School of Agriculture, Food and Ecosystem Sciences - Research Publications
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ItemImpact of microwave disinfestation treatments on the bacterial communities of no-till agricultural soils(WILEY, 2020-11)Abstract Growing herbicide resistance has encouraged the development of new technologies for weed control. Microwave (MW) heating of soil before sowing has been shown to reduce weed establishment in no‐till farming systems and substantially increases crop productivity. However, the effect of this technology on the soil microbial community in general, and on beneficial soil microbes such as ammonia oxidizers in particular, warrants further study. In order to check the effect of MW soil disinfestation treatments on the soil biota, indigenous soil microcosms were treated under a horn antenna of the MW prototype for three distinct durations. Immediately after heating (T0) and 28 days after heating (T28) the soil was collected at two penetration depths (0–5 and 5–10 cm) of MW energy to determine the bacterial community responses based on 16S rRNA amplicon sequencing and the total abundances of bacteria and ammonia oxidisers with qPCR. Although total bacteria and ammonia oxidizer abundances exhibited no response to the MW treatments, bacterial community composition differed according to the treatment durations. Community responses clustered into two categories: no effect at low heating intensities (0 and 30 s, 17–45°C) and strong effect at high heating intensities (60 and 90 s, 65–78°C). For the latter group, community richness did not recover to its pre‐heating levels within the 4 weeks studied. Immediately after high heating intensity treatments, the relative abundance of Firmicutes increased and that of Proteobacteria decreased significantly regardless of penetration depth. The relative abundances of beneficial soil microbes (Micromonosporaceae, Kaistobacter and Bacillus) were significantly higher as soils recovered from high heating intensities compared with untreated soils at T28. Our findings suggest that although pre‐sowing MW treatments alter the soil microbial community, beneficial soil microbes exhibit faster recovery. Highlights High heating intensities reduced bacterial community richness that did not recover to pre‐heating condition. Heat resistant bacterial taxa survived high heating intensities < 28 days after heating regardless of penetration depth. High‐intensity heating did not induce a negative impact on the abundance of ammonia‐oxidizing bacteria and archaea. Relative abundances of dormant heat‐resistant beneficial taxa exhibited recovery after 28 d.
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ItemMicrowave Soil Treatment and Plant Growth(IntechOpen, 2019-10-15)Crop yield gaps can be partially overcome by soil sanitation strategies such as fumigation; however, there are fewer suitable fumigants available in the marketplace and growing concerns about chemical impacts in the environment and human food chain. Therefore, thermal soil sanitation has been considered for some time and microwave soil treatment has some important advantages over other thermal soil sanitation techniques, such as steam treatment. It is also apparent that microwave soil sanitation does not sterilize the soil, but favors beneficial species of soil biota making more nutrients available for better plant growth. From these perspectives, microwave soil treatment may become an important pre-sowing soil sanitation technology for high value cropping systems, allowing agricultural systems to better bridge the crop yield gap.
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ItemDrying Tectona grandis Boards Using the Simulating Solar Kiln Conditions Technique(North Carolina State University, 2020-11-01)Timber cracking, drying stress residuals, and the change of moisture content profile were investigated during the drying of Tectona grandis boards in a conventional laboratory kiln. The study applied a technique that simulated solar kiln conditions using a conventional laboratory kiln to dry timber, based on Vientiane’s climatic conditions (Laos). The theoretical recharge and discharge model was used to generate the potential drying schedule for the Vientiane area; then the drying schedule was mimicked in a conventional laboratory kiln. Timber cracking and drying stress residual were monitored and measured using Image J software, and the change of moisture content profile was determined, based on the oven dry method. Measured moisture content data were compared with the theoretical drying model. The results showed that teak boards, of 25 mm thick, had no cracking. The drying stress residual was 0.8 ± 0.3 mm with the maximum of 1.53 mm. The initial average moisture content of 62% decreased to 12% within 16 d, while the case and core moisture contents reached 12% and 14%, respectively. The drying model described the changes of moisture content profile during drying, with a maximal error of 5%.
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ItemCorrection to: Decision support tools for wind and solar farm site selection in Isfahan Province, Iran (Nov, 10.1007/s10098-020-01978-w, 2020)(SPRINGER, 2020-12-24)In the original publication, the figures 4 and 5 were swapped mistakenly. The correct figures with their caption are provided in this correction.
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ItemDevelopment of Microwave Slow-Wave Comb Applicators for Soil Treatment at Frequencies 2.45 and 0.922 GHz (Theory, Design, and Experimental Study)(MDPI, 2020-12)In agriculture and industry, it is often necessary to heat surface layers of material like soil, timber, concrete, and so on, with microwave (MW) energy. Traditional MW irradiators (antennas) cannot restrain their heating to the surface, with the energy penetrating deeply into the material. Slow-wave comb applicators can provide the required energy distribution in the surface layer. Theoretical analyses of the comb applicators used for heating were carried out and on this basis, three comb applicators were designed and made for soil treatment: two applicators Comb 1 and Comb 2 for frequency 2.45 GHz and Comb 3 for frequency 0.922 GHz. An experimental study of applicators was carried out using two MW plants: 30 kW (2.45 GHz) and 60 kW (0.922 GHz) for heating soil with moisture content in the range from 32% to 173% and density 460 to 1290 kg m−3. The study showed that comb applicators provide the following advantages: reduction in energy dissipation in material depth and release of the significant part of applied MW energy in layers close to the applicator surface. Comb applicators can provide the required soil top layer treatment (sterilization) with reasonable efficiency and can be recommended for practical use in shallow soil treatment for weed seed and pathogen control in agricultural applications. Comb applicators can also be used for effective heating and MW treatment of the surface layers of wood, concrete, bricks, plastics, and other dielectric materials.
