Marc W Van Iersel

University of Georgia | UGA · Department of Horticulture

Fast growth and rapid turnover is an important crop trait in controlled environment agriculture (CEA) due to its high cost. An ideal screening approach for fast-growing cultivars should detect desirable phenotypes non-invasively at an early growth stage, based on morphological and/or physiological traits. Hence, we established a rapid screening pro...

Global population growth has increased food production challenges and pushed agricultural systems to deploy the Internet of Things (IoT) instead of using conventional approaches. Controlling the environmental parameters, including light, in greenhouses increases the crop yield; nonetheless, the electricity cost of supplemental lighting can be high,...

Supplemental lighting is an effective means for increasing greenhouse productivity. Recently, the use of light-emitting diodes (LEDs), capable of precise and quick dimmability, has increased in greenhouses. However, electricity cost of lighting can be significant, and hence, it is necessary to find optimal lighting strategies to minimize electrical...

Photons above 700 nm have minimal photosynthetic activity when applied alone (Emerson and Lewis, 1943; McCree, 1971) and have thus been excluded from the definition of photosynthetically active radiation (PAR; 400 to 700 nm). However, those longer-wavelength photons have synergistic activity with photons in the PAR range (Emerson et al., 1957). Rec...

The current definition of photosynthetically active radiation includes only photons from 400 up to 700 nm, despite evidence of the synergistic interaction between far‐red photons and shorter‐wavelength photons. The synergy between far‐red and shorter‐wavelength photons has not been studied in sunlight under natural conditions. We used a filter to r...

Controlling the environmental parameters, including light in greenhouses, increases the crop yield; however, the electricity cost of supplemental lighting can be high. Therefore, the importance of applying cost-effective lighting methods arises. In this paper, an optimal supplemental lighting control approach is developed considering a variational...

Shade tolerance is a highly desirable trait when breeding new bermudagrass (Cynodon spp.) lines, but current screening methods can take many years to complete. There is a clear need for large-scale turfgrass breeding programs to reliably, accurately, and quickly predict shade tolerance in their germplasm. The objectives of this research were to: (i...

Controlling the environmental parameters, including light in greenhouses, increases the crop yield; however, the electricity cost of supplemental lighting can be high. Therefore, the importance of applying cost-effective lighting methods arises. In this paper, an optimal supplemental lighting control approach is developed considering a variational...

Canopy imaging is a good phenotyping approach to non-invasively quantify parameters such as canopy size, stress symptoms, and pigment concentrations. Unlike destructive measurements, canopy imaging is fast and easy. However, analysis of the images can be time consuming. To facilitate large-scale use of imaging, the cost of imaging systems needs to...

Vertical farming is increasingly popular due to high yields obtained from a small land area. However, the energy cost associated with lighting of vertical farms is high. To reduce this cost, more energy efficient (biomass/energy use) crops are required. To understand how efficiently crops use light energy to produce biomass, we determined the morph...

Plants naturally contain high levels of the stress-responsive fluorophore chlorophyll. Chlorophyll fluorescence imaging (CFI) is a powerful tool to measure photosynthetic efficiency in plants and provides the ability to detect damage from a range of biotic and abiotic stresses before visible symptoms occur. However, most CFI systems are complex, ex...

Red and blue light are traditionally believed to have a higher quantum yield of CO2 assimilation (QY, moles of CO2 assimilated per mole of photons) than green light, because green light is absorbed less efficiently. However, because of its lower absorptance, green light can penetrate deeper and excite chlorophyll deeper in leaves. We hypothesized t...

Fertilizer recommendations for peach cultivation in the southeastern United States were developed decades ago and may not reflect the peach trees’ needs under current cultivation practices. Adequate fertilization for young peach trees induces a balanced vegetative/reproductive growth, ensures efficient resource use, and is environmentally sound. Dr...

New peach orchards in the southeastern United States are often not irrigated until 3 or 4 years after planting. During those years, the only water comes from rainfall. Droughts in the region are becoming more common, making irrigation more important. At the same time, fertilization practices follow recommendations developed decades ago and may not...

