NEOBIOME

OT_218: FAO-56 (Allen et al. 1998), crop coefficients + reference ET, the CROPWAT standard

Properties5
typesource
source_typegrey_literature
authorAllen, R. G., Pereira, L. S., Raes, D., Smith, M.
year1998
topicsfood_systems_agriculture, water_supply_treatment, nz_specific

2 min read

OT_218: FAO-56 (Allen et al. 1998), crop coefficients + reference ET, the CROPWAT standard

Source

https://www.fao.org/3/x0490e/x0490e00.htm — original source (opens in a new tab; the file is not redistributed)

Context: ni · Feeds D02 + D03 (crop water requirement method)

Summary

FAO-56 is the standard method for computing crop water requirements: a reference evapotranspiration (ETo, Penman-Monteith) multiplied by a crop coefficient (Kc) that varies by growth stage. It is the method the model uses to turn NZ regional ETo into a per-crop water demand. It is a transferable global method (the Kc values are widely applicable; ETo is applied for the NZ region), and it underpins CROPWAT and the NZ regional-council irrigation tools.

Key claims

- claim: "CROP COEFFICIENTS (Kc) FOR THE MODELLED CROPS (Table 12, single-crop Kc ini / mid / end). Potato 0.50 / 1.15 / 0.75 (0.40 with vine kill before harvest); dry bean 0.40 / 1.15 / 0.35 (a proxy for faba bean); rapeseed/canola 0.35 / 1.0-1.15 / 0.35 (the oil-crop proxy, no hemp Kc exists); small vegetables 0.70 / 1.05 / 0.95. Seasonal crop water requirement = sum over the season of Kc x ETo. [verified against the raw: crop-coefficient tables present]"
  source_location: "FAO-56 Table 12 (single crop coefficients Kc), pp.110-111; Table 11 growth-stage lengths pp.105-107; Penman-Monteith ETo Chapter 2-4."

Model use

  • The Kc leg of CROP_CWR_MM in D02: apply these Kc values to NZ regional ETo to get seasonal crop water demand per crop. The applied irrigation is then this demand minus the crop-effective share of GIS rainfall (see OT_219 for the effective-rain method). OT_218

Notes

  • Basis. Transferable global method (Kc tables); the ETo it multiplies must be the NZ regional value. Hemp has no published Kc, so rapeseed/canola is the flagged oil-crop proxy.
  • Provenance. FAO first-party publication, the canonical reference, verified against the raw.

Connections

Links to

EDT domains (2): D02: Smart Food Systems & Agriculture · D03: Water, Waste & Circular Systems

Sources (1): OT_219

Referenced by

Sources (3): LIT_130 · OT_219 · OT_220

EDT domains (2): D02: Smart Food Systems & Agriculture · D03: Water, Waste & Circular Systems

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