Three geometrically identical Lysimeters (A, B and C) installed in a paddy field have uniform initial ponding depths of 12 cm. After a week, the recorded water depths in A, B and C are 10.4 cm, 8.6 cm, and 7.0 cm, respectively. Rainfall received during this week is 15 mm, and the crop coefficient of paddy is 0.94. Lysimeter 'A' has a closed bottom with no plant. Lysimeter 'B' has an open bottom with no plant. Lysimeter 'C' has an open bottom with paddy plants. Neglecting the boundary effects and groundwater contribution in the Lysimeters, the weekly potential evapotranspiration will be _______ cm.
Official Answer Key:
5.00 to 5.00
Step-by-Step Solution & Explanation
Water balance for each lysimeter: initial depth + rainfall − losses = final depth. Rainfall = 15 mm = 1.5 cm.
A (closed bottom, no plant) — loss is evaporation only:
E = 12 + 1.5 − 10.4 = 3.1 cm.
B (open bottom, no plant) — loss is evaporation + deep percolation:
E + DP = 12 + 1.5 − 8.6 = 4.9 cm ⇒ DP = 4.9 − 3.1 = 1.8 cm.
C (open bottom, with plants) — loss is ET_actual + deep percolation:
ET + DP = 12 + 1.5 − 7.0 = 6.5 cm ⇒ ET_actual = 6.5 − 1.8 = 4.7 cm.
PET = ET_actual/K_c = 4.7/0.94 = 5.0 cm.
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