title: A comparison of soil moisture sensors for space flight applications.
abstract: Plants will be an important part of future long-term space missions. Automated plant growth systems require accurate and reliable methods of monitoring soil moisture levels. There are a number of different methods to accomplish this task. This study evaluated sensors using the capacitance method (ECH2O), the heat-pulse method (TMAS), and tensiometers, compared to soil water loss measured gravimetrically in a side-by-side test. The experiment monitored evaporative losses from substrate compartments filled with 1- to 2-mm baked calcinated clay media. The ECH2O data correlated well with the gravimetric measurements, but over a limited range of soil moisture. The averaged TMAS sensor data overstated soil moisture content levels. The tensiometer data appeared to track evaporative losses in the 0.5- to 2.5-kPa range of matric potential that corresponds to the water content needed to grow plants. This small range is characteristic of large particle media, and thus high-resolution tensiometers are required to distinguish changing moisture contents in this range.
authors.affiliation: Biosystems and Agricultural Engineering Department, University of Kentucky, Lexington, KY 40546-0276, USA. jnorikane@bae.uky.edu
authors.forename: J H
authors.initials: JH
authors.lastname: Norikane
authors.forename: J J
authors.initials: JJ
authors.lastname: Prenger
authors.forename: D T
authors.initials: DT
authors.lastname: Rouzan-Wheeldon
authors.forename: H G
authors.initials: HG
authors.lastname: Levine
mesh_terms: D015374:Biosensing Techniques / Q000295:instrumentation*; D003470:Culture Media; D018504:Ecological Systems, Closed; D025802:Electric Capacitance; D004784:Environmental Monitoring / Q000295:instrumentation*; D005069:Evaluation Studies as Topic; D008021:Life Support Systems / Q000295:instrumentation*; D012987:Soil; D013026:Space Flight / Q000295:instrumentation*; D013696:Temperature; D014867:Water; D014893:Weightlessness
chemical_list: D003470:Culture Media; D012987:Soil; D014867:Water