opening in the greenhouse (e.g. cracks and doors), therefore, it is likely that ..... An ebb and flood bench (2 m by 3m) covered with a black rubber liner was .... Columns A and J can be considered guard rows, as they are on the edge of the.
i
Supplemental Lighting Strategy for Greenhouse Strawberry Production by JOSHUA S. GOTTDENKER A thesis submitted to the Graduate School-New Brunswick Rutgers, The State University of New Jersey In partial fulfillment of the requirements For the degree of Master of Science Graduate Program in Plant Biology Written under the direction of Gene A. Giacomelli And approved by ____________________________________ ____________________________________ ____________________________________
New Brunswick, New Jersey May, 2001
ii
ABSTRACT OF THE THESIS Supplemental Lighting Strategy for Greenhouse Strawberry Production By JOSHUA S. GOTTDENKER Dissertation Director: Gene A. Giacomelli, Ph.D.
Using supplemental lighting within a greenhouse strawberry production system demonstrated the potential for increasing yields. A Controlled Environment Agriculture (CEA) greenhouse was used to issue four Daily Light Integral (DLI) treatments. Supplemental lighting accelerated fruit development, increasing early season yields in both the first (9/1/99) and second (12/29/99) planting. The plants were environmentally conditioned to initiate flowering. The environmental conditioning technique of Durner (1999) that was applied in a growth chamber, with a subsequent adaptive High Pressure Sodium (HPS) supplemental lighting strategy in a greenhouse, was highly effective means to initiate fruiting. Plants began to yield as soon as 59 days from transplant into the greenhouse. The procedure of night interruption (lighting for three hours at midnight with incandescent bulbs) was effective in encouraging petiole and inflorescence elongation and continuation of the reproductive response. An adaptive supplemental lighting control strategy was provided by computer control. The computer was programmed to operate supplemental lighting to achieve a daily light integral objective. Daily light integral (DLI) represents the summation of all
iii irradiance (Photosynthetic Photon Flux, PPF) that strikes a given area in an entire day. The supplemental lighting strategy (SLS) treatments aimed for 12, 9, and 6 moles of Photosynthetically Active Radiation (PAR, 400 – 700 nm) m-2 day-1 and were named SLS12, SLS9, and SLS6 respectively. The control treatment received only natural light and was named natural light. For the first planting, SLS9 produced greater early-season yields than the other SLS treatments. Between 9/1/99 and 12/29/99, the SLS9 treatment supplemented 154.5 moles PAR m-2 and produced an average of 137 grams plant-1 compared to the SLS6 treatment that received 79.4 moles of supplemental PAR m-2 and produced 118 grams plant-1. For the overall experiment, (9/1/99 - 5/30/00), the plants that were exposed to the SLS9 treatment received an average of 9.2 moles PAR m-2 day-1, of which 23% was from supplemental lighting. The SLS6 treatment (target of 6 moles PAR m-2 day-1) also received an average 9.2 moles PAR m-2 day-1. Due to inconsistent shade from overhead equipment and greenhouse and surrounding structures the SLS6 treatment received significantly more natural light than the other treatments. Thus less supplemental light was applied. Only 7% of the average DLI for the SLS6 treatment was from supplemental lighting. Given the identical average DLI, SLS9’s advantage in the rate of fruit development indicated that the spectral quality of the HPS lamps may have had a positive effect on the SLS9 treatment. Although the fruit from SLS9 developed more rapidly, SLS6 eventually yielded comparable overall average fresh fruit yield (300 and 330 grams plant-1) for the entire harvest window (between 10/29/99 and 5/30/00). The natural light treatment (natural light), which received an average of only 7.0 moles PAR m-2 day-1, ultimately produced the largest average fruit size (12.2 grams per berry) for the original
iv planting. The relatively low average DLI of the natural light treatment was due to shade cast by West wall and the ventilation window screening. The average yields per plant from SLS9, SLS6 and natural light for the entire harvest window were not significantly different, as determined by a Fischer’s protected LSD test (=0.05), however, the mean fruit size from the natural light treatment was significantly greater than the other treatments. SLS12 (target of 12 moles PAR m-2 day-1) achieved 11.2 moles PAR m-2 day-1 of which 20.9% was from supplemental lighting. Compared to the other treatments, the plants from SLS12 were most damaged by Pythium in the initial part of the experiment. In the later part of the experiment, when losses to disease were equal over all SLS treatments, SLS12 produced less than SLS9. These counter-intuitive results could not be explained and demand further investigation. It is suspected that adding supplemental lighting above the photosynthetic saturation point may have caused a physiological stress on the plants, which provided an advantage to the opportunistic fungal pathogen, Pythium. The results of the current investigations indicate that a cultural practice including the conditioning treatment developed by Durner (1999) and a supplemental lighting strategy aiming for 9 moles PAR m-2 day-1 would be best for the fall, winter, spring production period in the greenhouse in the northeast US. It may be advisable to limit the implementation of the supplemental lighting strategy to a select window of time or to a select portion of the facility, but this speculative concept requires repeated experimental confirmation before it can be conclusive. Supplemental lighting should be added during the day and an upper limit irradiance value based on plant photosynthetic saturation
v should be implemented to prevent ineffective use of supplemental lighting when the natural solar radiation is above 500 mol PAR m-2 s-1. This threshold value of 500 mol PAR m-2 s-1 was calculated based on canopy photosynthesis work published by Yoshida and Morimoto (1997) as well as information from Yoshida (2000). Bumble bees should be used for the pollination of flowers to produce high-quality well-shaped fruit. Supplemental lighting should be shut off before sunset to prevent disruption of the bees. Organic integrated pest management (IPM) should be used to protect the plants without endangering the bees with chemical pesticides. A properly monitored and controlled environment is required, including carbon dioxide enrichment, and a heating and ventilation system to ensure that night temperatures fall below 18 C, and to guard against temperatures above 30 C and below 10 C. (Oda, 1997)
vi
Acknowledgements A sincere thanks to the Bioresource Engineering Department. It seems that I may be the last individual to receive the departmental general assistantship, and for this support and the support for my travels to Spain, I am very grateful. To my advisor, Dr. Gene Giacomelli, for providing the opportunity and setting for an excellent learning experience and for your acceptance, assistance and advisement, I will be forever thankful. I will remember and revere our enjoyable times together both here and over seas. To Dr. Ed Durner, for providing my first strawberry plants, and much advise about how to keep them alive. To Dr. Joe Goffreda for his expert service as my academic track coordinator and committee member. To Mark Lefsrud for his consistent and reliable assistance throughout this endeavor. To the rest of the wonderful faculty, staff and students at BRE and Plant Biology, I wish you all the best and I appreciate the enjoyable times we were able to share and all of the help that you have provided. To my friends and especially my roommates for your support, assistance, tolerance, and much needed and enjoyable distraction. To my amazing parents, without you I would be lost. Your undying support, love, and encouragement are unparalleled, thank you for all of your gentle advice and enduring integrity. Last, but most certainly not least, to my JLZ, you are truly a treasure, thank you for all your support and love, please know that you are cherished. In an age full of power, greed and domineering, I have been blessed, you have all given me freedom and encouragement, devoid of judgment or constraint, and that is truly exceptional. Thank You.
vii
Table of Contents
ABSTRACT OF THE THESIS
ii
Acknowledgements
vi
Table of Contents
vii
Index of Photos, Tables, and Figures
ix
Chapter 1.0
1
Introduction
1.1 Background 1 1.1.1 Demand 3 1.1.1.1 Strawberry Quality and Value 4 1.1.1.2 Flowering and Fruit Production 5 1.1.2 Meeting the Demand for fresh Strawberries 6 1.1.2.1 Technology in the Field, in Protected Cultivation, and in Controlled Environments 8 1.1.2.1.1 Protected Cultivation 9 1.1.2.1.2 Propagation 10 1.1.2.1.3 Controlled Environment Agriculture 12 1.1.2.2 Sustainability – How closed is closed? 14 1.1.3 Supplemental Lighting for physiological and morphological plant response 18 1.1.3.1 Physiological implications of Supplemental Lighting 19 1.1.3.1.1 Photosynthetic Saturation 20 1.1.3.1.2 Adaptive Supplemental Lighting Strategy 21 1.1.3.2 Effects of irradiance on salable produce 22 1.1.3.3 Economic – Return on Supplemental Lighting Investment 23 Chapter 2.0
Objectives
24
Chapter 3.0
Materials and Methods
26
3.1 Experimental Facilities 3.1.1 Precision Growth Chamber 3.1.2 Controlled Environment Agriculture Greenhouse
26 26 27
3.2 Investigations 3.2.1 Supplemental Lighting for Daily Light Integral Treatments 3.2.1.1 Pre-Growth Chamber
28 28 29
viii 3.2.1.2 Precision Growth Chamber 3.2.1.3 CEA Greenhouse 3.2.1.3.1 Transplant and placement of conditioned runners into CEA GH 3.2.1.3.2 Nutrient Delivery System 3.2.1.3.3 Integrated Pest Management 3.2.1.3.3 Data Collection 3.2.1.3.4 Night Interruption 3.2.1.3.5 Supplemental Lighting Control Strategy 3.2.2 Planting Density 3.2.3 Economic Investigation Chapter 4.
Results and Discussions
30 31 31 33 33 35 36 36 40 43 45
4.1 Supplemental Lighting Investigation 4.1.1 Early Season Yield 4.1.2 Late Season, Original Plants 4.1.3 Late Season, Second Plants, HP 4-7, 2/2000 - 5/2000 4.1.4 Overall Harvest Window (Original Plants, HP 1-7, 11/1999 - 5/2000)
45 49 50 51 54
4.2
Confounding Factors
56
4.3
Data Discussion
59
4.4
Functional Photosynthetic Saturation Threshold
61
4.5 Economic Investigation 4.5.1 Strawberry Factory
64 69
Chapter 5.
