NE1017: Developing and Integrating Components for Commercial Greenhouse Production System
Statement of Issues and Justification
The goal of this project is to make significant advances in greenhouse production by improving the utilization of water and nutrients with related reduction in negative environmental impact, developing a control strategy for natural ventilation of greenhouses, and improving the integration of automation, plant culture and environment into a cost effective, sustainable production system for vegetables, specialty and floricultural crops.Greenhouse production, often called Controlled Environment Agriculture (CEA), is a high cost system for high-value crop production. This system allows production of plants out of season, provides for more efficient use of resources, and increases yields per unit area compared to tunnel or field crop production. It is also very dependent on advanced technologies and requires high-energy input. Detailed understanding of the interaction between physical and biological components within a CEA system is essential for successfully using advanced technologies.
Continued advancements are dependent on continued research to improve the understanding of the relationships and to use this information in improving the design and management of greenhouse systems. Decision-support models that link plant performance with environmental variables must be developed and then coupled with efficient, economic controls within an environmentally sustainable system. Because of the broad range of greenhouse designs, crops and differences in prevailing environmental conditions associated with different climatic zones, decision support systems are needed that are broadly applicable. Interdisciplinary cooperation of horticultural physiologists and agricultural engineers is needed to address this complex technology.
USDA Economic Research Service data (2001) show the size of the greenhouse/nursery industry in the US as $13,794,634,000, which was 6.8% of the value for all US commodities. Unfortunately, the data do not distinguish between greenhouse and nursery production. Nevertheless, the 2001 data shows that the greenhouse/nursery industry in the ten NE-164 member states generated approximately $2,418,738,000 in sales (approximately 17.5% of all sales in the greenhouse/nursery nationwide). Three of the ten member states (NJ, CT, NH) have greenhouse/nursery sales ranked the highest of all agricultural commodities within that state. It is clear that this segment of the agricultural industry is of significant importance throughout the NE-164 member states.
Most state experiment stations are ill equipped to individually address all of the problems associated with complex CEA production systems and the wide range of crops produced in these systems. Because of the limit on expertise and resources associated with individual stations and individual Hatch projects, multi-state research collaboration is the most appropriate means for approaching the problem of developing useful CEA decision-support systems that require input from multiple disciplines and replication over different climatic zones. The regional approach also allows collaborative research to be conducted at individual institutions with expensive, complex, or unique facilities, e.g. open roof, flood floor greenhouse at Rutgers and the hydroponic lettuce greenhouse at Cornell.
The NE-164 group has a strong history of collaborative research programs and years of collective experience on all aspects of greenhouse systems. The initial focus was on structural design and glazing systems (Roberts and Mears, 1969; Roberts, et al., 1985; Roberts, et al., 1989; Aldrich and Bartok, 1994) and environmental control [heating, cooling, and ventilation] (Aldrich and Bartok, 1994; Elwell, et al., 1984a and 1984b; Short and Breuer, 1985; Short and Bauerle, 1989). The subsequent focus was on crop production systems (Both et al., 2001; Giacomelli and Gottdenker, 2000; Giacomelli, et al., 1994b). A recent focus has been on greenhouse lighting by NJ, NY, and NH (Donnelly and Fisher, 2002a; Fisher and Donnelly, 2002).
NE164 members have conducted needs assessment from the stakeholders through several methods, including individual observations and discussions at grower facilities, tracking the issues related to questions, and discussions at various meetings. Based on grower inputs and evaluation of the skills and interests of members and the available facilities, the committee has identified three high priority topics to address over the next 5 years. They are (1) managing nutrients and water in greenhouses, (2) managing the aerial environment for greenhouse plant production, and (3) integrating sustainable and economically profitable systems and processes for the greenhouse industry. These issues are discussed separately in each of the following proposal sections. The objectives for these topics are all technically feasible based on current knowledge, past work, and available facilities.
Topic No. 1, Managing nutrients and water in greenhouses: One fundamental component of Controlled Environmental Plant Production Systems (CEPPS) is the nutrient delivery system (NDS). The NDS consists of the hardware components that transport nutrient solution (water and soluble fertilizer) from a central location to each individual plant according to predetermined specifications. Irrigation frequency and duration may be based on fixed time intervals determined from past grower experiences, or be more specific to plant demands, and be based proportionate to measured canopy solar radiation (Giacomelli and Ting, 1997) and plant responses to drought stress (Chen et al., 2002; Yang and Ling, 2002). Examples may include systems of drip irrigated rock wool culture for tomatoes or other large plants (Rorabaugh, et al., 2001; Ivey, et al., 2000), or aeroponic culture of small plants whereby the suspended plant root zone is irrigated with a nutrient spray (Hayden, et al., 2002).
