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Agricultural Sciences
Agronomy
1977
Intermediate

Crop Water Balance

ETc=Kc⋅ET0,ΔS=P+I−ETc−R−DET_c = K_c \cdot ET_0,\quad \Delta S = P + I - ET_c - R - D

Crop evapotranspiration and soil storage balance rainfall, irrigation, runoff, and drainage.

By FAO, Irrigation engineers

Agricultural Sciences
Crop Water Balance
1977 · FAO
Why it matters: Turned water budgeting from guesswork into quantitative farm management.

Discoverers: FAO, Irrigation engineers (1977)

What does it mean?

Crop evapotranspiration and soil storage balance rainfall, irrigation, runoff, and drainage.

Why should I care?

Turned water budgeting from guesswork into quantitative farm management.

Variables & Units

SymbolNameUnitMeaning
ETcET_cCrop ET—mm/day
KcK_cCrop coefficient—Dimensionless
PPPrecipitation—mm
IIIrrigation—mm
ΔSΔSStorage change—mm

Worked Example

Tomatoes with K_c=1.15 and ET₀=5 mm/day → ET_c ≈ 5.75 mm/day.

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Crop Water Balance

ETc=Kc⋅ET0,ΔS=P+I−ETc−R−DET_c = K_c \cdot ET_0,\quad \Delta S = P + I - ET_c - R - D

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Crop evapotranspiration and soil storage balance rainfall, irrigation, runoff, and drainage.

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