The controlled water table irrigation system (CWT) consists of a capillary mat placed on a level bench so one side extends over the edge of the bench into a trough containing a nutrient solution maintained at a controlled distance below the bench. The nutrient solution is drawn by capillarity up to and over the bench surface. As plants use the nutrient solution or as water evaporates from the media, it is replaced from the trough. The automatic system maintains a constant air/water ratio in the growing media. Study 1: Geraniums were grown in 15-cm pots at 0, 2, and 4 cm CWT. Geraniums at 0 and 2 cm CWT had the greatest leaf area and dry weight. Plants at 0 and 2 cm CWT were more than 25% greater at 4 cm CWT. The roots of plants at 0 cm CWT were concentrated at 2 to 4 cm above the bottom of the container; whereas roots at 2 cm CWT uniformly extended from the center to the bottom. Study 2: Water potential in a coarse and fine textured media was determined at the bottom, middle and top of the container at 0, 2, and 4 cm CWT every 2.5 h during the light period. Water potential was about the same in each media within each CWT treatment. At the container bottom at 0 CWT water potential was 0; whereas the water potential at 2 and 4 CWT was lower. The water potential from top to bottom decreased slightly about mid afternoon on a sunny day when water demand was the greatest. The CWT system is potentially a commercially adaptable irrigation system for container crops. It also is a cheap, reliable tool for studying water stress on the crop growth and quality.
Jack W. Buxton
Jack W. Buxton and Wenwei Jia
Cabbage seed was germinated and grown to transplanting size in a 98-cell tray using an automatic irrigation system based on the principle of maintaining a constant water table (CWT) relative to the growing medium in transplant trays. Seedlings obtained a nutrient solution from a capillary mat with one end suspended in a trough containing the solution. The distance between the nutrient solution surface and the transplant tray bottom was regulated with a water level controller. The nutrient solution was resupplied from a larger reservoir. A polyester material on top of the capillary mat allowed solution movement to the roots but prevented root penetration into the mat. The water table placement below the tray determined the water content in the growing medium. Seedling growth was evaluated using two growing media combined with two water table placements. Excellent quality seedlings were produced; the CWT irrigation system satisfactory provided water and nutrients for the duration of the crop. The only problems observed were dry cells, less than 2%, because of no media–mat contact and algae growth on the media surface using the higher water table. The CWT irrigation system is adaptable to existing greenhouse vegetable transplant production systems. It is automatic and can provide a constant optimum amount of moisture for seedling growing. It can be adjusted for phases of seedling growing such as more water during germination and can create water stress near transplanting time to either harden off or hold plants because of unfavorable planting conditions.
Guoqiang Hou and Jack W. Buxton
Through control of light intensity and CO, concentrations, three levels of starch (low, medium and high) in marigold seedlings existed at sunset. The range in starch concentration represented that encountered under average greenhouse conditions. For each starting starch concentration, an optimum temperature was initially determined based on first and second order reactions on the corresponding starch decline curve. Every day, during seedling growth in the greenhouse, the starch concentration at sunset was predicted based on primarily the quantity of light received throughout the day; the night temperature was adjusted to the predicted optimum night temperature setting. Based on these studies a significant improvement in seedling growth can be achieved with significantly less heating cost.
Jack W. Buxton and Wenwei Jia
Lettuce was produced using a new concept of hydroponics. The system is based on maintaining a constant water table (CWT). Plants grew on a flat surface and obtained the nutrient solution from capillary matting. One end of the mat was suspended in a trough containing the nutrient solution. The distance between the nutrient solution in the trough and the bench top was kept constant with a water level controller. The nutrient solution was resupplied from a larger reservoir. A ground cover on top of the capillary mat provided nutrient movement to the roots but prevented root penetration. Lettuce seedlings, germinated in small plug trays, were placed in holes cut in a 2.5-cm-thick styrofoam sheet. The styrofoam provided seedling support as well as protected the roots. Roots grew on the surface of the ground cover and were easily removed at harvest. The CWT could be adjusted by changing the height of the water level controller. The CWT concept of hydroponic production does not require pumps nor large storage reservoirs. No runoff occurs; the only nutrient solution used is that required by plants and a minimum amount of evaporation from the ground cover surface. Disease potential should be less than in other systems.
Guoqiang Hou and Jack W. Buxton
The relationship between initial total non-structural carbohydrate concentration (TNCi) in marigold seedlings, night temperature, and night length were evaluated. Seedlings containing an average of 7.2, 18.1, and 23.5 mg/100 mg dwt of nonstructural carbohydrate (TNC) at sunset were treated with night temperatures of low (10°C), medium (17°C), and high (24°C). Starch and soluble sugars were determined at intervals during the night. TNC concentration at the end of the night is a function of the night temperature, TNCi concentration at sunset, and the night length. A model describing the relationship of these variables and their interactions was derived to estimate TNC concentration at any time during the night. This model when solved for temperature (t) establishes a temperature that will regulate the metabolic rate so the TNC concentration is metabolized efficiently to some minimum concentration by the end of the dark period. t = (–2.93 + 1.14 TNCi + 0.74 T – TNC – 0.48 TNCi * T)/(–0.18 + 0.011 TNCi + 0.04*T), R 2 = 0.88**). Thus, by knowing TNCi (possibly by near-infrared spectroscopy), the length of the night, and, assuming some minimum concentration for TNC by the end of the dark period, the night temperature is established.
