Rockwool Slab Drip Irrigation
Rockwool (an inert fibrous material produced from a mixture of volcanic rock, limestone, and coke melted at 1500 to 2000˚C extruded as fine fibers and pressed into loosely woven sheets) has excellent water-holding and aeration characteristics, making it a very desirable rooting medium. A typical rockwool slab (0.3 x 0.8 x 3.6 meters) is encased in plastic. Small holes or cuts are made along the base of the plastic casing that allows excess nutrient solution to flow from the slab while keeping a small depth of nutrient solution in the bottom of the plastic casing.
This method of growing is as follows: a tomato seed is germinated in a small rockwool cube; and when the tomato seedling has initiated true leaves, the cube is placed into a larger rockwool block. When the plant roots are about to emerge from the base of the block, the rockwool block is placed on an opening in the rockwool slab. The nutrient solution or water is delivered at the base of the plant in the rockwool block with sufficient volume so that the solution will flow into the rockwool slab. The management of the growing system in terms of nutrient solution composition, and frequency and amount delivered to the plant is based on environmental factors, such as temperature and light conditions, and plant status, such as size and stage of growth.
The nutrient solution that accumulates in the slab must be periodically monitored for its electrical conductivity (EC), and when reaching a certain level, the slab is leached with pure water to remove accumulated salts, with the leaching water being applied through the drip irrigation system. Therefore, an environmentally acceptable means of disposal of the effluent from the slab is needed. A rockwool slab can be reused several times and then discarded. In the Colorado greenhouses, the rockwool slabs are replaced on a schedule of 16-18 months. Currently for the hydroponic growing of tomato, rockwool is the preferred rooting medium worldwide.
Perlite Bag Drip Irrigation
Perlite (a natural substance crushed and heated to 1000˚C forming a white, lightweight aggregate with a closed cellular structure) is placed in a plastic bag of about the same dimensions as a rockwool slab. Small holes or cuts are made along the base of the plastic bag that allow excess nutrient solution to flow from the bag while keeping a small depth of nutrient solution in the bottom of the bag.
A tomato seed is germinated in either a rockwool or germination cube; and when the tomato plant has true leaves, the cube is placed into either a larger rockwool block or a cup containing either perlite or rockwool. When the roots are about to emerge from the base of the block or cup, the plant is placed into an opening in the perlite bag.
The nutrient solution or water is delivered to the base of the plant in the rockwool block or cup by means of a drip irrigation system. The composition of the nutrient solution and its schedule for delivery are based on environmental conditions and plant growth stage as described for the rockwool slab method. The nutrient solution in the perlite bag is monitored for its EC, and when the EC reaches a certain level, the bag is leached with pure water applied through the drip irrigation system. Therefore, an environmentally acceptable means of disposal of the effluent from the perlite bags is needed. The perlite in the bag can be used to produce two crops and then must be discarded.
