水稲栽培において夏季の水位の管理は作物への水分供給としてはもちろん，温度管理や疫病予防にも関わり極めて重要である．現在にいたるまで我が国では水田水位の管理は人手によって行うことが一般的であり，稲作農家は定期的に圃場を訪れ水位を確認する巡回作業を行ってきた．近年，専業農家の高齢化に伴い，農業生産法人や余力のある農家への農地集約が散発的に発生した結果，これらの大規模農家が所有する水田が広域に点在し，農業従事者が各農地を水位管理のために巡回することが労働生産性の向上を妨げるようになっている．そこで，水位管理の自動化に向けた水田水位計の設置が検討されている．水位計としては超音波や浮体を利用したものが存在するが，設置環境の制約が少なく，機械的故障も発生しない静電容量型が有力である．本研究では，櫛形電極を利用した水田用静電容量式水位計を薄膜印刷技術を活用して低価格に実現した．静電容量式水位計で高精度の測定を行うには設置環境にあわせた校正が必要になるが、我々は基準となる櫛形電極を追加することで自動校正を可能にし、設置するのみで校正済みの測定が可能である．これにより低価格で設置も容易な水田水位計が実現され，労働生産性の向上に寄与すると考えている．

Water management is one of the most critical task in paddy rice cultivation. Tight observation of water level is not only important for irrigation but also related to temperature management of paddy field or epidemic prevention process. Currently, the observation of paddy field in Japan is done generally by human. That is, farmer will keep patrolling multiple paddy field for a specific period of time. However, along with the aging of farmers in Japan, the fact that paddy fields in possession of one farmer are scattering in a large area makes the patrolling more and more laboring. Therefore, an fully automatic system for gathering water levels will be big improvement for the cultivation of paddy field. There are several types of water level sensors on the market such as ultrasonic based sensor or mechanical based sensor. However, these type of sensors either require tight control of the setup environment or are prone to be broken. To deal with those problems, the capacitive based sensor is a suitable candidate. In this research, we proposed the use of multiple interdigital capacitors (IDCs) to measure the level of water in paddy fields. Our sensor is able to self-calibrate with the change of environment. This is very important as the properties of paddy field environment is supposed to change during cultivating season. The self-calibration is implemented by adding reference IDCs (water reference and air reference).

【参考文献】

Tung Ta Duc, Masaru Mizoguchi, Yoshihiro Kawahara, Tohru Asami, “Error Reduction in Capacitive Based Water Level Sensor for Paddy Field,” 信学総大 2016, B-18-16, March 2016.