Researchers Tackle Critical Topics For Greenhouse Growers

From greenhouse basics to IPM programs, the 2011 Greenhouse Crop Production and Engineering Design Short Course focused on growing solutions for tomorrow using controlled environment agriculture, hydroponics, and aquaponics.

Organized by the University of Arizona Controlled Environment Agriculture Center (UA-CEAC), the short course was held April 5 to 8 at the Westward Look Resort in Tucson, AZ. Attendees traveled from as far as Barbados, Washington, Ohio, Qatar, and Mexico to learn from the UA-CEAC.

The lectures were presented by the faculty/staff of the University of Arizona, a group that collectively has more than 250 years of knowledge and experience in controlled environment agriculture and hydroponics.

To begin the course, Gene Giacomelli, professor and director of the CEAC, imparted these insightful words: “Remember, highly controlled greenhouses, modified environment high tunnels, and closed systems of food production are all similar practices. The basics needed by plants for their growth is the same for all plant production systems.” From the hottest desert in the Middle East to the South Pole in Antarctica, and possibly Mars and the moon, as long as plant needs are met, it will produce, he added.

Kicking things off was Murat Kacira, an associate professor who discussed basic greenhouse structures and how different greenhouse designs apply better to specific environments. He elaborated with the example that the sawtooth greenhouse design is better for tropical/desert areas, as it uses the prevailing wind for passive cooling. On the other hand, he said the A-frame greenhouse is ideal for tall plants, such as tomatoes.

Climate Control And Fertigation
Greenhouse climate control is so essential to meeting the plants’ needs that both Giacomelli and Kacira focused on the topic. According to Kacira, meeting those needs in a controlled environment varies from LED lights for the physiological process to the possibility of using alternative heating sources to warm the plants. Giacomelli added that growers need to be wary of pollutants from unvented heaters as they can damage the plants.

Moving from climate control to fertigation, associate professor Peter Waller discussed fertilizer application through  irrigation systems and provided various equations for determining nitrogen application rates, late-season application rates, nutrient concentrations, and for checking the source water for nutrients. Various pumps can be used in the fertigation process, explained Waller, but the most important thing to remember when fertigating is water quality.

Integrated Pest Management Pointers
Roger Huber, professor emeritus in entomology, tackled the topic of IPM. According to Huber, to have a good IPM program, growers need to follow four key points:

1. Monitoring and record keeping
2. Knowing your management options
3. Implementing the management plan
4. Reviewing the plan and revising it annually

Trial Results And Postharvest Handling
Professor emeritus Merle Jensen demonstrated various greenhouse trials performed to find the best growing media, with the results leading to coconut coir. He added that graft transfers, elevated platforms, and drain systems also are considerations for greenhouse growers. Jensen stressed the importance of using white poly to cover the floor, stating that not only does it look cleaner but it helps reduce the risk of disease.

He also emphasized the importance of a good marketing strategy, whether a grower is selling to a chain store or farm market. Citing cherry tomatoes as an example, Jensen suggested growers produce a couple of plants that are not the traditional red and package those tomatoes with the red tomatoes to offer consumers some variety.

To package or sell tomatoes, Jensen also suggested leaving them on the vine for several reasons: customers believe they are fresher than those removed from the vine, growers save time when picking-, the presentation is more visually appealing, and they appear to be locally grown.

Jorge Fonseca, assistant specialist and assistant professor at the University of Arizona Cooperative Extension, discussed enhancing produce quality/nutritional value and postharvest handling. “Once harvested, the quality of the produce cannot be improved; you can only prolong a particular quality to a certain point,” he said.

The greatest losses can occur during the postharvest stage. Fonseca recommended that growers develop a postharvest handling plan that consists of eight parts:
1. Pre-harvest preparation
2. Review the practical harvest index
3. Field/greenhouse handling
4. Cooling process
5. Postharvest treatments and technology
6. Packaging and transportation
7. Minimal processing (only shipping a processed product i.e. potato slices to be made into French fries).
8. Labor management (sanitation)

Aquaponics
Last but not least, the discussion turned to aquaponics, which is the combination aquaculture and hydroponics. Aquaponics is said to be the fastest growing sector of the ag industry and has the potential to offer many benefits to growers.

Professor Kevin Fitzsimmons and Jason Licamele of Fish Farmacy, LLC, said the most important factor with this technology is water. Generally speaking, they said that any water that is suitable for people to drink can be used to start an aquaponics system.

The next step is to add the fish, keeping in mind that approximately 24 to 48 hours needs to pass to allow the residual chlorine to dissipate. It is important to add the fish next, as their waste needs to accumulate to provide nutrients for the plants. The presenters stressed the importance of monitoring the water’s pH, conductivity, dissolved solids, suspended solids, and oxygen.

Aquaponics also requires extensive analysis of the nutrient balance of the water, they explained. The food for the fish provides a basic input of nutrients for not only the fish but also for the plants.

Once there is sufficient fish waste accumulated, the plants can be placed in the water, similarly as with hydroponics. The solid wastes of the fish are filtered out and only the nutrients and water supply connect with the plants.

Source: Maria Davila, assistant editor of Productores de Hortalizas, a Meister publication.