Hydroponic Lettuce Handbook

1 ` Cornell University CEA Program 2013 Cornell Controlled Environment Agriculture Hydroponic Lettuce Handbook This Hydroponic greenhouse production system was designed for small operations to provide local production of head Lettuce as well as employment to the proprieters. Our research group has experimented with many forms of hydroponics but have found this floating system to be the most robust and forgiving of the available systems. This system is built around consistent produciton 365 days of the year. This requires a high degree of environmental control including supplemental lighting and moveable shade to provide a target amount of light which, in turn, results in a predictable amount of daily growth. by Dr. Melissa Brechner, Dr. Both, CEA Staff ` Cornell University CEA Program 2013 Table of Contents Chapter 1: Greenhouse Hardware .. 6 Nursery or Seedling production 6 Ebb and Flood Benches.

2 6 Solution Tank and Plumbing .. 8 Lighting .. 9 Pond Area .. 12 Lighting .. 13 Lighting Configuration and High Intensity Discharge (HID) Lamps .. 14 Paddle Fan .. 14 Aspirated Box .. 15 System Component Information .. 16 Dissolved Oxygen Sensor .. 16 Compact Submersible Centrifugal Pump .. 16 Flow 16 Chapter 3: Computer Technology and Monitoring .. 17 Biological Significance of Environmental Parameters .. 17 Temperature .. 17 Relative 17 Carbon Dioxide or CO2 .. 17 Lights .. 17 Dissolved 18 pH .. 18 ` Cornell University CEA Program 2013 Electrical Conductivity .. 18 Monitoring .. 18 Set-points .. 19 Chapter 4: Lettuce Production .. 20 Chapter 5: Packaging and Post-Harvest Storage .. 26 Chapter 6: Crop Health .. 27 Disease .. 27 Pests .. 27 Chapter 7: References .. 28 Appendix .. 47 Table of Figures Figure is a photo of an empty Ebb and Flood bench while the bench is flooding for sub-irrigation.

3 6 Figure 2. Bench for seedlings.. 7 Figure 3. Seedling area on edge of pond in greenhouse.. 7 Figure 4. Breaker on the end of a wand for hand-watering.. 7 Figure cover propped against a sheet of rockwool.. 8 Figure solution reservoir fiberglass tank (A), Pump (B), Piping (C), and Valve (D). The bottom of the germination bench can be seen in (E).. 8 Figure (A) and incandescent (B) lighting in the growth room. Fluorescent lighting is used for plant biomass production and incandescent lighting is used for photoperiod control.. 9 ` Cornell University CEA Program 2013 Figure 8. High Pressure Sodium (A) and Metal Halide (B) lamps in a growth chamber.. 9 Figure 9. High Intensity Discharge (HID) luminaire in a greenhouse.. 10 Figure box in a greenhouse. A fan draws air from the bottom of the box over the sensors.. 11 Figure 11. Aspirated box opening on bottom of box.

4 11 Figure 12. Empty pond with liner.. 12 Figure of pond detail. The inside edges of two separate ponds made of wood and separated by structural members is shown on left. The right hand picture shows a concrete 13 Figure 14. Paddle fan to increase vertical air movement and therefore evapotranspiration. This is important for the prevention of tipburn.. 14 Figure 15. Aspirated box with digital output screen in greenhouse.. 15 Figure 16. Model: H-03216-04: 65 mm variable area aluminum flow meter with valve and glass float for O2. Manufacturer: Cole Parmer Instrument Co., Niles, IL .. 16 Figure 17. Quantum PAR sensor to measure light available for photosynthesis. Foot-candle sensor and lux meters are inappropriate because they are designed to quantify the sensitivity of the human eye and overestimate (~25%) the light available for photosynthesis .. 19 Figure 18.

5 Dissolved oxygen sensor. DO levels should be greater than 4 ppm to prevent growth inhibition. Visible signs of stress may be observed at 3 ppm.. 19 ` Cornell University CEA Program 2013 Table of Abbreviations and Units A Area Square feet or square meter. CEA Controlled Environment Agriculture Producing plants in a greenhouse or other space. cm centimeter A unit of length CWF Cool White Fluorescent A type of supplemental lighting DLI Daily Light Integral The sum of photosynthetic (PAR) light received by plants in a day. DO Dissolved Oxygen Oxygen concentration in nutrient solution measured in parts per million. EC electrical conductivity An indirect measurment of the strength of a nutrient solution. HID High Intensity Discharge A type of HID supplemental lighting hp horsepower A unit of power HPS High Pressure Sodium A high intensity discharge lamp/luminare type for supplemental lighting kPa kilopascals A unit of pressure, force per unit area MH Metal Halide A type of HID supplemental lighting mol pronounced 'mole' A number of anything equal to x 1023 items.