The cost of providing lighting in greenhouses and plant factories can be high. In the case of variable electricity prices, providing most of the light when electricity prices are low can reduce costs. However, it is not clear how plants respond to the resulting fluctuating light levels. We hypothesized that plants that receive a constant photosynth...

Light-emitting diodes allow for the application of specific wavelengths of light to induce various morphological and physiological responses. In lettuce (Lactuca sativa), far-red light (700–800 nm) is integral to initiating shade responses which can increase plant growth. In the first of two studies, plants were grown with a similar photosynthetic...

Light recommendations for horticultural crops often focus on the optimal daily light integral (DLI) without regard to how that light is delivered throughout each day. Because photosynthesis is more efficient at lower photosynthetic photon flux density (PPFD), we hypothesized that longer photoperiods with lower PPFD results in faster growth than sho...

The use of supplemental lighting is an effective way for increasing greenhouse productivity. Recently, using light-emitting diodes (LEDs), capable of precise and quick dimmability, has increased in greenhouses. However, electricity cost of lighting can be significant, and hence, it is necessary to find optimal lighting strategies to minimize supple...

Blueberry fruit are perishable after harvesting due to fruit softening, water loss and susceptibility to pathogens. Light, especially blue light, increases the accumulation of anthocyanins and reduces postharvest decay in some fruits, but the effect of blue light on postharvest fruit quality attributes in blueberries is unknown. In this study, we e...

Supplemental light can increase growth and accelerate production of greenhouse crops, but it can be expensive if not provided in a way that promotes efficient use of the light. Dimmable light-emitting diode (LED) fixtures have the potential to reduce lighting costs because the output can be precisely controlled to meet crop needs. Because light is...

Controlled environment crop production recommendations often use the daily light integral (DLI) to quantify the light requirements of specific crops. Sole-source electric lighting, used in plant factories, and supplemental electric lighting, used in greenhouses, may be required to attain a specific DLI. Electric lighting is wasteful if not provided...

Seedlings may be grown indoors where environmental conditions can be precisely controlled to ensure consistent and reliable production. The optimal spectrum for production under sole-source lighting is currently unknown. Far-red light (λ = 700–800 nm) typically is not a significant part of the spectrum of light-emitting diode (LED) grow lights. How...

Supplemental lighting can improve the growth of greenhouse crops, but the electricity required for supplemental lighting can be a significant expense for greenhouse growers. Lighting control strategies that use the dimmability of light-emitting diodes (LEDs) have the potential to decrease this cost. In our experiments, we tested the hypothesis that...

A soil moisture sensor-based automated irrigation system was trialed in a commercial ornamental nursery over the 2014-2015 growing seasons. In both years, use of the sensor-based system resulted in an approximate 50% reduction in irrigation application (volume) when compared to grower-managed irrigation. No differences in growth and equivalent or s...

To acquire accurate volumetric water content (VWC) measurements from horticultural substrates using dielectric sensors, a substrate-specific calibration is critical. Calibrations typically are conducted with a substrate without plants, but water in the root system may affect soil moisture sensor readings. We investigated the effect of root growth o...

Bedding plants are at increased risk for exposure to drought stress during production because they are grown in small containers. Physiological mechanisms of bedding plants at leaf and cellular scales that regulate whole-plant photosynthesis under drought conditions are not well understood. This information can be useful for screening bedding plant...

Free download through early June 2019: https://authors.elsevier.com/a/1Yxy05Tbkk5R0V • Electricity use of greenhouse lights can be reduced using dimmable LEDs. • An optimization problem is formulated to minimize electricity use for lighting. • The problem is solved using a quick and computationally-simple algorithm. • Lettuce lighting requireme...

Plant light use efficiency decreases as light intensity is increased, and a better understanding of crop-specific light responses can contribute to the development of more energy-efficient supplemental lighting control strategies for greenhouses. In this study, diurnal chlorophyll fluorescence monitoring was used to characterize the photochemical r...

