High Tunnel Coverings Alter Crop Productivity and Microclimate of Tomato and Lettuce

The implementation of high tunnels has shown to increase marketability and/or yield of tomato (Solanum lycopersicum) and lettuce (Lactuca sativa) crops compared with open-field systems. These structures provide the opportunity to alter light intensity and spectral quality by using specific polyethylene (poly) films and/or shadecloth, which may affect microclimate and subsequent crop productivity. However, little is known about how specific high tunnel coverings affect these parameters. The overall goal of this study was to evaluate the impact of various high tunnel coverings on the microclimate and crop productivity of tomato and lettuce. The coverings included standard, ultraviolet (UV)-stabilized poly film (standard); diffuse poly (diffuse); full-spectrum clear poly (clear); UV-A/B blocking poly (block); standard + 55% shadecloth (shade); and removal of standard poly 2 weeks before initial harvest to simulate a movable tunnel (movable). Microclimate parameters that were observed included canopy and soil temperatures, canopy growing degree-days (GDD), and photosynthetic active radiation (PAR), and crop productivity included yield and net photosynthetic rate. Hybrid red ‘BHN 589’ tomatoes were grown during the summer, and red ‘New Red Fire’ and green ‘Two Star’ leaf lettuce were grown in both spring and fall in 2017 and 2018. Increased temperature, GDD, and PAR were observed during the spring and summer compared with the fall. The soil temperatures during the summer increased more under the clear covering compared with the others. For tomato, the shade produced lower total fruit yield and net photosynthetic rate (Pn) compared with the other treatments, which were similar (P < 0.001 and <0.001, respectively). The greatest yield was 7.39 kg/plant, which was produced under the clear covering. For red leaf lettuce grown in the spring, the plants under the clear, standard, and diffuse coverings had significantly greater yield than the movable and shade coverings (P < 0.001). The coverings had less effect on the yield during the fall lettuce trials, which may have been attributed to the decrease in PAR and environmental temperatures. The findings of this study suggest that high tunnel coverings affect both microclimate and yield of lettuce and tomato.

The diversity of Passalora fulva Isolates Collected from Tomato Plants in US high tunnels

High tunnels extend the growing season of high value crops, including tomatoes, but the environmental conditions within high tunnels favor the spread of the tomato leaf mold pathogen, Passalora fulva (syn. Cladosporium fulvum). Tomato leaf mold results in defoliation, and if severe, losses in yield. Despite substantial research, little is known regarding the genetic structure and diversity of populations of P. fulva associated with high tunnel tomato production in the United States. From 2016 to 2019, a total of 50 P. fulva isolates were collected from tomato leaf samples in high tunnels in the Northeast and Minnesota. Other Cladosporium species were also isolated from the leaf surfaces. Koch’s postulates were conducted to confirm that P. fulva was the cause of the disease symptoms observed. Race determination experiments revealed that the isolates belonged to either race 0 (six isolates) or race 2 (44 isolates). Polymorphisms were identified within four previously characterized effector genes Avr2, Avr4, Avr4e, and Avr9. The largest number of polymorphisms were observed for Avr2. Both mating type genes, MAT1-1-1 and MAT1-2-1, were present in the isolate collection. For further insights into the pathogen diversity, the 50 isolates were genotyped at 7,514 single-nucleotide polymorphism loci using genotyping-by-sequencing: differentiation by region but not by year was observed. Within the collection of 50 isolates, there were 18 distinct genotypes. Information regarding P. fulva population diversity will enable better management recommendations for growers, as high tunnel production of tomatoes expands.

