Evaluating the 2-D Distribution of Volumetric Water Content and Electrical Conductivity with Cloud-Based Drip Fertigation System.

Due to the accident of the Fukushima Daiichi Nuclear Power Plant in 2011, surrounding farms were contaminated with radioactive cesium (Cs). Contaminated but fertile surface soil was successfully decontaminated by replacing a less-fertile sandy soil, implying that crop productivity might be hindered. We thought that applying a fertilization irrigation technology could overcome the problem in crop production in a less-fertile soil. In this research, we evaluated the distribution of water and electrical conductivity in the less-fertile soil growing bell peppers in a greenhouse. A cloud-based drip fertigation system, ZeRo. agri (Routrek Networks, Inc., Kawasaki, Japan), determined the quantity of water for drip irrigation once an hour based on soil water content and solar irradiance using a pyranometer outside the greenhouse. To monitor the time series of 2-D distribution of volumetric water content and electrical conductivity in soil, time domain reflectometry (TDR) probes were horizontally installed, perpendicular to a drip line, at 5, 10, 20, and 30 cm below the soil surface. Thermocouple junctions (Type-T) for measuring soil temperature were installed at the same location as the TDR probes. Volumetric water content was little changed before and after irrigation during irrigation period in a day. This result suggested the amount of irrigation water supplied by the ZeRo. agri system was appropriate, meaning no excess water nor deficiency for bell pepper.