Research Accomplishment Reports 2009

Optimizing the Water and Air Relationship and Nutrient Concentration in a Controlled Water Table Irrigated Container Growing Medium

J.W. Buxton
Department of Horticulture

 

Non-Technical Summary

Maintaining optimum ranges of water and fresh air in a container growing medium during a crop production cycle. A container growing medium must supply optimum concentrations of all nutrients. Fluctuating water/air ratio in the growing medium will create a better root growing environment. Gradually changing the concentration of nutrients in the fertilizer solution.

2009 Project Description

The water and air relationship in container growing medium is critical to optimum plant growth. The Controlled Water Table Irrigation System (CWT) was modified and improved for use in the commercial greenhouse and nursery industry. CWT is capable of maintaining an optimum air/ water relationship in a container growing medium during crop production.

The CWT is a modification of traditional capillary mat irrigation. A capillary mat is placed on a level surface with one side suspended in a trough of water maintained at a constant level (water table) at or below the bench surface with a float valve. The capillary mat draws water by capillarity, from the trough upward and then horizontally across the level bench. The water content in the capillary mat is constant across the bench at equilibrium. A root barrier on top of the capillary mat prevents roots from growing into the mat, but allows water movement to the container growing medium. The growing medium, by capillarity, absorbs water from the mat. As the vertical distance between the water in the trough (water table) and the container bottom increase, the amount of water in the capillary mat and container growing medium decrease and is at an increasing lower water potential. Water from the capillary mat replaces the water absorbed by plant roots or is loss through evaporation. The water absorbed from the capillary mat is replaced by water from the trough, which in turn is resupplied from the water source. Individual plants on the bench regulate the amount of water absorbed from the growing medium.

Studies:

A.The optimum distance between the water table and container bottom was evaluated for combinations of growing medium texture, depth of growing medium, and plant development stage.

B. the water table fluctuate between an upper level and a lower level.

C. Evaluated fertilizer concentration at stages of plant development.

Dissemination of information: Oral or poster presentations at professional, local or regional trade association meetings; abstracts and proceedings of meetings.

Use in other research programs:

A. To automatically irrigate plants on small to large areas in research greenhouses;

B. To produce clean roots for extraction of bioactive sorghum root exudates.

Student projects:

automatically irrigate plants in retail sales area; grow a small quantity of lettuce in the home; and study fertilizer concentrations on plant growth.

Course demonstrations:

study nutrient deficiencies; and show the effect of water stress on plant growth. Extension publication: Detailed construction of a CWT irrigation system.

In preparation:

modifying a pet watering system to maintain plants in the home; and automatic irrigation of an outdoor flowerbed.

2009 Impact

Lettuce: Seedlings, growing in Oasis cubes, were placed directly on surface of capillary mat/root barrier. Roots grew between the root barrier and a sheet of Styrofoam. Lettuce grew better if the CWT was at 0 cm than at 1 or 2 cm. However, the size of plant decreased as the distance from the trough increased and correlated with a change in the concentration of elements in the capillary mats. Water content and plant growth: The water content in growing medium decreased linearly from 0 cm to 12 cm in plug containers and 0 cm to 5 cm in 15 cm tall containers. The water content in 2.6 and 4.4 cm plugs was 45% and 41% greater at CWT of 0 cm than at 12 cm. In the 15 cm container the water content at 0 cm was 11% greater than at 5 cm. Crops were grown in several growing medium textures and depths ranging from plug trays to 1+-gallon containers. The best placement of the water table for seed germination was 1 to 2.5 cm below the container bottom to ensure that sufficient water reached the seed. After germination, the water table was dropped to 2 to 3 cm below the bench to prevent excess water in the growing medium.

Geraniums: A. Plants grown at CWT of 0 and 2 cm were larger than those at CWT of 4 and 6 cm. Plants near the trough were larger than those on opposite side of bench. An analysis of capillary mat water showed that the concentration of elements N, P, K decreased from the trough to the fifth or sixth plant from the trough. B. A trough in middle of bench, compared to on the side of bench, reduced distance between the trough and containers. Visual differences were not observed between plants. C. The fertilizer concentration was changed during the production. The leaf area of plants grown continuously at 100 ppm was less than with 150 ppm N for 2, 4 or 6 wks of the 8 wk production period. D. The water potential decreased linearly from CWT of 0 cm to 6 cm. At mid-day, on bright days, the water potential was slightly lower from growing medium surface to container bottom regardless of water table placement. E.

Other studies: CWT was successfully used for the commercial production of many species of bedding plants, vegetable transplants, chrysanthemums, poinsettias, tomatoes etc. The principles of CWT were employed in designing a system for automatically growing and maintaining plants in the home and in an outdoor flowerbed.

CWT irrigation has several advantages over other commercial irrigation systems: a. Constant and optimum moisture and air content maintained in growing media regardless of varying environments within greenhouse. b. Water stress reduced and growth rate and quality of plants potentially increase. c. No runoff occurs, thus no pollution of natural water sources; the nutrient solution is held within the capillary mat under constant tension; water is lost only through transpiration and evaporation. d. reduced potential for disease transfer. e. large pumps and holding tanks not used.

2009 Publications

Buxton, Jack W., Janet Pfeiffer, Darrell Slone. 2008. Controlled Water Table Irrigation for Container Crops. HO- 84:www.ca.uky.edu/agc/pubs/ho/ho84/ho84.html

Geneve, R.L., Kester, S.T. and Buxton, J.W. 2004. Capillary mats alter the water content in medium during mist propagation of Dendranthema. HortScience 39(4):1-4.

Buxton, J. W., J. Pfeiffer and D. Slone. 2004. Fluctuating Controlled Water Table Irrigation. (Abstract) HortScience 39(4): 769.

Lewis, Kyle and J.W. Buxton. 2004. Automat Irrigation of Container Plants in Outdoor Sales Area. (Abstract) HortScience 39(4):769.

Buxton, J.W. and J.A. Pfeiffer. 2003. Fluctuating Controlled Water Table Irrigation on Geraniums. New Crop Opportunities Research Report. Agriculture Experiment Station.

Buxton, J. W. and J. A. Pfeiffer. 2002. Constant compared to fluctuating controlled water table irrigation on geraniums. (Abstract) HortScience. 37:

Buxton, J. W. and Robert McNeil. 2001. Controlled water table irrigation for nursery crops. Proceedings of International Plant Propagators. 46:606.

Buxton, J.W. and T.D. Phillips. 2000. A laboratory demonstration of water stress on plant growth. (Abstract)97th International Conference of the American Society for Horticultural Science. HortScience 35:465.

Mach, C. and J.W. Buxton and R.S. Gates. 2000. Controlled water table irrigation system effect on growing medium water potential. (Abstract) Southern Region of American Society for Horticultural Science. Lexington Ky. HortScience 35:565.

Buxton, Jack W. and Wenwei Jia. 1999. A controlled water table irrigation system for hydroponic lettuce production. Proceedings of the International Symposium on Growing Media and Hydroponics. Acta Horticulturae No. 481:281-287.

Buxton, J.W. and T. Phillips. 1999. Using a controlled water table irrigation system for class demonstrations of plant growth. (Abstract)96th International Conference of the American Society for Horticultural Science. HortScience 34:470.

Buxton, J.W. and Wenwei Jia. 1999. An automatic, controlled water-table irrigation system for vegetable transplant production. (Abstract)96th International Conference of the American Society for Horticultural Science. HortScience 34:523.