Lysis of soil microbial cells by CO2 or N2 high pressurization compared with chloroform fumigation

The classical chloroform fumigation-incubation (CFI) and fumigation-extraction (CFE) methods are nowadays among the most used for determining soil microbial biomass, although the chloroform lysing of microbial cells is not always complete. Here, we have tested a physical method, used for sterilizing foods but never in soil, based on N-2 or CO2 high pressurization (N2HP or CO2HP, respectively) to cause microbial cell lysis. The N2HP and CO2HP were tested on two soils differing for their organic matter content, one agricultural (AGR) and one forest (FOR), and firstly were compared with the CFI. The CO2 extra-flush from both soils during 10-d incubation by N2HP was lower than that by CFI method, whereas that by CO2HP was greater. Then, the lysis by CO2HP was compared with that by the CFE method by varying CO2 pressure and duration. The CO2HP, at proper conditions, was more efficient than CFE method to cause the lysis of soil microbial cells. Moreover, both CO2 pressure value and duration were important in increasing the extractable organic C compared to the CFE. The most successful combination of high CO2 pressure and duration was 4.13 MPa and 32 h. However, we cannot exclude that CO2HP might have caused the release of soil organic C not ascribable to living organic matter. Further studies using C-13 and/or N-15-labeled microbial cells should assess the release of abiotic organic C

Effetti degli oli essenziali di agrumi applicati in post-emergenza sul controllo delle infestanti e sulla comunit\ue0 microbica del suolo

Sebbene gli erbicidi sintetici ad oggi siano il mezzo pi\uf9 utilizzato per il controllo delle erbe infestanti, \ue8 ampiamente dimostrato che essi hanno un impatto negativo sul suolo, sull'ambiente e, inoltre, iniziano a manifestarsi fenomeni di resistenza. Pertanto, \ue8 importante sviluppare mezzi alternativi che siano al contempo efficaci e rispettosi dell\u2019ambiente. Gli olii essenziali estratti dalle piante sono stati da sempre utilizzati per molteplici usi come agenti battericidi, virucidi, fungicidi, insetticidi, medicinali e cosmetici. Diversi studi hanno dimostrato tali attivit\ue0 degli oli essenziali estratti dagli agrumi, ma scarsi sono gli studi che hanno investigato il loro potenziale uso come erbicidi. Inoltre, anche se diversi studi hanno dimostrato un effetto antimicrobico, tali studi sono stati condotti prevalentemente in vitro e non in vivo. Obiettivo del presente lavoro \ue8 stato quello di valutare la potenzialit\ue0 degli oli essenziali estratti dalle bucce di limone e arancia i) per limitare lo sviluppo delle erbe infestanti e ii) il loro effetto sulla comunit\ue0 microbica del suolo. Gli oli essenziali testati sono stati estratti per idrodistillazione e con pressa a freddo: LI e AI, olio essenziale di limone e arancio, rispettivamente, estratti con pressa a freddo; LU e AU, olio essenziale di limone e arancio, rispettivamente, estratti tramite idrodistillazione. Ai fini del presente lavoro, il suolo utilizzato \ue8 stato prelevato presso un campo sperimentale dell'Universit\ue0 degli Studi di Palermo. Dopo il prelievo, il suolo \ue8 stato essiccato all'aria e setacciato con setaccio con fori del diametro di un centimetro. Successivamente, 500 grammi di suolo sono stati posti in 20 vaschette di alluminio (10 7 20 cm) ed incubati in condizioni naturali. Durante l\u2019incubazione il suolo \ue8 stato mantenuto al 50% della sua capacit\ue0 idrica di campo (WHC). Dopo l\u2019emergenza delle piantine, ovvero alla comparsa della terza foglia (ventesimo giorno dall\u2019inizio dell\u2019incubazione), ciascun olio essenziale \ue8 stato applicato nebulizzandolo sulle piantine, a giorni alterni per una settimana (tre applicazioni in totale). Per ogni vaso e per ogni trattamento, sono stati applicati 5 mL di una soluzione contenente 1 L di acqua, 10 mL di olio essenziale e 1 mL di emulsionante. Nel suolo di controllo la soluzione applicata alle piantine non conteneva olio essenziale. Dopo 15 giorni dall\u2019ultima applicazione dei trattamenti, i suoli sono stati campionati in modo totale, setacciati ed analizzati per la determinazione del carbonio della biomassa microbica (metodo fumigazione-estrazione), respirazione basale (emissione di CO2) e struttura della comunit\ue0 microbica (analisi degli acidi grassi dei fosfolipidi). Inoltre, per ogni trattamento sono stati determinati alcuni parametri delle piante come peso secco e fresco totale, numero di specie e numero di piante per specie. In questo lavoro vengono riportati e discussi i principali risultati