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ItemMicrowave Heat Treatment Induced Changes in Forage Hay Digestibility and Cell Microstructure(MDPI, 2020-11)To investigate the effects of microwave (MW) treatment on hays nutritive value, five types of hay (50 g) were treated with MW for 0 (control), 20, 40, 60, and 80 s (0, 440, 880, 1320, and 1760 kJ kg−1 of MW energy, respectively) and analyzed for nutritive value prior to scanning by an electron microscope to observe microstructure changes. The dry matter (DM) % of hays were increased with increasing treatment time (p < 0.001). The improved DM and digestible organic matter in the DM were recorded from MW treated lucerne (60 s), wheat (40 s), and canola (20 s) (p < 0.001), which might have been due to the MW ruptured cell wall. The MW energy required for maximal DM digestibility improvement was linearly related to control hay crude protein content (r2 = 0.79; p < 0.001). Overall, the study showed MW treatment can increase some hays’ digestibility. In addition, the crude protein content from control hay may be a proxy to indicate DM digestibility improvement.
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ItemAn In-Situ Assessment of Wood-in-Service Using Microwave Technologies, with a Focus on Assessing Hardwood Power Poles(MDPI, 2020-09)Wooden power poles and their ongoing inspection represent a significant investment for most electrical power utilities. This study explored the potential for using microwave fields to non-invasively assess the state of hardwood power poles in a field experiment. Two strategies were assessed: 2.4 GHz microwave field transmission through the pole; and mutual coupling between antennae using a 10.525 GHz radar module applied to the surface of the pole. Both systems distinguished between sound hardwood poles and those which were compromised by decay and subterranean termite attack and infestation.
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ItemMeasurement and modelling of soil dielectric properties as a function of soil class and moisture content(Taylor & Francis, 2020-01-18)In this study, four textural classes of soil (Clay, Clay Loam, Loam, and Loamy Sand) were used to investigate the dielectric properties of soils, using a vector network analyser with an open-ended coaxial probe kit at room temperature (25 ± 2°C) in the 700–7000 MHz microwave frequency range. Four levels of soil moisture content (oven dry, 33% field capacity, 66% field capacity and 100% field capacity) were maintained to perform the experiment with three replication and three observation each. The results showed that, with increasing soil moisture, from oven dry conditions to 100% field capacity, both the real (Dielectric Constant) and imaginary (Loss Factor) components of the dielectric properties increased; however, the responses were not linear. The dielectric properties of oven dry soils were very low compared with the soils with higher moisture content. Therefore, soil moisture was the major contributor to the dielectric behaviour of soil. The dielectric properties of sandy soil were much lower than the other soils; however, the dielectric loss factor of the Dookie clay soil was higher compare with the other soils. Models were developed to explain the dielectric properties of soils as a function of frequency and moisture content. The goodness of fit (r2) for these models varies between 0.952 for the Dookie Sandy Soil to 0.997 for the Dookie Loam Soil, suggesting that these models were adequate to describe the dielectric properties of these soils over the range of frequencies and moisture contents assessed in this study. Another model was developed to estimate the expected penetration depth of electromagnetic waves in these soils, based on the model of the dielectric properties. It was clear that penetration decreases with both frequency and moisture content. Low frequencies penetrate further into the soils than higher frequencies. Similarly, dry soils allow further penetration than moist soils.
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ItemMicrowave fluidised bed drying of red lentil seeds: Drying kinetics and reduction of botrytis grey mold pathogen(Elsevier, 2020-01-01)Botrytis grey mould (BGM) is a problematic seed-borne disease of lentil crop, with little known about its possible physical control. Microwave fluidized bed dryers have been widely studied for grain, fruit and vegetable drying. In the present study, simultaneous drying and disinfection of red lentil seeds, were investigated in a microwave fluidized bed at 4 microwave powers of 0, 300, 400 and 500 W using fluidizing hot air at 50 and 60 °C. Moisture diffusivities of lentil seeds were defined by considering the Fick's second law of diffusion in one direction in a sphere with convective boundary conditions as well as negligible external resistance to mass transfer. They varied from 0.44 × 10−10 for hot air alone at 50 °C to 3.06 × 10−10 m2/s for microwave power and air temperature combinations of 500 W and 60 °C by considering convective boundary condition for the seeds. Drying times obtained from well-fitted Page's model were applied for drying of the seeds contaminated with BGM. The results indicated that infected seeds percentage (IS%) could be reduced by 30% by applying combinations of microwave power and hot air at 300 W and 60 °C or 400 W and 50 °C, without a significant loss of seed viability. Thus, microwave fluidized bed drying has a good potential to reduce seed born BGM in lentil crop.
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ItemThe drying performance and post-drying qualities of Eucalyptus saligna exposed to intermittent and continuous drying(Ministry of Environment and Forestry, 2020-04-01)Eucalyptus saligna tends to develop defects during its drying process, thus limiting its use as construction or furniture material. Intermittent drying, which applies non-heating phases between heating phases, has the potential to overcome this issue. This study evaluated the effects of 3 intermittent and 1 continuous schedule on the species’ drying performance and post-drying qualities. The results showed that the boards from all intermittent schedules exhibit significantly slower drying rates (from -9.4x10-3 /hour to -1.57 x10-2 /hour) than those from the continuous schedule (from -5.12 x10-2 /hour to -1.03 x10-2 /hour). The intermittently-dried boards also developed lower collapse depth (1.162-2.032 mm) than the continuously-dried boards (5.12 mm). Nevertheless, applying higher temperature than that used in the continuous schedule, during the heating phase of the intermittent schedule, potentially increased the moisture gradient, residual drying stress, end check length, internal check percentage, and spring depth.