Can you help me understand the different types of hydroponic systems?

Answer: In its most basic definition, hydroponic production is the production of plants in a nutrient solution rather than soil. Many variations on this theme exist, but most production occurs in greenhouses. The investment required for a hydroponic greenhouse is typically higher than in-ground greenhouse production, but you have more flexibility with the plants and can grow in higher density, as well as charge a premium, so the returns can be higher. There are two basic hydroponic systems, non-recycled nutrient, where the nutrient solution is used once, and recycled nutrient systems. There are many variations within those two, but I will explain how they both work below. Non-recycled Nutrient SolutionPerhaps the most simplified system for producing greenhouse vegetables is where the floor of the greenhouse is used as the media for growing plants. This system can be on the ground or in a bed or trough, but usually consists of sand, perlite, pine bark, or gravel approximately 10 to 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 ? inches deep for sand and 3 inches deep for bark, with a fall of 2 inches per 100 feet 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 1,000 ppm.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 that contains the growing media. In this growing system, plants are handled just as if they were in a container. Recycled Nutrient SolutionThis can be used with gravel as medium or in troughs and the nutrient solution is pumped through the plants no less than every 30 minutes. The tank that contains the bulk nutrient solution should be of a capacity to supply three 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 3,500 ppm.The Nutrient Film Technique was invented in Britain but is commonly used for smaller crops such as herbs and lettuce. The plants are placed in shallow plastic troughs and the nutrient solution is continually pumped over the roots without any medium to hold the plants. The troughs are on a slope, so the nutrient solution is constantly recirculating. To learn more about hydroponics, consult the following resources: Cornell University Controlled Environment Agriculture programThere are many manuals and resources for Controlled Environment Agriculture (hydroponics) on the program web page. www.cornellcea.com/resourcesPublications/CornellPublications/index.html Resh, Howard. 2013. Hydroponic Food Production: A Definitive Guidebook for the Advanced Home Gardener and the Commercial Hydroponic Grower. Seventh Edition.This is a comprehensive guide to soilless culture with extensively new and updated contents from the previous edition published in 2001.