Scientific Publications on Hydroponic Lettuce Production

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Abstracts

Albright, L.D., A.J. Both, and A.J. Chiu. 2000. Controlling greenhouse light to a consistent daily integral. Transactions of the ASAE 43(2):421-431.

Abstract

Lettuce growth data are presented that show the importance of the daily light integral for predictable vegetative growth. Dry mass accumulation is shown to be proportional to the light integral, and a consistent daily light integral is proposed to be central to consistent production. Supplemental lighting control rules are defined and described and a computer implementation is used in conjunction with ten years of hourly weather data to test (by simulation) adequacy of the rules to control supplemental lights and movable shades in greenhouses to achieve a consistent daily integral of Photosynthetically Active Radiation (PAR), mol-m^-2-day^-1, on days of either insufficient or excess solar irradiation, which are most days. The rules require neither historical data bases of weather characteristics nor daily weather forecasts. Control decisions are suggested to be made hourly, based on the current day’s accumulating solar PAR integral inside the greenhouse. The model is sensitive to time-of-day electrical rates, changing seasons, weather, greenhouse and component characteristics, and greenhouse location (latitude and longitude). The rules contain parameters with values suggested for northeastern United States solar conditions but which may be adjusted for local solar climates that are significantly different.

Albright, L.D. 1997. Greenhouse thermal environment and light control. In Plant Production in Closed Ecosystems, E. Goto et al. (eds.). Kluwer Academic Publishers, the Netherlands. pp. 33-47.

Abstract

Greenhouse thermal environment results from the interactions among numerous factors: solar insolation; structural thermal characteristics; operation of heating, ventilation, and cooling systems; supplemental lighting; and properties of the greenhouse crop are among the most important. As greenhouse technology and sophistication evolve and environmental control becomes more complete, the importance of supplemental lighting increases. Luminaires contribute a sensible cooling load directly, and a latent cooling load indirectly by influencing transpiration. The objectives of this paper are to provide a general overview of greenhouse thermal environment, outline a methodology for greenhouse supplemental lighting control, and explore the interactions of supplemental lighting and the thermal environment. The approach used is based on modeling of greenhouse thermal processes, and simulations of supplemental lighting system control.

Albright, L.D. 1995. Controlling Greenhouse ventilation inlets by pressure difference. HortTechnology 5(3):260-264.

Summary

Computerized control of greenhouse climate has increased the importance of air distribution and mixing. This report reviews the fluid mechanics aspects of air flow through ventilation inlets, and external pressures imposed by winds, and applies the analyses to suggest methods of inlet control that improve traditional greenhouse ventilation. The suggested improved control has been implemented in a five-section research greenhouse on the Cornell campus and has improved climate control significantly during times of ventilation. Potential pitfalls in implementing the improved control methods are discussed.

Albright, L.D. 1995. Greenhouse lighting control to daily PPF integral, with energy and cost consequences. ASAE paper No. 954487. ASAE, 2950 Niles Road, St. Joseph, MI 49085-9659, USA. 22 pp.

Abstract

Supplemental lighting control rules are defined and, from them, an accompanying computer simulation program is used in conjunction with ten years of hourly weather data to test the efficacy of the rules applied to commercial greenhouses to achieve a consistent daily PPF integral every day. Control decisions are based on the current day's accumulating solar data. The rules do not require historical databases of weather characteristics, nor do they require daily weather forecasts. The model is sensitive to time-of-day electricity rates, changing seasons, weather, greenhouse and component characteristics, and greenhouse location (latitude and longitude). The rules contain several parameters with values suggested for northeastern United States solar conditions, but which may be adjusted for local solar climate should it be significantly different.

Both, A.J., L.D. Albright, S.S. Scholl, and R.W. Langhans. 1999. Maintaining constant root environments in floating hydroponics to study root-shoot relationships. Acta Horticulturae 507:215-221.