6 We use it to quantify the number of photons between 400-700 nm of PAR light plants receive. mol/m2/d moles per square meter per day Integrated PAR light mol/m2/s moles per square meter per second Instantaneous PAR light nm nanometer Unit of length in SI, one billonth of a meter PAR Photosynthetically Active Radiation The portion of the electromagnetic spectrum between 400-700 nm plants use for photosynthesis ppm parts per million A unit that describes dimensionless quantities such as volume fractions. For describing carbon dioxide concentrations it is a molar basis. SI System Internationale International system of units aka metric system - built around 7 basic units of measurements mol/m2/s micro-mole per square meter per second Instantaneous PAR light S/cm microsiemens per centimeter A unit of measurement for electrical conductivity ` Cornell University CEA Program 2013 Chapter 1: Greenhouse Hardware Of fundamental importance to Hydroponic Lettuce production are the physical components of both the germination area and the pond area.

7 It is necessary to have not only an idea of the physical components associated with each area, but also a good understanding of their purposes. Nursery or Seedling production Area The first 11 days of Lettuce production takes place in the seedling production area. Seedlings develop best under constant lighting conditions with specific, closely controlled temperature, relative humidity, carbon dioxide, and irrigation. These conditions can only be met in a controlled area, whether that is a greenhouse or a growth room, with the following equipment: Ebb and Flood Benches, Tables, or Ponds Solution Tank and Plumbing Supplemental Lighting Aspirated sensor Box Sensors Ebb and Flood Benches Figure is a photo of an empty Ebb and Flood bench while the bench is flooding for sub-irrigation. To uniformly supply the germinating seedlings with water and nutrients, Ebb and Flood benches (approximately by m or 8 by 4 foot) are periodically (2 to 4 times per day for approximately 15 minutes) flooded.

8 These benches were specifically designed to supply water and nutrients through sub-irrigation. Through a pump and piping, the fertilizer solution is pumped into the Ebb and Flood bench. The solution is then automatically drained after a given time period. ` Cornell University CEA Program 2013 Figure 2. Bench for seedlings. Ponds Figure 3. Seedling area on edge of pond in greenhouse. Figure 4. Breaker on the end of a wand for hand-watering. Alternately, the rockwool slabs in trays sitting on a bench (Figure 2) or the edge of a pond (Figure 3) may be overhead watered with a hose that has a breaker (see Figure 4 above) on it that slows the flow of high velocity water so that fragile seedlings are not damaged. ` Cornell University CEA Program 2013 Figure cover propped against a sheet of rockwool. Humidity covers (Figure 5) are used to provide a high humidity environment around the germinating seeds.

9 They are required if seeding with bare (not pelleted) seed. Solution Tank and Plumbing Figure solution reservoir fiberglass tank (A), Pump (B), Piping (C), and Valve (D). The bottom of the germination bench can be seen in (E). A fiberglass tank (A) see Figure 6, holds the nutrient solution used for sub-irrigating the seedlings. A plastic tank could also be used but may not be as strong as the fiberglass. Care must be taken to procure a plastic vessel that will not degrade quickly in sunlight if germination area is in a greenhouse. Any vessel that is used should be sufficiently opaque to prevent algae growth. Approximately 250 L (66 gallons) of nutrient solution is sufficient to prime the system (given above-listed bench size), fill the bench, and provide nutrient solution for the first 11 days of growth for approximately 2000 seedlings. A small (1/50 ) pump (B) is used to pump the solution to the bench.

10 The piping (C) should be flexible to adjust to individual germination area needs. A throttling or gate valve (D) is included to control the flow of the nutrient solution to the Ebb and Flow bench. The bottom of the sub-irrigation bench (E) is visible in the photo above. ` Cornell University CEA Program 2013 The pump may be operated on a time clock so that irrigation can occur without human intervention. Lighting Figure (A) and incandescent (B) lighting in the growth room. Fluorescent lighting is used for plant biomass production and incandescent lighting is used for photoperiod control. Figure 8. High Pressure Sodium (A) and Metal Halide (B) lamps in a growth chamber. Germination Room In general, a separate room for germination of seedlings is very energy intensive. Our experience was that the improvement in growth obtained by utilizing a germination room was not worth the large amount of energy such a room used and its use was discontinued.