Soil phosphorus status in organic and conventional vegetable farms in Southeast Queensland, Australia

The soil phosphorus (P) status (0-10 cm) of two farming systems (organic (OF) and conventional (CF) vegetable farms) at two locations (Gatton and Stanthorpe) was examined amongst a suite of soil fertility indicators. The P status was similar between farming systems, in contrast to some broad-acre organic systems. Examination of farm management records revealed substantial overlap between P inputs at both localities with CF systems also receiving organic inputs, e.g. green manure and composts. A statistical analysis of the effects of different inputs also indicated that P fertility did not vary significantly between farms. Soil P levels were medium to high across farm types indicating a potential environmental risk for vegetable producers particularly in sandy well drained soils. The three methods of extraction Colwell, Olsen and Resin were well correlated with each other and produced similar results indicating the similar nutrient pools exist between farming system

Carbon losses in terrestrial hydrological pathways in sugarcane cropping systems of Australia

Climate change and carbon (C) sequestration are a major focus of research in the twenty-first century. Globally, soils store about 300 times the amount of C that is released per annum through the burning of fossil fuels (Schulze and Freibauer 2005). Land clearing and introduction of agricultural systems have led to rapid declines in soil C reserves. The recent introduction of conservation agricultural practices has not led to a reversing of the decline in soil C content, although it has minimized the rate of decline (Baker et al. 2007; Hulugalle and Scott 2008). Lal (2003) estimated the quantum of C pools in the atmosphere, terrestrial ecosystems, and oceans and reported a “missing C” component in the world C budget. Though not proven yet, this could be linked to C losses through runoff and soil erosion (Lal 2005) and a lack of C accounting in inland water bodies (Cole et al. 2007). Land management practices to minimize the microbial respiration and soil organic C (SOC) decline such as minimum tillage or no tillage were extensively studied in the past, and the soil erosion and runoff studies monitoring those management systems focused on other nutrients such as nitrogen (N) and phosphorus (P)

Ανάλυση και βελτιστοποίηση της επίδοσης cloud εφαρμογών σε διαμοιραζόμενα περιβάλλοντα με προσαρμοστική ανάθεση πόρων

Intensive tillage, high fertiliser inputs, and plastic mulch on the soil surface are widely used by vegetable growers. A field investigation was carried out to quantify the impact of alternate land management and fertiliser practices designed to improve offsite water quality on the productivity of vegetable rotations within a sugarcane farming system in a coastal region of subtropical northeast Australia. Successive crops of capsicum and zucchini were grown in summer 2010–2011 and winter 2011, respectively, using four different management practices. These were ‘Conventional’—the current conventional practice using plastic mulch, bare inter-rows, conventional tillage, and commercial fertiliser inputs; ‘Improved’—a modified conventional system using plastic mulch in the cropped area, an inter-row vegetative mulch, zonal tillage, and reduced fertiliser rates; ‘Trash mulch’—using cane trash or forage sorghum residues instead of plastic mulch, with reduced fertiliser rates and minimum or zero tillage; and ‘Vegetative mulch’—using Rhodes grass or forage sorghum residues instead of plastic mulch, with minimum or zero tillage and reduced fertiliser rates. During the second vegetable crop (zucchini), each management practice was split to receive either soil test-based nutrient inputs or a common, luxury rate of nutrient addition. The ’Trash mulch’ and ‘Vegetative mulch’ systems produced up to 43% lower capsicum and zucchini yields than either of the plastic mulch systems. The relative yield difference between trash systems and plastic mulch management systems remained the same for both the soil test-based and high nutrient application strategies, suggesting that factors other than nutrition (e.g., soil temperature) were driving these differences

Contrasting agricultural management effects on soil organic carbon dynamics between topsoil and subsoil

