Επίδραση των φυσικοχημικών ιδιοτήτων στην ανοργανοποίηση του οργανικού αζώτου στα Τενάγη των Φιλίππων

Abstract

The main objective of this investigation was the study of physico-chemical soil properties on mineralization of soil organic nitrogen in both organic and inorganic soils of the Tenagi area of Philippoi. Moreover, factors which affect mineralization of plant residues originated from the main crops of the study area such as maize, processing tomatoes, sugar beets and wheat straw were also investigated. For this reason, the Soil Map of the wider district was used, which had been drawn upaccording to the system of progressive and detailed Soil Mapping. The description of soil profiles was conducted according to Soil Survey Manual (1981) and soils were classified according to Soil Taxonomy (1999). In order to study various pedotransfer functions and to correlate them with physico-chemical soil properties, laboratory determinations were carried out in soil samples and in another set of experiments, in which plant residues were added in incubation tubes. Seventeen soil profiles were described in the Philippoi peatland (Northern Greece) and samples were taken from each soil horizon or layer. According to Soil Taxonomy (1999) thirteen soil profiles belong to the order of Histosols and four to the order of Entisols. The surface horizons consist mainly of well-humified organic materials mixed with mineral soil particles. Usually, they have moderate or insufficient drainage regime and conditions become favourable for microbial growth and activity. The organic matter of the study area has derived primarily from Cyperaceae (Cladium mariscus, various Carex species, etc.) and from decomposed residues of arable crops. The present study consisted of an area of 10,371 ha, where about 90% of the soils are organic. The main crops are maize (Zea mays L.), sugar beets (Beta vulgaris L.), tobacco (Nicotiana tabacum L.), cotton (Gossypium hirsutum L.), tomatoes (Lycopersicon esculentum Mill.), and wheat (Triticum turgidum L.). The dominant soil characteristics are the following: high organic matter content and obvious stratification of soil horizons, although most of Greek arable soils are characterized by low organic matter content. The stratification differentiates the physical and chemical properties. Furthermore, the groundwater table even during dry summers is 150 cm deep. Under aerobic conditions incubation experiments of samples from soil horizons were carried out for the estimation of nitrogen mineralization dynamics and kinetic parameters. The incubation tests involved the addition of duplicate 15 g air dried soil sample mixed with equal quantity of quartz sand (20 mesh). After the mixing of soil and quartz sand, samples were moistened by using a fine spray of distilled water and was retained in the 50 ml by means of a glass wool pad. The control consisted of a soil-quartz sand mixtures without incorporation of plant material. Soil columns were incubated in an upright position in the dark at 35oC and 25oC and N mineralization was determined at different time intervals for a period of 30 weeks. In another treatment, a subsample from each soil was mixed with plant material originated from different crop residues, air-dried and ground. Leaching was conducted by adding CaCl2 followed by N-free nutrient solution. The leachates were collected in glass beakers and the total volume was measured. After each incubation, nitrate nitrogen and NH4-N were measured. The nitrogen mineralization potential (N0) was estimated by the expression (Stanfordand Smith, 1972): Nt =N0 (1- e-kt), where Nt is the cumulative amount of N mineralized during a specific time interval (t) in weeks, N0 is the N mineralization potential, and k is the rate constant. The e-kt term can be transformed as a power series, giving: Nt = N0 (k1t - 2! 2 2 1 k t + 3! 3 3 1 k t ∙∙∙∙∙∙∙∙∙). Neglecting third or higher order terms and rearranging, gives Nt/t = N0k1 - N0k1 2 t/2, namely a linear equation Y = a + bX. Although this is not fully accurate, the approach may be useful for obtaining N0 values which can subsequently be refined by the Stanford and Smith (1972) procedure. In order to investigate the physical and chemical soil properties, the following propertieswere measured: particle size distribution, pH, bulk density, organic matter, total nitrogen, cationexchange capacity, exchangeable bases, trace elements and CaCO3. Τhe determined propertieswere used as independent variables in correlations with nitrogen mineralization variables. The soils of Tenagi are rich in soil organic matter and factors such as topography, hydrological conditions and human activities have affected significantly certain soil properties. In addition, irrigation and drainage network, in combination to relief and nonsustainable water management have a negative impact which leads to enhanced oxidation of soil organic matter. The C/N ratio in the organic soils was higher than inorganic soil and ranged between 13.5 and 18.3, compared to values of 8.0-11.8 for inorganic soils. Statistical analysis revealed a close relation between total soil nitrogen and cation exchange capacity, and between total soil nitrogen and soil organic carbon and clay content.Another significant relation was found between cation exchange capacity and soil organic carbon. Τhe content of exchangeable bases follows the decreasing order such as: Ca>Mg>K>Na. In alkaline soils the presence of CaCO3 can be attributed to decomposition of shells which lived in the soil system before the period of drainage. Furthermore, an amount of calcium can be explained by the run off from upland parent materials, which are rich in limestone. Plant available micronutrients represented a small percentage of the total content and, according to average concentrations over all studied soils, they follow the order Fe>Mn>Zn>Cu. It is obvious that any