71
Conclusions
5.1
Objective Attainment
71
5.2
Strategic Suggestions and Future Investigations
72
APPENDIX B – Greenhouse Daily Light Integral Data
80
APPENDIX C – Guard-Row Discussion
96
Acronyms
97
Literature Cited 98
ix
Index of Photos, Tables, and Figures Figure 1-1 Figure 1-2 Photo 1-1 Photo 1-2 Figure 1-3 Photo 1-3 Photo 3-1 Photo 3-2 Table 3-1 Figure 3-1 Table 3-2 Table 3-3 Table 3-4 Figure 3-2 Figure 3-3 Photo 3-3 Photo 3-4 Photo 3-5 Photo 3-6 Photo 3-7 Photo 4-1 Table 4-1 Figure 4-1 Figure 4-2 Figure 4-3 Table 4-2 Figure 4-4 Figure 4-5 Figure 4-6 Table 4-3 Figure 4-7 Table 4-4 Table 4-5 Figure 4-8 Table 4-8 Table 4-9 Table 4-10 Table A-1 Table A-2 Table A-3 Figure A-1 Figure A-2 Figure B-1 Table B-1
The distribution of farmland in the U.S Strawberries are the third most valuable Non-citrus Fruit Perfect berry ripe for harvesting. Ugly berry Distribution of Strawberry production in the US A California field worker harvesting strawberries Cut runners being conditioned CEA Greenhouse The Conditioning Treatment. Environmental Setpoints Plant placement and position on GH bench IPM biological control organism release calendar Daily light integral objectives for each of four treatments Irradiance output from HPS lamps The most difficult type of day for the SLS system Density Study Layout Density Study with screening border Line meter above canopy, facing up Line meter below canopy, facing up Line meter without screening, facing sideways Line meter with screening, facing sideways Early Season advantage of supplemental lighting Harvest Data Divisions Yield per Original Plant for HP1-HP3 Yield per Original Plant for HP4-HP7 Supplemental Light Integral and Cost (Second Plants) Average Yield Per Second Plant Yield per Second Plant for HP4-HP7 Accumulated Yield per Second Plant for Each Treatment Supplemental Light Integral and Cost (Original Plants) Average Yield Per Original Plant Accumulated Yield per Original Plant Average Fruit Size for the original plants Average Fruit Size for the second plants Estimated rate of PS Typical Retail Prices per 12 oz. Pint The "break-even" price for the original plants The "break-even" price for the second plants Average Day/Night Temperatures (°C) by Month Overall Average Day/Night Temperatures (°C) Average Air Temperature Distribution CO2 and ppf in the growth chamber Temperature and RH in the growth chamber DLI appendix Chart Explanation DLI and SLI averages and proportions
1 2 4 4 6 9 27 28 30 31 34 37 38 39 41 41 42 42 42 42 47 48 49 50 51 52 53 53 54 54 55 55 55 61 67 68 69 78 78 78 79 79 80 81
1
Chapter 1.0 1.1
Introduction
Background As integral as agriculture is to the sustenance of the human race, it is must still
remain viable as a business. However, agriculture is a business that has a distinct, inherent importance over all other business, which is embodied in the simple fact that, for humans, starvation is the alternative to growing food. There will be a day, possibly in the not so distant future, that this issue will manifest itself in magnitude that is
Figure 1-1. The distribution of farmland in the U.S. implies that the densely populated Northeast region must obtain food from other regions (NASS, 1999). not ignorable. On this day society will be forced to change its focus and priorities towards a concerted effort to feed the world in a sustainable manner. By this I mean, a
2 manner in which food is provided without environmental detriment and ecosystem destruction, and where the natural cycles of the earth are respected and even enhanced. The Food and Agriculture Organization (FAO) of the United Nations has already begun to push agricultural projects that encourage “greater community participation” (FAO, 2000). This type of group effort is assumed to be necessary in developing nations to create a viable agricultural system. Although capitalistic society has brought much apparent wealth and convenience to the American lifestyle, it is quite obvious that we do not actually take responsibility for providing our own nutrition. Especially in the Northeast United States (see Figure 1-1), the supermarket is as close as most consumers get to a farm. Just as with any economic system, demand in the marketplace drives a supply system to produce.
Figure 1-2. Strawberries are the third most valuable Non-citrus Fruit (NASS, 2000a)
3 1.1.1
Demand Strawberries (Fragaria Sp.) are far from being a staple crop, but the California
Strawberry Commission surveys (Anonymous, 1999) claim as many as 94% of families in the US purchase and consume strawberries. The wealth of society and the widespread fondness of strawberries have put this “luxury crop” in high demand. The following information, obtained primarily from a 1995 USDA Economic Research Service statistical bulletin (Bertelsen, 1995), indicates the importance of the strawberry as a US farm crop. -
Americans consumed 5 pounds of strawberries per capita in 1993, up from 3 pounds in 1970
-
Between 1970 and 1993 U.S. production increased (+290%), both total consumption (+100%) and exports (+300%) increased, and imports (-75%) decreased
-
Strawberries are the third most valuable non-citrus fruit at $1.12 Billion in 1999 (Pollack et al., 2000; NASS, 2000a) (Figure 1-2)
1.1.1.1
Strawberry Quality and Value
4 In general, the expression of biological characteristics is governed by both genetics and environment. The quality of a strawberry fruit is no exception. Size, shape, flavor, aroma, texture, and color are all characteristics that make up the physical quality of a berry. Of course, different consumers will prefer different characteristics, but typically, Photo 1-1 A perfect red berry ripe for harvesting, beside a developing shiny dark red berry is more appealing and desirable than a secondary berry. tiny, misshapen, bland, mealy, dull, anemic berry. Even plants of an superior cultivar a large, smooth, sweet and flavorful, fragrant, juicy yet firm,
with the genetic potential to consistently grow top-quality berries, will not realize that potential if the microenvironmental parameters supporting the growth of those plants are not maintained within acceptable levels. Photo 1-2 Ugly berry Strawberry consumers who do not grow their own and are not located in close proximity to a production farm are likely settling for a drastically poorer quality product than the consumers who have the luxury of purchasing locally grown berries. Berries that are picked ¾-ripe will have a shelf life of up to seven days, but will have poorer overall quality (flavor and texture), lower vitamin C and sugar content and higher organic acid content, than berries that are picked fully ripe. Such berries last a maximum of 3 days after pre-cooling, transport and cold storage. (Mokkila et al., 1997) The quality characteristics discussed above are not the only factors affecting the value of strawberries. As consumers are becoming more conscious of the issue of sustainability, some seek out products that were produced by sustainable and organic
5 methods. Major supermarkets now offer organic foods in addition to traditional foods. Although not all organic foods are produced by sustainable methods, some consumers pay premium prices for these organic products because they want to support their belief in sustainability and some prefer that their food be grown without chemical pesticides and fertilizers. Knowing the range of production methods permitted to adorn a particular label (e.g., “organic”) will empower consumers to purchase foods that are produced by methods that are consistent with their individual beliefs. In many cases, the use of inorganic fertilizer solution would exclude a hydroponically grown crop from being labeled organic. However, there may be consumers who would much prefer a crop grown hydroponically to a crop that was fertilized with municipal sewage sludge, which is certified organic. Perhaps more specific labeling should be used to encourage the consumers to make better-educated decisions.
1.1.1.2
Flowering and Fruit Production The branching of a typical inflorescence (i.e. a branched stem full of flowers) has
one primary, two secondary, four tertiary, and eight quaternary flowers. However, different varieties have different types of inflorescences and even any one variety may have many types depending in part on the geographic location of its culture. Primary and secondary strawberries from each inflorescence tend to be the largest and the highest quality. Plants will tend to produce higher quality fruit, earlier in their first year of production, while larger, older plants (second and third year of perennial culture) are more susceptible to disease (Meesters and Pitsioudis, 1997).
6 Consumers demand strawberries year round. At certain times of year, there are distinct niche markets that could consistently secure elevated prices. The winter holidays are a prime example. High quality strawberries are very rarely found in the supermarkets of the Northeastern U.S. during the autumn and early winter months. Another demand that could be met by strawberry growers, is the demand for high quality strawberry plants. Other commercial growers who are not able to produce their own healthy runner plants each year are reliant on suppliers. Garden centers also carry strawberry plants, but there is plenty of room for improvement both in the window of time that these plants are available and the quality of these plants.
Strawberry Production California 80%
Others 4% Tri-State 2%
Oregon 4%
Florida 10%
Figure 1-3. Distribution of Strawberry Production in the U.S. by state. (Bertelsen, 1995) Tri-State refers to New Jersey, New York and Pennsylvania combined. 1.1.2
Meeting the Demand for fresh Strawberries Meeting the demands of consumers is the primary objective of strawberry
production. There are many methods for doing so, some more technologically advanced than others. The following subsection will describe several of the methods used to culture strawberries. Culture methods will first be discussed based on their technology
7 level, followed by general environmental impact considerations. A given culture method may only be economically viable for implementation within a particular supply system if it is capable of producing a sufficient quantity and quality of fruit to meet the specific target-market’s demands. Bertelesen’s statistical bulletin (Bertelesen, 1995) provides most of the following information about the strawberry supply system: -
Nearly 80% of the 1.4 billion pounds of strawberries produced in the US in 1993 were grown in California
-
The remainder of the distribution is shown in Figure 1-3
-
US spring acreage is up 4% from 1999 and 5% from 1998. (NASS 2000b)
-
Since 1970, California’s per acre yields have increased by one-third to 45,000 pounds per acre, which is nearly double the national average. The drastic increase in production per unit area is attributed, primarily, to the
adoption of annual methyl bromide soil fumigation and clear polyethylene mulch techniques (Bertelsen, 1995). In 1993 the Clean Air Act declared methyl bromide an ozone depleting compound. (CDFA, 2000) The EPA plans to limit the amount of methyl bromide produced or imported by 50 percent in 2001 and by 70 percent in 2003. (EPA, 2000) Viable pathogen control alternatives must be found, as yields can be expected to decrease without methyl bromide.
8 1.1.2.1
Technology in the Field, in Protected Cultivation, and in Controlled Environments In order to be a successful grower, it would be beneficial to have a working
knowledge of the important parameters that constitute the plant microenvironment. It is important to know the range of conditions that are considered optimal and how deviations from this range of conditions will affect plant growth and production. Once this knowledge is obtained, the grower can adopt affordable methods of modifying the plant microenvironment in an effort to maintain optimal plant production conditions. A simple way to categorize agricultural systems into technology levels is to define production practices as part of traditional field, protected cultivation, or controlled environment (CEA) agriculture. A field system is one that uses no structural materials to change the plant microenvironment. A low-tech field system could be called simple if no intervention is employed other than planting and harvesting. A high-tech field system could be called precise if measurements and experience are used to make decisions about the controlled application of fertilizers, pesticides and water. Of course, there exists a technology gradient between simple agriculture and, what is termed, precision agriculture. Different methods of measurement and application can foster greater precision, often at greater expense. In an economically driven system, the primary factor in the decision to upgrade the technology level of a crop production system the potential to consistently provide an attractive return of investment. An example of a simple field system need not be extensively discussed, as it consists simply of plants and soil. In an ideal location with ideal natural conditions, a simple system has the potential of producing comparable quantities of high-quality fruit
9 as a multi-million dollar, precisely controlled greenhouse system. What this simple system does not have is the ability to continuously control the plant microenvironment to ensure optimal conditions for production. Adding cultural practices such as fertilization, irrigation and pest control can be done in many ways, organic or chemical, environmentally responsible or not, precise or less than precise. 1.1.2.1.1
Protected Cultivation
Protected cultivation can be a moderately expensive, for both capital and operating expenses, but also a technically effective way to increase returns. Many systems use “plastic mulch” to warm the soil, reduce weeds, and affect light reflection. Plastic mulch is a thin film of plastic placed on the ground, and the seedlings are transplanted through holes in the plastic. Photo 1-3. A California field worker harvesting strawberries
This technique usually requires drip/trickle irrigation for providing nutrients and water and can provide good plant protection from soil borne diseases. The
California ‘annual’ system couples this plastic mulching and drip irrigation technique with yearly soil fumigation and an excellent natural climate to produce 80% of the berries in the U.S. Photo 1-3, of the field worker, shows the plastic covered rows (bottom left corner) used in a majority of California’s culture systems. It also indicates the difficult working conditions required during harvest. Simultaneous crouching, bending and foraging is ergonomically incorrect and can lead to chronic body pain (Schlosser, 2000).
