Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2015
Publication Date: 3/10/2015
Citation: Evett, S.R. 2015. Soil moisture monitoring methods: Strengths and limitations. Meeting Abstract. Class room seminar, Manhattan, KS, March 11, 2015.
Technical Abstract: All soil water content sensors require soil-specific calibration – but calibration of capacitance sensors, whether in the laboratory or in the field, doesn’t ensure accuracy in the field. EM fields from capacitance sensors do not uniformly interrogate the soil and are influenced by soil structure – leading to unrealistic spatial variation of reported water contents. Effects of bulk electrical conductivity and bound water are not corrected in most EM sensors, but are much reduced with TDR. MAD irrigation scheduling & ET estimation using the capacitance type EM sensors is problematic due to these effects. Many of the research results discussed here were the result of an international study commissioned by the International Atomic Energy Agency (IAEA) that sought to compare and evaluate the neutron probe, time domain reflectometry and capacitance methods of soil water content sensing. The IAEA was searching for a method that would replace the neutron probe for the agricultural research efforts that it supports in many countries around the world. Through the IAEA, the research team published a book, Field Estimation of Soil Water Content (Evett et al., 2008), that documented many of its results, including its definitive conclusion that, "with the possible exception of tensiometers and the granular matrix resistance sensors, none of the sensors studied is practical for on-farm irrigation scheduling; they are either too inaccurate (capacitance sensors) or too costly and difficult to use (TDR and NMM); (6) for research studies, only the NMM, conventional TDR and direct measurements have acceptable accuracy".