Effects of NIR Reflective Film as a High Tunnel-Covering Material on Fruit Cracking and Biomass Production of Tomatoes

Tomatoes require higher irradiance, although the incidence of physiological disorders in fruit increases at high temperatures. Near-infrared (800–2500 nm) (NIR) reflective materials are effective tools to suppress rising air temperatures in greenhouses. We examined the physiological and morphological changes in tomato growth and fruit quality when grown in a high tunnel covered with NIR reflective film (NR) and in another covered with polyolefin film (PO; control). There was no relationship between the fruit cracking rate and mean daytime temperature under NR. The fruit temperature at the same truss was lower and the increase in air temperature was slow under NR. Fruit dry matter (DM) content under NR was also significantly decreased. These findings suggest that the reduction in fruit cracking under NR results from a decrease in fruit DM content as a consequence of lower fruit temperature and a decrease in total DM (TDM). Total fruit yield did not differ, whereas TDM was significantly decreased under NR. This was considered to result from a lower transmitted photosynthetic photon flux density (400–700 nm) (PPFD) and LAI, and lower photosynthetic capacity in single leaves because of a decrease in both total nitrogen and chlorophyll content. We conclude that NR film reduces fruit cracking in exchange for a slight reduction in TDM.

Fruit Quality and Yield of Three Highbush Blueberry (Vaccinium corymbosum L.) Cultivars Grown in Two Planting Systems under Different Protected Environments

Due to the increasing interest in highbush blueberry (Vaccinium corymbosum L.) among consumers, together with the problems of climate change and specific substrate requirements, a novel approach to intensive blueberry production is required. Here, ‘Duke’, ‘Aurora’, and ‘Brigitta’ blueberry cultivars were planted under the protective environments of a high tunnel and black hail net, each using ridge and pot planting systems. The high tunnel increased the maximal air temperature on average by 7.2 °C compared to the hail net. For all three cultivars, harvest began 6 to 18 days earlier under the high tunnel than under the hail net; however, lower yields and individual phenolics contents were obtained for the fruit. In ‘Aurora’ and ‘Brigitta’, environmental conditions under the high tunnel also reduced plant volume and fruit sugar/organic acid ratio. Growing blueberry plants in 60 L pots had no negative effects on plant volume and fruit ripening time, yield, firmness, color, and chemical composition. This study represents the first to compare highbush blueberry grown under the high tunnel and hail net protective environments using ridge and pot planting systems across three different cultivars. Here, we can conclude that optimal highbush blueberry production of ‘Duke’, ‘Aurora’, and ‘Brigitta’ under the climate conditions of the study provides earlier ripening times under the high tunnel. However, according to fruit yield and quality, all three cultivars benefit from the hail net over the high tunnel, while ‘Duke’ and ‘Brigitta’ also benefit in particular from the hail net combined with growth in pots.

Analysis on Operation Risk of Continuous Sunken Tunnel on Expressway

Based on the number of 519 tunnel risk incidents that occurred in the two tunnels of the Qifu Tunnel and the Zhongcun Tunnel during the period from 2018 to 2019 of Guangming Expressway, this paper studies the temporal and spatial characteristics and the risk distribution of the sunken continuous tunnel during the operation period of the expressway. Type of risk event. The results show that January, May, June and September of the year, as well as 14:00–16:00 and 16:00–18:00 during the day are periods of high tunnel risk; at the entrance section of continuous tunnels, Compared with other locations, the number of risk events in the transition section and the open section with sudden environmental changes and gradient changes is more; the types of risk events include safety hazards, roadblocks, vehicle failures, rear-end collisions, and equipment failures. The main types are vehicle failures. There are certain differences in the east-west direction. There are more vehicle breakdowns in the east-bound direction, more roadblocks in the west-bound direction, and more rear-end collisions in the east-bound direction. The main types of risk events are cars and trucks. Both cars and trucks have major risk event types. It is a vehicle failure. In rear-end collisions, small cars account for 65% of the risk models; risk identification methods include gun patrol discovery, road administration reporting, etc., of which gun patrol discovery is the most important identification method, accounting for 65% of the total. Through the analysis of the risk event characteristics of the sunken continuous tunnel of the expressway, it provides reference opinions for perfecting the research deficiencies in related fields in our country.