Optimizing the management of nutrient concentrations, through control of electrical conductivity (EC), can ensure plants are only delivered the fertilizer concentration needed for healthy growth (Biernbaum, 1992), without risk of nutrient deficiencies or the potential for nutrient toxicities and fertilizer runoff that result from fertilizer over-application. Controlling nitrate-nitrogen runoff from greenhouses has been a primary focus of research (Biernbaum, 1992). The actual amount required by the crop is significantly less than is typically applied in commercial production (Yelanich and Biernbaum, 1994). Much of the excess nitrogen applied to crops grown with high fertilizer concentrations and heavy leaching can be lost into the environment. Soluble phosphate and heavy metal trace elements also are used extensively (Nelson, 1990).
Media pH has a major effect on nutrient availability and subsequent plant growth (Bailey, 1996; Peterson, 1981). Half of all nutritional disorders associated with bedding plant production can be attributed to pH-related problems (Nelson, 1994). Optimum pH varies among crop species, but is generally in the range of 5.8 to 6.2 (Warncke and Krauskopf, 1983). A low medium pH can lead to micronutrient toxicities, for example iron and manganese toxicity in geraniums (Nelson, 1994). Conversely, a high medium pH can lead to micronutrient deficiencies, for example, iron deficiency in petunias. Management of potting medium solution pH and micronutrient levels can reduce overall fertilizer load by ensuring that all applied nutrients are available for plant growth, and by avoiding the need to increase concentration of all nutrients (including NPK) in a complete blended fertilizer in order to correct deficiency of a single micronutrient (e.g., iron at high medium-pH; (Argo and Fisher, 2002)). Continued understanding of the relationships between pH and plant nutrient use is critical to optimizing the nutrient delivery to the plants.
Optimizing fertilizer and water management will reduce pesticide use. Excess fertilizer use and over watering often result in damage to plant roots, and provide ideal conditions for infestation with Pythium and other root-rot organisms, along with fungus gnat populations (Nelson, 1994). Infestations with these pest organisms can be devastating, and can require curative pesticide drenches. Application of fungicidal and insecticidal drenches is the current routine practice in greenhouse production, with monthly fungicidal drenches recommended for long-term crops such as poinsettia (Ecke et al., 1990). Management of the root zone environment (i.e., water and fertilizer) is recommended as the basis for integrated pest management approaches to this problem (Ecke et al., 1990; Styer and Koranski, 1997). The research to improve the plant root environment will reduce pesticide use while improving plant quality and growth.
In all watering systems, recycling of nutrient solution to eliminate contamination of the environment is possible, but such practices require a high level of management of nutrient concentrations and water supply. Closed irrigation systems pose several unique challenges: (1) a large storage container is needed to collect the drain water and to store the solution volume needed for the next irrigation cycle, (2) the system needs to be properly designed to prevent any leaks, (3) the potential exists for disease organisms to spread rapidly throughout the entire solution volume, (4) unwanted residues (e.g., from chemical applications) can accumulate over time, (5) nutrient settling and aeration, and (6) closed systems may be more expensive to install and maintain. Despite these challenges, many growers are highly interested in closed irrigation systems because of the belief that future regulations will restrict the practice of uncontrolled discharge of nutrient solutions to the environment. Growers are asking for systems that will recycle the nutrient solutions without risking the spread of disease while maintaining good nutrition management and avoiding toxicity. Particularly, challenges (3) and (4) will be further investigated as part of this project.
Without research on managing nutrients and water, growers are going to be forced into expensive waste water treatment systems, are going to face challenges of growing plants in less than ideal conditions because of limiting the use of nutrients and water, or be forced out of business.
