日本地球惑星科学連合2018年大会

講演情報

[EE] ポスター発表

セッション記号 A (大気水圏科学) » A-GE 地質環境・土壌環境

[A-GE31] 地質媒体における物質移動,物質循環と環境評価

2018年5月21日(月) 10:45 〜 12:15 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:小島 悠揮(岐阜大学工学部)、濱本 昌一郎(東京大学大学院農学生命科学研究科)、斎藤 広隆(東京農工大学大学院農学研究院、共同)、森 也寸志(岡山大学大学院環境生命科学研究科)

[AGE31-P06] Simultaneous measurement of soil matric potential and water content with dual probe heat pulse

*川島 知之1小島 悠揮2登尾 浩助3神谷 浩二2 (1.岐阜大学大学院自然科学技術研究科、2.岐阜大学工学部、3.明治大学農学部)

キーワード:マトリックポテンシャル、土壌水分量、双子プローブ熱パルス、熱伝導率、体積熱容量、多孔質体

Soil matric potential (Ψm) and soil volumetric water content (θ) are important hydraulic properties which control liquid water transfer in vadose zone. Those properties also can be utilized for evaluating slope stability and for managing irrigation. There are several methods to measure Ψm and θ, e.g., tensiometer, time domain reflectometry, and capacitance sensor. Those sensors have been commercialized and widely used. However, there are no commercialized sensor which can measure both Ψm and θ simultaneously, and, thus, they have been measured independently by installing multiple sensors at the same location. In that case, there are several problems that sensors interact one another, each sensor has different sampling volume, and moreover, purchasing multiple sensors requires a large cost. Therefore, the objective of this study is to develop a sensor that can measure Ψm and θ simultaneously, and to evaluate its performance.

We developed a sensor measuring Ψm and θ simultaneously by improving the sensor design of a Ψm sensor made of porous media in conjunction with dual probe heat pulse (DPHP) technique developed by Kojima et al. (2017). DPHP is a method to simultaneously measure volumetric heat capacity (C) and thermal conductivity (λ) of soil. Kojima et al. (2017) applied DPHP to a porous medium made of Kaolinite and equilibrated with surrounded soil. They measured C and λ of the porous medium and converted them into Ψm by the preliminary obtained relationship. We extended the DPHP probe in the porous medium from 40 mm to 80 mm, and made them projecting into soil. By this change, the sensor can measure thermal property in two places, i.e., in porous media and in soil. Ψm is estimated from the thermal properties of porous media, and θ is estimated from C of soil.

An experiment to obtain relationships between thermal properties of porous media and Ψm, and to evaluate the accuracy of θ estimation by the developed sensor (hereafter, DPHP Ψm-θ sensor). A cylindrical container (46 cm diameter and 9 cm height) was filled with soil (Andisol) with a bulk density of 0.84 Mg cm-3. Five DPHP Ψm-θ sensors, two 5TEs (METER Group, Inc.) which measure θ, two MPS-6s (METER Group, Inc.) which measure Ψm, and one tensiometer were inserted at 4.5 cm depth. The soil in the container was left in a constant temperature room (20°C) after it was saturated by tap water. The soil was naturally dried by evaporation for 30 days. The relationship between thermal properties of porous media measured with DPHP Ψm-θ sensor and Ψm measured with tensiometer and MPS-6 was evaluated. And the accuracy of θ estimation with DPHP Ψm-θ sensor was evaluated by comparing the estimated θ to that measured with 5TE.

The relationships between Ψm and C or λ of porous media could be expressed by a modified water characteristics curve model. Accuracies of Ψm estimation from C were 13%-18%, and those from λ were 13-15%. Thus, Ψm estimation from λ is more accurate than that from C. In addition, the measurable range of Ψm with λ was wider than that with C. While using λ to estimate Ψm had advantages in sensor performance, using C to estimate Ψm was more practical because the relationship between Ψm and C did not show significant inter-individual differences and temperature dependence. Each thermal property has advantages so that we can use both properties to accurately determine Ψm. The accuracy of θ estimation with DPHP Ψm-θ sensor was 6% which is sufficiently high.

In this study, a DPHP based sensor measuring Ψm and θ simultaneously was developed. The developed sensor could estimate Ψm and θ accurately, thus, it can be a powerful tool for variety of studies in vadose zone.



Citation: Kojima, Y., K. Noborio, M. Mizoguchi, and Y. Kawahara. 2017. Matric potential sensor using dual probe heat pulse technique. Agricultural Information Research. 26(4):77-85