10 Unheated polyethylene covered tunnels are another example of protected cultivation. Radajewska and Dejwor (1997) describe a system where black plastic mulching and low-tunnel polyethylene row covers are combined. With these systems, as in the California field systems, first-year plants produce the most attractive fruits. Although perennial culture leads to greater ‘total yields’ and larger fruit, it is not always advisable due to delayed yields and disease and quality issues (Meesters and Pitsioudis, 1997). Polyethylene row covers costing $3,000 to $4,000 per hectare can last for at least three seasons and provide frost protection leading to increased early-season yields. Frost protection can be accomplished when precision sprinkler irrigation is employed with or without row covers, but drip-irrigation showed negligible benefit for frost protection (Hochmuth et al., 1993). Frost protection techniques can positively affect total yields as well as timeliness, which are both very valuable.
1.1.2.1.2
Propagation
Breeders tend to select cultivars that are homogenous for desirable traits. The concept of polyploid heterozygosity refers to the difficulty of doing so in species with more than two copies of each chromosome (i.e. polyploid instead of diploid). The presence of multiple copies of a chromosome makes breeding a homozygous individual much more difficult. Strawberry plants are octoploid (have eight copies of each chromosome), which makes seed propagation extremely impractical due to polyploid heterozygosity. The lack of cultivars that are homozygous for desirable traits leads to excessive variability in seed-borne offspring. The alternative is vegetative propagation, which happens to require little effort and is effective due to the tendency of strawberry
11 plants to grow vegetative offshoots called runners. Runner plants (vegetative offspring), can be propagated by conventional cuttings or by In Vitro micro-propagation (tissueculture) (Dijkstra, 1993). Micro-propagation can be an effective way to produce disease free plants for use as mother plants (plants that produce runners) (Turemis et al., 1997). Use of micro-propagated plants as commercial plug plants (rooted runners sold in plug trays) is not considered ideal. Hyperflowering, small flowers and variable fruit and plant sizes are all problems associated with using first generation micro-propagated plants for commercial production (Szczygiel and Borkowska, 1997). Lopez-Aranda et al. (1997) determined that there were no differences in commercial runner production from mother plants which were propagated using different multiplication methods over two years of study. However, differences may not be noticeable until viral and bacterial diseases begin to build up in third and subsequent generation runners from conventionally propagated plants. In Vitro propagation (sterile meristem culture) has the capability to produce disease-free mother plants, which are suspected to produce healthier and “cleaner” (more disease-free) offspring. Of course, the health of the runner plants depends not only on the health and genetics of the mother plants, but also on the environment in which they are raised. Many Dutch and Belgian systems plant cold-stored, or “frigo” plants. Before cold storage, frigo plants can be full sized plants, runners that root in soil and are dug, or runners that are cut and rooted under mist into sterile media. Lieten and Goffings (1997) showed that a cold storage air temperture of -1C was optimal for plants of the cultivar ‘Elsanta’ that were dug in December and cold-stored until planting in July. The
12 productivity of these frigo plants has been shown to be positively correlated with their size (Faby, 1997). Meesters and Pitsioudis (1997) described Belgian cultural practices for the dayneutral cultivar ‘Selva’. Autumn planting of freshly rooted runners led to higher yields than frigo plants planted in spring. Also plants that were potted before transplanting yielded 12% more than bare-rooted frigo plants. Fruit harvest was shown to be earlier on black plastic mulch or in plastic tunnels and greenhouses. Mowing instead of manual flower removal was an effective way to delay harvesting as long as the spring temperatures did not fall too low.
1.1.2.1.3
Controlled Environment Agriculture
Combining precision agriculture techniques, protected cultivation, and careful environmental control results in controlled environment agriculture (CEA) (Ting and Giacomelli, 1992). The most effective way to optimize the growth and yield of a plant is to precisely control the micro-environment surrounding that plant. Greenhouses and growth chambers are the common structures used to grow crops in CEA systems. One primary advantage of greenhouse culture is air and root zone temperature control. Using a greenhouse that has the ability to maintain air temperature at a desired set point enables crop production throughout the cold season. Precise temperature control is often used to condition plants in an effort to elicit a specific response. Implementing shading, ventilation and evaporative cooling during the warmer months can protect plants from over-heating. During periods when ventilation will be infrequent, CO2 enrichment can boost photosynthesis rates. For strawberry, optimum levels for CO2
13 enrichment are reported to be between 700 and 1000 ppm (Oda, 1997; Yoshida and Morimoto, 1997). Humidity control is possible, however dehumidification is much less practical due to cost. Fog emitters and evaporative cooling pads offer both cooling and the potential to increase humidity. Pest exclusion is another important aspect of greenhouse crop production. However, a greenhouse is not an airtight structure. To allow air exchange for cooling and air moisture reduction, many greenhouses are equipped with vent windows and some also employ fans for forced ventilation. If a vent window is not screened, insects and fungal spores will find their way into the greenhouse. The vent window is usually not the only opening in the greenhouse (e.g. cracks and doors), therefore, it is likely that these pests will find their way in regardless of screening. Depending on how accessible a given greenhouse is to pests and depending on the prowess of the grower at combating pests, various levels of disease and infestation may be seen in different systems. Integrated Pest Management (IPM), has been shown to be effective in the pest control for greenhouse strawberry culture. Sterk and Meesters (1997) specifically mention success with predator mites (Amblyseius californicus) for two-spotted spider mite (Tetranychus urticae) control and Encarcia formosa for whitefly (Trialeurodes vaporiorom) control. An additional benefit of chemical-free pest control is that bumble bees can be used for pollination without the risk of killing the bees with pesticides. In addition to air temperature, CO2, and pest concerns the plants need water and nutrients. Hydroponic nutrient delivery systems (NDS) are often employed within a greenhouse to provide a solution of essential nutrients in water. The plants can be grown in many types of media. Perlite, a popped volcanic glass, is an excellent choice of media
14 for hydroponic strawberry culture, as it provides a recyclable, light weight, porous medium that retains moisture and air while it is also non-compacting (Stirling, 1997). In the traditional Belgian system, as described by Lieten (2000), high quality plants from the outdoors are transplanted into peat bags in late summer. The bags are placed on high benches in glasshouses and drip fertigated, while the bottom of the bags are slit for drainage. Berries are harvested 90-100 days after transplant and subsequent plantings with fresh or frigo plants are performed to target different harvest windows. The short-day cultivar ‘Sweet Charlie’ (Fragaria x ananassa Duch. cv. Sweet Charlie) is known to produce “distinctively sweet” fruit significantly earlier than many other cultivars, including ‘Oso Grande’ (Chandler et al., 1997). Durner (1999) has shown that pre-conditioned ‘Sweet Charlie’ transplants, grown in vertical PVC pipes filled with perlite (32 plants m-2), can produce an average of 368 grams of fresh fruit per plant between December and April, when planted in a polyethylene covered hoop house in late August in New Jersey. These plants were grown with 6 hours of high intensity discharge (HID) supplemental light (one, 1000 W Metal Halide lamp per 4 m2) each day from 02:00 AM to 08:00 AM to provide long day conditions necessary for fruiting and petiole elongation throughout the winter season. However, other than demonstrating feasibility of using supplemental lighting, no indication of optimum irradiance or photoperiod were determined.
1.1.2.2
Sustainability – How closed is closed? The viability of a system should not be determined strictly by its ability to
produce a profit. The word sustainable is defined by (Webster’s Online Dictionary) as:
15 1: capable of being sustained 2a: of, relating to, or being a method of harvesting or using a resource so that the resource is not depleted or permanently damaged b: of or relating to a lifestyle involving the use of sustainable methods . Although not included in this definition, the issue of environmental impact of human action has more recently been integrated into the meaning of sustainability. In addition to consuming resources conservatively and responsibly, a sustainable system must be designed to minimize detriment to the environment. This concept is all encompassing, as environmental concern begins with the manufacture of materials used within a system, and it carries through to production practices including energy usage and waste discharge methodologies. Some of the common materials used to construct a greenhouse and crop production system are plastics (such as: polycarbonate, polyethylene, PVC), glass, metal, and wood. Evaluating the sustainability of each material’s manufacturing process system is beyond the scope of this study, but should not be ignored in the long term. The durability of a material can determine its longevity. When a material has degraded beyond utility, the ability of that material to be recycled and the ramifications of disposal must be considered. Polycarbonate contains bisphenol-A (BPA), a compound that has been shown to induce estrogenic responses (Feldman 1995). The long-term effects of BPA discharge into the environment, and the typical quantity of this compound in polycarbonate production plant effluents certainly deserve investigation and can be considered to affect the sustainability rating of a system that uses polycarbonate. Although a detailed environmental impact analysis will not be found within this thesis, the above example is given to show that discharging effluent into the environment
16 can impact biosystems. When hormone mimicry is considered, the quantity of a chemical that is needed to affect an organism is extremely small. Analysis of effluent for such minute amounts of compounds is futile, especially since more and more such compounds will likely be discovered in the future. Environmentally conscious engineers have already begun to design systems that do not discharge effluent. Such systems are referred to as closed systems. Most systems are designed as semi-closed, as effluent is discharged, but at a lowered rate or decreased frequency. A truly closed system is currently less economical, and is thus not often implemented. This is likely to remain true in agriculture as in industry, until a policy is implemented to adjust taxation based on the sustainability rating of a production system. The excessive application of chemical fertilizers and pesticides can result in chemical run-off. The ultimate sink for these chemicals cannot be known nor can all of their far-reaching effects be known. Environmentally responsible agriculture is just as important as environmentally responsible manufacturing plant design and management. Agricultural systems can employ various techniques to decrease chemical run-off. In a field agriculture situation precision techniques are implemented to measure environmental factors and apply chemicals via an adaptive strategy. A prime example of an adaptive chemical application strategy is to use the measurement of humidity, rainfall and temperature to make decisions when to apply fungicide based on knowledge and modeling of the lifecycle of a fungal pathogen. In addition to controlling the frequency of applications, it is also possible to precisely control the quantity and location of each application. Erecting protective structures, such as insect screening, can decrease the need for insecticide application, increasing environmental responsibility.
17 Controlled environment greenhouse agriculture, offers perhaps the greatest opportunity for a grower to be environmentally responsible. However, this responsibility does not come automatically when a greenhouse is erected. In addition to the materials manufacturing, chemical leaching and off-gassing issues, cultural practices must be carefully considered. An entirely environmentally benign CEA system would need to be completely airtight and water-tight, allowing zero effluent discharge. The greenhouse would need to be constructed of materials that were manufactured in closed, environmentally benevolent systems and these materials would need to be 100% stable so that no harmful off-gassing or leaching would occur once the greenhouse was erected. Materials would also need to be durable and 100% recyclable. The perceived value of implementing such a system has not yet overcome its exorbitant cost, as such structures do not exist. The characteristics of the structures and systems that were used for this investigation are discussed in the following chapter. The purpose of the previous discussion comparing an ideal, benevolent CEA system to a less environmentally responsible field system is to introduce the concept that cultural practices can affect the environmental impact of the system. Even high-technology CEA systems can be designed and managed irresponsibly if the well-being of the environment is considered low on the priority list. One way to decrease or eliminate nutrient solution run-off is to implement a recirculating nutrient delivery system (NDS). Ebb and flood and nutrient film technique are two examples of recirculating NDSs. Although recirculating systems tend to decrease run-off, they can also cause crop production problems. Several fungal root pathogens,
18 such as Pythium sp., propagate via water-borne flagellate spores (Agrios, 1997). Recirculating NDS systems offer these spores repeated opportunities to infect roots (Stanghellini and Rasmussen, 1994; Hockenhull and Funck-Jensen, 1983). 1.1.3
Supplemental Lighting for physiological and morphological plant response Plants use light as a source of energy, as well as, a developmental signal. CEA
growers often amend the natural light (natural light) by employing supplemental lighting to elicit a specific growth response from the plants. High intensity discharge (HID) lamps have proven to be most economical for providing photosynthetically active radiation (PAR), which is within the 400-700 nm waveband. Metal Halide and High Pressure Sodium (HPS) are two examples of HID lighting. If a long-day photoperiodic response is desired, incandescent bulbs can be used to provide a night interruption (NI) treatment (Runkle et al., 1998; Durner et al., 1984). A light integral is the mathematical summation of the amount of radiant energy (irradiance) that has accumulated over a unit of time. Irradiance is measured in incident energy per unit area per unit time (e.g. mol (PAR) m-2 s-1 or Watts (PAR) m-2 s-1 ). The measurement of light energy can be limited to PAR or include the total waveband of sunlight, 300-1100 nm) . A daily light integral (DLI) (Nui et al., 2000) is frequently measured in moles of PAR m-2 day-1. In a system where supplemental lighting is used in addition to natural light, such as the greenhouse, the DLI will be equal to the summation of the natural and supplemental light received per unit area.