Abstract

The design and operation of a floating hydroponic system are described. The nutrient solution temperature and dissolved oxygen concentration in this hydroponic system were maintained with two simple control mechanisms. During a 24 day growth trial with lettuce (Lactuca sativa L., cv Vivaldi), nutrient solution temperature was controlled to 24 ± 0.3ºC and the dissolved oxygen concentration to 8.4 ± 0.2 mg-L^-1. Measurements of shoot fresh and dry mass as well as root dry mass of plants aged from 11 to 35 days after sowing were taken. Desired nutrition and pH levels in this closed recirculation system were maintained manually. Greenhouse air temperature and daily integrated light level were precisely maintained at consistent levels throughout the experiment. Example data of plant response showed a rapid decline in root-shoot ratio shortly after transplant, followed by a gradual decline towards final harvest (35 days after sowing). Root-shoot ratio at final harvest was 10%. Percentage of shoot dry matter declined steadily from 8% at transplant to 4% at final harvest. Results showed an improved environment control can result in highly uniform plant production.

Both, A.J., L.D. Albright, and R.W. Langhans. 1999. Design of a demonstration greenhouse operation for commercial hydroponic lettuce production. ASAE paper No. 994123. ASAE, 2950 Niles Road, St. Joseph, MI 49085-9659, USA. 12 pp.

Summary

A long-term research project resulted in the design, construction, and operation of a commercially scaled demonstration greenhouse for hydroponic lettuce production. One full year of production is planned to verify the economic feasibility of the developed growing system. An agricultural cooperative plans to use the demonstration greenhouse as a training facility and license the developed technology to prospective greenhouse growers. The ultimate goal is to create new and exciting opportunities in an emerging high-tech vegetable industry.

Both, A.J., L.D. Albright, and R.W. Langhans. 1998. Coordinated management of daily PAR integral and carbon dioxide for hydroponic lettuce production. Acta Horticulturae 456:45-51.

Abstract

The interaction between daily integrated photosynthetically active radiation (PAR) and elevated aerial CO₂ concentration was studied during plant growth experiments with leaf lettuce (Lactuca sativa L., cv. Vivaldi) grown in a nutrient film technique system in a greenhouse. Accurate control of all environment parameters (except relative humidity) and four identical greenhouse sections constituted the experimental setup. Supplemental lighting (high pressure sodium lamps) was used to provide additional PAR to the lettuce on days when too little sunlight was available to reach the required daily light integral. Two experiments with four treatments each were performed to investigate six integrated PAR/CO₂ concentration combinations: 11/1500, 12/1250, 13/1000, 14/750, 15/530, and 16/400 (mol-m^-2-d^-1/µmol-mol^-1). The target integrated PAR levels were accurately maintained during each treatment but the two highest CO₂ concentrations could not consistently be maintained because periodic ventilation was required for accurate temperature control. Lettuce plants were grown for 24 days under these conditions after being grown in a growth room under optimum conditions for 11 days. Periodic harvests during the greenhouse growing phase provided shoot dry-mass data. Shoot fresh-mass and number of leaves per plant were determined at the final harvest 35 days after seeding. Plant growth under the six different treatments was virtually identical and resulted in an average shoot fresh-mass of 190 g with a dry matter percentage of 3.7%. The results of the described experiments show a flexible management strategy regarding daily integrated PAR level and aerial CO₂ concentration can be employed for the most economical lettuce production.

Both, A.J., L.D. Albright, R.W. Langhans, R.A. Reiser, and B.G. Vinzant. 1997. Hydroponic lettuce production influenced by integrated supplemental light levels in a controlled environment agriculture facility: experimental results. Acta Horticulturae 418:45-51.

Abstract

Bibb lettuce (Lactuca sativa L., cv. Ostinata) was grown in peat-vermiculite plugs placed in a recirculating hydroponic (NFT) system. Supplemental lighting was used to reach different PPF_target levels in each of 35 treatments. A second order exponential polynomial was developed to predict dry weight (DW) accumulation for PPF_target levels between 8 and 22 mol-m^-2-d^-1. Little difference in DW production was noted between lettuce grown under daytime and nighttime lighting. Tipburn was prevented using a fan blowing greenhouse air vertically down onto the lettuce plants. Marketable (150 g fresh weight) lettuce heads were produced in 24 days after transplant while receiving an average PPF_integral of 17 mol-m^-2-d^-1.

Both, A.J., L.D. Albright, R.W. Langhans, B.G. Vinzant, and P.N. Walker. 1997. Electric energy consumption and PPF_i output of nine 400 watt high pressure sodium luminaires and a greenhouse application of the results. Acta Horticulturae 418:195-202.

