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  • Author or Editor: Rhuanito Soranz Ferrarezi x
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Basil (Ocimum sp.) is a fast-growing, high-value cash crop for aquaponics. Plant suitability evaluation in tropical conditions is critical to recommend new cultivars, increasing grower portfolio and minimizing the production risks associated with untested selections. Two trials were conducted to identify suitable basil cultivars for tropical outdoor aquaponics production using the University of the Virgin Islands (UVI) Commercial Aquaponics System in the U.S. Virgin islands. We evaluated five basil cultivars in Summer 2015 (Genovese, Lemon, Purple Ruffles, Red Rubin, and Spicy Globe), and seven cultivars in Fall 2015 (Cinnamon, Genovese, Lemon, Purple Ruffles, Red Rubin, Spicy Globe, and Thai). In both trials, 3-week-old seedlings were transplanted in net pots at a density of 1.5 plants/ft2 (16.15 plants/m2). The 6-inch portions and upper portions of the canopy were harvested as a salable product and the resultant material (leaves and stems) considered as total yield per square meter. In the summer, yield was higher in ‘Genovese’ (14.91 kg·m−2) and ‘Spicy Globe’ (13.99 kg·m−2); ‘Purple Ruffles’ resulted in the lowest yield (4.18 kg·m−2). Leaf anthocyanin was greater for the red cultivars Red Rubin [28.35 anthocyanin content index (ACI)] and Purple Ruffles (34.36 ACI) compared with the other cultivars. Chlorophyll content was the highest in ‘Genovese’ [48.59 chlorophyll content index (CCI)]. In the fall, ‘Cinnamon’ (6.60 kg·m−2), ‘Genovese’ (6.70 kg·m−2), and ‘Spicy Globe’ (6.35 kg·m−2) showed the highest yield and ‘Purple Ruffles’ the lowest (1.68 kg·m−2). Leaf anthocyanin differed in all cultivars, with the higher values in Purple Ruffles (80.5 ACI) and Red Rubin (36.5 ACI). Chlorophyll content was a response of plant growth and cultivar, with values increasing over time and ranging from 12.06 (Lemon) to 17.99 CCI (Cinnamon). Plant growth index (PGI) was higher than that of other cultivars in Genovese and Lemon on day 58 (summer), and higher in Cinnamon on day 87 (fall). Yield was greater during the summer, which was calculated from May to August, in comparison with the fall, calculated from September to November. Yield declined for the fourth harvest in the summer, indicating that growers may need to end production after the third harvest and replant the crop. The results of this experiment indicate that basil has potential as a specialty, short-season, and high-value crop in the UVI Commercial Aquaponics System. Of the cultivars tested, Genovese and Spicy Globe were the highest yielding cultivars within the environmental and geographical conditions of this study for two consecutive seasons (summer and fall).

Open Access

Precision agriculture involves applying artificial intelligence, computers, sensors, and automation to improve crop field productivity while monitoring environmental conditions to conserve soil, water, and other natural resources focusing on agricultural sustainability. Despite many applications in agriculture, data monitoring and recording technologies have limited use due to the price. Low-cost open-source systems, like the ones available with the Internet of things (IoT) world, can potentially be developed as a universal-fit and cloud-connected technology for multiple applications. We designed and built a basic data collecting system using a commercial standalone embedded computer with Python programming language, serial data interface (SDI)-12/analog sensor adaptor, and digital sensors to monitor soil moisture and transmit the data remotely. SDI-12 is a standard communication protocol that transfers digital sensor measurements to a data recorder. We set up a pilot study that automatically collected and uploaded the data into the Internet to allow remote data transfer and access. The system performed reliably over 1 week with potting soil under field conditions without maintenance and successfully recorded data in real-time. The volumetric water content ranged from 0.03 to 0.23 m3·m−3, dielectric permittivity from 3.3 to 18.9 (unitless), EC from 0.0 to 0.3 dS·m−1, and soil temperature from 20.7 to 44.8 °C. All the data were successfully collected and uploaded to the cloud every 20 min, allowing users to remotely monitor the data using a free online application. However, heavy rainfall and high insolation could damage the system through excessive moisture or overheating, requiring a waterproof and heavy-duty protection case. The ThingSpeak channel allows customizing to suit a user’s specific requirements or adding more features for further development, such as automated irrigation, which can improve irrigation and fertilization efficiency by applying water and fertilizers at the right time based on sensor readings.

