SOILLESS CULTURE TECHNIQUE AND ITS RELATION TO THE GREENHOUSE CLIMATE
Soilless culture techniques can be divided in different systems. The most important are substrate with a drainage system (a), substrate with recirculation of the nutrient solution (b), nutrient film technique (c) and ebb and flood system (d). With crops with a long growth/production period especially system a is used and rockwool is the most common substrate. The interest for peat as a substrate is declining. The risk of spread of diseases with recirculation of the nutrient solution is the main reason for the choice of the drainage system. Crops with a restricted growing period are often cultivated in systems b, c and d.
Soilless culture techniques allow a more accurate control of the root environment which offers possibilities for increase of the production and improvement of quality. It has the additional advantages of optimal use of water and nutrients, energy saving while soil disinfection is no longer necessary. On the other hand investments have to be done in construction and maintenance of the systems.
Control of the root environment means control of water and nutrient supply and temperature. Information on the needs of plants in relation to these factors is available and also still increasing. It is known that the water uptake of a plant depends on the level of transpiration. This level is influenced by climate factors inside and outside the greenhouse, but also characteristics of the plant are of importance (habitus, length, leaf area). Transpiration models are developed with which water supply can be automatized.
Need of nutrients is also influenced by climate factors, and by the growth stages of the crop, the desired quality level of the product and other factors. Computer based control systems for ionic composition and nutrient concentration will be available in the near future.
Nowadays computer-based control systems are being developed for optimization of growth, development and production of greenhouse crops. As mentioned also computer-based systems for control of water and nutrient supply are on the way. Because of the inter-dependence of factors of the root environment and the greenhouse climate, connections have to be made between the computer programmes for control of the greenhouse climate and root environment. In this combined control programme economic factors must also be incorporated in order to produced a high quantity and quality of products with low costs.