19 1.1.3.1
Physiological implications of Supplemental Lighting As plants are phototropic, light is their primary source of energy. Plants use
energy from photons of light to charge ADP and NADP molecules into their high-energy counterparts ATP and NADPH. The energy that is temporarily stored in ATP and NADPH is later used to fix carbon and synthesize sugars, which are in turn used to produce plant structures and facilitate chemical processes (Taiz and Zeiger, 1998). It is specific structures produced by the plant that the grower hopes to harvest. The day-length (i.e. the number of hours of the daily photoperiod) has been shown to have very strong signaling effects in plants (Garner and Allard, 1920). The morphological decision to flower is often times elicited by changes in phytochrome status, which is influenced by day-length (Taiz and Zieger, 1998). The ‘Sweet Charlie’ strawberry has shown to be an atypical short-day plant. It requires a short-day induction period with cool nights, to initiate the flowering response. However, a continuation of short-day conditions will foster a very compact plant with short petioles and inflorescences, which is unfavorable for optimum light interception and inconvenient for harvesting (Durner, 1999). With the use of supplemental lights, it is possible to follow a short-day induction period with long days. HID lamps can be used to simulate a long-day in the winter months, by adding photosynthetically active radiation for several hours before sunrise and continue past sunrise, or prior to sunset and continue into the night. An alternative strategy is to use incandescent bulbs to provide night interruption (NI). NI has been shown to induce the long-day response of plants, with reduced capital and operating costs relative to HID lamps (Durner et al., 1984).
20 Spectral efficiency is a calculated coefficient that provides a relative value for light efficiency from a particular source, and it is based on the comparison of the spectrum of light that plants require for photosynthesis and the spectral composition of the light source. Spectral efficiency is defined as the ratio of the spectral output of a light source multiplied by McCree’s quantum weighting factors, divided by the number of photons between 400 and 700 nm. (Bugbee, 1994) Curiously enough, HPS lamps have a higher spectral efficiency than sunlight, .95 and .88 respectively. This does not mean that HPS lamps are an entirely preferable light source to the sun, as the intensity and full spectrum of PAR from the sun are certainly important factors. Since light plays such an important role in building the desired plant structures, it may be valuable for a grower to include supplemental light into the greenhouse production system. The primary questions then become: What are is the optimal ranges for the intensity and the duration of application of the supplemental light. Basic plant physiology can help answer those questions.
1.1.3.1.1
Photosynthetic Saturation
As the irradiance increases, assuming that other environmental factors are not limiting, the rate of photosynthesis will tend to increase, but only within a range of irradiance values. There is a minimum value for photosynthetic compensation (i.e. the irradiance value where the plant respiration is equal to photosynthetic production) and a maximum value, which is saturation (i.e. the irradiance value where the plant or leaf photosynthetic rate is at a maximum).
21 There have been conflicting values published for leaf and canopy light saturation values in strawberry. Generally, a study will report the relationship between photosynthesis and irradiance at multiple CO2 levels in graphical form. As the curve produced by the relationship of CO2 consumption versus irradiance ‘flattens out’ (i.e. for a given increase in irradiance, there is an insignificant plant response) at higher irradiance values, the plant is considered to be approaching light saturation. The value for photosynthetic saturation can be used along with the known irradiance provided by supplemental lights to determine a functional photosynthetic saturation threshold. This threshold can be used to prevent the operation of supplemental lights when they will not make a significant contribution to the growth of the plant.
1.1.3.1.2
Adaptive Supplemental Lighting Strategy
An adaptive control strategy, which uses real-time measured incident irradiance to make decisions about the operation of the HID lamps has the potential of saving operational expense (Humphreys, 1995). Implementation requires light sensors and decision-making electronics. Such a strategy should include a “cut-off point” so that it will automatically prevent adding supplemental lighting when natural irradiance is approaching the functional photosynthetic saturation. Excessive radiation on a leaf will also increase the temperature of that leaf, which will increase the transpiration demand, in turn increasing the demand for water absorption from the roots. Thus, adding light above the saturation point places physiological pressure on the plant, in addition to wasting electrical energy. This pressure not only demands that the plant allocate energy to dissipating the surplus heat and light (Taiz and Zeiger, 1998), but also the resultant stress
22 creates opportunity for looming pathogens to attack and hinder plant growth and development (Agrios, 1997). A viable supplemental lighting strategy will add light only when that light will make a significant physiological contribution, positively affect commercial yield, and provide an adequate return on the operational and capital expenses.
1.1.3.2
Effects of irradiance on salable produce Determining an effective supplemental lighting scheme is a first step in
developing a system of cultural practices that can optimize production. The physiological effects that light has on plants suggest that fresh fruit yield will be affected by DLI. However, just as a plant leaf can only accommodate a certain instantaneous irradiance (saturation), it is assumed that linear increase in DLI will not perpetually result in a linear increase in fresh fruit yields. Just as it is useful to know how a range of instantaneous irradiances will affect the photosynthesis rate of a leaf and canopy, it is important to know how a range of DLI will affect the ultimate fresh fruit yield. The structure of the canopy will affect the ability of the plants to accommodate higher light irradiances, for example, taller canopies saturate at higher irradiances (Bugbee, 1994). Strawberries have a very shallow and rather sparse canopy (low leaf area index) in a horizontal bench-top system (Yoshida and Morimoto, 1997). In a taller canopy (e.g. tomato) there are several lower levels of leaves that can intercept the irradiance that transmits through the upper leaves. These lower leaves are protected from the heat energy by the shading and transpiration of the upper layer of the canopy and are able to photosynthesize with the lower intensity light that filters down to them.
23
1.1.3.3
Economic – Return on Supplemental Lighting Investment HID lamps are very expensive, both to install and to operate. 400 Watt HPS
ballasts and lamps cost between $150 and $300 (U.S. 1999) per fixture. One 400 Watt HPS lamp is required for every two square meters of bench-top area to provide 90 mol PAR m-2 s-1 to a canopy located two meters below. Once installed, it costs 0.024 $ hour-1 to operate each lamp at 0.12 $ kWh-1. When determining a supplemental lighting strategy it is very important that a grower carefully weigh the installation and operation costs against the value of the increased production potential that supplemental light provides (Humphreys, 1995). In order to do so, the grower must be aware of a quantitative and qualitative value for this potential increase in production. Consistency and repeatability are very important to a grower who needs to maintain a system that is economically viable. Many years of well-controlled investigations would be necessary to accurately estimate the value of supplemental light in a CEA strawberry system. With time as a constraint, this investigation can hope only to provide suggestions based on a single season of observations. Further experiments and quantification will certainly be necessary to provide authoritative information about the variable range of increased production that a given supplemental lighting strategy could provide.
24
Chapter 2.0
Objectives
The objective of this research was to develop a viable strategy for the utilization of supplemental lighting in a greenhouse strawberry production system, by focusing on the following goals: o To observe and analyze the effects of daily light integral on fresh fruit yield of ‘Sweet Charlie’ strawberry plants grown in the greenhouse, o To estimate the light saturation point of ‘Sweet Charlie’ strawberry leaves under growth chamber conditions, o To determine a range of planting densities for ‘Sweet Charlie’ strawberry plants grown in the greenhouse, and o To determine the economic implications of adding supplemental light to a commercial greenhouse strawberry production system
A list of the investigations, designed to meet the above goals, and the primary directives of these investigations are given below. Supplemental Lighting To develop a gradient of daily light integral treatments by varying the irradiance and duration of operation of high pressure sodium (HPS) lamps, and to examine plant response to these treatments Photosynthesis To determine a functional photosynthetic saturation point of strawberry plants, by analyzing previously published information and develop a complementary test procedure.
25 To develop a numerical framework for the discussion of the plant physiological value of operating supplemental lighting in addition to natural sunlight Planting Density To determine the effects of different planting densities by examining plant yields and average fruit size Economics To determine the minimum sale price that would be required to balance the operational cost of supplemental lighting with the resulting increase in observed yields, in an effort to estimate the potential value of adding supplemental lighting to a greenhouse strawberry production system Strategic Suggestions To integrate the information gathered throughout these investigations into a suggested strategy for applying supplemental lighting to a greenhouse strawberry production system
26
Chapter 3.0 3.1
Materials and Methods
Experimental Facilities The investigations were performed at the Bioresource Engineering Department of
Rutgers University, Cook Campus, New Brunswick, New Jersey. Two primary growing systems were utilized: a precision growth chamber (GC) and a climate-controlled greenhouse (GH).
3.1.1
Precision Growth Chamber The conditioning treatment was executed in the growth chamber (GC). The GC
is actually a converted meat-locker (Kania, 1992), which was designed to provide temperature control within a 1 C range, humidity control within 5% RH and supplemental light and CO2. The GC is divided in half to accommodate a control room and a growth room, each measuring 2.9 m by 3.4 m by 2.6 m high. Six, 400W HPS lamps were suspended from the ceiling of the growth room to provide an average irradiance of 200 mol m-2 s-1 with a range between a minimum 185 and maximum 230 mol m-2 s-1. An ebb and flood bench (2 m by 3m) covered with a black rubber liner was equipped with a 378 L (100 gallon) tank and submersible pump to provide nutrient delivery. A Crowcon DeltaGas meter and bottled gas was used for CO2 measurement and supplementation. The nutrient delivery system (NDS) and all environmental parameters were controlled by a computer system utilizing Paragon process control software (Intec Controls, Walpole, Massachusetts) and Opto22 hardware (Temecula, California). Type T
27 thermocouples, Li-Cor quantum sensors (Lincoln, Nebraska) and a Vaisala (Columbus, Ohio) temperature/RH sensor were used for environmental measurements, taking readings each second and reporting fifteen-minute averages.
Photo 3-1. 3.1.2
Cut runners being conditioned in the precision growth chamber.
Controlled Environment Agriculture Greenhouse A 11 by 17 meter, computerized, climate-controlled, commercially available
greenhouse (GH) with a crop production system (Humphreys, 1995) was used to culture plants for each of the investigations. The environmental control systems of the GH included: high-pressure sodium (HPS) photosynthetic supplemental lighting, ebb and flood nutrient delivery (Fischer, 1990) on raised benches, and computer-based electronic environmental monitoring and control. All climate control strategies, including supplemental lighting duration and timing, day/night air temperature, and watering
28 frequency were programmed and implemented automatically by computer. The atmospheric CO2, air temperature, and relative humidity were continually monitored and recorded each second and thirty-minute averages were recorded to daily data files. The greenhouse was clad with air-inflated, double-polyethylene film, oriented with its ridge in east to west direction (40o 30’ N latitude, 74o 28’ W longitude).