Abstract

The PPF_i (instantaneous photosynthetic photon flux, in µmol-m^-2-s^-1) output and electric energy consumption of nine different 400 watt high pressure sodium (HPS) luminaires were measured at six mounting heights from 0.5 to 3.0 m in 0.5 m increments. Differences in luminaire efficacy and PPF_i distribution patterns were found, but too few luminaires were tested to reach statistically valid conclusions. The most efficient luminaire proved 25% more energy efficient than the least efficient luminaire. PPF_i data from one of the luminaires tested was used to design a research greenhouse, which required uniform PPF_i distribution patterns at various PPF_i levels.

Ciolkosz, D.E., L.D. Albright, and A.J. Both. 1998. Characterizing evapotranspiration in a greenhouse lettuce crop. Acta Horticulturae 456:255-261.

Abstract

Tipburn, a physiological disorder of lettuce, has been linked to insufficient evapotranspiration (ET). Better understanding of ET in greenhouse lettuce crops may be useful as a management tool to control tipburn. A regression model is presented to characterize ET from greenhouse lettuce (Lactuca sativa L., cv. "Vivaldi") based on data from twelve crops grown in a nutrient film technique (NFT) system. Several CO₂ concentrations and daily light integrals were applied to the lettuce crops and the resulting daily ET integrals were measured. A regression model was derived for daily ET as a function of growth rate and the resulting daily and cumulative ET values were calculated and compared to measured values. ET rate was found to vary linearly with growth rate (R sq. (adj) = 0.63) but higher CO₂ levels were associated with lesser values of the slope of the relationship. Modeled and measured data were in good agreement even though relative humidity was not included in the model. An equation is presented that may be useful to calculate daily ET targets that must be achieved to prevent tipburn in hydroponic lettuce.

Ciolkosz, D.E. and L.D. Albright. 1997. Evaluation of whole plant transpiration as affected by greenhouse air movement. ASAE paper No. 974029. ASAE, 2950 Niles Road, St. Joseph, MI 49085-9659, USA. 18 pp.

Abstract

Investigations were conducted to determine the degree to which evaporation of reverse osmosis treated water from petri dishes can be used to predict evapotranspiration in hydroponic greenhouses and, in turn, to evaluate airflow systems for their ability to induce evapotranspiration. The relationship between crop evapotranspiration and dish evaporation was found to be linear, with a R²_adj of 0.592. Adding CO₂ concentration to the relationship improved the R²_adj to 0.895. Severity of tipburn also evinced a relationship with dish evaporation rate, but as a step function. Dish evaporation rates greater than 2 cm per day resulted in the least tipburn on the crops. The crop coefficient, K_c, varied in a manner consistent to that of field crops, except for a sharp drop at the time of plant respacing. The pan coefficient, K_c, showed no noticeable trends with respect to time, and had an average of 0.215. Side by side comparisons of different air distribution systems suggested that air distribution has a large effect on dish evaporation (and, hence, plant evapotranspiration) and that unit heaters placed in a collision flow or shear flow configuration can achieve a greater level of uniformity of evaporation than use of overhead turbulator fans. The application of this information to the design of air distribution systems for greenhouses is discussed.

Goto, E., L.D. Albright, R.W. Langhans, and A.R. Leed. 1994. Plant spacing management in hydroponic lettuce production. ASAE paper No. 944574. ASAE, 2950 Niles Road, St. Joseph, MI 49085-9659, USA. 13 pp.

Abstract

Spacing is an important management tool in hydroponic lettuce production. Improved spacing management is expected to reduce unused growing area and result in higher productivity. However, no method has been proposed to evaluate and compare different spacing management options. In this study, three different spacing options were tested in a hydroponic lettuce production system. Two kinds of productivity are discussed in relation to plant form, growth rate and quality: productivity per gross growing area and productivity per net growing area. The area covered by plants (net area) was estimated from the projected plant area using an image analysis technique. A growing area utilization efficiency factor is introduced to compare practical spacing management with idealized spacing management for individual days during a production period, and over the entire production period.

Goto, E., A.J. Both, L.D. Albright, R.W. Langhans, and A.R. Leed. 1996. Effect of dissolved oxygen concentration on lettuce growth in floating hydroponics. Acta Horticulturae 440:205-210.