Agricultural practices (e.g. tillage, crop rotation and fertiliser application) have a strong influence on the balance between carbon (C) input and output by altering physicochemical and microbial properties that control decomposition processes in the soil. Recent studies suggest that the mechanisms by which agricultural practice impacts soil organic carbon (SOC) dynamics in the topsoil may not be the same as those in the subsoil. Here, we assessed SOC stock, soil organic fractions and nitrogen availability to 1.0 m in soils under a cotton (Gossypium hirsutum L.)-based cropping system, and assessed the impact of agricultural management (three historical cropping systems with or without maize (Zea mays L.) rotation) on SOC storage. We found that the maize rotation and changes in the particulate organic fraction influenced SOC stock in the topsoil, although the overall change in SOC stock was small. The large increase in subsoil SOC stock (by 31%) was dominated by changes in the mineral-associated organic fraction, which were influenced by historical cropping systems and recent maize rotation directly and indirectly via changes in soil nitrogen availability. The strong direct effect of maize rotation on SOC stock, particularly in the subsoil, suggests that the direct transfer of C into the subsoil SOC pool may dominate C dynamics in this cropping system. Therefore, agricultural management that affects the movement of C within the soil profile (e.g. changes in soil physical properties) could have a significant consequence for subsoil C storage

Phosphorus uptake in faba bean, field pea, and corn cultivars from different sources: preliminary studies of two options for organic farmers

Low soil phosphorus (P) availability commonly limits yield in Australian broadacre organic production systems where superphosphate fertiliser is not permitted, and alternative P nutrition strategies are sought. Glasshouse experiments were conducted to investigate the potential of faba beans (Vicia faba L.) (FB), or field peas (Pisum sativum L.) (FP), grown in acidic sandy loam or alkaline clay, to accumulate P, which could then be supplied to a subsequent crop as part of a green manure rotation or after harvest. Another experiment investigated differences in growth and P acquisition between corn (Zea mays L.) cultivars: Hycorn 424 (a modern hybrid), and four traditional cultivars used in organic production. The experiments were carried out under conditions of P stress and had rock phosphate (RP), poultry manure (PM), or single superphosphate (SP) applied at 50 kg P/ha. For FP, maximum P input to the soil from incorporation would occur at or after pod initiation. However, P uptake by both legumes in both soils from sparingly soluble RP was low, with fertiliser P-use efficiencies of 0–1.3% compared with 1.8–12.7% for PM and 6.1–9.9% for SP. In the corn experiment, P fertiliser source had much larger effects than cultivar on plant biomass and P uptake, with responses generally ranked SP >PM>> RP > Control. Hycorn 424 generally produced higher dry matter and P uptake than the traditional cultivars under all P treatments. The implications of these preliminary investigations for Australian broadacre organic agriculture are discussed

Increasing soil organic carbon with maize in cotton-based cropping systems: Mechanisms and potential

In a rotation, the use of crop species with large root biomass is thought to increase soil organic carbon (SOC) storage deeper in the soil profile, yet the processes and mechanisms that control SOC dynamics at depth are poorly understood. Using a cotton-based field trial, we examined how maize may impact SOC dynamics up to 1 m depth in three systems that differed in tillage and wheat rotation by examining the changes in δ13C signature of SOC and soil C fractions associated with maize during a two-year period. The inclusion of maize increased the whole-profile SOC stock, particularly in the subsoil under minimum tillage and wheat rotation. The increase was associated with the stable C fraction, and could not be attributed solely to the C contribution from maize root biomass alone. We propose that C movement in the form of dissolved organic C (DOC) may have contributed to the observed increase in SOC stock. The strong temporal changes and the possible mechanisms behind the increase suggest that the introduction of maize into cotton-based cropping systems may not yield a consistent benefit. This study highlights the role of DOC in subsoil C stock and the importance of understanding whole-profile SOC dynamics in evaluating the potential of management practice in increasing SOC stock

Isotopic tracing of phosphorus uptake in corn from ³³P labelled legume residues and ³²P labelled fertilisers applied to a sandy loam soil