3.2
Investigations The methods that were used for each of the four investigations are described.
3.2.1
Supplemental Lighting for Daily Light Integral Treatments
Photo 3-2. CEA Greenhouse. The supplemental lighting investigation can be broken into three segments by location: Pre-Growth Chamber, Precision Growth Chamber (GC), and CEA Greenhouse (GH) (Photo 3-2). The Greenhouse segment can be broken into two segments by time:
29 Pre-Harvest Window and Harvest Window. The Harvest Window can then be broken into seven, Harvest Periods of approximately 30 days each which occurred between Nov 1999 and May 2000.
3.2.1.1
Pre-Growth Chamber Cut runners of Sweet Charlie (certified disease free stock of – Fragaria x
Ananassa Duch. cv. Sweet Charlie) were obtained from Jersey Asparagus Farms, Inc (Pittsgrove, NJ). The runners were planted into 5cm (2 in.) round plug trays (holding 38 plants each) full of extra coarse perlite on 7/29/99, and placed into an unscreened commercial greenhouse in Burlington County, NJ. They were treated with a fungicide drench on 8/3/99. This drench consisted of 29 ml (1 oz.) of Subdue and 591 ml (20 oz.) of Cleary’s 3336, per 800 ft2 sprayed. On 8/10/99 the plants were treated with a preventative foliar insecticide spray. The concentrations of the chemicals used were: 2 grams of Sanmite, 2ml Conserve, and 6 ml Cleary’s 3336 per gallon of water. This was the last time the plants were sprayed with non-organic chemicals. Refer to the IPM section for descriptions of subsequent pest-control methodologies. The plants were misted with tap water three times daily to promote rooting. The frequency of misting was gradually decreased over the course of the 8 days following planting. After misting was no longer needed the plants were watered from overhead with a weak nutrient solution (1/4 strength Peter’s Hydrosol for another week. The plants were moved from the rooting greenhouse into the growth chamber on 8/12/99.
30 3.2.1.2
Precision Growth Chamber The GC provided control of the plant micro-environment. The plants were placed
in the GC to provide a conditioning treatment, to encourage early flowering and fruiting. Dr. Edward Durner developed this conditioning treatment, and the environmental parameters are outlined in Table 3-1 (Durner, 1999). This treatment does not specify an optimal set-point value for irradiance nor for relative humidity. The maximum irradiance (200 mol m-2 s-1) that the lamps could achieve was used during the lighted period of the day. Relative Humidity was set lower during the day and higher at night based on information provided by May and Pritts (1990) to encourage more optimal nutrient uptake.
Table 3-1. The Conditioning Treatment. Environmental Setpoints (8/12 – 8/20). Day ( 10 AM – 7 PM ) Night ( 7 PM – 10 AM ) ( 9 hrs) ( 15 hrs ) Air Temperature (C) 21 21 Relative Humidity (%) 50 75 CO2 (ppm) 1000 400 Irradiance (mol PAR m-2 s-1) 200 0 Between 8/21 – 8/30 the night air temperature set-point was reduced to 12 C to elicit the desired flowering response and all other env conditions remained the same. The ebb and flood bench was flooded to a depth of between 2 and 3 cm three times daily. The electrical conductivity (EC) of the nutrient solution was kept between 1.0 mS/cm and 1.2 mS/cm until the plants were transplanted into the GH in the evening of August 31. EC control is accomplished by adding more salts (in the 1:2:3 ratio as described in the Nutrient Delivery System section of Section 3.2.1.3) to increase the EC
31 and adding water to decrease the EC. No pH control was performed because the pH was consistently between 6.0 and 7.0.
3.2.1.3
CEA Greenhouse
3.2.1.3.1
Transplant and placement of conditioned runners into CEA GH
The rooted, conditioned plants were transplanted with wet, well established, 2 inch round root balls into dry perlite in 15 cm (6 in) round plastic pots. The pots are arranged in a staggered pattern, with 72 plants per bench (12 rows of 6 plants per row at a density of 11 plants m-2 (1 plant foot-2). Each bench sits two meters below a bank of lamps. Each bank of lamps was used to provide a supplemental lighting treatment. Since all plants on a given bench receive the same treatment, each bench can be referred to as a treatment bench. After the least vigorous 12 plants were removed from each bench, the plants were assigned positions for record keeping purposes, as shown in Figure 3-1. Prior
A 1
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E
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H
I
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2 3 4
Drain Basin
5 6
Figure 3-1. Plant placement and position grid on greenhouse bench. Sixty plants grew on each bench (2m x 5m) in a staggered pattern at 11 plants per m 2, each plant was assigned a position, indicated by A1 through J6. Rows 1 and 6 and Columns A and J can be considered guard rows, as they are on the edge of the treatment bench. to transplant the empty pots were covered with black on white polyethelyne film (white
32 side up) which was attached to the edges of the bench. Holes were made in the plastic to provide access to each pot for transplanting. The rationale for using this plastic film was to reflect light back to the plants, inhibit algae growth on the bench and to keep fruit from contacting the nutrient solution during irrigation. Twelve plants were removed from each bench by 9/15/99, as disease and transplant shock caused early season problems. Root-borne fungal disease continued to affect the plants, and as plants died they were temporarily replaced with non-data plants, until late December. On 12/29/99, the 20 least vigorous (visually determined) plants were set aside. The remaining healthy plants were removed from the benches and the benches were scrubbed clean and the tank was emptied in an attempt to remove disease propagules and the Zero-Tol treatments as described in the Section 3.2.1.3.3 were continued. Twenty freshly conditioned runners were placed onto each bench along with the surviving original plants and the changes in original plant locations were noted. The twenty plants that were removed from the natural light treatment bench were transferred to the SLS12 bench. This resulted in each treatment bench having 20 new plants and 40 original plants, except SLS12, which had 20 new, 20 original, and 20 from natural light. The natural light plants were moved to the SLS12 bench so that disease incidence could be observed and compared to the plants that remained on the natural light bench. Any plants that were subsequently lost to disease were replaced with non-data plants to prevent side-lighting from confounding the results.
33 3.2.1.3.2
Nutrient Delivery System
An under ground nutrient tank was automatically maintained at a level of 1400 L by a float sensor and computer controlled solenoid valve. The benches fill with nutrient solution in five minutes and drain within fifteen-minutes. The plants were watered with tap water the morning of 9/1/99. Nutrient salts were added to tap water on 9/2/99 in the following proportions: 1:2:3 ratio of Mg(SO4) : Ca(NO3)2 : Chemgro 5-11-26 hydroponic nutrient (Durner, 2000). The respective amounts of 200, 400 and 600 grams were added to the 1400 L storage tank to create the original nutrient solution (NS), which resulted in an electrical conductivity (EC) reading of 1.2 mS. Salts were added in the same proportions to maintain an EC of between 0.8 and 1.2 mS/cm throughout the investigation. The plants were flooded once daily until 9/13/99. Disease problems persisted through September, and irrigation was manually prevented on cloudy days, to reduce root-zone humidity, which was considered less favorable for root pathogens.
3.2.1.3.3
Integrated Pest Management
On 8/30/99 the first application of biological control organisms was released according to the suppliers release methods recommendations. The beneficial insects were purchased from IPM Laboratories, Locke, NY.
34 Table 3-2. IPM biological control organism release calendar and target pests. Two Spotted Spider Mite Predators P/C Mix = P. persimilis/N. californicus L/C Mix = M. longipes/N. californicus White-Fly Parasites Encarcia Formosa Thrip Parasites NcucSRB = Slow release bags of N. cucumeris Aphid (and others) Predators LB = Lady Beatle 8/30/99 9/13/99 10/25/99 11/1/99 11/15/99 12/15/99 12/20/99 3/20/00
1000 P/C Mix, 1000 L/C Mix, 1 cup LB 1000 P/C Mix, 1000 L/C Mix, 1 cup LB 1000 Encarcia, 12x300 NcucSRB, 1000 P/C Mix, 1000 L/C Mix 1000 Encarcia 1000 Encarcia 1 pint LB, 1000 Encarcia 2000 Encarcia 1 quart LB, 3000 Encarcia, 1000 L/C Mix
Four hundred milliliters of Zero-Tol ( BioSafe Systems – Hydrogen Dioxide) was added to the 1400 L nutrient solution tank on 9/20 and 9/21. This initial shock treatment noticeably reduced algae growth, especially near the bench drains where there was no plastic covering and previously significant algae growth. The manufacturer claimed that it also killed many fungal and bacterial pathogens that may be present in the nutrient solution and in the perlite. On 10/15 the dilution of Zero-Tol in the nutrient solution was tested with a BioSafe systems test kit and adjusted to a 1:500 dilution of Zero-Tol. Subsequently, this level was tested and adjusted weekly to attempt to maintain a 1:1000 dilution until December when the tank and benches were emptied and scrubbed clean. The use of Zero-Tol was discontinued in February when the supply was depleted, and the decision was made that the value of the treatments did not justify the expense.
35 3.2.1.3.3
Data Collection
Daily Light Integral (DLI) was automatically calculated and recorded, throughout the plant life cycle for each of four treatment benches, by summing the total moles of PAR received by the LI-COR quantum sensors (placed 10 cm above crown-level, at the plant canopy of each treatment). The quantum sensors constantly transform the flux of photons in the 400-700 nm waveband into an electrical signal of a proportional strength. This analog signal is converted to a digital signal by Opto-22 hardware and the personal computer operating GENESIS process control software constantly monitors this digital signal. Six-second sliding averages were used to calculate thirty-second averages and thirty-second integrals, which were used to control the supplemental lighting strategy. Thirty-minute averages are included in the daily data set for the point sensor located on each treatment bench. Thirty-minute siding averages of the dry bulb greenhouse and outdoor air temperature, humidity, and nutrient solution temperatures were all included in the daily data set. Electrical conductivity (EC) and pH of the nutrient solution were manually monitored with hand held meters bi-weekly (EC – Hanna Instruments, EC #4, pH – Corning, pH #30). The number and weight of each harvested fruit was recorded, for each plant within each treatment, twice weekly between 10/29/99 and 11/24/99, and once weekly between 12/3/99 and 5/30/00. Berries that weighed less than a tiny yet arbitrary four grams and those that were terribly misshapen or discolored were discounted as culls. The remainder of the berries were included in the yield data analysis.
36 3.2.1.3.4
Night Interruption
A procedure of night interruption (Runkle et al., 1998; Durner et al., 1984) was implemented on September 23, to elicit the desired plant morphological responses of elongated petioles and inflorescences, as well as, to maintain long-day photoperiod conditions during the short-day winter period. The NI procedure was two, 40 Watt incandescent lights that were installed two meters above each ten m2 bench to provide lighting each night for the three hours surrounding solar midnight. This was accomplished by calculating the length of each night and operating the lamps for three hours starting one and a half hours before the time that is half-way between sunset and sunrise.