Open Access

We evaluated the performance and determined the efficiency parameters of an automated subirrigation system in a commercial greenhouse facility for clonal eucalyptus (Eucalyptus sp.) seedling production to improve subirrigation management practices. A methodology based on the mass balance of the irrigation system was established to determine the volumes of nutrient solution (NS) applied, drained, stored, evapotranspirated, and leaked in each subirrigation bench. The application, drainage, and NS dwell time in the 55-cm3 conic containers (0.125 m height × 0.03 m diameter) and the depth of NS reached inside the bench were also assessed. The values of application efficiency, irrigation efficiency and system transport (supply and drainage), and disposal losses of NS were estimated for each bench and inferred for the entire subirrigation system. The benches had average application and irrigation efficiency values of 0.84% and 98.38%, respectively. The system showed irrigation efficiency values of 27.59% and the sum lost by transport, leakings, and disposal in the water treatment plant of 72.41%. The continuous return of NS because of the high irrigation frequency contributed to this loss, resulting in 10,070 L of NS consumed by the plants and 26,430 L lost after 15 days of cultivation. Our results demonstrated that the system presented an adequate irrigation efficiency, but a low application efficiency caused by the constant return of NS because of the high irrigation frequency and the excess of losses from leaking and disposal of NS after 15 days of cultivation. Nevertheless, the system operated like a hydroponic system, which kept the containers partially immersed in the NS and did not use the full substrate container capacity to provide adequate moisture. This reduced the overall system irrigation and the substrate storage efficiencies, which needs to be improved by proper equipment design, operation, water and nutrients use efficiency, and management to achieve all the benefits that subirrigation possess.

Full access

Subirrigation can reduce water loss and nutrient runoff from greenhouses, because used nutrient solution is collected and recirculated. Capacitance moisture sensors can monitor substrate volumetric water content (θ) and control subirrigation based on minimum θ thresholds, providing an alternative to timers. Our objectives were to automate an ebb-and-flow subirrigation system using capacitance moisture sensors, monitor moisture dynamics within the containers, and determine the effect of five θ thresholds (0.10, 0.18, 0.26, 0.34, or 0.42 m3·m−3) on hibiscus (Hibiscus acetosella Welw. ex Hiern.) ‘Panama Red’ (PP20,121) growth. Subirrigation was monitored using capacitance sensors connected to a multiplexer and a data logger and controlled using a relay driver connected to submersible pumps. As the substrate θ dropped below the thresholds, irrigation was turned on for 3 min followed by 3-min drainage. Capacitance sensors effectively controlled subirrigation by irrigating only when substrate θ dropped below the thresholds. Each irrigation cycle resulted in a rapid increase in substrate θ, from 0.10 to ≈0.33 m3·m−3 with the 0.10-m3·m−3 irrigation threshold vs. an increase in θ from 0.42 to 0.49 m3·m−3 with the 0.42-m3·m−3 irrigation threshold. Less nutrient solution was used in the lower θ threshold treatments, indicating that sensor control can reduce water and thus fertilizer use in subirrigation systems. The water dynamics showed that the bottom part of the pots was saturated after irrigation with θ decreasing quickly after an irrigation event, presumably because of drainage. However, the water movement among substrate layers was slow with the 0.10-m3·m−3 irrigation threshold with water reaching the upper layer 5.5 to 20 h after irrigation. The 0.10-m3·m−3 θ threshold resulted in 81% fewer irrigations and 70% less nutrient solution use compared with the 0.42-m3·m−3 θ threshold. However, the 0.10-m3·m−3 θ threshold also reduced hibiscus shoot height by 30%, shoot dry weight 74%, and compactness by 63% compared with the 0.42-m3·m−3 θ threshold. Our results indicate that soil moisture sensors can be used to control subirrigation based on plant water use and substrate water and to manipulate plant growth, thus providing a tool to improve control over plant quality in subirrigation systems.

Free access

Substrate volumetric water content (VWC) is a useful measurement for automated irrigation systems. We have previously developed automated irrigation controllers that use capacitance sensors and dataloggers to supply plants with on-demand irrigation. However, the dataloggers and accompanying software used to build and program those controllers make these systems expensive. Relatively new, low-cost open-source microcontrollers provide an alternative way to build sensor-based irrigation controllers for both agricultural and domestic applications. We designed and built an automated irrigation system using a microcontroller, capacitance soil moisture sensors, and solenoid valves. This system effectively monitored and controlled VWC over a range of irrigation thresholds (0.2, 0.3, 0.4, and 0.5 m3.m−3) with ‘Panama Red’ hibiscus (Hibiscus acetosella) in a peat:perlite substrate. The microcontroller can be used with both regular 24-V alternating current (AC) solenoid valves and with latching 6- to 18-V direct current (DC) solenoid valves. The technology is relatively inexpensive (microcontroller and accessories cost $107, four capacitance soil moisture sensors cost $440, and four solenoid valves cost $120, totaling $667) and accessible. The irrigation controller required little maintenance over the course of a 41-day trial. The low cost of this irrigation controller makes it useful in many horticultural settings, including both research and production.

