Cereals
Sorghum Irrigation Guide
Sorghum runs a 125-day season with water demand peaking at a crop coefficient of 1.1. On a hot mid-summer day (ETo of 6 mm), that is about 6.6 mm per day, or 46 mm (1.8 inches) per week. Every number on this page comes from the FAO-56 standard and is exactly what RainRule schedules with.
Season length
125 days
20 + 35 + 40 + 30 by stage
Root depth
1.2 m
≈ 3.9 ft at maturity
Peak daily use
6.6 mm
at mid-season, ETo 6 mm/day
Depletion threshold
55%
of available water before stress
Crop coefficient (Kc) through the season
Multiply any day's reference evapotranspiration (ETo) by the Kc below to get Sorghum's actual water use that day.
| Stage | Length | Kc | What's happening |
|---|---|---|---|
| Initial | 20 days | 0.35 | Establishment: bare soil dominates, low water use |
| Development | 35 days | 0.35 → 1.1 | Canopy closes; demand ramps day by day |
| Mid-season | 40 days | 1.1 | Full canopy: peak water use, most stress-sensitive |
| Late season | 30 days | 1.1 → 0.55 | Maturation: demand tapers toward harvest |
Refill points by soil type
Total available water (TAW) is what your soil holds across Sorghum's 1.2 m root zone. Irrigate when the running deficit crosses the refill point (RAW), 55% of TAW for Sorghum, so the crop never enters stress.
| Soil | Holds (TAW) | Irrigate at (RAW) | Days of peak use per refill |
|---|---|---|---|
| Sand | 84 mm | 46.2 mm | ~6 days |
| Sandy Loam | 144 mm | 79.2 mm | ~12 days |
| Loam | 180 mm | 99 mm | ~15 days |
| Silt Loam | 204 mm | 112.2 mm | ~17 days |
| Clay Loam | 192 mm | 105.6 mm | ~16 days |
| Clay | 168 mm | 92.4 mm | ~13 days |
Sandy soils hold the least water, so Sorghum on sand needs small, frequent irrigations; clay holds the most and supports longer intervals with bigger applications.
Worked example: a peak-summer week
Take Sorghum at mid-season on a week averaging an ETo of 6 mm/day:
- Daily crop use: 6 mm × Kc 1.1 = 6.6 mm/day
- Weekly demand: 6.6 × 7 = 46.2 mm (1.8 inches)
- On loam (99 mm refill point), a full profile lasts about 15 days with no rain before irrigation is due.
Real weeks aren't averages: ETo swings with heat waves and rain changes everything. That's the gap between a rule of thumb and a live schedule.
Related cereals guides
Get a live schedule for your sorghum field
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