In low input (e.g. organic) farming systems where soil phosphorus (P) fertilisers such as superphosphate are not used, maintaining sufficient available soil P for plant growth can be a major challenge. The use of P accumulating cover crops may increase P availability for subsequent crops. We hypothesised that P release from organic residues of legumes (faba bean ('Vicia faba') and field peas ('Pisum sativum')) could supply adequate P to meet the needs of a subsequent crop in a low P soil. A pot experiment was conducted to determine the contribution of P by legume green manure to subsequent corn using ³³P labelled legume residues and ³²P labelled inorganic fertiliser (KH₂PO₄). The treatments included two rates of P application, (a) 10 kg P ha⁻¹ as legume root and shoot residues or as inorganic fertiliser with and without a C source, and (b) 38 kg P ha⁻¹as a combination of legume shoot and root residues or a combination of root and inorganic fertiliser and inorganic fertiliser alone. An absolute control (zero P) was also used. Shoot dry matter, P uptake and P source (residues or fertilisers) of total P in corn were measured at harvest. Faba bean and field pea residues alone or in combination with fertilisers contributed up to 10% and 5% of the total P uptake by corn respectively, compared with up to 54% by inorganic fertilisers. Incorporation of field pea and faba bean residues with P concentrations higher than those observed under field conditions, may not always lead to adequate net P release to supply the early growth phase of subsequent crops

A comparison of soil properties under organic and conventional farming in Australia

Organic farming is an alternative to conventional farming for providing sustainable crops with high export demand. This review analyses research findings on organic farming in Australia, with an emphasis on soil health. Several reports have indicated that organic farm management generally improves soil physical properties in Australia and elsewhere. Although low nitrogen (N) availability can constrain yields, organic farmers can improve N supply through legume green manures. Plant available phosphorus (P) is a more serious limiting factor in organic farming, particularly in Australia with naturally low P levels. Phosphorus is less easily replaced in the soil than N, and there is a need for alternate sources of organic-certified P and methods to enhance P availability from existing inputs such as rock phosphate. The role of micro-organisms in improving soil health nutrient availability is discussed, as well as the use of P accumulator crops such as Acacia and Tithonia, which could be incorporated as border crops or green leaf manure

Numerical simulation of wave propagation over variable bathymetry regions using MIKE 21 BW boussinesq wave model by DHI