Application of Precision Agriculture for the Sustainable Management of Fertilization in Olive Groves

Olive tree growing (Olea europaea L.) has considerably increased in the last decades, as has the consumption of extra virgin olive oil in the world. Precision agriculture is increasingly being applied in olive orchards as a new method to manage agronomic variability with the aim of providing individual plants with the right input amount, limiting waste or excess. The objective of this study was to develop a methodology on a GIS platform using GEOBIA algorithms in order to build prescription maps for variable rate (VRT) nitrogen fertilizers application in an olive orchard. The fertilization plan was determined for each tree by applying its own nitrogen balance, taking into account the variability of nitrogen in soil, leaf, production, and actual biometric and spectral conditions. Each olive tree was georeferenced using the S7-G Stonex instrument with real-time kinematic RTK positioning correction and the trunk cross section area (TCSA) was measured. Soil and leaves were sampled to study nutrient variability. Soil and plant samples were analyzed for all major physical and chemical properties. Spectral data were obtained using a multispectral camera (DJI multispectral) carried by an unmanned aerial vehicle (UAV) platform (DJI Phantom4). The biometric characteristics of the plants were extracted from the achieved normalized vegetation index (NDVI) map. The obtained prescription map can be used for variable rate fertilization with a tractor and fertilizer spreader connected via the ISOBUS system. Using the proposed methodology, the variable rate application of nitrogen fertilizer resulted in a 31% reduction in the amount to be applied in the olive orchard compared to the standard dose

Metabolic responses of microbial community in soil amended with fresh leaves and leaf extracts from eucalyptus spp.

Field observations reveal that often large areas of soil surface beneath Eucalyptus occidentalis Endl. are completely bare or with scant vegetation. Moreover, previous studies have showed that other species of Eucalyptus, such as Eucalyptus camaldulensis Dehn, may be effective in suppressing seed germination and weed growth. Such effects have been ascribed to the large number of secondary metabolites within Eucalyptus leaves. Due to their inhibition activity against weeds, leaf extracts might be used for an integrated weed management context, in accordance with the Directive 2009/128/EC. Several studies exist about the effects of Eucalyptus leaf extracts on weeds, whereas they are lacking on soil microorganisms. Therefore, the aim of this study was to assess the effects of Eucalyptus leaf extracts on soil microbial biomass and activity, as well as on the relative abundance of main microbial groups. The extracts were obtained by hydrodistillation [essential oils (EOs) and hydrolates] and by water cold extraction (aqueous extracts) from leaves of both E. camaldulensis and E. occidentalis. Also, fresh leaves were tested. The soil was spread with EOs at doses of 2.64 or 3.52 \uf06dl g-1. They were applied by adding a proper water solution containing the given amount of EOs to 350 g of dry soil, so reaching 50% of its water holding capacity. The above solution held the emulsifier Fitoil at 0.5 mL L-1. Fresh leaves, dried at 40\ub0C for 48 hours, were chopped and applied at doses of 6.6 and 5.0 mg g-1 of dry soil for E. camaldulensis and E. occidentalis, respectively. Such litter application doses were those found, at field conditions (780 and 575 g m-2, respectively). Two controls were also prepared: one with water and another with water and Fitoil. After the addition of all the treatments, soils were incubated at room temperature (20-23\ub0C) in the dark for 35 days. At days 7 and 35, soils were analyzed for soil microbial biomass C and N. At the same days, the main microbial groups were investigated through the ester linked fatty acids (FAMEs). Moreover, 20 g of soil were incubated as above in 200 mL jars to determine the soil respiration rate (CO2 emission) during 36 days of incubation. Preliminary results showed, that EOs from the two species and at both doses exerted a significant biocidal action on soil microorganisms, while hydrolates, aqueous extracts and fresh leaves stimulated both microbial biomass and activity

Cover crop impact on soil organic carbon, nitrogen dynamics and microbial diversity in a mediterranean semiarid vineyard

Cover crop (CC) management in vineyards increases sustainability by improving soil chemical and biological fertility, but knowledge on its effects in semiarid soils is lacking. This study evaluated the effect of leguminous CC management on soil organic carbon (SOC) sequestration, soil nitrate content and microbial diversity in a semiarid vineyard, in comparison to conventional tillage (CT). SOC and nitrate were monitored during vine-growing season; soil respiration, determined by incubation experiments, microbial biomass and diversity was analyzed after CC burial. The microbial diversity was evaluated by bacterial and fungal automated ribosomal intergenic spacer analysis (ARISA) and high-throughput sequencing of 16SrDNA. CC increased nitrate content and, although it had no relevant effect on SOC, almost doubled its active microbial component, which contributes to SOC stabilization. An unexpected stability of the microbial communities under different soil managements was assessed, fungal diversity being slightly enhanced under CT while bacterial diversity increased under CC. The complete nitrifying genus Nitrospira and plant growth-promoting genera were increased under CC, while desiccation-tolerant genera were abundant in CT. Findings showed that temporary CC applied in semiarid vineyards does not optimize the provided ecosystem services, hence a proper management protocol for dry environments should be set up

