Development of an automatic ebb and flood watering system with estimation of evapotranspiration of a plug sheet

摘要

Soil-mix moisture in a plug tray with limited-volume can be easily changed by watering and evapotranspiration from a plug sheet consisting of plug seedlings, soil mix and a tray. Thus, timing and amount of watering are most important parts of skills in plug seedling production. An automatic ebb-and-flood watering system for controlling soil-mix moisture in a plug tray was developed and applied to tomato plug sheets. A plug tray with 128 cells (2.8 l/tray volume) was used for the experiment. The plug sheets were placed on a bench with an ebb-and-flood system. A plug sheet located in the center of the bench was weighed with an electric balance by suspending it from a steel frame. When integrated evapotranspiration of the plug sheet, estimated from decrease in weight of the plug sheet, reached over a setpoint of 1 100 g/tray during the daytime, all the plug sheets were watered from below. After the water in the bench drained, the integrated evapotranspiration was reset to zero. In this way, soil-mix moisture in the plug tray was controlled accurately in a proper range for growth of the plug seedlings during the culture period.