Jack W. Buxton and John N. Walker
Natural-light growth chambers constructed within a greenhouse compartment were equipped with a ventilation/circulation system, two stages of heating, and evaporative cooling. Air drawn from the greenhouse compartment continuously ventilated the chambers; the air was heated or cooled to the set-point temperature. A computer-controlled environmental system maintained uniform temperatures within the chambers and maintained the temperature within ±1C of the set point at night and during periods of low solar radiation; during higher solar radiation periods, control was not as precise. Carbon dioxide concentration was accurately maintained, and the photosynthetic photon flux from supplemental high-pressure sodium lamps was ≈200 μmol·m-2·s-1. The natural-light growth chambers provide a means for studying the interactive effects of temperature, light, and other environmental variables in experiments to increase production efficiency.
Kyle P. Lewis* and Jack W. Buxton
Maintaining adequate water for container plants in outdoor sales areas is difficult during the late spring and summer. In mass marketing areas employees are uninformed about the water requirements of plants under various environmental conditions. Plants often are severely stressed and over all quality reduced. A system was developed to automatically irrigate container plants in an outdoor sales area. The system is a modification of the Controlled Water Table (CWT) irrigation system developed at the Univ. of Kentucky (U.K.). The sales area consisted of 2 shelves each 2.44 m long and 0.28 m wide. A trough was constructed from a 5-cm diameter pipe with a 1/4 slot; it was attached to the back side of the shelf. One side of a capillary mat, placed on the shelves, was suspended in the trough containing water. Two systems were used to maintain the level of water in the trough. One was a small float valve installed in a 10-cm PVC pipe which was attached to the 5-cm PVC pipe. The float was adjusted to maintain the water in the trough 2 cm below the top of the shelf. The water reservoir consisted of a 20-cm diameter PVC pipe, 1.22 m long that held 70 L of water. A second system maintained a constant water level in the trough using Torricellian tube principle. The water reservoir was the same as above except it was tightly sealed so no air could leak from the system. The water table was maintained 2 cm below the bench surface by rotating a hole in small cap. A variety of plants in containers, ranging from 10 cm to 5 L pots were maintained without water stress, in a greenhouse environment as well in an outdoor environment for several weeks.
Jack W. Buxton*, Janet Pfeiffer, and Darrell Slone
A controlled water table irrigation system (CWT) automatically provides water to plants. One edge of a capillary mat, on the bench surface, draws water from a trough (water table) below the bench. Each treatment trough was 30 cm long. As the distance between the water surface and the bench surface increases, the water in the growing medium decreases, the air increases; and the water potential decreases. In previous studies a constant CWT of 2 cm below the bench surface was the optimum placement for producing 15-cm pots of geranium. In this study the water table fluctuated between two distances below the bench surface. The fluctuating treatments were 2 cm to 3 cm, 2 cm to 4 cm, and 1 cm to 4 cm. The control treatment remained at a constant 2 cm below the bench surface. The fluctuating treatments were established by using two liquid level controllers connected to a switching mechanism that allowed the water table to fluctuate between the treatment settings. The rate of movement from the higher level to the lower level was determined by the rate of transpiration and evaporation occurring in individual treatments. The amount of water used for each treatment was determined by counting the number of times the solenoid turned on and multiplying this by the amount of water added to the trough. The leaf area and dry weight were the same for plants grown in 2 cm, 2 to 3 cm, and 2 to 4 cm treatments and these treatments were significantly greater than plants in the 1 to 4 cm treatment. The amount of water used by all treatments was nearly the same.
Jack W. Buxton, Wenwei Jia, and Guoqiang Hou
The automatic subirrigation system consists of a capillary mat placed above a constant water level in a reservoir. The optimum mat height above the water level was established by slanting a flat surface so the difference in vertical height from one end of the surface to the other was 25 cm. A ground cover providing water movement but not root penetration was placed over the mat. The capillary mat extended beyond the lowest end of the slopped surface and into the reservoir, the mat at the lowest end of the slopped surface was at the same vertical height as the water in the reservoir and remained constantly saturated. Plug trays were placed at intervals of 2.5 cm in vertical height above the water level. An average of 96-100% germination was obtained with marigold, tomato, impatiens and pepper seed in trays placed 5-7.5 cm in vertical height above the water level. These seedlings continued to develop and reached transplanting stage quicker than other trays. The rate and % germination was less in trays placed on the surface nearer to the height of the water in the reservoir. Germination in trays above 12.5 cm was greatly reduced and seed that did germinate did not develop and eventually died.
Jack W. Buxton, Donna Switzer, and Guoqiang Hou
Marigold seedlings, 3 weeks old, were grown in natural light growth chambers at 3 day/night temperature regimes, 8°N/16°D, 13°N/20°D and 18°N/24°D, in a factorial combination with ambient and 1000-1500 ppm CO2. Seedlings were harvested at regular intervals during a 24 hr period and were analyzed for soluble sugars (reducing sugars and sucrose) and starch. Neither temperature nor CO2 concentration affected the accumulation of soluble sugars or starch during the day or night. The soluble sugar concentration ranged from 3% of dry weight at sunrise to 6% at mid-day; the concentration changed little during the night. Light intensity was different during replications of the experiment. Increased light intensity appeared to cause a slight increase in the soluble sugars maintained by the seedling during the day. Accumulated starch increased 6% to 8% from sunrise to late afternoon. Preliminary results indicate that light intensity greatly affected the concentration of starch. On the higher light intensity day, starch accumulated to a maximum of 18% of dry weight; whereas on the lower light intensity day the maximum concentration was 10%. During the night following the lower light intensity day, the starch concentration decreased to approximately 3% by the end of the night; following a brighter day the starch content was 13% at the end of the night.