Soil Water Depletion & Irrigation Scheduling Calculator

Finds how depleted the root zone is right now — fraction depleted, fraction remaining, available water capacity, and soil water deficit — based on field capacity, wilting point, and current water content (Table 2.3 can supply planning-level θ_fc/θ_wp defaults if you don't have measured values).

Calculator

Auto-fill θ_fc / θ_wp from soil texture (optional)

Field capacity (θ_fc)

Wilting point (θ_wp)

Current water content (θ_v)

Root zone / soil layer depth

About this calculator

Available water capacity (AWC) is the depth of water per unit soil depth that's actually usable by the plant — held between field capacity and the wilting point. As the crop uses water, the fraction depleted (f_d) climbs from 0 (at field capacity) toward 1 (at the wilting point). Soil water deficit (SWD) is the depth of water needed to refill the root zone back to field capacity — i.e., how much to irrigate right now.

AWC = θ_fc − θ_wp — f_d = (θ_fc − θ_v) / AWC — SWD = (θ_fc − θ_v) × L — TAW = AWC × L

Textbook Example 2.3: A silt loam soil (θ_fc = 0.34, θ_wp = 0.16) with a current water content of 0.26, over a 36-in root zone: f_d = 0.44, f_r = 0.56, AWC = 0.18 in/in, SWD ≈ 2.9 in. Click "Load textbook Example 2.3" above to see it worked through.