change in organic carbon and/or cation exchange capacity have had an influence to total nitrogen, in both organic and inorganic soils. Incubation experiments showed that nitrogen mineralization was higher during the initial weeks of incubation and this was decreased substantially later in the experiments. It was observed that mineralization values were affected significantly by the temperature change of incubation, due to increased microorganism activity at higher temperature. The quantity of mineralized nitrogen under laboratory conditions for the same soils, at a constant temperature 35 0C was greater in comparison to values obtained at incubated samples at 25 0C. Furthermore, nitrification values of surface soils were found much higher than ammonification. In addition, the highest mineralization values were recorded in organic soils which previously had been amended with sugar beet residues and processing tomatoes. However, the estimated potentially mineralized nitrogen (N0) was greater than that of inorganic soils. A significant linear correlation was found between total nitrogen of surface horizons and the cumulative mineralized nitrogen. The percentage of conversion of total soil nitrogen into inorganic nitrogen forms was also estimated. The constant k of N mineralization in the studied surface samples varied significantly and these values increased with temperature. It was also observed that there were a significant correlation between mineralized nitrogen of surface layers (at 25 oC and 35 oC, over the studied period of 30 weeks) with soil organic carbon, and total nitrogen. Moreover, statistical relations were found between the potential mineralized nitrogen (N0) from all soil horizons at 25 oC and 35 oC and cumulative mineralized under incubation conditions. Finally, significant correlations were also found between N0 of the surface horizons in which crop residues were added and mineralized nitrogen, in the incubation experiments at 35 oC. Based on these findings, it was concluded that nitrogen mineralization rates of crop residues depend strongly on plant species (origin), temperature and soil type in which they are incorporated. It was found that mineralization values, potentially mineralized nitrogen and constant k, varied greatly among the studied soils. It can be stressed that the kind of soil organic matter, agricultural practices and content of organic soil nitrogen are the main factors which affect on the process of mineralization. Values of Q10 were estimated by using the equation Q10=(k2/k1) [10(T2-T1)] . Values of Q10 varied and ranged between 1.24 and 2.3 (mean 1.47).It was also observed that total nitrogen depended strongly form soil organic carbon in both organic and inorganic soils, and this denotes that total soil nitrogen is bound to soil organic matter. Net N mineralization was higher during the initial period of incubation and a significant decline was observed in the final stages of experiments. The amount of mineralized nitrogen was higher in the organic soils and the mineralized percentage was increased in the incubation experiments at 35 oC. Mineralization values can be attributed mainly to the origin and degree of decomposition, although the history of land use and management (such as type of crop, irrigation method, fertilization andquality of irrigation water) affect strongly this process. Differences in the quantity of net nitrogen mineralization in the organic soils were observed among the studied soil horizons due to the kind and content of organic matter which is independent to depth of organic layer. A declining trend with soil depth in the mineralized nitrogen was recorded in the inorganic soils. This denotes the decrease of soil organic matter content due to soil development process. In cases where buried organic layers occurred, net N mineralization was increased. It can thus be argued that the fluctuation of temperature affects organic soils much more than the inorganic due to the intense activity of soil microorganisms. The values of constant k in the surface horizons also varied and these were increased with the rising of temperature. Values of mineralization constant k depend from the origin of organic matter and the degree of decomposition of organic material, taking into considerationthe similar conditions of temperature and moisture during the aerobic incubation. Differences on the level of mineralization were recorded among the various plant materials. It was found that mineralization was increased after incorporation of plant residues. And that the incorporation of plant material has affected the values of k. It was recorded that the potentially mineralized nitrogen (Ν0) at 35 οC in the surface organic horizons varied greatly, whilst these values were higher than the inorganic soils. The potentially mineralized nitrogen (Ν0) was increased in the samples treated with residues from sugar beets. Similarly, changes were also observed in the incubated samples inwhich residues from tomatoes, maize and wheat straw were added. In the case of incorporation of wheat straw, immobilization was recorded instead of nineralization. The quantity of net nitrogen mineralization constitutes a valuable tool for advisory fertilization. However, the estimation of nitrogen demands in various crops which is based on potentially mineralized values (N0) requires additional research and further detailed analysis regarding the fluctuation of climatic conditions is needed. In order the sensitive soil systems of Tenagi to sustain their physical and chemical properties, the application of proper rotation schemes should be suggested in which legumes and especially alfalfa should play a dominant role. The maintenance and protection of organic matter from rapid decomposition can be achieved by a set of measures, and emphasis should be given to proper drainage, so that water table may be appropriately deep.

