Plants thrive under moveable shade
2003 Arizona Agricultural Experiment Station Research Report

Written by Susan McGinley

The difference couldn’t be more dramatic: the basil plants in the ground outside look small and spindly compared to the luxuriant green and purple-leaved specimens growing in the retractable roof greenhouse. Part of a study exploring niche markets for fresh herbs, basil is one of several projects in progress inside this commercial grade facility at the University of Arizona’s Campus Agricultural Center in Tucson.

Inside the quarter-acre building, plants get the best of both sun and shade depending on prevailing conditions. Too much wind? Let down the side walls. Need more sun? Roll back the flat roof a little. Somewhat less enclosed than a regular greenhouse, the retractable roof greenhouse is the next best thing to being outdoors if you’re a plant, according to plant scientist Ursula Schuch. You get the ventilation and light while controlling for wind, too much sun, or cold temperatures.

“We can completely open or close the roof and side walls,” she says. “The roof is water permeable so rain can leak through slowly—unless it’s more than two inches per hour, which would be too much.” Water congregates along driplines in the spun polyethylene roofing material. Woven in two different thicknesses, the fabric provides 35 percent and 50 percent shade in an alternating arrangement down the length of the building. A black ground covering keeps out weeds and prevents crop roots from growing out of pots into the ground. Each of the six growing bays is 60 feet by 180 feet, enough to accommodate several rows of pots fitted with hydroponic tubing.

All of this flexibility gives faculty and students the chance to test herbs, bedding plants, shrubs, trees and vegetables using varying amounts of solar radiation and ventilation. They use gauges to check soil temperature and relative humidity around the plant canopy; computers regulate the timing and operation of the roof panel motors and also the amount and timing of irrigation and fertilizing.

Retractable roof greenhouses have been around for about 15 years but are still considered relatively new, Schuch says. Most growers install them in units of one to several acres, so this one is fairly small by industry standards. She and several graduate students thus are conducting experiments using the same technology available to the nursery industry, but their emphasis right now is on crops that are not currently grown in Arizona on a commercial scale.

The goal is to find out what grows well in desert retractable roof greenhouses and determine the best techniques for producing high-value crops in them. Workshops and tours are offered periodically to share research results with growers. Experiments are sponsored by different organizations. (see more in the PDF article)

More information is available with the PDF article "Retractable Roof Greenhouse Cultivation Offers Flexibility", published January 2004          ...download PDF

Stephen Kania, Research Specialist, Agricultural and Biosystems Engineering, CEAC
Cooperators: Dr. Merle Jensen, Dr. Patricia Rorabaugh, Dr. Gene Giacomelli
The Fertigator (Qcom Corp.) is a special purpose computer designed specifically to control fertilizer injection(and acid for pH control) based on measured environmental parameters. The parameters used in the CEAC Hydroponic Greenhouse are the light intensity outside the greenhouse and the electrical conductivity (EC), and hydrogen ion concentration (pH) of the input water.Other parameters that may be installed to increase the sophistication of the control include soil temperature, soil moisture content, air humidity, and water flow rate.

The irrigation cycles are initiated whenever the measured integrated solar radiation (400 - 1100nm) value exceeds a user-set threshold. This automatically compensates for days of high solar intensity when the plants require greater amounts of nutrient solution. A second user-set value regulates the maximum time interval between cycles, which can become important on warm but overcast days when the solar threshold is not often reached but plant needs remain moderate. The instantaneous solar radiation values are entered into a 30 minute 'sliding' average (as new values are added, the oldest values are discarded from the average). This average represents the solar intensity over time for each day. The purpose of a 30 minute average for control is to reduce variation of the value and thus the cycling rate of the equipment. Based on user-set threshold values, the EC of the solution provided the plants would be raised or lowered. The reasoning is that under low solar conditions the plants require less water relative to the nutrients in the water and so the EC is kept at a relatively high level. Under high solar conditions, more water is needed for transpiration to keep the plants cool relative to the amount of dissolved fertilizer, so the EC target is lower.