Free access

Citrus rootstock production in Brazil commonly uses manual overhead irrigation systems to water plants. Manual irrigation systems present low efficiency, apply more water than needed, and result in release of nutrients and pesticides into the soil with a potential to contaminate groundwater. Closed irrigation systems that avoid the disposal of nutrient solutions like subirrigation can be used to increase production efficiency and reduce the environmental contamination. Our objective was to evaluate the effect of subirrigation applied by a prototype tray on plant growth and morphological and physiological responses of Rangpur lime (Citrus limonia Osbeck ‘Limeira’) seedlings subjected to different water levels in conic containers filled with pine bark substrate. We tested three treatments: T1) subirrigation with water reaching two-thirds of the container height (8 cm); T2) subirrigation with water reaching one-third of the container height (4 cm); and T3) control with manual overhead irrigation. Subirrigation resulted in higher plant growth of Rangpur lime seedlings. At 90 days after sowing (DAS), we observed significant effects of T1 over the other treatments on plant growth, as indicated by higher total dry mass (P = 0.0057), shoot/root ratio (P = 0.0089), shoot height (P = 0.0004), leaf area (P = 0.0005), and root length (P = 0.0333). The number of bifurcations was 400% higher in T3 than at the subirrigated treatments, which can lead to an increase in the labor costs for pruning. Seedlings grown under T1 presented leaf water potential 13% higher compared with T3 at predawn, which was the time of highest stomatal efficiency, presenting the lowest water loss, maximum stomatal closure, and higher transpiration at lower stomatal resistance. T2 plants displayed intermediate water status with a water potential 5% higher than T3. T3 plants showed a higher transpiration rate under maximum stomatal closure, reducing leaf water potential. The subirrigated treatment with water level of two-thirds of container height (8 cm) induced higher plant growth and shortened the crop cycle, anticipating the transplanting to the next phase (grafting) with the possibility of reducing production costs in the nursery.

Free access

The bacterial disease Huanglongbing (HLB) has drastically reduced citrus production in Florida. Nutrients play an important role in plant defense mechanisms and new approaches to manage the disease with balanced nutrition are emerging. Nutrients like nitrogen (N), calcium (Ca), and magnesium (Mg) could extend the productive life of affected trees, although interactions among these nutrients in HLB-affected citrus trees are still unclear. A 2-year study was established in Florida to determine the response of HLB-affected trees to applications of N, Ca, and Mg. The study was conducted with ‘Valencia’ trees (Citrus sinensis L. Osbeck) on Swingle citrumelo (Citrus paradisi Macf. × Poncirus trifoliata L. Raf.) rootstock on a Candler sand. Applications of N at 168, 224 (recommended rate), and 280 kg⋅ha−1 N were used as the main plots. Split-plots consisted of a grower standard treatment receiving only basal Ca (51 kg⋅ha−1) and Mg (56 kg⋅ha−1); supplemental Ca (total Ca inputs: 96 kg⋅ha−1) only; supplemental Mg (total Mg inputs: 101 kg⋅ha−1) only; and supplemental Ca (total Ca inputs: 73.5 kg⋅ha−1) and Mg (total Mg inputs: 78.5 kg⋅ha−1). The following variables were measured: tree size, fruit yield, and juice quality. Although some differences in tree growth among treatments were statistically significant (e.g., greater canopy volume with Mg fertilization at 168 kg⋅ha−1 N), there was no clear and consistent effect of plant nutrition on these variables. Fruit yield was higher with Ca and Mg relative to the grower standard at the lowest N rate in 2020, and there were no other statistically significant differences among treatments. Juice acidity was significantly higher with Mg fertilization relative to other treatments in 2019. As N rates had no significant effect in this study, unlike secondary macronutrients, N rates could potentially be reduced to 168 kg N⋅ha−1 in HLB-affected citrus without affecting vegetative growth, fruit yield, and juice quality. However, this will require optimizing the supply of secondary macronutrients and all other nutrients to develop a balanced nutritional program. Ultimately, the effects of N, Ca, and Mg obtained in this 2-year study should be confirmed with longer-term studies conducted at multiple sites.