A soil moisture sensor-based automated irrigation system was trialed in a commercial floriculture greenhouse to determine what benefits these types of systems may offer to herbaceous ornamental producers. Water use, crop quality and growth, and grower behavior toward adoption of the new technology were monitored, when all decision making related to...

Building on existing technology that utilizes capacitance sensors and low-cost microcontrollers, we designed, assembled and tested a self-contained irrigation system for controlling substrate volumetric moisture content in container-grown ornamental plants. In the prototype system described here, compatible software is embedded within the microcont...

Linear electron transport depends on balanced excitation of photosystem I and II. Far‐red light preferentially excites photosystem I (PSI) and can enhance the photosynthetic efficiency when combined with light that over‐excites photosystem II (PSII). The efficiency of different wavelengths of far‐red light at exciting PSI was quantified by measurin...

Water-efficient soilless substrates need to be engineered to address diminishing water resources. Therefore, we investigated soilless substrates with varying hydrologies to determine their influence on crop growth and plant water status. Aged loblolly pine (Pinus taeda) bark was graded into four particle size fractions. The coarsest fraction was al...

Greenhouse agriculture is a highly efficient method of food production that can greatly benefit from supplemental electric lighting. The needed electricity associated with greenhouse lighting amounts to about 30% of its operating costs. As the light level of LED lighting can be easily controlled, it offers the potential to reduce energy costs by pr...

Dielectric moisture sensors are particularly suitable for irrigation management in greenhouse soilless production. Identifying the practical effects of substrate water content set-points on crop performance is crucial for successful sensor-based irrigation. We designed and constructed a prototype cloud-connected system for wireless, sensor-based ir...

Supplemental lighting is often required for greenhouse production of annual bedding plants in early spring. However, supplemental lighting is generally provided in an inefficient manner, in terms of photosynthetic light use. We used a series of models to construct an optimal supplemental lighting strategy, using an adaptive lighting control approac...

Supplemental lighting is often needed in controlled environment agriculture to produce high-quality crops. The cost of the electricity needed to provide this lighting can be high. Light emitting diodes (LEDs) provide unique, new opportunities to reduce the cost of supplemental lighting. Compared to high-intensity discharge lights, and specifically...

Photosynthetic responses to light are dependent on light intensity, vary among species, and can be affected by acclimation to different light environments (e.g., light intensity, spectrum, and photoperiod). Understanding how these factors affect photochemistry is important for improving supplemental lighting efficiency in controlled-environment agr...

Phalaenopsis orchids are an increasingly popular potted house plant in the United States. New cultivars have a long display life in home environments, but these epiphytes are often overirrigated by consumers. Irrigating potted Phalaenopsis orchids weekly with ice cubes has been recommended as a simple solution to help consumers, but concern has bee...

Real-time irrigation monitoring and control afforded by dielectric soil moisture sensors allows for precise substrate volumetric water content (VWC) to be maintained under dynamic experimental conditions. A case study was conducted with Petunia ×hybrida ‘Dreams Red’ grown using a sensor-based irrigation system with half of the plants infected with...

A weather station is a collection of instruments and sensors that measure atmospheric and soil conditions. Commonly measured environmental variables include light, temperature, relative humidity, rain, and wind. Soil conditions include soil moisture, soil temperature, and soil bulk electrical conductivity. An on-site weather station allows for moni...

Photosynthesis is the basic process driving the growth of plants, and growers therefore need to know how to create conditions to allow plants to photosynthesize efficiently. There are many cultural and environmental factors that affect photosynthesis. Optimizing only some of these factors without paying attention to others may not result in a stimu...

FREE DOWNLOAD TILL FEBRUARY 15 AT: https://authors.elsevier.com/a/1UI9Fe3VOXVFg. The efficiency of monochromatic light to drive photosynthesis drops rapidly at wavelengths longer than 685 nm. The photosynthetic efficiency of these longer wavelengths can be improved by adding shorter wavelength light, a phenomenon known as the Emerson enhancement e...

