Speaking Plant/Fruit Approach for Greenhouses and Plant Factories

Abstract

Plant control systems are usually characterized by complexity and uncertainty. A skilled grower can deal well with various plants and yield good products using intuition and visual information, communicating with the plants. To realize such tasks scientifically, it is important to measure physiological responses of the plant using sensors and then use that information for environmental control for optimization. Such an approach is called the ‘speaking plant approach (SPA)’. This approach is also easy to apply storage processes. Such an application could be a ‘speaking fruit approach (SFA)’. Measurement, identification and optimization of plant responses (or fruit responses), as affected by environmental factors, are important tasks for the SPA (or SFA). It is, however, difficult to sufficiently address these tasks because plant responses are quite complex and uncertain, but intelligent control techniques can facilitate such tasks. This paper presents the concepts of SPA and SFA, an intelligent control technique for realizing the SPA (or SFA), and their applications for optimizing cultivation and storage processes, aimed at qualitative improvement of plants and fruits. In the cultivation process, the net photosynthetic rate of a tomato was maximized by the drainage and supply operation of a hydroponic solution and tomato growth during the seedling stage was optimized by nutrient concentration of a hydroponic solution. For the storage process, the rate of water loss in tomatoes was minimized by temperature. The optimal value of each environmental factor was not assigned a constant value but rather an optimal combination of maximum and minimum values. These results suggest that the optimal application of environmental stress to the plant allows for qualitative improvement of plants and fruits.