Note: Within any soil texture there will be some variability in the actual
water-holding capacity of the soil. This is primarily due to the variable size in sand
particles (i.e., very coarse, coarse, medium, fine, and very fine) as well as the percent
and type of clay minerals (e.g., montmorillonites vs. Kaolinites), percent organic matter,
percent lime, percent silt, cultivation practices, residue management, etc., which modify
the soil structure and aggregation phenomena of the soil matrix (e.g., bulk density and
porosity). Thus, the above values should be used as a guide in planning irrigation
practices such as: irrigation scheduling, irrigation time sets, leaching requirements,
application uniformity and amount, etc.
Water-Holding Capacity
This represents the approximate amount of water that a soil can retain
following an irrigation (i.e., about 24-48 hours after the irrigation). At this time
excess water has drained from the macro pores & the soil is at Field Capacity (FC).
About 30-50% of the available water is depleted at the time of irrigation. The unavailable
water can’t be used by crop plants because it adsorbed too tightly for plant roots to
extract.
Macro Pores: the approximate volume of soil occupied by air immediately
following an irrigation when the soil is at FC.
Technical Questions about HIT may possibly be quickly answered by
contacting:
Rudy Garcia
Natural Resources Conservation Service
Soil Conservationist & Water Quality Specialist
e-mail: rgarcia@nm.nrcs.usda.gov
or call: 1-505-522-8775, extension 116
