| dc.description.abstract | This study reviews the abundant research on FAO56 crop coefficients, published following introduction of
the FAO56 paper in 1998. The primary goal was to evaluate, update, and consolidate the mid-season and
end-season single (Kc) and basal (Kcb) crop coefficients, tabulated for many field crops in FAO56. The review
found that the prevalent approach for estimating crop evapotranspiration (ETc) is the FAO56 Kc-ETo approach,
i.e., the product of the Kc and reference evapotranspiration (ETo). The FAO56 Kc-ETo approach requires
use of the FAO56 PM-ETo grass reference equation with appropriate crop-specific Kc and/or Kcb. Reviewed
research provided various approaches to determine Kc and Kcb and used a variety of actual crop ET (ETc act)
measurements. Significant attention was placed on accessing the accuracy of the field measurements and
models used in these studies. Accuracy requirements, upper limits for Kc values, and related causal errors
are discussed. Conceptual approaches relative to Kc transferability requirements are provided with focus
on standard crop conditions and use of the FAO56 segmented Kc curve. Papers selected to update Kc∕Kcb
used the FAO56 PM-ETo, provided accurate measurements to determine and partition ETc act, and satisfied
transferability requirements. Selected observed Kc and Kcb values were converted to standard, sub-humid
climate as adopted in FAO56. Observed values, with respect to tabulated FAO56 Kc and Kcb, were used in
consolidating updated values for crops within general categories of grain legumes, fiber crops, oil crops, sugar
crops, small grain cereals, maize and sorghum, and rice. | en_US |