Abstract

Lettuce growth experiments were carried out to study the effect of sub- and super-saturated dissolved oxygen (DO) concentrations on the growth in floating hydroponic systems. The hydroponic systems had the pure O₂ and N₂ gas supply apparatus with a precise DO control. The system made it easy to increase DO concentration higher than the saturated level. Lettuce plants of Day 11 were grown until Day 35 under various DO concentrations: sub-saturated, saturated, and super-saturated concentrations. There was no significant differences in fresh weight, shoot and root dry weights among the DO concentrations: 2.1 (25% of the saturated at 24ºC), 4.2 (50%), 8.4 (saturated), and 16.8 (200%) mg/L. The critical level for lettuce growth was considered to be lower than 2.1 mg/L. Neither root damage nor delay of shoot growth was observed at any of the studied DO concentrations. From the results, it can be concluded that the designed DO control system is a practical and economical method to maintain an optimum DO concentration for lettuce production in floating hydroponics.

Setiawan, A., L.D. Albright, and R.M. Phelan. 1998. Simulation of greenhouse air temperature control using PI and PDF algorithms. Proceedings of the first IFAC Workshop on Control Applications and Ergonomics in Agriculture, Athens, Greece. June 15-17, 1998. pp. 111-116.

Abstract

Pseudo-Derivative-Feedback (PDF) control is compared to PI control through simulation using an approximated dynamic system thermal model of the greenhouse and through experimental results. The effects of time delays on control system performance for both PDF and PI control are demonstrated. Results showed PDF control to have a better load handling capability than PI control. PDF control was exceptionally better than PI for systems without time delay and significantly better for systems with time delay.

Thompson, H.C., R.W. Langhans, A.J. Both, and L.D. Albright. 1998. Shoot and root temperature effects on growth of lettuce, Lactuca sativa, in a floating hydroponic system. Journal of the American Society for Horticultural Science 123(3):361-364.

Abstract

Butterhead lettuce (Lactuca sativa L., cv. Ostinata) was used to study lettuce production at varied shoot (air) and root (pond) temperatures. A floating hydroponic system was used to study the influence of pond temperature on lettuce growth for 35 days. Pond water temperature set points of 17, 24 and 31ºC were used at air temperatures of 17/12, 24/19, and 31/26ºC (day/night). Pond temperature affected plant dry mass, and air temperature significantly affected growth over time. Maximum dry mass was produced at the 24/24ºC (air/pond temperature) treatment. Final dry mass at the 31/24ºC treatment did not differ significantly from the 24/24ºC treatment. The 24ºC pond treatment maintained market quality lettuce head production in 31ºC air. Using optimal pond temperature, lettuce production was deemed acceptable at a variety of air temperatures outside the normal range, and particularly at high air temperatures.

Wheeler, E.F., L.D. Albright, R.M. Spanswick, L.P. Walker, and R.W. Langhans. 1998. Nitrate uptake kinetics in lettuce as influenced by light and nitrate nutrition. Transactions of the ASAE 41(3):859-867.

Abstract

A mathematical relationship was developed which shows environmental influences of light and nitrate nutrition on growth and nitrate uptake kinetics. Growth chamber experiments provided data for model development and validation. Ion-specific macroelectrodes determined nitrate depletion from recirculating solutions in short-term kinetic tests. Lettuce (Lactuca sativa, cv. Ostinata) was grown under three light levels and three nutrient solution nitrate contents which represented a range of adequate and inadequate environments. Larger, faster-growing plants should have a larger demand for nitrate and hence larger uptake rates than smaller, environmentally stressed plants. Results showed higher sustained levels of nitrate uptake by larger plants. Neither the severity of stress under which a plant was grown nor the plant size were the sole determinants of maximum potential uptake behavior, however. Increased light level was related to an increased ability to transport nitrate on a short-term basis. Increased light level was associated with increased maximum nitrate uptake rates (V_max) as described by the Michaelis-Menten relationship. The effects of environmental light and nitrate levels on nitrate uptake was incorporated into a power relationship where the maximum uptake velocity was determined in relation to the shoot growth rate.

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Last updated: 11/17/02