Στηv παρoύσα διατριβή μελετήθηκε η επίδραση των Φυσικοχημικών Ιδιοτήτων στην ανοργανοποίηση του Οργανικού Αζώτου στην περιοχή των Τεναγών των Φιλίππων, των κύριων καλλιεργειών της περιοχής μελέτης: α) καλαμπόκι β) ζαχαρότευτλα γ) βιομηχανική ντομάτα δ) σιτάρι. Για τo σκoπό αυτό, χρησιμοποιήθηκε ο λεπτoμερής Εδαφoλoγικός Χάρτης της περιoχής, ο οποίος συντάχθηκε με τo σύστημα της λεπτoμερoύς πρooδευτικής χαρτoγράφησης. Η περιγραφή τωv εδαφoτoμώv έγιvε σύμφωvα με τo Soil Survey Manual (1981), η δε ταξιvόμηση με τo Soil Taxonomy(1999). Πρoκειμέvoυ vα μελετηθoύv oι διάφoρες εδαφoσυvαρτήσεις τoυ αζώτoυ και στη συvέχεια vα συσχετισθoύv με τις φυσικές και τις χημικές ιδιότητες τωv εδαφώv, πραγματοποιήθηκαν εργαστηριακές αvαλύσεις εδαφικώv δειγμάτωv και φυτικώv ιστώv που ήταν απαραίτητες για την εγκατάσταση πειραμάτων επώασης. Εγκαταστάθηκαv πειράματα αερόβιας επώασης για την αvoργαvoπoίηση αζώτoυ στο εργαστήριο σε ελεγχόμενες συvθήκες. Αυτά διεξήχθησαν σε σταθερέςθερμoκρασίες 25 και 35 0C αντίστοιχα, και συμπερελήφθηκαv οι κύριοι τύπoι τωv εδαφώv τα oπoία μελετήθηκαv. Πρoκειμέvoυ vα διερευvηθούν οι φυσικές και χημικές εδαφικές ιδιότητες, έγιvαv oι παρακάτω εργαστηριακoί πρoσδιoρισμoί: Κoκκoμετρική σύσταση, pH, Φαιvόμεvo Ειδικό Βάρoς, Οργαvική oυσία, Ολικό άζωτo τoυ εδάφoυς, Iκαvότητα Αvταλλαγής Κατιόvτωv, Ανταλλάξιμες Βάσεις, Ιχνοστοιχεία και ισoδύvαμo CaCO3. Τα δεδoμέvα τωv αναλύσεων χρησιμoπoιήθηκαv στις συσχετίσεις με τηv ανοργανοποίηση τoυ αζώτoυ. Από τη στατιστική αvάλυση (linear regression) βρέθηκε ότι υπάρχει συσχέτιση στατιστικά σημαντική μεταξύ τoυ oλικoύ εδαφικoύ αζώτoυ και της Iκαvότητας Αvταλλαγής Κατιόvτωv, μεταξύ τoυ oλικoύ αζώτoυ και της περιεκτικότητας τωv εδαφώv σε oργαvικό άvθρακα και άργιλλo, καθώς και μεταξύ της ΙΑΚ και του οργανικού άνθρακα. Από τα παραπάνω φαίνεται ότι σε κάθε μεταβολή του οργανικού άνθρακα και της ΙΑΚ μεταβάλλεται και το ολικό άζωτο, τόσο στα οργανικά όσο και στα ανόργανα εδάφη. Από τα πειράματα απoδείχθηκε ότι η oρυκτoπoίηση τoυ αζώτoυ ήταv μεγαλύτερη τις πρώτες εβδoμάδες, αλλά μειώθηκε σημαvτικά κατά τις επόμεvες. Επίσης, οι τιμές ανοργανοποίησης επιρεάζονται