3.2.1.3.5
Supplemental Lighting Control Strategy
The computer was programmed to target a specific daily light integral (DLI) for each treatment bench as outlined in Table 3-3. This target DLI can be considered the objective, and it represented the sum of the natural photosynthetic light plus a controllable additional amount of supplemental light. DLI objective values of 12, 9, and 6 mol m-2 day-1 were used for the SLS12, SLS9, and SLS6 treatments, respectively. SLS9 and SLS6 had one-half the number of lamps as SLS12. Table 3-4 shows information about the irradiance from the HPS lamps, including average, standard deviation, maximum and minimum irradiance (mol m-2 s-1) values for each treatment, with and without guard rows. The guard rows are the plants that are on the outer most positions around the perimeter of the benches. So the data that excludes the guard rows is only considering the plants on the interior of the bench. This data was obtained at night (when
37 there was no sunlight) by manually measuring PPF with a quantum point sensor at various positions within each bench. Table 3-3. Daily light integral objectives (mol m -2 day-1), and supplemental irradiance (mol m-2 s-1), for each of four treatments. Control, SLS 12 SLS 9 SLS 6 natural light Objective 12 9 6 None (mol m-2 day-1) supplemental light Irradiance 180 90 80 0 -2 -1 (mol m s )
38 Table 3-4. Irradiance from HPS lamps. Including Guard Rows Average st. dev. max min SLS12 180.1 14.7 202.0 140.0 SLS9 89.6 4.6 97.0 79.0 SLS6 81.6 3.3 87.0 76.0 Minus Guard Rows Average st. dev. max min SLS12 186.1 9.9 200.0 161.0 SLS9 91.3 3.4 97.0 85.0 SLS6 81.8 2.9 87.0 77.0 The computer continuously monitored the irradiance for each treatment bench using a Li-Cor quantum sensor mounted at each plant canopy. Every thirty seconds, the computer calculated DLI that was received up to that point of the day [DLIcurrent]. A phased-shifted cosine function model was used to estimate the total expected DLI for the day, based on the amount of DLI received up to that moment. This model calculated the percentage of a treatment DLI objective that should have accumulated by a specific time of the day [DLIexpected], by multiplying the objective of the treatment (12, 9, or 6) by the percentage that should have accumulated by the current time of day. If the DLIcurrent lagged behind the DLIexpected, for example as a result of poor weather conditions, then the decision was automatically made to begin operating the supplemental lights. This decision occurred when the difference of the DLIexpected and the DLIcurrent equaled the maximum amount of supplemental irradiance [supplemental light] that could be provided if the lights were operated for the remainder of the natural photoperiod. These values were based on the available constant supplemental irradiance of 0.64 mol m-2 hour-1 for the SLS12 treatment and 0.32 mol m-2 hour-1 for the SLS9 & SLS6 treatments. If at the end of the natural photoperiod, the DLIexpected [i.e. the DLI objective] was still less than the DLIcurrent, the supplemental lights would be stopped for the dark period, but
39 would be operated immediately at sunrise the following day, until the deficit [DLIexpected -
moles per square meter
DLIcurrent] from the previous day was eliminated.
10
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scaled current time(3.14=Sun Rise) lights(1=on)
DLI(ideal for 9)
DLI (simulated)
NL
DLI(ideal for 5.4)
Figure 3-2. The most difficult type of day (bright morning – dark afternoon) for the computerized supplemental light strategy. The most difficult day to attain the DLI objective using the described strategy was a day with a bright morning and dim afternoon, illustrated in Figure 3-2. Ideal curves display the theoretical rate of accumulation of irradiance if the sun provided irradiance in a perfect sine curve (Albright et al., 2000). The ideal curve for 9 moles m-2 represents the DLI[expected]. The bright morning actually provided an integral of light greater than DLI[expected] at mid-day (Figure 3-2, notice NL is above ideal). After midday the NL line deviates significantly from the DLI(9) line, because clouds must have darkened the sky. The decision to light did not occur until later in the day when it was too late to make up the entire deficit. This deficit is eliminated the following morning by operating the lights at sunrise.
40 A functional saturation threshold (cut-off point) was also used to prevent the operation of the supplemental lights when the incident natural irradiance was above a threshold level. This level was arbitrarily set before information about the saturation point of strawberry was obtained. Refer to Sec 4.4 for a discussion of a proposed method to estimate the Functional Photosynthetic Saturation Threshold. 3.2.2
Planting Density Movable benches within a large-scale plant production are placed side-by-side to
utilize the maximum greenhouse growing space. An aisle separating the benches is only temporarily created when worker access is necessary, otherwise benches are placed directly adjacent to one another. This results in a majority of the plants being grown within a virtually infinite canopy. To mimic the effect on the plant growth of a continuous canopy, guard rows of plants were provided around the measured data plants. Proper use of guard rows and screening material can adequately simulate a continuing canopy and help to prevent side-lighting from severely confounding the results of an investigation (Bugbee, 1994; Cavazonni, 2000) Adjacent plants within a canopy will certainly cast less shade when they are younger and smaller. Any canopy, regardless of age and density, will cast different amounts of shade at different times of the day, and this shade will be cast in different directions depending on the angle of the sun and whether the light is primarily diffuse or direct. The amount of shading or the percent attenuation or percent absorbed can be calculated by comparing the PAR above and below the canopy. % absorbed = ( PAR above the canopy – PAR below the canopy ) PAR above the canopy.
41
A canopy is considered closed when leaves from each plant are infringing on the growing space of the adjacent plants. This is apparent when leaves from adjacent plants are obviously touching and when percent absorbed is greater than an arbitrary threshold. The purpose of the planting density investigation was to measure the effects of two density treatments on fresh fruit yields (yield per plant and berry size), while measuring the effectiveness of screening to simulate the shading effects of a virtually infinite canopy. A Li-Cor line sensor was used to obtain average values for canopy PAR. This instrument
Figure 3-3. Density Study Layout. 14 data plants (red) are surrounded by guard plants and window screening.
measured the average irradiance (mol m-2 s-1) sampled along a distance of one meter. Its narrow shape allowed placement beneath the plant canopy. On 3/7/2000 14 data plants grown in 15 cm round plastic pots and surrounded by a border of guard plants were placed staggered (Figure 3-5) on one ebb and flood bench in the greenhouse at densities of 40 plants m-2 and 20
Photo 3-3. Density Study with screening to prevent confounding from side-lighting.
42 plants m-2. All flowers were removed and the plants were trimmed to approximately 7 leaves. A screening suspension scaffold (plastic string attached to metal supports) was erected as shown in Photo 3-3 on 3/24/2000. Screening was implemented when the plants had extended their leaves beyond the perimeter of the 15 cm pots. On 4/24/2000 (Photo 3-3) the dense canopy was beginning to shade adjacent plants but was not dense enough to be considered closed. Two layers of screening were installed vertically around the perimeter of the treatment areas to simulate a continuing canopy. Screening was hung at the height of the canopy and adjusted weekly to “grow” with the canopy, ie. The top of the screening was kept near the level of the canopy.
43 Measurements of canopy light attenuation were taken for top (Photos 3-4 and 3-5)
Photo 3-4. Line Meter Above Canopy, facing up.
Photo 3-6. Line Meter without screening, facing sideways.
Photo 3-5. Line Meter Below Canopy, facing up.
Photo 3-7. Line Meter with screening, facing sideways.
and side lighting (Photos 3-6 and 3-7). Depending on the position of the Li-Cor line meter and the direction that it was facing, one of two methods was used to determine light attenuation. If the meter was placed such that the canopy was providing the primary shading effect, the canopy attenuation was measured by recording PPF both above and below the canopy level (Photos 3-4 and 3-5). If the meter was placed such that the screening was providing the primary shading effect, the screening attenuation was measured by placing the meter on the edge of the pots (Photos 3-6 and 3-7) and recording PPF both with and without the screen. This experiment is being included in the thesis primarily for design value. These plants did not mature quickly nor yield significantly,
44 and the experiment was terminated just as the canopy was closing. Side lighting is an important factor to consider when performing plant growth experiments and using screening can be a reasonable way to minimize confounding by side lighting. Because the data was insignificant, it is not included in this thesis.
3.2.3
Economic Investigation Two distinct economic questions were raised within this study: 1. Does adding
supplemental lighting to a CEA greenhouse strawberry production system justify the capital and operating expenses, and 2. In general, can a CEA greenhouse strawberry production be a profitable venture? The electrical cost of operating HID HPS lamps was calculated to be $0.048 m-2 hr-1 for SLS12. This is based on a supplemental irradiance of 180 mol m-2 s-1. This cost was $0.024 m-2 hr-1 for SLS6 and SLS9 based on a kWh price of $0.12 based on a supplemental irradiance of 90 mol m-2 s-1. Comparing the yield from the SLS treatments to the natural light (NL) treatment can provide a relative value for the advantage of a SLS treatment over natural light in terms of fresh fruit yield. The yield advantage per plant was calculated for each harvest treatment using cumulative per plant yields and cumulative cost of supplemental lighting and was converted to the yield advantage (grams m-2) using a theoretical planting density of 32 plants m-2. Note that the pint (approximately 150 grams) is the traditional U.S. retail container size for fresh strawberries. The return ($ pint-1) from the sale of fresh strawberries (“break-even price”) that was required to equal the operational cost of each SLS treatment was calculated by
45 dividing the cost of issuing a particular SLS treatment ($ m-2) by the yield advantage (grams m-2) and multiplying by 150 grams pint-1.
46
Chapter 4. 4.1
Results and Discussions
Supplemental Lighting Investigation Environmental data is provided for the Growth Chamber (GC) and the
Greenhouse (GH) in Appendix A. Figures A-1 and A-2 show the measured environmental parameters for a typical day in the GC during the second week of the conditioning treatment. For the GH, average indoor and outdoor temperatures are given for each month in Table A-1. The distribution of temperature data within five-degree ranges is shown in Table A-3. Temperatures above 40C and below 10C are considered to be well outside of the optimal range. Unfortunately the control system did not successfully prevent temperatures from deviating into these ranges, but Table A-3 shows only five occasions (3 above 40C and 2 below 10C) when these sub-optimal temperatures occurred. To accurately represent yields from each group of plants, the harvest data and related discussion must be specially segregated in order to make fair and logical comparisons. Sixty ‘original plants’ for each treatment bench, were transplanted into the greenhouse on 9/1/99. As plants desiccated (caused by Pythium), they were removed from the treatment benches. On 12/29/99, twenty conditioned plants for each treatment were transplanted into the greenhouse. These plants will be referred to as the ‘second plants’ and were placed in the first two rows along the long edge of the bench. The first three harvest periods occurred prior to yields from the second planting, so HP1, HP2, and HP3 consist entirely of yields from ‘original plants’. The subsequent harvests consisted
47 of yields from both plantings (‘original plants’ and ‘second plants’). These yields are analyzed separately within harvest periods. Plants that did not survive were removed from the statistical calculations. This was accomplished by removing data points recursively, starting with the harvest period in which a particular plant died. The data point for that same plant was removed for each previous harvest period that it failed to yield. For example, if the plant that occupied the position A4 died in the last week of harvest period 3 (HP3), and it had yielded during the first week of that same harvest period (HP3), it would be removed from harvest period four (HP4) and subsequent harvest periods, but not from HP3 since it had yielded fruit during that HP. If the plant in position B5 died during the last week of HP3, and it hadn’t yielded since HP1, it would be removed from HP2 and HP3, as well as subsequent harvest periods. The primary unit used to report yields is fresh weight of berries (grams) per plant. The significance of treatment effects was determined within each harvest period using Fischer’s Protected LSD, mean separation technique (with =0.05), and the general linear models procedure. If multiple harvest periods were combined and discussed together, the mean yield per plant values for each harvest period were added together to arrive at a cumulative value. Due to differences in sample size over time, it is often not possible to statistically analyze these cumulative values. Of the 60 plants on each treatment bench, 28 are edge plants. The yields from these plants were removed from the primary data set and the rows of plants on the edge of each bench were considered “guard-rows”. Discarding the yields from guard-rows is a method to avoid confounding the effects of side-lighting. Generally, the primary concern
48 is that these plants will have an unfair light harvesting advantage, which could result in greater yields. Unless otherwise indicated all yields reported are excluding the guardrows. Refer to Appendix C for further discussion and statistical analysis of the guard-row issue. The harvest data was segregated by time and planting date. The supplemental lighting integral (SLI) was calculated for each segment of time, using the mean value for irradiance and the measured duration of operation. The cost of operating the lamps for each SLS treatment calculated using an electrical cost of $0.12 kWh. The DLI for each day and the average DLI and SLI for each 7-day and 28-day period are provided in Appendix B.