Growth and Yield Responses of Pot-Grown Long Bean and Luffa to Nitrogen Rates

Optimizing nitrogen (N) input rates for vegetable production is crucial in Florida to reducing production costs and enhancing environmental sustainability. Asian vegetables emerging and expanding in Florida not only increase profit for growers, but also enhance food diversity for consumers. The objective of this study was to gain a better understanding of the partitioning and usage of N and carbohydrates in two Asian vegetable crops: long bean (Vigna unguiculata ssp. sesquipedalis (L.) Verdc.) and angled luffa (Luffa acutangular (L.) Roxb.). Four N rates (0, 0.91, 1.36, and 1.81 g N pot−1) were compared in a high tunnel trial to understand the influence of N fertilization on the two crops. For long bean, plant biomass was highest at the highest N input, and N-fertilized plants had significantly higher leaf greenness than the control at the flower initiation and mid-reproductive stages. However, N inputs had no apparent effect on yield, nitrogen use efficiency (NUE), blade total N concentration, roots (length, volume, dry biomass, and root-to-shoot ratio), or nodules (number plant−1 and biomass). For luffa, the highest N input had significantly greater total yield, fruit number, and leaf greenness at the flower initiation and mid-reproductive stages, although there was no significant difference in shoot biomass, blade total N content, or NUE among treatments. Within the range of these N rates, our results suggest that higher N inputs promoted vegetative growth of long bean, whereas reproductive growth was promoted in luffa. This study highlights differences in the sink–source relationship of N for long bean and luffa production in high tunnel, which can guide N input decisions for these two crops that are rapidly expanding in the USA.

Magnetic tunneling junctions based on 2D CrI3 and CrBr3: spin filtering effects and high tunnel magnetoresistance via energy band difference

Recently, the study on two-dimensional materials expands to the field of spintronics. The intrinsically ferromagnetic van der Waals materials such as CrI3 and CrBr3 receive much attention due to nearly 100% spin polarization and good stability, resulting in excellent performance in magnetic tunnel junctions. In this work, we design the magnetic tunnel junctions of Cu/CrI3/Cu and Cu/CrBr3/Cu with the electrodes of Cu(111) and the tunneling barrier of 4-monolayer CrI3 or CrBr3. Our first-principle calculations combined with nonequilibrium Green’s function method indicate that the CrBr3-based MTJ has a larger maximum tunneling magnetoresistance ratio than the CrI3-based MTJ. In a wide bias voltage range, the CrI3-based MTJ can maintain high spin filtering performance, while that of the CrBr3-based MTJ degrades sharply as the bias voltage increases. It is noted that negative differential resistance effect is observed in the CrBr3-based MTJ. The differences of spin transport properties between the CrI3-based MTJ and the CrBr3-based MTJ are clarified in terms of the inside device physics, including the spin-dependent projected density of states, band structures, Bloch states, and the electron density difference. This work provides some physical insights for the design of 2D van der Waals MTJ.

Winter Production of Asian Leafy Greens in High Tunnels Using Biodegradable Mulches

Use of season extension tools such as high tunnels and diverse vegetable crops have been crucial in improving competitiveness of vegetable growers in Mississippi who operate on small- to medium-sized farms. Chinese cabbage, also known as pak choy or bok choy, has become increasingly popular due to numerous cultivar choices, fast maturity, high productivity, tolerance for frost, and its potential use for winter production in high tunnels in a subtropical climate. Five Chinese cabbage cultivars including ‘Asian Delight’, ‘Black Summer’, ‘Red Pac’, ‘Rosie’, and ‘Tokyo Bekana’ were evaluated for plant growth, yield, and mineral nutrient concentrations when grown with three types of biodegradable plastic mulches (BDMs) and one polyethylene (PE, or plastic) mulch in a high tunnel in two experiments from 30 October 2019 to 18 March 2020. The five tested cultivars varied in plant height, widths, leaf SPAD, fresh and dry plant weights, marketable yield, and macro- and micro-nutrient concentrations. ‘Tokyo Bekana’ produced the highest marketable yield and fresh and dry plant weights in both experiments. The three BDMs resulted in similar marketable yield and mineral nutrients in tested cultivars and similar temperatures of leaf, mulch, and substrate compared to the PE mulch. The high tunnel provides a viable way for the winter production of selected Chinese cabbage cultivars in a subtropical climate with possible different yields between production cycles due to varying microenvironment in those months.