Re: Definition of Water Holding Capacity

[Dr. Ronald L. Elliott, P.E. <relliot@okstate.edu>]

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In my reading and experience, "water holding capacity" is considered to be
synonymous with "available soil water".  ASAE Standard S526.1 ("Soil and
Water Terminology") defines water holding capacity as "Amount of soil water
available to plants (see available soil water)."  That Standard defines
available soil water as "The portion of water in a soil that can be readily
absorbed by plant roots.  It is the amount of water released between in
situ field capacity and the permanent wilting point."

Other terms are available for describing the amount of soil water above
oven-dry, including simply "water content".

Reference for the Standard:
"Soil and Water Terminology"
ASAE S526.1 MAR95
pp. 968-984 in ASAE Standards 1999: Standards, Engineering Practices, Data.
American Society of Agricultural Engineers
St. Joseph, Michigan, USA

Also, it may be preferable to use units of m/m (or mm/mm) for water holding
capacity or available soil water.

Dr. Ronald L. Elliott, P.E.
Professor
Biosystems & Agricultural Engineering Department
Oklahoma State University
116 Ag Hall
Stillwater, OK  74078-6016
USA
e-mail:  relliot@okstate.edu
voice:  405-744-8423
fax:  405-744-6059