Irrigation scheduling means deciding when to irrigate and how much water to apply. Getting it right saves water, energy and fertilizer, and protects yield. Getting it wrong – too much or too little – costs money either way: under-watering stresses the crop at critical stages, while over-watering leaches nutrients, wastes pumping costs and can cause waterlogging and root disease.
Three ways to schedule irrigation
1. Fixed calendar schedule
Irrigating every set number of days is simple, but it ignores weather. A hot, windy week and a cool, cloudy week get the same water. It is a starting point, not a strategy.
2. Soil moisture-based scheduling
Irrigate when soil moisture in the root zone falls to a set level. You can check moisture by:
- Feel method: squeeze a handful of soil from root depth. If it crumbles and will not form a ball, it is likely time to irrigate. It is free, but it takes experience.
- Tensiometers: measure how hard roots must pull to extract water. Good for vegetables and orchards.
- Electronic soil moisture sensors: give continuous readings and can feed data into farm software.
3. Weather-based (evapotranspiration) scheduling
Crops lose water through evaporation from the soil and transpiration from leaves – together called evapotranspiration (ET). The standard approach estimates crop water use as:
Crop ET (ETc) = Reference ET (ET₀) × Crop coefficient (Kc)
ET₀ comes from weather data (temperature, humidity, wind and sunshine). Kc depends on the crop and its growth stage – low at establishment, highest around flowering, and declining towards maturity. When the water used since the last irrigation (minus effective rainfall) reaches the amount your soil can safely give up, it is time to irrigate.
How much water to apply
The right irrigation depth refills the root zone without pushing water below it. It depends on:
- Soil type: sandy soils hold little water, so they need smaller, more frequent irrigations; clay soils hold more and can go longer between irrigations.
- Root depth: shallow-rooted vegetables need less water per irrigation than deep-rooted crops like sugarcane or orchard trees.
- Allowable depletion: many field crops tolerate using around half of the available water before irrigation is needed; sensitive crops and critical stages call for less depletion.
- System efficiency: drip delivers most water to the root zone; flood irrigation loses more to runoff and deep percolation, so more must be applied. Compare systems in drip vs sprinkler vs flood irrigation.
Critical growth stages – never skip these
Every crop has stages where water stress hurts yield the most. Typical examples:
- Wheat: crown root initiation, flowering and grain filling
- Rice: tillering, panicle initiation and flowering
- Maize: tasseling, silking and grain fill
- Pulses and oilseeds: flowering and pod formation
- Vegetables: transplant establishment, flowering and fruit development
When water is limited, prioritise these stages over others.
Practical irrigation scheduling tips
- Irrigate early morning or evening to reduce evaporation losses.
- Check the weather forecast – skip or delay irrigation if meaningful rain is expected.
- Record every irrigation: field, date, duration and water source. Over time you will see actual water use per crop.
- Watch for signs of over-irrigation: yellowing lower leaves, standing water, algae on the soil surface.
- Maintain your system – clogged drippers and leaking pipes undo good scheduling.
Manage irrigation with data
AgriFarm irrigation management logs every irrigation per field, schedules upcoming turns as tasks, and shows them alongside the weather forecast so you can skip unnecessary watering.
Frequently asked questions
How do I know if I am over-irrigating?
Persistently wet soil at root depth, yellowing leaves, poor root growth and water pooling or running off the field are common signs. A soil moisture check before each irrigation is the simplest safeguard.
Where can I find reference ET data?
Many agricultural universities and meteorological departments publish daily ET₀ values, and some weather services and farm apps calculate it from local forecasts.
