Chapter 15

Greenhouse Production Systems

Soilless Culture

Soilless culture cultivation is intensively used in greenhouses to improve control over the growing environment and to avoid uncertainties in the water and nutrient status of the soil. Soilless culture is an artificial means of providing plants with support and a reservoir for nutrients and water. Soillesss culture systems have been recognized as a viable method of producing vegetables (tomatoes, lettuce, eggplant, spinach, melons, cucumbers, and peppers) as well as ornamental crops such as herbs, roses, freesia, and foliage plants. Some fruit crops—for example, strawberries and raspberries—are also well-suited to soilless culture systems. The classification of soilless culture considers the type of substrate and container, how the nutrient solution is delivered to the plant (e.g., drip irrigation; subirrigation; flowing, stagnant or mist nutrient solution culture) and the fate of the drainage nutrient solution: open (free-drain) or closed (recirculating water) systems. There are essentially two types of production systems used in soilless culture: (1) hydroponics and (2) substrate culture. Hydroponics is often reserved for those systems in which the plants are grown in water with no supporting medium for the roots. Substrate culture systems use substrate or media (e.g., sand, gravel, vermiculite, rockwool, peat moss, sawdust) to provide both physical support and the root environment required. Substrate culture is generally used for row crops, such as fruit vegetables (e.g., solanancea, cucurbits), strawberry and cut flowers (e.g., rose, gerbera, anthurium, etc.). Different containers (e.g., pots, bags, slabs) are used filled with substrate, or a combination of two or three different materials, such as the peat-perlite or peat-pumice mixture. These are illustrated in Figure 14.2.

Advantages and Disadvantages of Soiless Culture Systems

Advantages

The accurate control of plant nutrition compared to soil cultures, is also one of the most important advantages of soilless culture. When using water cultures or substrate cultures with inert substrates the level of nutrients, supplied to the crops are those chosen by the grower. This is not the case with soil cultures where in many cases excess nutrient levels in the soil from the previous crops led to salinity problems. Another advantage of the soilless culture related to plant nutrition is the ability to control the pH and the EC of the nutrient solution according to the requirement of the crop and the greenhouse conditions. Similar control in soil cultures is very difficult and expensive. The advantage of soilless culture related to the ease of irrigation applies mainly to certain soilless systems, such as nutrient-film technique (NFT) and other true hydroponic systems (where the plants have their roots immersed into the nutrient solution) and to sub-irrigated substrate culture and is not fully applicable to the rest of the soilless cultures using various inorganic or organic substrates.

Disadvantages

Introduction of soilless systems involves an increase of inputs for the construction and maintenance, compared to the cultivation in soil. The degree of increase of inputs depends on the soilless system and the degree of control measures required by the system adopted, i.e. the initial cost for establishing an NFT system is higher compared to the rockwool system, but the annual running cost is lower with the NFT system. To succeed with the soilless culture methods, one must have or to be able to learn and have some knowledge of how to grow the crop, plant physiology, elementary chemistry, familiarity with the control systems, etc. It is evident that soilless culture is not an easy operation. Successful commercial soilless cultures are demand good management and skilled staff.

Hydroponic Systems

Hydroponics, by definition, is a method of growing plants in a water based, nutrient rich solution. In hydroponic systems, no solid substrate is used except at the time of sowing, such as the case of vegetables where urethane sponges are used to raise seedlings. In hydroponic systems the roots of the plant are continuously or intermittently immersed in nutrient solution. Hydroponic systems are generally closed circuit with respect to nutrient-solution supply: the solution is recirculated from a supply reservoir either continuously or intermittently for a period of days or weeks. Hydroponics is a highly exacting and demanding system that requires a greater amount of production knowledge, experience, technical skill, and financial investment than many other greenhouse production systems. The three most common water culture systems in use today are nutrient-film technique (NFT), floating raft system, and aeroponic system.

Substrate Culture Systems

Substrate culture, commonly referred to as aggregate systems, involve the use of substrate materials such as sand, perlite, vermiculite, gravel, sand, peat moss, and rock wool. In this type of system, the role of the media is to support the plant roots and provide an environment for the water and needed nutrients. The substrate does not provide nutrients to the plants. Solutions provide the plants with essential nutrients. Differences in the media will require minor adjustments in the frequency and amounts of solution to be applied. Substrate culture systems are further categorized as open or closed irrigation systems. In an open irrigation system (e.g., drip, boom, sprinkler), nutrient solution is applied to the upper surface of the substrate in a bench or pot, and any excess solution applied is allowed to drain from the bottom of the container out to the environment. By contrast, a closed irrigation system (e.g., capillary mat, ebb-andflow, flooded floor) is any method for growing plants in which the nutrient solution is recirculated. Refer to Chapter 15, Greenhouse Irrigation Systems for a more indepth discussion on open- and closed-irrigation systems.

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