102 σ.Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Ναυτική και Θαλάσσια Τεχνολογία και Επιστήμη”Οι θαλάσσιοι κυματισμοί διαδίδοντας μεγάλα ποσά ενέργειας και δευτερευόντως μάζας, από την ανοιχτή θάλασσα προς τις ακτές, αποτελούν ένα πολύ σημαντικό παράγοντα που επιδρά στη διαμόρφωση των ακτών, στην ισορροπία του οικοσυστήματος στην παράκτια ζώνη, στην ρύπανση των ακτών, στην αλληλεπίδραση με τις παράκτιες κατασκευές κλπ. Συνεπώς, προκύπτει η ανάγκη για ορθή χρήση και εκμετάλλευση των παρακτίων ζωνών καθώς και η απαίτηση σχολαστικού σχεδιασμού τόσο από τεχνολογική όσο και από κατασκευαστική άποψη κάθε δραστηριότητας που λαμβάνει χώρα στο παράκτιο περιβάλλον. Αυτό καθίσταται περισσότερο σημαντικό λαμβάνοντας υπόψη ότι το παράκτιο περιβάλλον αποτελεί θέμα ζωτικής σημασίας από οικονομική και κοινωνική άποψη για την γενικότερη ανάπτυξη μίας περιοχής. Για την πρόβλεψη των χαρακτηριστικών διάδοσης των θαλασσίων κυματισμών σε μεταβαλλόμενη βαθυμετρία κοντά στην ακτή και των επιδράσεων τους, έχουν αναπτυχθεί διάφορες μεθοδολογίες και αριθμητικά μοντέλα, (βλ., π.χ., Beji & Battjes 1994, Beji & Nadaoka 1996, Belibassakis & Athanassoulis 2011 και τις αναφορές στις εργασίες αυτές). Αντίστοιχα, τα σχετικά φαινόμενα έχουν εκτεταμένα διερευνηθεί σε εργαστηριακό περιβάλλον (βλ., π.χ., Beji & Battjes 1993). Σε αυτήν την διπλωματική εργασία, γίνεται εφαρμογή ενός διαδεδομένου και ευρέως αποδεκτού και χρησιμοποιούμενου στην πράξη υπολογιστικού κυματικού μοντέλου, και συγκεκριμένα του MIKE 21 της εταιρίας DHI (Danish Hydraulic Institute), το οποίο βασίζεται σε εμπλουτισμένες εξισώσεις Boussinesq (βλ. Madsen & Sorensen 1992, Zhang et al. 2007), προκειμένου να προσομοιωθεί η κυματική διάδοση από την ανοιχτή θάλασσα προς την ακτή και να μελετηθεί η αλληλεπίδραση του κυματισμού με τον θαλάσσια πυθμένα. To μοντέλο εξετάζεται για την αξιοπιστία των προβλέψεων του σε μια και δύο οριζόντιες διαστάσεις και τα αποτελέσματα συγκρίνονται με πειραματικές μετρήσεις οι όποιες προέρχονται από πειράματα των Beji & Battjes (Numerical simulation of nonlinear wave propagation over a bar, Coastal Engineering 1993) και από το πείραμα που περιγράφεται από τους Berkhoff et al. (1982) και αναφέρεται στην διάδοση κυματισμού πάνω από μία ρήχωση ελλειπτικής μορφής που βρίσκεται πάνω σε κεκλιμένο πυθμένα. Εξάγονται έτσι συμπεράσματα για την βέλτιστη επιλογή των φυσικών και αριθμητικών παραμέτρων. Ακολούθως εφαρμόζεται σε πραγματικές περιοχές με σχετικά απλή μορφολογία. Τέλος, επιτυγχάνεται η εφαρμογή του μοντέλου για το υποθαλάσσιο φαράγγι που βρίσκεται στην παράκτια περιοχή της πόλης la Jolla, στην Καλιφόρνια των Ηνωμένων πολιτειών. Στη δεύτερη αυτή περίπτωση η μορφολογία πυθμένα διαθέτει πολύπλοκα χαρακτηριστικά που καθιστούν το κυματικό πεδίο επίσης πολύπλοκο, πράγμα που αναδεικνύει την αποτελεσματικότητα του αριθμητικού μοντέλου MIKE 21 BW. Ως αποτέλεσμα διατυπώνονται χρήσιμα συμπεράσματα για την εφαρμοσιμότητα του σε γενικές καταστάσεις.Sea waves, propagating large amounts of energy and secondarily mass, from the open sea to the coast, are a very important factor that affects coast stability, the balance of the ecosystem in the coastal zone, the interaction with coastal structures, coastal pollution etc. The appropriate use and exploitation of coastal zones is interconnected with the requirements of detailed planning concerning both technological and manufacturing activities that take place in the coastal environment. This becomes more important taking into account that the coastal environment is an extremely significant factor both in economic and social terms for the overall development of a region. To predict the propagation characteristics of sea waves in variable bathymetry regions and especially near the coast and their effects , various methods have been developed and corresponding numerical models (see, e.g., Beji & Battjes 1994, Beji & Nadaoka 1996, Belibassakis & Athanassoulis 2011 and references cited there). Moreover, relevant phenomena have been extensively experimentally investigated in laboratory environment (see, e.g., Beji & Battjes 1993). In this thesis, the widespread and widely accepted and used in practice numerical wave model MIKE 21 developed by DHI (Danish Hydraulic Institute) is applied to the prediction of wave characteristics in the nearshore and coastal regions. This model is based on enhanced Boussinesq equations (see Madsen and Sorensen 1992, Zhang et al. 2007), for the prediction of wave propagation from the open sea towards the coast and subsequently applied to the study of interaction of water waves with the sea bottom. The model is examined for its reliability concerning the estimates in one and two horizontal dimensions and the results are compared against experimental measurements, which are derived and presented by Beji & Battjes (Numerical simulation of nonlinear wave propagation over a bar, Voastal Engineering 1993), and in the case of underwater shoal experiment over an upslope, described by Berkhoff et al. (1982). The latter work refers to the obliquely incident wave propagation over an elliptical shape shoal which is locate over a sloping bed. As a conclusion estimates are derived for the optimal choice of physical and numerical parameters using MIKE 21 BW model. In the final part of the thesis the same wave model MIKE 21 BW is investigated as concerns its applicability to real coastal locations. First a case characterized by relatively simple seabed and coastline morphology such as the coastal zone around the city of Rethymno (Crete) is investigated. Then, the model is implemented in the case of the submarine canyon located in the coastal area of the La Jolla (San Diego), in California in the United States. In this case, the bottom topography includes very complex features with almost vertical underwater walls, that highlight the effectiveness and efficiency of the above numerical model for such difficult topographies.Ιωάννης Γ. Καζάκη