Photo 4-1. Early season advantage of supplemental lighting is evident when the first harvest in November is examined (Total harvested yield (11/1/99) from SLS6 is shown in the quart on the left, beside total yield from natural light, on the right).
49
The harvest was segregated within the seven month harvest window(11/1999 – 5/2000) by dividing it into approximately 30 day harvest periods (HP). The initial plants were transplanted on 9/1/99 and were harvested from HP1 through HP7. The second group of plants were planted on 12/29/99 and were harvested from HP4 through HP7. Table 4-1. Harvest Data Divisions - Season, Crops, Harvest Period, Date and corresponding section of the thesis Section Season Plants Harvest Dates Period 4.1.1 Early Original HP 1-3 11/1999 – 1/2000 4.1.2 Late Original HP 4-7 2/2000 – 5/2000 4.1.3 Late Second HP 4-7 2/2000 – 5/2000 4.1.4 Overall Original HP 1-7 11/1999 – 5/2000
Note: The second plants did not yield in the early season, so the late season yields represent the overall yields for the second plants.
50 4.1.1
Early Season Yield The early season plant yield for the original plants during harvest periods 1
through 3, 11/1999 - 1/2000 are show in Figure 4-1. There was a significant advantage in yield per plant for the SLS9 treatment for the first two harvest periods (Figure 4-1). All plants were conditioned together, so they were all on a similar flowering schedule. The plants yielded the largest flush of primary berries during harvest period one, there were new inflorescences growing and secondary and tertiary berries harvested during harvest period two, and then another large flush of primary berries during harvest period three.
g ra m s p e r p la n t
Original Plants 80 SLS12
60
SLS9
40
SLS6
20
NL
0 1
2 Harvest Period
Figure 4-1.
Yield per Original Plant for HP1-HP3
3
51 4.1.2
Late Season, Original Plants Later in the season, SLS6 showed increased yields ( compared to the early season,
as did NL to a lesser degree. It is interesting to note, that although SLS9 provided much more supplemental lighting, the average DLI values for SLS6 and SLS9 were measured to be identical to the tenth of a Mole m-2. This can most likely be explained by differences in shadows cast by overhead equipment and structures surrounding the greenhouse.
g ra m s p e r p la n t
Original Plants 100 80
SLS12
60
SLS9
40
SLS6
20
NL
0 HP4
HP5
HP6
Harvest Period
Figure 4-2.
Yield per Original Plant for HP4-HP7
HP7
52 4.1.3
Late Season, Second Plants, HP 4-7, 2/2000 - 5/2000 Figure 4-3 shows the amount of supplemental light that was applied (the bars) as
well as the cost to operate the supplemental lighting in U.S. dollars (the lines). Electrical cost was based onIn an ofC $0.12 kWh. teestimate gral and ost o f Supplemental Lighting
300 250 200 150 100 50 0
24 16 8
U .S . $ m - 2
M o l PA R m -2
SecondPlanting
0 HP4
HP5
HP6
HP7
SLS12 SLS9 SLS6 SLS12 SLS9 SLS6
MontlyHarvest Periods 2/2000-5/2000
Figure 4-3. Total Supplemental Light Integral (SLI) and Cumulative Operational Costs of SLS treatments (2/2000-5/2000).
There were very few differences in the mean separation of the treatments when the guard-rows were included and excluded, but the overall tendency of the edge-plants was to yield insignificantly more. The lack of mean separation is in part, due to the small sample size for the second planting (eight second plants per treatment were not edge plants), which is due to the decision that excluding the guard rows was most appropriate and the decision to place the second plants along the edge of the benches.
53 Table 4-2. Average Yield Per Second Plant, for each harvest period (separately and grouped cumulatively), for each treatment. Both, including guard-rows (a.) and excluding guard-rows (b.) a. HP4 HP5 HP6 HP7 HP HP HP 4-5 4-6 4-7 SLS12 14.8 a 56.5 A 30.0 a 71.6 a 71.4 ab 101.3 a 172.9 a SLS9 16.4 a 61.4 A 34.3 a 71.8 a 77.9 a 112.2 a 184.0 a SLS6 14.2 a 43.7 A 28.6 a 57.1 a 57.8 ab 86.4 a 143.5 a NL 8.1 a 42.1 A 40.3 a 76.6 a 50.2 b 90.5 a 167.1 a b. HP4 HP5 HP6 HP7 HP HP HP 4-5 4-6 4-7 SLS12 18.9 a 48.0 A 26.3 a 59.9 a 66.8 a 93.1 a 153.0 a SLS9 22.1 a 68.6 A 35.7 a 46.6 a 90.6 a 126.3 a 172.8 a SLS6 19.3 a 37.6 A 29.0 a 42.3 a 56.9 a 85.9 a 128.2 a NL 10.9 a 45.7 A 35.4 a 76.8 a 56.6 a 91.9 a 168.7 a Mean separation by Fischer’s Protected LSD test. (=0.05) Figure 4-4 shows the cyclical nature of yields over time and Figure 4-5 shows the accumulation of those yields for each treatment.
54
g ra m s p e r p la n t
Second Plants 100 80
SLS12
60
SLS9
40
SLS6
20
NL
0 HP4
HP5
HP6
HP7
Harvest Period
Figure 4-4. Yield (grams per plant) of Second Planting for harvest periods HP4 to HP6.
g ra m s p e r p la n t
Second Plants 200 HP7
150
HP6
100
HP5
50
HP4
0 SLS12
SLS9
SLS6
NL
Harvest Period
Figure 4-5. Accumulated Yield (grams per plant) of Second Planting for harvest periods HP4 to HP6.
55
600 500 400 300 200 100 0
48 40 32 24 16 8 0 HP1 HP2 HP3
HP4
HP5 HP6 HP7
U .S . $ m -2
M o l P A R m -2
Integral andCost of Supplem ental Lighting riginal P lantsHP 1-7, 11/1999 - 5/2000) 4.1.4 Overall Harvest WindowO (Original Plants, SLS12 SLS9 SLS6 SLS12 SLS9 SLS6
MontlyHarvest Periods 9/1999- 5/2000
Figure 4-6. Total Supplemental Light Integral (SLI) and Cumulative Operational Costs of SLS treatments. The bars show cumulative SLI applied to the treatment benches and the lines show cost in U.S. dollars based on an electrical cost of $0.12 kWh. Table 4-3. Average Yield Per Original Plant, for each harvest period, for each treatment. Both, including guard-rows (a.) and excluding guard-rows (b.) a. HP1 HP2 HP3 HP4 HP5 HP6 HP7 SLS12 49.8 b 19.5 ab 47.4 a 13.4 b 46.7 b 39.0 B 22.2 b SLS9 63.3 a 25.9 a 47.7 a 17.6 ab 66.1 b 36.8 B 49.3 a SLS6 48.6 b 17.5 b 52.1 a 19.8 ab 94.3 a 41.1 B 57.2 a natural 47.4 b 19.3 ab 55.7 a 26.2 a 67.6 b 62.5 A 44.4 a light b. HP1 HP2 HP3 HP4 HP5 HP6 HP7 SLS12 51.7 b 19.3 b 51.9 a 19.0 a 48.8 b 39.4 B 25.0 b SLS9 71.9 a 31.5 a 50.5 a 22.6 a 67.3 ab 38.3 B 56.5 a SLS6 52.6 b 19.5 b 54.6 a 18.4 a 98.0 a 40.6 B 65.0 a natural 49.3 b 19.5 b 56.2 a 27.6 a 67.3 ab 69.1 A 50.1 ab light Mean separation by Fischer’s Protected LSD test. (=0.05)
In Figure 4-6, SLS9 provided significantly more HPS supplemental lighting than SLS6, however, from Figure 4-7 and Table 4-2, the accumulated average yield per plant was not significantly different. The natural light treatment was also nearly equivalent to both the SLS6 and SLS9.
56
g ra m s p e r p la n t
Guarded 400 350 300 250 200 150 100 50 0
HP7 HP6 HP5 HP4 HP3 HP2 HP1 SLS12
SLS9
SLS6
NL
Figure 4-7. Accumulated Yields per Plant for the original planting for the entire harvest window excluding guard-rows.
Table 4-4.
Average Fruit Size for the original plants Average Fruit Size (grams) SLS12 11.0 b SLS9 10.5 b SLS6 11.3 ab natural 12.2 a light Mean separation by Fischer’s Protected LSD test. (=0.05)
Table 4-5.