Secondary metabolites and eco-friendly techniques for agricultural weed/pest management

In agro-ecosystems, pests (insects, weeds, and other plant’s parasites) compete with crops for edaphic resources, negatively affecting quality and crop yields [1]. Nowadays, synthetic pesticides, easy to apply and accessible to farmers, are the most common and effective methods for pest management [2]. Nevertheless, the negative impact of these chemicals on the environment, human health, and the development of herbicides/pesticides-resistance are shifting the attention to alternative pest control technologies based on natural compounds [3–6]. Therefore, new eco-friendly agronomic techniques and the use of natural or natural-like molecules might represent a valid alternative strategy for pest control in the framework of sustainable agriculture [7–9]. The Special Issue “Secondary metabolites and eco-friendly techniques for agricultural weed/pest management” is timely and could offer interesting contributions to readers on the most recent aspects related to this pivotal topic. It includes 12 research papers (11 original articles and a scientific review) in which different aspects of pest management, from basic research to potential practical approaches, have been investigated through the latest and innovative technologies

The influence of solid retention time on IFAS-MBR systems: Assessment of nitrous oxide emission

The aim of the present study was to investigate the nitrous oxide (N2O) emissions from a moving bed based Integrated Fixed Film Activated Sludge (IFAS) - membrane bioreactor (MBR) pilot plant, designed according to the University of Cape Town (UCT) layout. The experimental campaign had a duration of 110 days and was characterized by three different sludge retention time (SRT) values (\ue2\u88\u9e, 30 d and 15 d). Results highlighted that N2O concentrations decreased when the biofilm concentrations increased within the aerobic reactor. Results have shown an increase of N2O with the decrease of SRT. Specifically, an increase of N2O-N emission factor occurred with the decrease of the SRT (0.13%, 0.21% and 0.76% of influent nitrogen for SRT = \ue2\u88\u9e, SRT = 30 d and SRT = 15 d, respectively). Moreover, the MBR tank resulted the key emission source (up to 70% of the total N2O emission during SRT = \ue2\u88\u9e period) whereas the highest N2O production occurred in the anoxic reactor. Moreover, N2O concentrations measured in the permeate flow were not negligible, thus highlighting its potential detrimental contribution for the receiving water body. The role of each plant reactor as N2O-N producer/consumer varies with the SRT variation, indeed the aerobic reactor was a N2O consumer at SRT = \ue2\u88\u9e and a producer at SRT = 30 d

From wastes to resources: citrus hydrolatesas natural biostimulants of soil microorganisms

The hydrolates result from the industrial extraction process of the essential oils through cold pressing of the citrus peels. Today, they are considered a waste to be disposed of. However, due to the presence of water soluble compounds (sugars, polyphenols, acids), hydrolates could be reused instead of being, due to the high economic burden, a problem in the disposal of the same, charged to the company.The aim of this work was to evaluate the effects of citrus hydrolate when directly applied as irrigation water on soil microbial biomass, activity and structure community. The soil used for the experiment was collected from the topsoil (0-10 cm) of a citrus orchard, air-dried and sieved at 2 mm. Then, 450 g of soil were placed in 1L plastic bottles and moistened up to 50% of the water holding capacity (WHC) by applying hydrolates and/or water. The tested hydrolates were obtained from three citrus species: Citrus Sinensis, Citrus Limon and Citrus Reticulata. The hydrolates were applied at three different doses to reach 1/3, 2/3 and 3/3 of the 50% of soil WHC. Respectively, 35, 70 and 105 mL of hydrolate were added to 450 g of air-dried soil. Distilled water was added when necessary to complement the 50% of WHC. Control soil was moistened up to 50% of its WHC with distilled water only. At the same time, 20 g of soil per each treatment were similarly incubated in 200 mL jars, sealed with rubber stopper holding silicon septa to monitor the emission of CO2. Four replicates per treatment were run. Soil samples were incubated in the dark at constant temperature (23.0 ± 0.5°C) and their humidity weekly adjusted up to 50% of WHC by adding distilled water. Microbial biomass C was determined according to the fumigation-extraction method after 1, 4, 8, 12 and 16 weeks of incubation. At the same time, soil fatty acid methyl esters were determined and used as indicators of the main microbial groups. The CO2 accumulated in the headspace of the jars was measured at days 2, 5, 7 during the first week, then weekly for the following month and finally bi-weekly until day 112. The preliminary results provided evidence that the three hydrolates, at different extent, stimulated the activity of soil microorganisms and affected soil microbial biomass and community structure