Topic No. 2, Managing the aerial environment for greenhouse plant production: The aerial environment includes the temperature, light, relative humidity and airflow through the plant canopy. Ventilating greenhouses by replacing the warmer, higher humidity air with cooler, drier outside air is used as part of managing the aerial environment. The ventilation process is critical for cooling and for reducing humidity levels within the greenhouse. Reducing heat stress and the diseases caused by high humidity have a direct affect on the profitability of the greenhouse operation. Greenhouse cooling is essential for controlling the physiological response of a crop (MI, NY, NJ, CT). The process is more complex when insect screening is used (NJ). CO2 conservation is a dominant consideration (NY).
Early greenhouses used sidewall and ridge openings for natural ventilation to cool the air and reduce humidity. When energy was cheap, there was little concern about over ventilating since heat could be added to maintain temperature. As electricity became available, fan-ventilated greenhouses were developed. The control of the fans and heating systems has evolved as control technology has evolved. Today, several companies provide computer control systems that will operate the mechanical ventilation and heating system based on a variety of control strategies, sensor inputs from the plant area and weather station data.
The past few years have seen a major shift back to the installation of naturally ventilated greenhouses along with research to study proper design. OH is using a computational fluid dynamics program, FLUENT, to evaluate and illustrate the natural ventilation patterns and airflow rates of low cost, double poly, gutter connected greenhouse designs.
The modeling work has helped identify better designs for air inlets and outlets. The program requires too much time to run a simulation to be useful in the control of greenhouse openings. Ideally, the cross sectional area of the opening would vary in response to measured changes in wind direction and/or velocity and thermal buoyancy forces. Brocket and Albright (1987) developed a model for inlet control with natural ventilation based on the concept of neutral pressure level for animal housing. This model has the ability to make quick calculations. Therefore, it could be appropriate for control of natural ventilation systems for greenhouses. However, the model needs wind pressure coefficients for openings under various climatic conditions. These coefficients can be determined by using FLUENT. Combining FLUENT coefficients with the neutral buoyancy model will result in an improved model for natural ventilation control. Without this research, growers will continue to guess how to set greenhouse inlets with resulting decrease in plant performance from inadequate ventilation. They will also miss the opportunity for increased production from controlled airflow through the plant canopy.
Topic No. 3, Integrating sustainable and economically profitable systems and processes for the greenhouse industry: Sustainable, predictable crop quality can be achieved within efficient, cost effective well-designed greenhouses. There are many structural configurations, both in design and in dimensions, which encompass a wide range of environmental conditions. These systems contain many individual but interrelated components and processes. However, there are fundamental similarities in design requirements, physical components and production expectations that are necessary to establish an economically viable production system.
Light is a critical component of an optimum microclimate. The intensity of these wavelengths (400 - 700 nanometers) of photosynthetically active radiation (PAR) directly influences growth and development in green plants. Therefore, the properties of the greenhouse glazing and support structure are extremely important in greenhouse design. They are well understood and documented (Aldrich and Bartok, 1994; He et al., 1991; Lee et al., 2000).
However, natural PAR light levels often limit the photosynthetic activity of plants. Supplemental lights have been added to greenhouses to increase the light intensity and the length of light periods. While, some work has been done to improve proper use of lights, more research is needed to optimize the design and management of lighting systems for economical plant growth. Without this research, electrical energy can be wasted by over lighting or under lighting; therefore, expected plant growth is not achieved. At other times, the solar irradiance intensity is so high that the greenhouse overheats and the plant temperatures get so hot that plant growth is reduced. Under these conditions, shading to diminish light intensity within the greenhouse and at the plant canopy may increase production. More research is needed on the optimization of shading so that the growing season can be extended into hotter, brighter times of the year. Using shading to lengthen the production time for vegetables, such as tomatoes, will allow the grower to obtain more income from the original investment that is required to grow the plant to the production stage.
Greenhouse production is generally considered more efficient in water usage than field production. For example, approximately 2,400 kg water (on average) was estimated to be consumed to produce 1,000 kg harvest of tomato fruits in greenhouse, while 13,900 kg water was used per 1,000 kg harvest in field production (Castillo, unpublished), showing that greenhouse water utilization efficiency is 5.8 times of that in the field. In addition, greenhouse enables longer production seasons with more intensive production, and thereby, the annual yield per hectare in greenhouse can be more than 10 times than that in the field production. However, despite the high water utilization efficiency in greenhouse, the total water consumption per hectare per year in greenhouse can exceed that in the field production. Water usage in greenhouses is important since it has a potential impact on water resources, especially in states where water supplies are limited.
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