Innovations in crop production: a matter of physiology and technology

Crop production per unit greenhouse area has doubled during the last 25 years in The Netherlands, while the energy use has been drastically reduced. The growth conditions for plants have been improved significantly through understanding crop physiology in combination with new technologies. In this paper some of the recent innovations in greenhouse horticulture are discussed. Semi-closed greenhouses combine energy saving by storing heat in aquifers with yield improvement. These effects on yield are mainly due to a higher CO2 concentration. The next generation cultivation focuses on energy saving with lower costs. The main components of this concept are an intensive use of energy screens to conserve heat, controlled inlet and distribution of outside air to regulate air humidity, and flexible temperature set-points based on energy losses and plant demand. Greenhouse covers that scatter direct solar radiation without influencing the transmissivity improved crop production in several crops up to 10%. In tomato this increase was due to the improved vertical and horizontal light distribution, a larger photosynthetic capacity of the lower leaves and a larger leaf area index. In heavily shaded potted plants like anthurium and bromeliads, substantially less shading is necessary under diffuse light and well controlled growth conditions, which enhances crop photosynthesis. In this way yield improvements of up to 50% were observed. Some growers have already installed LED lamps as source for assimilation light. Modern LEDs may convert electricity into light 25% more efficiently than high pressure sodium lamps. Even more important are the possibilities to influence physio-logical and morphological processes by manipulating the positioning, timing and spectrum of the lamps. A large number of these innovations began with crop and greenhouse models, which are powerful tools in research. New developments in simulating plant processes can be found in functional-structural models (FSPM) and systems biology models. They can be used to design new production systems or to predict the ideal phenotype of plants. Plant monitoring based on combinations of plant sensors (e.g., chlorophyll fluorescence) and models will be used more and more to adjust the greenhouse envi¬ronment to the needs of the plants. Application of models through web-based services are likely to be at the point of large scale introduction to support growers in their decisions.