How is soil moisture deficit calculated in a water balance?

SMD_new = SMD_previous + ETc - (Pe + I), where ETc is daily crop ET (mm), Pe is effective precipitation (mm), and I is irrigation applied (mm). When SMD reaches the management allowed depletion (MAD × RAW), irrigation is triggered. RAW (readily available water) = MAD × TAW = MAD × (FC - WP) × Zr × 1000 mm.

What are typical soil field capacity and wilting point values?

Volumetric water content at field capacity (FC) and wilting point (WP): Sandy soil FC=0.12, WP=0.04; Sandy loam FC=0.20, WP=0.10; Loam FC=0.28, WP=0.14; Clay loam FC=0.36, WP=0.22; Clay FC=0.42, WP=0.28. Values from USDA-NRCS National Engineering Handbook Part 630, Table 4-2.

Soil Moisture Deficit Calculator

Calculate soil moisture deficit (SMD) and available water capacity for irrigation trigger determination and soil-water balance modeling.

2D stress state at a point. All stresses in MPa.

σx — Normal Stress X (MPa)

σy — Normal Stress Y (MPa)

τxy — Shear Stress (MPa)

⚙ Mechanical Note: Results are based on standard textbook formulas and ISO/AASHTO references. Always verify critical designs with applicable codes (ISO 898, AASHTO 1993, AISC, Eurocode 3) and a qualified engineer.

How to Use

Enter the values for the patient or scenario you are assessing. Calculate soil moisture deficit (SMD) and available water capacity for irrigation trigger determination and soil-water balance modeling. Use the soil moisture deficit result to inform your clinical assessment.

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