn με βάση την αθροιστική κατανάλωση νερού και στη συνέχεια τον έλεγχο της αξιοπιστίας των εκδοχών που προέκυψαν από την βαθμονόμησή για τα δύο αυτά ιχνοστοιχεία.Μια κανονική και μια υψηλή συγκέντρωση Mn (10 και 160 μM) συνδυάστηκαν με αντίστοιχες συγκεντρώσεις (4 και 64 μM) Zn σε ΘΔ που δόθηκε σε φυτά αγγουριάς σε 16 ανεξάρτητα κλειστά υδροπονικά συστήματα. Συμπτώματα τοξικότητας Mn και Zn εμφανίστηκαν όταν η συγκέντρωση του Mn και του Zn στα φύλλα έφτασε τα 900 και 450 mg kg-1 σε ξ.β. αντίστοιχα. Οι υψηλές συγκεντρώσεις Mn και/ή Zn στα φύλλα μείωσαν την βιομάζα των καρπών λόγω μείωσης του αριθμού των καρπών /φυτό, καθώς επίσης και τον καθαρό ρυθμό αφομοίωσης. Για την εκτίμηση της απορρόφησης του Mn και του Zn από την αγγουριά στις μεσογειακές συνθήκες καλλιέργειας εφαρμόστηκαν 4 επίπεδα Mn και 4 Zn. Οι συγκεντρώσεις απορρόφησης (ΣΑ) του Mn και του Zn που εκτιμήθηκαν με την εφαρμογή δύο διαφορετικών μεθόδων έδωσαν παρόμοιες ΣΑ για το Mn στο χαμηλό επίπεδο τροφοδοσίας Mn και για τον Zn σε όλα τα επίπεδα τροφοδοσίας. Ωστόσο, στα τρία υψηλότερα επίπεδα Mn, οι τιμές που εκτιμήθηκαν με βάση την απομάκρυνση από το ανακυκλούμενο θρεπτικό διάλυμα (ΑΘΔ) ήταν σημαντικά υψηλότερες από αυτές που βρέθηκαν με την μέτρηση της περιεκτικότητας σε Mn της φυτικής βιομάζας και αποδόθηκαν στην μερική δέσμευση του Mn από οξειδωτικά βακτήρια στο ΘΔ.Προκειμένου να ποσοτικοποιηθεί η σχέση, μεταξύ της ΣΑ και της συγκέντρωσης στο ΑΘΔ χρησιμοποιήθηκε μια διαφορική εξίσωση που σχετίζει τον ρυθμό συσσώρευσης του Mn ή του Zn με τον ρυθμό πρόσληψης του ΘΔ που χρησιμοποιήθηκε για την αντιστάθμιση των απωλειών διαπνοής. Όπως έδειξε ο έλεγχος αξιοπιστίας της βαθμονόμησης των μοντέλων για το Mn και τον Zn, οι συγκεντρώσεις τους στο ΑΘΔ μπορούν να προβλεφτούν με αποδεκτή ακρίβεια χρησιμοποιώντας τα παραπάνω μοντέλα, αλλά μόνο στην περίπτωση υψηλών συγκεντρώσεων των στοιχείων αυτών στο ΑΘΔ

Developing an Open-Source IoT Platform for Optimal Irrigation Scheduling and Decision-Making: Implementation at Olive Grove Parcels

Climate change has reduced the availability of good quality water for agriculture, while favoring the proliferation of harmful insects, especially in Mediterranean areas. Deploying IoT-based systems can help optimize water-use efficiency in agriculture and address problems caused by extreme weather events. This work presents an IoT-based monitoring system for obtaining soil moisture, soil electrical conductivity, soil temperature and meteorological data useful in irrigation management and pest control. The proposed system was implemented and evaluated for olive parcels located both at coastal and inland areas of the eastern part of Crete; these areas face severe issues with water availability and saltwater intrusion (coastal region). The system includes the monitoring of soil moisture and atmospheric sensors, with the aim of providing information to farmers for decision-making and at the future implementation of an automated irrigation system, optimizing the use of water resources. Data acquisition was performed through smart sensors connected to a microcontroller. Data were received at a portal and made available on the cloud, being monitored in real-time through an open-source IoT platform. An e-mail alert was sent to the farmers when soil moisture was lower than a threshold value specific to the soil type or when climatic conditions favored the development of the olive fruit fly. One of the main advantages of the proposed decision-making system is a low-cost IoT solution, as it is based on open-source software and the hardware on edge devices consists of widespread economic modules. The reliability of the IoT-based monitoring system has been tested and could be used as a support service tool offering an efficient irrigation and pest control service

A web-based GIS platform supporting innovative irrigation management techniques at farm-scale for the Mediterranean island of Crete

This study was performed in the context of NSRF 2014-2020 project MIS: 5028242 “DEcision system For Irrigation in Crete based on Innovative Technologies - DE.F.I.C.I.T.”, which is co-financed by the Crete Operational Program and the European Regional Development Fund (ERDF).Summarization: The aim of this paper is the creation of an integrated and free-access web platform for parcel irrigation water management on a large spatial scale (Water District of Crete, in Greece) in order to: a) accurately determine the irrigation needs of the main crops for Crete such as olives, citrus, avocados and vineyards, b) design strategies, for optimal adaptation of the agricultural sector in the context of climate change, and c) incorporate the dynamic integration of the above information through the creation of a digital platform. In the proposed decision-making system, essential factors are taken into account, such as real-time meteorological data, information about the type and spatial distribution of the agricultural parcels in Crete, algorithms for calculation crop evapotranspiration per development stage and age of the crops, satellite remote sensing techniques in combination with field surveys to depict accurate soil texture map for the whole island of Crete as well as sustainable cultivation practices for saving water per crop and parcel geomorphology. Based on the proposed decision-making system, users will have the opportunity in any specific location/farm in Crete to know the irrigation needs of the crops in real-time and obtain information about proper climate-water adaptation practices. The main novelty points of the proposed platform include the derivation of parcel-level soil texture data from Sentinel-2 satellite imagery and field samples, the comprehensiveness of the irrigation management information, the relatively low data requirements and the application interface simplicity provided to the end-user.Presented on: Science of the Total Environmen