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ARS Home » Plains Area » Bushland, Texas » Conservation and Production Research Laboratory » Soil and Water Management Research » Research » Publications at this Location » Publication #208347
Title: Field estimation of soil water content: A practical guide to methods, instrumentation and sensor technology

Author
item Evett, Steven - Steve
item HENG, LEE - FAO/IAEA
item MOUTONNET, PIERRE - IAEA
item NGUYEN, M - IAEA

Submitted to: Complete Book
Publication Type: Book / Chapter
Publication Acceptance Date: 2/7/2007
Publication Date: 2/1/2008
Citation: Evett, S.R., Heng, L.K., Moutonnet, P., Nguyen, M.L. 2008. Field Estimation of Soil Water Content: A Practical Guide to Methods, Instrumentation and Sensor Technology. IAEA-TCS-30. International Atomic Energy Agency, Vienna, Austria. ISSN 1018-5518. 131 p.

Interpretive Summary: A major user of soil water sensors for agricultural research and development is the joint division of the United Nations Food and Agriculture Organization and the International Atomic Energy Agency. At the behest of the joint division, an expert group from five nations and three continents did comparative trials of soil water sensing methods under laboratory and field conditions, resulting in this guide to field estimation of soil water content. The Soil and Water Management Research Unit of the USDA at Bushland, Texas, was a major contributor to this work, guided work in Texas, California and Austria, wrote or co-authored eight of the nine chapters and edited the book. The book gives an overview of soil water content that includes discussion of both direct and indirect measurements, followed by eight chapters on specific methods. The book is a useful guide both for irrigation managers and for researchers aiming to improve the efficiency with which water is used in agriculture. The authors show conclusively that the newer sensor technologies based on electrical properties of soils are as yet too inaccurate to be used for irrigation scheduling and research in general. Guidance is given as to which methods are sufficiently accurate; and conclusions are drawn that point the way to development of new sensors that avoid the problems that are delineated in the book.

Technical Abstract: An expert group from five nations and three continents did comparative trials of soil water sensing methods under laboratory and field conditions for the International Atomic Energy Agency, resulting in this guide to field estimation of soil water content. The book gives an overview of soil water content that includes discussion of both direct and indirect measurements, of variability caused by instrumental noise and by spatial variability of soil properties, and of important interferences to the main methods and how calibration may be done to minimize problems of interference and variability. The overview is followed by eight chapters, each of which focuses on an important method or particular instrument that is representative of a class of instruments. Chapter 2 discusses gravimetric and volumetric direct measurements of soil water content. Chapter 3 discusses the neutron moisture meter. Chapters 4-7 discuss the indirect methods that rely on the electromagnetic characteristics of the soil (time domain reflectometry (TDR), capacitance-based systems, and two quasi-TDR systems). The final two chapters discuss tensiometers and electrical resistance sensors, both of which are used to sense soil water potential rather than water content. Each of the chapters 2-9 gives information on manufacturers and model numbers, theory of operation, guidance in installation and operation, discussion and guidance on calibration methods, discussion of major problems and interferences with each method, and hints and tips for successful use. The forward to the book states six conclusions that point towards a need for further development of soil water sensors for accurate automated measurement.