Pump injection and valve delays are available, to add flexibility for the system to interface with many types of irrigation scenarios. In the CEAC hydroponic greenhouse, local water pressure is sufficient for dripper function. Solenoid valves on each row of plants are activated, then the injectors begin to pulse at user-set frequencies. Injection is achieved with the use of compressed air. Calculations from the input water analysis (performed each year before the crop is started), and anticipated plant needs determine the stock solution composition and concentrations. Additional adjustments available on the Fertigator include milliliters of nutrient stock solution input per pulse, initial pulse rates, and irrigation cycle duration. This gives greater control over the absolute quantity of fertilizer that is injected per irrigation cycle.

Records of minimum, average, and maximum EC and pH levels during injection are retained for several days and can be viewed at any time. This is an important diagnostic for determining when an injector may have failed (usually due to air in the line with the injector subsequently losing prime).

Dr. Teena Hayden, Native American Botanics Corporation
Cooperators: Chris Pagliarulo, undergraduate student, Plant Sciences, Dr. Gene Giacomelli, Dr. Patricia Rorabaugh, Stephen Kania
Medicinal root crops like Echinacea and Burdock are under investigation to determine whether aeroponic technology can improve the quality, quantity, and cost efficiency of their production. Aeroponics is a form of hydroponics in which plants are grown with their roots suspended in a misted nutrient environment. Because aeroponic systems maximize the availability of oxygen to the roots, aeroponically cultivated plants can exhibit phenomenal growth. The technique also provides effective control over root zone, which is important when the desired products are chemicals within the roots. Root zone environmental conditions can be manipulated to maximize production of desired phyto-chemicals and not others, something impossible to do in soil.

Dr Chris Choi, Agricultural and Biosystems Engineering, CEAC
Cooperators: Stephen Kania, Dr. Gene Giacomelli. Dr. Chieri Kubota
A nominal 3.05 meter by 3.66 meter and 2.49 meter tall (10 by 12 by 8 foot) growth chamber is being constructed (inside area, 9.5 square meters). For maximum sensing and control capabilities, a commercially constructed insulated box (walls and roof only) will be used. All utilities and data acquisition and control systems will be added. The insulated box will stand upon a 0.76 meter high platform so that gravity-drain hydroponic systems can be installed beneath. The height above floor level also affords simpler and less visible installation of utilities, data signal and control conduits.

Environmental parameters that will be monitored and fully controlled include air temperature, air relative humidity, air carbon dioxide concentration, light intensity and duration, nutrient solution electrical conductivity and pH. The hydroponic nutrient delivery system will feature two separate systems which may be combined and fed from a single tank, or isolated and fed from separate tanks if different fertilization regimes are required. Type of nutrient delivery (drip, NFT, ebb/flood), cycling duration, flow rate, and frequency will be controllable. All liquid waste and runoff streams (hydroponic return water, bench overflow, system leaks, leachate (from soil-based systems), tank overflow, room drain, evaporator condensate water) will be controlled and collected to provide a totally contained structure.

HID lighting featuring remote ballasts to reduce growth chamber cooling load will be installed. Two light intensity levels will be available, with a maximum intensity of approximately 500 µMol m-2 s-1, roughly 25% of maximum outside solar radiation intensity. Lamp height and location will be adjustable to achieve the most uniform chamber intensity pattern, or concentrated for higher than design intensity over a smaller area.

Fail-safe systems will include auto-water-fill and overflow protection on the hydroponics tanks, dehumidification equipment lockout based on condensing coil condition, and carbon dioxide input lockout based on room concentration. The computerized control system will be interfaced with a PC and which will be able to be accessed remotely for monitoring and changes of control parameters.

Dr. Patricia Rorabaugh, Plant Sciences, CEAC
Cooperators: Dr. Merle Jensen, Dr. Gene Giacomelli, Dr. Chieri Kubota, Mr. Stephen Kania
The experiments serve a two-fold purpose: to educate the students about scientific experimental procedures; to provide information on a pertinent subject of interest to the industry.

Testing Rooting Medias for Commercial Application (1998-1999 and 1999-2000) The first two years the PLS 217 class was taught (1998 & 1999), several types of rooting media were tested including Rockwool, perlite, coconut coir, peat/vermiculite and urethane foam. There were no significant differences found among the different media treatments when plant growth and tomato harvest yields were compared. This indicates that a wide variety of rooting materials can be used with similar results.

