Greenhouse Management: Why did BioSafe Systems choose to discuss algae remediation for this piece?

ES: Algae can be ubiquitous in greenhouses and is exacerbated by high humidity, especially where I’m from in Florida. It is found in irrigation tanks, ponds, reservoirs nourished by the moist and damp environments. Outside of water systems, there are types of algae that develop on the greenhouse floors that can create hazardous conditions for employees. On the crops themselves, another kind of algae can spread from the racks, trays, pots to the soil at the base of the plant. Often different approaches are necessary for different types of algae and specific target areas. We’ve helped growers manage their algae issues for many years with multiple products for surfaces and for the plants themselves. We have products for algae control in greenhouses that cover and protect from top to bottom and treat irrigation systems too.

GM: BioSafe Systems offers multiple solutions, but is there a specific product you’d like to highlight?

ES: There are two that we would focus on for greenhouse use. The first would be ZeroTol 2.0 as a chemigation application for young plants. ZeroTol 2.0 can be injected at extremely low rates into propagation water, which helps eliminate algae on plugs, trays, and on the floors, benches, and walls of the facility. With an application via an injection system — which can be very simple to set up with a Dosatron pump — they can also treat the foliage, the plants themselves, and surrounding surfaces. The second option would be GreenClean PRO, which is a granular algaecide. Its focus is twofold, and it is excellent for treating algae on floors and other hard surfaces. If you have concrete walkways, ground cloth, or dirt, or gravel floors, the product has tremendous on-contact results. Additionally, some facilities have a 10,000-gallon water storage tank. When algae gets in there, we can treat those tanks with GreenClean PRO to kill the algae and still save that water for the plants.

GM: How do growers figure out what is best for them?

ES: All greenhouses could use GreenClean PRO because algae frequently grows on floors and it can be treated with a granular very easily. ZeroTol 2.0 is more for foliar sprays if a greenhouse has algae growing on plants, soil, or trays. Or if growers want to treat their irrigation water itself and spray the treated water to keep everything clean.

Greenhouse Management: What is the most common reason that most growers will look at adding automation to their greenhouse workflow?

Steven Biles, TTA: The biggest one is clearly labor. A grower I was working with recently told me she estimates that she spends close to 70% of her time each week dealing with labor and hiring and managing her employees. That is time she is spending not directly managing the grow and the plants themselves. Say you are a smaller grower and you’ve got somewhere between five and ten full-time year-round employees, and maybe every spring you bring in five or ten seasonal full-time people to ramp up. Typically, with automation we can cut that total labor force in half, and the grower can still produce the same number of plants and the same quality.

GM: Aside from labor and saving money on employees, are there secondary benefits that growers will enjoy?

SB: One of the significant secondary benefits to the smaller grower is that with automation they can often delay the start of planting by a few weeks, they do not have to start planting so early in late winter anymore because now it does not take three weeks of crews working around the clock to get those plugs transplanted. With a transplanter like our PackPlanter 1450S, they do not have to start so early so they will save money on heating the greenhouse, because while many will still be heating the roof to melt snow load, they’ll still see savings on their heat expenses because they won’t have to heat the bays around the clock for growing.

GM: How does the start of shipping season constrain an operation’s labor, and how can automation help alleviate that?

SB: Once shipping starts for a lot of these smaller greenhouse operations, they will have the same labor crew that was manually transplanting plugs, now those same workers are also responsible for pulling plants and getting them prepped to ship. If you do not have a large employee pool to pull from, you might not have anyone to continue planting new plugs while the rest of the crew ships. With an automated transplanter they can send a crew to the shipping area to deal with shipment orders, and then they can keep a few employees in the planting area to keep that part of the business humming as well. Now, you can get those three to four crops turned in the greenhouse that the smaller growers need to generate better revenues. Growers know that their first to second turns pay their costs of labor and material, the last turns are their PROFITS!

The 2021 California Summer Trials, scheduled for June 23-27, mark a few changes with the annual California pilgrimage for growers, brokers and breeders.

To begin, there’s the obvious one: when it’s happening.

Historically, the acronym CAST has stood for the California Spring Trials with the event taking place sometime in the early spring over the course of a week. In 2020, the event just so happened to coincide with the beginning of the ongoing COVID-19 pandemic. As a result, the event did not happen with the various stops across the state shuttered. By virtue of unfortunate timing, CAST 2020 was the first horticulture industry event directly impacted by the pandemic. Each stop canceled its showcase and long-booked plans largely fell by the wayside. Some breeders, however, were able to pivot to digital and host webinars to showcase new varieties, but others were left with no real outlet to market their plants.

The 2021 event is scheduled for June for specific reasons. One is COVID-19 and the hope that the event wouldn’t have to be canceled again due to the virus. At the time of this publication, that appears to be a winning bet. The idea was to, in theory, allow more people to attend during a slower time of the year instead of the peak spring. And, as an added bonus, early summer means a larger diversity of crops — such as perennials and annuals that perform well in the heat — to be spotlighted in a more normal growing climate.

CAST 2021 also sees a different shape to the event with the number of participating breeders dropping. This shift actually began in 2020 when Proven Winners declined to participate, even before COVID-19 was a concern. (Proven Winners announced its decision not to participate in CAST 2020 in July 2019.) Citing declining attendance and a desire to “broaden the pool” of industry members who were able to participate, Proven Winners went digital while still planning to showcase its varieties at other industry events. For 2021, Danziger and Terra Nova Nurseries are among the breeders declining to participate, and it’s unclear if any will re-join the event in the future.

