Soilless Culture Systems for Greenhouse Vegetables
Greenhouse vegetables can be grown using several different types of cultural systems. These include gravel, sand, troughs, containers, bags, etc. In each of these systems, nutrients can be supplied on a žone-time basisÓ or recycled continuously. Although there are several variations of each, the following is a brief description of some of the common soilless culture systems used for greenhouse vegetables.
Non-Recycled Nutrient Solution
Perhaps the most simplified system for producing greenhouse vegetables is where the floor of the greenhouse is used as the media for growing plants. This žwhole floorÓ system usually consists of sand or pine bark approximately 10-12 inches deep, separated from the underlying soil by a plastic barrier. To provide adequate drainage, a drain line should be installed under each pair of rows. Drain lines should be approximately 1 1/4" I.D. for sand and 3" I.D. for bark, with a fall of 2" per 100' of row.
Irrigation water and nutrients are supplied by a drip system with enough emitters per plant to provide sufficient quantities of solution. Leachates should be monitored frequently for total dissolved solids. When levels exceed 3500 ppm media should be leached with water until leachates are less than 1000 ppm.
Troughs and beds are also used for the production of greenhouse vegetables. These may be filled to a depth of 8:-10" with materials such as: sand, pine bark, rice hulls, cedar chips, perlite, sawdust, etc. Beds and troughs are usually 30 inches wide with a minimum of 24 inches between rows. A drain line (1 1/4" - 3" I.D.) should be placed at the bottom of each structure with a fall of 2" per 100'. Irrigation and nutrient solution are supplied using a drip system as described above.
Many greenhouse vegetables can also be grown in containers using the same type of media discussed for bed and trough culture. Containers should be of sufficient size to provide good aeration and drainage. Three to five gallon containers appear to be best. Irrigation water and nutrient solutions are supplied by a drip irrigation system.
Bag culture is similar to the use of containers with the only exception being that plants are grown in the bag which contains the growing media. In this growing system, plants are handled just as if they were in a container.
Recycled Nutrient Solution
Gravel culture utilizes beds (as previously described) filled with non-calcarious gravel from 1/8" to ½" in diameter. In this system, the nutrient solution is pumped through the beds frequently enough to prevent the plant from going into water stress. The irrigation frequently should not exceed 30 minutes.
The tank which contains the bulk nutrient solution should be of a capacity to supply 3 gallons per plant. Beds are irrigated to about 1" below the surface of the gravel and the tank refilled with the premixed nutrient solution daily or at least once every third day. The nutrient solution should be monitored frequently for total solids and replaced when levels approach 3500 ppm.
The nutrient flow technique can also be effectively used for vegetable production. In this system, nutrients flow either continuously or very frequently through a tube in which the plants are being grown. The volume and quality of the nutrient solution are maintained similarly to that in gravel culture.Hydroponics Index |