Evaluating a Cloud-Based Drip Fertigation System.

Due to the accident of the Fukushima Daiichi Nuclear Power Plant in 2011, surrounding farmlands were heavily contaminated with radioactive cesium (Cs). Since a fertile surface layer of the farmlands was replaced by non-fertile sand as a result of decontaminating processes, resuming crop production may be hindered by less fertile soils. We thought that using fertigation techniques would overcome problems on crop production in less fertile soils. A commercially-available cloud-based fertigation system (CBFS) was evaluated while green pepper was grown in a green house. To monitor temporal changes in water and solute contents in the 2-D soil profile, time domain reflectometry (TDR) probes for measuring volumetric water content and electrical conductivity were horizontally installed under a drip line in a less fertile soil at 5, 10, 20, 30, 40 cm deep from the soil surface. Type-T thermocouple junctions for measuring soil temperature were also installed at the same location as the TDR probes. Through the Internet, the CBFS collected soil water content measured with a single soil moisture sensor installed at the soil surface in addition to solar irradiance measured with a pyranometer outside the green house. The CBFS regulated irrigation rates based on solar irradiance to compensate the amount of water consumed on a day before the day. Liquid fertilizer was applied with water every hour between 8 a.m. and 5 p.m. Soil water was symmetrically distributed under a dripper as the shape of a water droplet all day long. Daily changes in volumetric water content were ranged between 0.30 and 0.31 m³ m^-3 whereas electrical conductivity of soil water, representing fertilizer concentration, started decreasing from 75 mS m^-1 at around 8 a.m. up to 11 a.m., and leveled off with 60 mS m^-1 unil 12:20 p.m, then started increasing again until 6:00 p.m. to 75 mS m^-1. This result implied that a bell pepper plant absorbed nutrients only during daytime when the liquid fertilizer was supplied. There were no excess water and fertilizer leached out from the root zone, i.e. 40 cm deep.