Open Access

Subirrigation is a greenhouse irrigation method that relies on capillary action to provide plants with water and nutrients from below their containers. The first documented subirrigation system was described in 1895, and several variations on the basic design were used for research purposes before the modern ebb-and-flow type systems emerged in 1974. Most subirrigation systems apply the fertilizer solution to a waterproof bench or greenhouse section, allowing the substrate to absorb the water through holes in the bottom of the containers. Because there is little or no leaching, subirrigation typically allows for the use of lower fertilizer solution concentrations. Although excess fertilizer salts typically accumulate in the top layer of the substrate, this does not seem to have a negative impact on plants. Subirrigation can conserve nutrients and water, reduce labor costs, and help growers meet environmental regulations. A challenge with subirrigation is the potential spread of pathogens via the fertilizer solution. When this is a concern, effective disinfection methods such as ultraviolet radiation, chlorine, or ozone should be used. Sensor-based irrigation control has recently been applied to subirrigation to further improve nutrient and water use efficiencies. Better control of irrigation may help reduce the spread of pathogens, while at the same time improving crop quality. The primary economic benefit of subirrigation is the reduction in labor costs, which is the greatest expenditure for many growers.

Free access

Huanglongbing (HLB), or citrus greening disease, affects practically all fruit-bearing trees in commercial citrus orchards in Florida with no cure identified yet. High-density plantings and enhanced nutritional programs such as application of controlled-release fertilizer (CRF) with higher micronutrient levels can mitigate disease symptoms and extend the tree life span of sweet oranges (Citrus sinensis). The objective of this study was to evaluate the effects of tree planting density and application of CRF blends differing in N to K ratio and micronutrient content on grapefruit (Citrus paradisi) plant health, canopy volume, fruit yield, and fruit quality in an HLB-affected orchard. A study was conducted in Florida for two growing seasons (2017–18 and 2018–19) to evaluate the response of ‘Ray Ruby’ grapefruit on Kuharske citrange (Citrus sinensis × Poncirus trifoliata) to three planting densities (300, 440, and 975 trees per ha) and two CRF blends [12 nitrogen (N)–1.31 phosphorus (P)–7.47 potassium (K) and 16N–1.31P–16.6K] with different nutrient sources and composition. According to quantitative real-time polymerase chain reaction testing, all sampled trees tested positive for Candidatus Liberibacter asiaticus, the pathogen associated with HLB. Trees planted at 975 trees per ha had 33% lower canopy volume per tree but 160% greater fruit yield per hectare and 190% higher yield of solids compared with 300 trees per ha. Fruit produced in high-density planting (975 trees per ha) was 18% more acidic with higher soluble solid compared with low-density planting (300 trees per ha). The use of a CRF blend with higher amounts of micronutrients along with lower K increased canopy volume in both seasons and resulted in 24% and 29% reduction in fruit yield per hectare and yield of solids, respectively, in 2017–18. Our results indicate that high-density plantings increase fruit yield per area, and regardless of the N to K ratio, the use of CRF blends supplemented with micronutrients may not increase fruit yield in HLB-affected grapefruit.

Open Access

Since the arrival of Huanglongbing (HLB) disease in Florida, several management approaches, including modification of orchard architecture design and nutritional therapy, have been explored. High-density plantings anticipate early economic returns from HLB-affected orchards. With no cure available for HLB, balanced nutrient application through soil and foliar spraying can mitigate the disease. A 2-year study was conducted to investigate the effects of three grapefruit (Citrus paradisi) planting densities [single-row (300 and 440 trees per ha), and double-row high-density (975 trees per ha)], two controlled-release fertilizer (CRF) blends, and foliar-applied micronutrients (FAM) (a blend of B, Mn, and Zn at 0, 1.5, 3, and 6 times the recommended rates) on grapefruit growth and fruit yield, physiological parameters, and foliar nutrient concentrations in an HLB-affected orchard. All the trees tested positive for HLB based on real-time quantitative polymerase chain reaction (qPCR) test. The highest planting density resulted in the lowest trunk diameter and canopy volume. Despite lower yield per tree in 2019–20, 975 trees per ha planting induced the greatest fruit and solid yields per ha. Also, the fruit produced from 975 trees per ha planting tended to be acidic with the deposition of more soluble solids. Use of CRF with higher micronutrients increased canopy volume with the expense of reduced fruit number in 2019–20. FAM did not affect cycle threshold (Ct) value and tree growth parameters. Fruit yield, photosynthesis rate, and stomatal conductance (g S) decreased, and all leaf nutrient concentrations except B increased in 2019–20 with all FAM rates tested. In conclusion, our study showed that high-density planting optimizes yield under HLB-endemic conditions. In addition, supplemental soil and foliar micronutrient application do not enhance yield of HLB-affected trees over a 2-year timeframe, warranting further research for confirmation of results.

Open Access