Over the past six years, our national team has developed, tested and commercialized wireless sensor networks (WSNs) and advanced software which allows for automated decision irrigation, based on grower-defined irrigation strategies. WSNs have been implemented in ten commercial greenhouses and nurseries across the Unites States, where irrigation eve...

Supplemental lighting in greenhouses is often needed for year-round production of high-quality crops. However, the electricity needed for supplemental lighting can account for a substantial part of overall production costs. Our objective was to develop more efficient control methods for supplemental lighting, taking advantage of the dimmability of...

Controlling the elongation of ornamental plants is commonly needed for shipping and aesthetic purposes. Drought stress can be used to limit elongation, and is an environmentally friendly alternative to plant growth regulators (PGRs). However, growers can be reluctant to expose plants to drought stress because they do not want to negatively affect o...

Drought stress reduces stem elongation and cell expansion. Since gibberellins (GAs) play an important role in controlling cell elongation, the objective of this study was to determine if the reduction in growth under drought stress is associated with altered GA metabolism or signaling. We exposed 'Moneymaker' tomato (Solanum lycopersicum) to drough...

Abscisic acid (ABA) is a plant hormone involved in regulating stomatal responses to environmental stress. By inducing stomatal closure, applications of exogenous ABA can reduce plant water use and delay the onset of drought stress when plants are not watered. However, ABA can also cause unwanted side effects, including chlorosis. Pansy (Viola×wittr...

Subirrigation applies water and nutrients to the bottom of pots without wetting leaves, improving water use and reducing disease spread compared to overhead irrigation systems. However, water levels applied within the benches are often higher than required to promote capillary action, applying more water than needed and wasting pumping energy. The...

The study compares the effects of: timer ('Timer') and soil moisture sensor-controlled irrigation on soilless lettuce; two volumetric water content (Θ) thresholds for irrigation (0.30 ('Θ = 0.3') and 0.40 m3/m3 ('Θ = 0.4')). The most nutrient solution (NS) was applied in 'Timer' where the lowest water use efficiency was observed, with 17 and 42% le...

Temperature and drought are major abiotic limitations to crop productivity worldwide. While abiotic stress physiology research has focused primarily on fully expanded leaves, no studies have investigated photosynthetic tolerance to concurrent drought and high temperature during leaf ontogeny. To address this, Gossypium hirsutum plants were exposed...

Supplemental lighting is often needed for crop production in controlled environments. Such supplemental lighting can be expensive and inefficient. Chlorophyll fluorescence is a valuable tool for monitoring light use efficiency in plants and can be used to determine the quantum yield of photosystem II (φPSII) and the electron transport rate through...

Photosynthetic lighting is one of the main costs of running controlled environment agriculture facilities. To optimize photosynthetic lighting, it is important to understand how plants use the provided light. When photosynthetic pigments absorb photons, the energy from those photons is used to drive the light reactions of photosynthesis, thermally...

Evaluation of plant response to nutrients may be difficult in soil grown plants due to complex nutrient chemical, physical and biological interactions. Hydroponics is an alternative method of plant nutrient supply which avoids soil-nutrient reaction complexities. Eucalyptus and related species are highly valued as fast-growing woody plants. We cond...

A new sensor for the measurement of electrical conductivity (EC) and moisture content, specifically designed for soilless substrates, has been released (GS3, Decagon Devices). The Hilhorst equation has been proposed as a tool to convert the measured bulk EC (ECb) into the pore EC (ECp, the EC of the solution in the pore spaces of the substrate). A...

The increasing availability of low-cost and reliable substrate moisture sensors offers interesting perspectives for rational and automatic irrigation management of soilless greenhouse crops and for research on plant water relations. The knowledge of the effects of different substrate volumetric water content (VWC) levels on plant growth is crucial...

As water becomes an increasingly precious commodity, greenhouse growers turn to closed subirrigation systems, which can not only conserve water, labor and fertilizer, but also can produce more uniform crops compared to overhead or drip irrigation. Subirrigation requires a different fertilization program than more traditional irrigation systems. Bec...