Benary, which is participating in the event, also made changes. Instead of limiting visitors to the official five-day window of CAST 2021, its gardens are open through Aug. 31 to anyone who books a visit ahead of time. The idea here is to not exclude a grower or someone else who maybe can’t make it in June, but could come later on in the summer.

In this preview, you’ll find information on all of the stops, as well as some of the new varieties that will be on display at CAST 2021. And if you’re planning on attending or are just planning to observe from afar, we’d love to hear from you. Drop us a line at cmanning@gie.net. – Chris Manning

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Greenhouses are controlled environments that have the potential to expand growth regions and seasons for food and flower production. Greenhouses can increase yield by an order of magnitude while reducing water and fertilizer consumption. However, the energy required to thermally regulate a greenhouse coupled with supplementary lighting makes greenhouses energy intensive, thereby hampering greenhouses from becoming environmentally sustainable.

Since the beginning of 2017, engineering, plant biology and physics researchers at North Carolina State University have been looking at ways to make greenhouses energy neutral using semi-transparent organic solar cells to harvest energy. These solar cells have the potential to compliment plant’s absorption spectra while generating power, thereby aiding plant growth while at the same time offsetting greenhouse energy demand. In this process, no additional land usage is required given that the solar cells can be integrated onto the greenhouse envelope.

Study intro

A systematic study focused on assessing greenhouse energy demand, synthesis of new materials to tune solar absorption spectra and the impact of different materials on plant growth. The feasibility of achieving energy neutral greenhouses is currently being evaluated.

These solar cells have the potential to compliment plant’s absorption spectra while generating power, thereby aiding plant growth while at the same time offsetting greenhouse energy demand.

Last year, Dr. Brendan O’Connor’s research group in Mechanical Engineering in collaboration with Dr. Heike Sederoff in Plant and Microbial Biology, Dr. Harald Ade in the Department of Physics and Dr. Carole Saravitz, Director at the Phytotron research facility developed an energy model to assess the ability of organic solar cells to meet the energy needs of greenhouses in climates across the US. It was found that energy neutral greenhouses can be achieved in warm and moderate climates. This was published in the study “Achieving Net Zero Energy Greenhouses by Integrating Semitransparent Organic Solar Cells”.

However, this came at the cost of losing nearly 30 percent of light in the Photosynthetically Active Radiation (PAR), in comparison to the reference greenhouse during winter. Hence, there was a need to ensure impact on crop yield is minimized. Now it has been demonstrated that it is possible to use semi-transparent organic solar cells that spectrally transmit and absorb light at various wavelengths to allow plant growth without any loss in yield. Their study was published recently in Cell Reports Physical Science.

Study methodology

To analyze crop yield, the researchers grew red leaf lettuce in a controlled environment growth chamber in the NC State Phytotron for 35 days, from germination to harvest. The chamber was equipped with ceramic metal halide and incandescent lights capable of providing a full spectrum of white light that comes closest to sunlight. Lettuce was selected because it forms an important greenhouse crop. It is also suitable for multiple replications in a reasonably short period and compact in size thereby allowing for the growth of these plants in the controlled environment growth chamber. All parameters, from temperature and water to fertilizer and CO2 concentration except for light, were controlled.

A control group of lettuces was exposed directly to the light source in the chamber, while the rest of the lettuces were divided into three experimental groups. Each of these groups was exposed to light through different types of filters that absorbed wavelengths of light equivalent to those that different types of semi-transparent solar cells would absorb. While the total light on the filters were maintained from one experimental group to the other, differences in filter transmittance meant plants experienced reductions in incident light by as much as 50 percent with respect to the control lettuce. Apart from changes in light intensity, the plants also experienced differences in ratio of blue to red light under the filters.

Study results

The researchers assessed various plant growth metrics like weight, leaf number, size and nutrient content. The amount of CO2 assimilation and chlorophyll content of the plants were also measured.

Promisingly, the researchers did not find any significant reduction in the yield and nutrient content of lettuce between the different filters and with respect to the control. Furthermore, a semi-transparent organic solar cell system design that absorbs light in a wavelength region highly complementary to the plant’s absorption spectra while also removing unwanted heat in the infrared wavelengths was demonstrated. The ability to tune absorption characteristics holds great promise to apply these cells in greenhouse that grow high light crops like tomato while also simultaneously aiding temperature control during hot summer months. Now there is a clear path to achieving a higher profit in the long term once growers can look past the initial investment in organic solar power technology.

Currently, Dr. Sederoff’s research group are now leading efforts to delve deeper and understand the effect of various wavelengths of light on the growth of not just lettuce but also tomatoes and other crops, such as greenhouse ornamentals A transcriptome analysis is currently being carried out that indicates certain filters have interesting effects on some molecular pathways effecting nutrient use efficiency and pathogen resistance. These preliminary results suggest the semitransparent solar cells may offer additional benefits for all plants.

The paper, “Balancing Crop Production and Energy Harvesting in Organic Solar Powered Greenhouses,” appears in the journal Cell Reports Physical Science. Co-lead authors of the paper are NC State Ph.D. students Eshwar Ravishankar and Melodi Charles. Ravishankar is a Ph.D student in the University’s Department of Mechanical and Aerospace Engineering, while Charles is a Ph.D student in the Department of Plant and Micorbial Biology. The paper also has several co-authors. The full research paper can be accessed here: bit.ly/NCSUstudy.