2066 Bhadra (old course) · 3 marks

Crop coefficient curve for rice

Short answer

The crop coefficient Kc for rice is about 1.05 in the initial stage (20-30 days), rises linearly to about 1.20 during mid-season (40-50 days), then falls to about 0.90 in the late stage (20-30 days). It is used in ETc = Kc × ETo.

Draw the crop coefficient curve for rice crop.

The crop coefficient curve shows how $K_c$ ( $ET_c/ET_o$ ) changes over the growing period. For rice (FAO), $K_c$ is about 1.05 at the initial stage, rises to about 1.20 in the mid-season and falls to about 0.9 at the late stage.

 Kc
1.2|              ______________
   |            /               \
1.1|          /                   \
1.0|  ______/                       \
0.9|                                  \__
   +-----+-----------+-------------+----+--> days
    Initial  Crop      Mid-season   Late
    (20-30d) development (40-50d)  (20-30d)

Initial stage: low ground cover; $K_c$ about 1.05 (standing water in a nursery/field makes evaporation high).
Development stage: $K_c$ rises linearly as the canopy develops.
Mid-season: $K_c$ at the maximum, about 1.2 (full cover, flowering).
Late-season: $K_c$ falls to about 0.9 (maturity and drying).

The values are typical (FAO Irrigation and Drainage Paper 24/56) and are used in $ET_c=K_c\,ET_o$ .

✓ Answer checked by Claude Opus 5.5 (high effort)

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Crop coefficient curve for rice

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