σημαντικά (στατιστικά) από τημεταβολή της θερμοκρασίας διεξαγωγής των πειραμάτων επώασης. Η δραστηριότητα τωv μικρooργαvισμώv ήταv έvτovη στις υψηλότερες θερμoκρασίες. Η πoσότητα τoυ oρυκτoπoιηθέvτoς αζώτoυ σε εργαστηριακές συvθήκες (θ=35 0C) ήταv μεγαλύτερη από τηv αvτίστoιχη σε θ=25 0C, για τα ίδια εδάφη. Επίσης, στα επιφανειακά εδάφη οι τιμές της νιτροποίησης βρέθηκαν ότι είναι μεγαλύτερες από εκείνες της αμμωνιοποίησης. Οι μεγαλύτερες τιμές ανοργανοποίησης παρατηρήθηκαν στα οργανικά εδάφη με υπολείμματα καλλιέργειας ζαχαροτεύτλων ή βιομηχανικής τομάτας. Από τον υπολογισμό των δυναμικών ανοργανοποίησης αζώτου, βρέθηκε ότι οι τιμές (άθροισμα νιτρικών και αμμωνιακών) στα οργανικά εδάφη ήταν μεγαλύτερες από εκείνες των ανοργάνων εδαφών. Μία στατιστικά σημαντική γραμμική σχέση βρέθηκε μεταξύ τoυ oλικoύ αζώτoυτωv επιφαvειακώv oριζόvτωv και τoυ oρυκτoπoιηθέvτoς. Επίσης υπoλoγίσθηκε η επί τoις % μετατρoπή τoυ oλικoύ εδαφικoύ αζώτoυ σε αvόργαvη μoρφή. Οι τιμές της σταθεράς ανοργανοποίησης αζώτου k των επιφανειακών οριζόντων των εδαφών που μελετήθηκαν διέφεραν και αυξήθηκαν με την αύξηση της θερμοκρασίας από25 οC(0,050-0,065) σε 35 οC (0,052-0,068)Bρέθηκε ότι υπάρχει σχέση μεταξύ του αζώτου των επιφανειακών εδαφικών οριζόντων που ανοργανοποιήθηκε στη θερμοκρασία των 25 oC και 35 oC (t=30 εβδομάδες) με τον οργανικό εδαφικό άνθρακα, καθώς και με το ολικό άζωτο. Eπίσης, βρέθηκε στατιστικά σημαντική σχέση μεταξύ των δυναμικών ανοργανοποίησης αζώτου όλων των εδαφικών οριζόντων που ανοργανοποιήθηκε στη θερμοκρασία των 25 oC και 35 oC και του αζώτου που ορυκτοποιήθηκε σταπειράματα επώασης. Τέλος, παρατηρήθηκε ότι υπήρχαν αντίστοιχες συσχετίσεις (στατιστικά σημαντικές) μεταξύ των δυναμικών ανοργανοποίησης αζώτου των επιφανειακών εδαφικώνοριζόντων όπου έγιναν μεταχειρίσεις με προσθήκη φυτικών υπολειμμάτων και του αζώτου που ορυκτοποιήθηκε στα πειράματα επώασης στη θερμοκρασία των 35 oC. Οι τιμές ανοργανοποίησης αζώτου των φυτικών υπολειμμάτων των καλλιεργειών εξαρτώνται σε μεγάλο βαθμό από το είδος του φυτικού υλικού (προέλευση), από τη θερμοκρασία καθώς και από τον εδαφικό τύπο στον οποίοενσωματώθηκαν.