Average Fruit Weight (grams per fruit) for the Second Plants Average Fruit Size (grams) SLS12 11.4 A SLS9 11.9 A SLS6 11.6 A natural 12.0 A light Mean separation by Fischer’s Protected LSD test. (=0.05)
57
4.2
Confounding Factors Adding supplemental lighting is only one of many cultural practices, and light is
only one of the many important environmental parameters within a CEA greenhouse strawberry culture system. It is a paramount challenge to create a well-controlled experiment where all other pertinent environmental factors are consistent for each plant and that only the daily light integral (DLI) is varied. One of the main limitations of all greenhouse environments, is the challenge of plant placement within the treatments. A traditional experimental design requires that any randomly selected position be considered an equivalent environment for any individual plant. The bench and its associated nutrient delivery system was successfully developed to provide uniform nutrient and water regimes for all plants. However, by such grouping of plants, the randomness of treatments was compromised. The concept of a ‘treatment bench’ must be discussed to demonstrate that this was not possible within the available greenhouse facility. Supplemental light was added to the greenhouse by a group of high intensity discharge (HID) lamps located at a fixed height above the bench. The lamps were arranged in a configuration that attempted to provide an even distribution of light across a given area of the greenhouse. The uniformity was evaluated by measurement of irradiance at regular intervals in the night to create a two-dimensional light map for evaluation of uniformity. This was completed after the lamps were mounted in place. Some movement of the lamps was possible to improve the uniformity after initial
58 mapping, however, this trial and error procedure was limited and perfect uniformity was not possible. Since the two factors that affect DLI are duration and irradiance, either or both of these factors can be altered to create an experiment with DLI as the independent variable. One way to alter the supplemental irradiance that the lamps can provide is to change the number, type, or power output of lamps per unit area. Both represent discrete parameter values, since there cannot be 1 ½ lamps installed, and practical lamp power output is available only as 400, 600 and 1000 W units. A bank of lamps is generally mounted above a bench and operated as a unit to add irradiance to a single bench. A bank of lamps can be operated for differing durations at a known, uniform irradiance to provide desired daily integrals of supplemental light. The summation of the incident solar irradiance and the supplemental light provides the daily light integral (DLI) value (measured in moles PAR m-2) for the treatment area. Although using specific banks of lamps to add supplemental light to specific benches is an effective method to issue treatments with different daily light integrals, it is not a method that allows implementation of a traditional statistical experimental design. As previously noted, each plant should be randomly assigned to a treatment and randomly placed within the experimental plot (in this case the greenhouse). Because the lamps within a bank are operated simultaneously and for the same duration, all plants that are placed on a given bench receive the same DLI treatment. To create a statistically sound experimental design, a facility must be advanced enough to provide multiple benches each with independent light banks and large enough so that replications of each treatment could be issued, on multiple benches, under separate banks of lamps. In the
59 case of this supplemental light investigation, each bench was a “treatment bench” and each individual plant became a replication in an experiment. The benches were distributed throughout the greenhouse, and were subject to the environmental inconsistencies that tend to exist within a greenhouse. If daily light integral is to be the only independent variable, not only must this DLI be consistent across a given treatment bench, all other pertinent variables should be consistent across all treatments. If there is a difference in temperature among the positions of the greenhouse, the effect of temperature could be confounding the apparent effect of the intended treatment. One of the most apparent confounding factors in this study was the variation of solar radiation caused by shadows from overhead equipment and surrounding structures. This structural interference was compounded by the use of a single point sensor (6 mm diameter) to measure the incident irradiance. A quantum line meter or moving sensor would have provide a much better sampling of the actual irradiance. This effect is most apparent in Figures 4-3 and 4-6. One would expect the SLS12 treatment to add more supplemental light than the SLS9 treatment, at all times. However, due to shading effects compounded by point sensor usage, this was not the case in the late season (Figure 4-3). Additional confounding of the experimental results is evident when temperature control of the greenhouse is considered. The greenhouse temperature was controlled by adding heat through the floor and overhead heating systems or removing heat by fan ventilation. The aspirated dry bulb thermocouple that provided the temperature measurement that the computer used uses to control the system was located in the geometric center of the four treatment benches. Although this may be an accurate
60 representation of the average or bulk mean greenhouse air temperature it includes the range of minimum to maximum air temperature values. Furthermore it does not necessarily provide an accurate representation of the average leaf temperature. Leaf temperature is actually more physiologically important that ambient temperature. Adding supplemental light! to a treatment bench via HID lamps can certainly increase leaf temperature without increasing the temperature reported by the aspirated shielded dry bulb temperature measured from the center of the greenhouse. Great expense and advanced, precision control would be required to remove these confounding factors. Infrared leaf temperature sensors would need to be implemented, and temperature would need to be precisely controlled for each bench, separately. The set-point would also need to be adaptive, based on the warmest leaf-temperature likely to result from the highest light treatment. 4.3
Data Discussion In appendix B, it is apparent that similar values for average daily light integral
(DLI) are reported for the SLS6 and SLS9 treatments. Assuming the calibration techniques were sound and the sensors were accurate, this similarity must have resulted from structural and overhead equipment differences that caused different shadowing and light transmission effects. It is certain that the HPS lamps ran much longer on the SLS9 treatment, providing 22.6% of the average DLI (9.2 moles m-2). The lamps above the SLS6 treatment provided 7.0% of an average DLI of 9.2 moles m-2. Although the mean DLI values are not significantly different via Fischer’s Protected LSD (=0.05), the mean supplemental light integral (SLI) values are significantly different. This information indicates that there was a difference in spectral quality among the treatments. This
61 difference appeared to strongly influence the timing of yields, as indicated by the superior early season fruit development in the SLS9 treatment (Figure 4-1). This could be partially explained by the greater spectral efficiency of HPS lamps (.95) compared to solar light (.88 on a clear day) (Bugbee 1994) “Spectral efficiency is defined as the ratio of the lamp spectral output multiplied by McCree’s quantum efficiency weighting factors, divide by the number of photons between 400 and 700 nm. An LED with a peak output at 610 nm would result in an efficiency close to 1. HPS lamps have a relatively high ratio (0.95) because most of their output is near the peak quantum yield.” Bugbee (1994) also reported that diffusion from clouds or low sun angles will tend to further decrease the spectral efficiency of solar light, it is assumed that diffusion from transmission through a plastic greenhouse covering has a similar effect. With a target DLI of 12 moles PAR m-2 day-1, the SLS12 treatment achieved 11.2 moles PAR m-2 day-1 of which 20.9% was from Supplemental light. However, the plants from SLS12 treatment were the most drastically damaged by Pythium in the first half of the experiment (from 9/1 – 12/30). In the second half of the experiment, when losses to Pythium disease were equal for all treatments, but 60%? less than the first half of the experiment (29 deaths vs. 12 deaths), the yields from SLS12 did not surpass SLS9. However, the air temperature, CO2 and light were very likely confounding the treatment effect. It is believed to be quite possible that, plants of the 12 moles per day treatment were often being photosyntheitcally saturated, especially without the availability of CO2 enrichment in this greenhouse. It is also possible that the increased daily light integral (DLI) and leaf temperature caused an increased transpiration demand that the plants were unable to accommodate due to pressure from root-borne pathogens such as Pythium. This point is supported by the fact that after the first two weeks in the greenhouse no
62 plants were lost on the natural light treatment bench to Pythium. Furthermore, plants that were moved from the Natural light bench to the SLS12 bench were later killed by Pythium while all of the other plants from the natural light treatment survived. Plants with Pythium infested roots, desiccated both before and after the Zero-Tol treatment, and since no controlled experiment was performed with the Zero-Tol, it is difficult to determine its effectiveness against Pythium. The bulk of the Zero-Tol treatments were during the winter months when temperature and light demanded less water uptake and transpiration. 4.4
Functional Photosynthetic Saturation Threshold Literature that specifically stated the photosynthetic saturation point of strawberry
leaves or canopies was not found. However, this information can be inferred from the report of Yoshida and Morimoto (1997) and further confirmed by personal communication with Dr. Yoshida (2000).
Light Saturation
1.6
-2
-1
(g CO2 m hr )
Photosynthesis
1.4
190
1.2 1 0.8
Es tim ated Saturation Point
0.6 0.4 0.2 0 0
50
100
150
200
250
300
Light intensity (W m -2) PS
Delta
Figure 4-8. Estimated rate of PS at different light intensities at ambient CO2. Delta refers to the percentage change in PS rate over the previous change in light intensity.
63 To determine a functional saturation point an arbitrary definition was used. If less than a 2% increase in net photosynthesis (Pnet) of the whole plant canopy was measured when the irradiance was increased 10 Watts m-2, the canopy was considered saturated. The canopy saturation point has been inferred from two studies two studies to be less than 200 Watts m-2 at ambient (F = 0.0005) yields per plant. However, when the means were analyzed for the second planting, it was determined that there was no significant difference (Pr>F = 0.259) between edge-plants and non-edge plants. If the edge plants were removed from the data set, the treatment means separated slightly differently. This indicated that being a member of a guard-row did not provide a significant yield advantage to the edge plants, but that placement on the bench was a potential confounding factor. Thus the guard rows were excluded from the primary data set, which was used to report the results in Chapter 4. Given this information it became obvious that the choice of placement of the plants for the second planting was incorrect. Placing these plants along the long edge of each bench rather than intermingled in the center of the bench led to the removal of more than half (12/20) of these plants from the data set. The resulting small sample size contributed to the lack of statistically significant differences between mean yield per plant values. This lack of statistical significance must be taken into account when analyzing the economic significance of the differences in yields.
97
Acronyms SLS12, SLS9, SLS6 – Supplemental lighting strategy (targeting 12, 9 and 6 moles PAR per day) supplemental light – Supplemental Light natural light – Natural Light NLI – Natural Light Integral SLI – Supplemental Lighting Integral DLI – Daily Light Integral (DLI=NLI+SLI) HPS – High Pressure Sodium HID – High intensity Discharge GH – Greenhouse GC – Growth Chamber CEA – Controlled Environment Agriculture NDS – Nutrient Delivery System ppf – photosynthetic photon flux PAR – photosynthetically active radiation (400 – 700 nm) EC – Electrical Conductivity
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101 Yoshida, Y. 2000. Personal Communication. Yoshida, Y. and Morimoto, Y. 1997. Measurement, modeling and seasonal changes of canopy photosynthesis in ‘NYOHO’ strawberry. ISHS - Acta Horticulturae 439(2):575582 Web Citations California Strawberry Commission http://www.calstrawberry.com/ CDFA. 1995. Alternatives to Methyl Bromide: Research Needs for California. Report of the Methyl Bromide Research Task Force To The Department of Pesticide Regulation and The California Department of Food and Agriculture. September, 1995 http://www.cdpr.ca.gov/docs/dprdocs/methbrom/mb4chg.htm Darrow, G.M. The Strawberry: History, Breeding and Physiology http://www.nal.usda.gov/pgdic/Strawberry EPA. 2000. U.S. EPA Methyl Bromide Phase Out Web Site http://www.epa.gov/docs/ozone/mbr/mbrqa.html Schlosser, Eric. 2000. In the Strawberry Fields. http://www.theatlantic.com/issues/95nov/strawber.htm ERS. 2000. Fruit and Tree Nuts Situation and Outlook Report. Market and Trade Economics Division, Economic Research Service, U.S. Department of Agriculture, March 2000, FTS-288. http://usda.mannlib.cornell.edu/reports/erssor/specialty/fts-bb/2000/fts288.pdf FAO. 2000. Rethinking agricultural planning. http://www.fao.org/news/2000/000503-e.htm NASS. 2000(b). National Agricultural Statistical Service Website. http://www.usda.gov/nass/ Pritts, M. 1990. http://www.fvs.cornell.edu/Faculty/php/MarvinPritts/grnhouse.html
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CDFA. 1995. Alternatives to Methyl Bromide: Research Needs for California. Report of the Methyl Bromide Research Task Force To The Department of Pesticide Regulation and The California Department of Food and Agriculture. September, 1995 http://www.cdpr.ca.gov/docs/dprdocs/methbrom/mb4chg.htm Darrow, G.M. The Strawberry: History, Breeding and Physiology http://www.nal.usda.gov/pgdic/Strawberry EPA. 2000. U.S. EPA Methyl Bromide Phase Out Web Site http://www.epa.gov/docs/ozone/mbr/mbrqa.html Schlosser, Eric. 2000. In the Strawberry Fields. http://www.theatlantic.com/issues/95nov/strawber.htm ERS. 2000. Fruit and Tree Nuts Situation and Outlook Report. Market and Trade Economics Division, Economic Research Service, U.S. Department of Agriculture, March 2000, FTS-288. http://usda.mannlib.cornell.edu/reports/erssor/specialty/fts-bb/2000/fts288.pdf FAO. 2000. Rethinking agricultural planning. http://www.fao.org/news/2000/000503-e.htm NASS. 2000(b). National Agricultural Statistical Service Website. http://www.usda.gov/nass/ Pritts, M. 1990. http://www.fvs.cornell.edu/Faculty/php/MarvinPritts/grnhouse.html
