title: An improved sensor for precision detection of in situ stem water content using a frequency domain fringing capacitor.
abstract: One role of stems is that of water storage. The water content of stems increases and decreases as xylem water potential increases and decreases, respectively. Hence, a nondestructive method to measure stem water content (StWC) = (volume of water) : (volume of stem), could be useful in monitoring the drought stress status of plants. We introduce a frequency domain inner fringing capacitor-sensor for measuring StWC which operates at 100 MHz frequency. The capacitor-sensor consists of two wave guides (5-mm-wide braided metal) that snugly fit around the surface of a stem with a spacing of 4-5 mm between guides. Laboratory measurements on analog stems reveals that the DC signal output responds linearly to the relative dielectric constant of the analog stem, is most sensitive to water content between the waveguides to a depth of c. 3 mm from the stem surface, and calibrations based on the gravimetric water loss of excised stems of plants revealed a resolution in StWC of < ± 0.001 v/ v. The sensor performed very well on whole plants with a 100-fold increased resolution compared with previous frequency domain and time domain reflectometry methods and, hence, may be very useful for future research requiring nondestructive measurements of whole plants.
authors.affiliation: Key Laboratory of Agricultural Information Acquisition Technology, Ministry of Agriculture, College of Information and Electrical Engineering, China Agricultural University, Beijing, 100083, China.
authors.forename: Haiyang
authors.initials: H
authors.lastname: Zhou
authors.affiliation: Key Laboratory of Agricultural Information Acquisition Technology, Ministry of Agriculture, College of Information and Electrical Engineering, China Agricultural University, Beijing, 100083, China.
authors.forename: Yurui
authors.initials: Y
authors.lastname: Sun
authors.affiliation: College of Forestry, Northwest A&F University, Yangling, Shaanxi, 712100, China.|Center for Nano- and Micro-Mechanics, Engineering Mechanics, Tsinghua University, Beijing, 100084, China.
authors.forename: Melvin T
authors.initials: MT
authors.lastname: Tyree
authors.affiliation: Key Laboratory of Agricultural Information Acquisition Technology, Ministry of Agriculture, College of Information and Electrical Engineering, China Agricultural University, Beijing, 100083, China.
authors.forename: Wenyi
authors.initials: W
authors.lastname: Sheng
authors.affiliation: Key Laboratory of Agricultural Information Acquisition Technology, Ministry of Agriculture, College of Information and Electrical Engineering, China Agricultural University, Beijing, 100083, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Cheng
authors.affiliation: National Research Center of Intelligent Equipment for Agriculture, 100097, Beijing, China.
authors.forename: Xuzhang
authors.initials: X
authors.lastname: Xue
authors.affiliation: Institute of Crop Science and Resource Conservation, The University of Bonn, 53115, Bonn, Germany.
authors.forename: Henrik
authors.initials: H
authors.lastname: Schumann
authors.affiliation: Department of Agricultural Engineering, The University of Bonn, 53115, Bonn, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Schulze Lammers
mesh_terms: D055864:Droughts; D025802:Electric Capacitance; D018547:Plant Stems / Q000502:physiology*; D013045:Species Specificity; D014867:Water / Q000502:physiology*; D052584:Xylem / Q000502:physiology
chemical_list: D014867:Water
keywords: frequency-domain sensor; nondestructive measurement of stem water content (StWC); plant water stress; stem water storage; volumetric water content