Tomato Heat Tolerance Variety Trials (2000-2001 and 2001-2002) Over the past century the techniques of greenhouse hydroponic tomato production have been highly developed in northern countries (e.g., Holland, Great Britain, Canada). Most of the traditional tomato varieties were bred for these low light, low temperature regions. However, many growers are now moving to high light regions (e.g., SW USA, Mexico, Spain, etc.) where production can continue year around.

Furthermore, we have to teach our classes in Tucson, AZ, a high light, high temperature area. Therefore, for the past two years heat tolerant tomato varieties have been evaluated for their productivity (plant growth, fruit yield and fruit quality) in the Tucson environment with special interest on high air temperatures using a commercial type high-wire, Rockwool production system with drip irrigation. Two varieties tested that show promise for use in commercial operations are Raspodie and Mariachi.

Dr. Merle Jensen, Plant Sciences, CEAC
Cooperators: Armando Suarez, Graduate Masters Student, Agri & Biosystems Eng'r, Stephen Kania
Countries like Holland, England are the leaders in the development of greenhouse technology. However the worldwide use of such techniques involve the development of procedures adapted and economically interesting for each geographical specific condition. In this trial we are evaluating 30 varieties (red, orange, and yellow) of bell peppers from 4 seed companies, and 2 countries [Israel and Holland] for production and quality under high light, high temperature, low humidity (desert conditions, totally opposite to the average condition in Netherlands). Plants are grown following commercial standard procedures, with drip fertigation, and Rockwool substrate. Environmental conditions are monitored periodically and maintained strictly between the optimal range (18-25°C).

Ten sensors have been incorporated into the greenhouse growing system to measure environmental parameters at different locations, and to ensure the function of the environmental control equipment (heater, fans, evaporative cooler, carbon dioxide generator, psychrometers). Other important parameters (e.g. relative humidity, total moles of light received per day) are calculated from the measured data values and graphs detailing weekly system performance are prepared. Environmental parameters that are being monitored include: wet and dry bulb air temperatures at one quarter and three quarters of the distance across the greenhouse, dry bulb air temperature in the center of the greenhouse (where the greenhouse control systems sensor is located), temperature of the root zone, plant canopy, and fruit, Photosynthetic Photon Flux (PPF) at the top of the canopy, and carbon dioxide concentration of the air.

Five graphs are made from the measured data. The air temperature graph reveals high and low temperatures for each day and night (15 minute averages), which can also help determine the effectiveness of the heaters, fans, and evaporative cooler. The carbon dioxide (CO2) concentration graph shows fluctuations over time and is diagnostic for CO2 generator function. PPF measured in mole m-2 per day is in another graph, to show how the total amount of usable light changes seasonally. The relative humidity at the one-quarter and three-quarter location across the greenhouse is also graphed, to determine how it varies spatially.

Paula Costa, PhD Student, Department of Agricultural and Biosystems Engineering
Cooperators: Dr. Gene Giacomelli, Dr. Chieri Kubota, Dr. Patricia Rorabaugh, Stephen Kania
While monitoring various tomato plant growth parameters, it has been observed that certain growth characteristics can define the state of the plant as being more vegetative or generative, (relative amount of leaves and stem thickness vs. flowers and fruits).

Knowledge of this state of the plant in relation to the environmental conditions can indicate the near-future yield and fruit quality.

In the current phase of this study, various plant growth parameters for cv. Rapsodie, are being measured on a weekly basis. The measurements are performed with plants growing under different micro-environmental conditions present within the greenhouse during the plant fruiting cycle (November 2001- mid June 2002). Furthermore, relationships among plant responses, and the micro-environmental conditions, nutrition program and crop management system, under which the plants are growing, are being studied.

The objective is to define a set of growth characteristics for cv. Rapsodie, for arid and semi-arid climates such as Arizona, which can be used as indicators of the tendency for vegetative or generative development. The environmental parameters revealing strong correlations with the measured plant growth responses will be selected and used in a second phase studies, performed under a higher environmental control level. In this second phase, the selected environmental variables will be used as treatments in order to study in detail their individual and combined effect on tomato growth, yield and fruit quality.

