Constant Water Table: A New Technique for Hydroponic Lettuce Production

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.

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498 PB 204 PROVIDING A CONSTANT, OPTIMUM, MOISTURE/AIR RATIO IN PLUG TRAYS DURING SEED GERMINATION AND SEEDLING GROWTH

HortScience ◽

10.21273/hortsci.29.5.502f ◽

1994 ◽

Vol 29 (5) ◽

pp. 502f-502 ◽

Cited By ~ 2

Author(s):

Jack W. Buxton ◽

Wenwei Jia ◽

Guoqiang Hou

Keyword(s):

Seed Germination ◽

Water Level ◽

Flat Surface ◽

Water Movement ◽

Ground Cover ◽

The Other ◽

Root Penetration ◽

The Difference ◽

Vertical Height ◽

Pepper Seed

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.

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Production of Vegetable Transplants with the Controlled Water Table Irrigation System

HortScience ◽

10.21273/hortsci.31.4.633a ◽

1996 ◽

Vol 31 (4) ◽

pp. 633a-633

Author(s):

Jack W. Buxton ◽

Wenwei Jia

Keyword(s):

Water Table ◽

Nutrient Solution ◽

Production Systems ◽

Irrigation System ◽

Root Penetration ◽

Growing Medium ◽

Cabbage Seed ◽

The Media ◽

Greenhouse Vegetable ◽

Solution Surface

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.

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