Tomato plants cv. Rapsodie are to be subjected to different combinations of environmental parameters, the most important being temperature regimes, and relative humidity conditions. The long-term goal is to develop a decision support system for the grower in regions with similar climate conditions as Arizona by defining the set of causes and related measured effects on the plant growth patterns, yield, and fruit quality. This decision support system would have two components: 1) a long-term planning tool such as an empirical model for crop yield prediction, and 2) a short-term management tool based on several plant growth indices.

Dr. Gene Giacomelli, Department of Agricultural and Biosystems Engineering
Cooperators: Dr. Dan Barta, Mr. Phil Sadler, Dr. Chieri Kubota, Dr. Joel Cuello, Stephen Kania, Lane Paterson
High Pressure Sodium (HPS) and Metal Halide (MH) High Intensity Discharge (HID) lamps are currently being employed by NASA's Advanced Life Support (ALS) research program for controlled environment horticultural experiments. HID lighting generates substantial thermal loading in closed and semi-closed applications. Incorporation of water jackets around the lamp can remove over 75% of the heat generated. The long thin orientation of the HPS and MH double-ended lamps to be utilized in this study enables the use of a very close fitting water jacket, creating a more compact light, which lowers the growing systems profile and reduces equivalent systems mass.

The goal is to analyze the thermal and spectral characteristics of the double-ended, water-jacketed HID lamps within a test stand at the University of Arizona to further develop and deliver improved versions of the lamp for the purpose of implementation within NASA ALS applications, such as Station. The technical objectives are to: test the design concept; categorize the double-ended, water-jacketed 400 W, HPS and MH lamps; conduct a thermal analysis of the lamp and water jacket system; improve the lamp body and luminaire; and initiate longevity evaluation of the lamps.

Dr Chris Choi, Agricultural and Biosystems Engineering, CEAC
Cooperators: Dr. Gene Giacomelli, Efren Fitz, Chris Pagliarulo, Stephen Kania, Jennifer Jannusch
see www.ag.arizona.edu/CEAC
A Digital Learning Website for Controlled Environment Agriculture (CEA) has been established to bring data and real-time images from the off-campus hydroponic greenhouse to UA classrooms, growers, and researchers. The website presents plant growth within the crop production system and emphasizes learning by virtual observation. It complements the current classroom lectures and promotes asynchronous learning opportunities.

Real-time video broadcasting using web cams and historical time-series photo/video clips effectively demonstrates plant growth and physiological responses from within the hydroponic greenhouse. Automated nutrient feeding, climate control systems, and real-time microclimate data will be presented in the near future. The website greatly facilitates interdisciplinary teaching, research, and demonstration of the hydroponic crop production system located within the Controlled Environment Agriculture Center facility at the Campus Agricultural Center.

It is used as an informational library and networking tool not only for UA academic courses, but for Arizona community colleges, prospective commercial growers, industry supporters, educators, and worldwide CEA colleagues.

Dr. Anita "Teena" L. Hayden, Native American Botanics Corp. Tucson, AZ
Cooperators: Dr. Gene Giacomelli, Dr. Lindy Brigham (Department of Plant Pathology)
www.NativeAmericanBotanics.com
The research involves developing an aero/hydroponic hybrid horticultural production system optimized for rhizome crops. Ginger (Zingiber officinale) rhizomes will be grown in this system in a greenhouse using different aggregate media in association with an aeroponic spray chamber. This layered design will provide precise control of the aeroponic root zone while protecting the rhizome from the nutrient salt spray.

Ginger is generally propagated by dividing and re-planting rhizome pieces. Because of the increased risk of pathogen transmission in crops transplanted from soil to hydroponic systems, micropropagation techniques will also be investigated for increasing the number of clean, disease-free plants and rhizome pieces available for future studies. The micropropagation activities will occur concurrently with the design and testing of the aero/hydroponic production system.

Expected outcomes include a greater understanding of the role of temperature and light in ginger growth and a prototype horticultural system that can produce clean, consistent rhizomes for use as raw materials in the phytopharmaceutical industry.
Pilot project funded by the Arizona Center for Phytomedicine Research, College of Pharmacy, University of Arizona, Tucson, AZ http://acprx.pharmacy.arizona.edu.

Flash movie of the ginger growth

ceac : research : Current Research Collaborations and Projects