This small-farm irrigation scheduling template helps you turn weather, crop stage, rainfall, soil-moisture readings, and system output into a practical weekly water budget. Use the formulas and field workflow below to plan irrigation minutes, spot overwatering, and keep records that improve the next decision.
Overview
A good irrigation schedule is not a fixed calendar. It is a repeatable process for estimating crop water demand, subtracting useful rainfall, checking what the soil can hold, and applying only what the root zone needs. That distinction matters on a small farm, where one schedule may cover several crops, soil types, planting dates, and irrigation zones.
Set up a weekly spreadsheet with one row for each field or irrigation zone. Useful columns include field name, crop, planting date, growth stage, area, soil type, estimated reference evapotranspiration (ETo), crop coefficient (Kc), rainfall, irrigation applied, soil-moisture reading, system flow, run time, and notes. Keep planned and actual water in separate columns. The comparison shows whether a scheduling assumption is working.
The basic relationship is:
Crop water use (ETc) = reference evapotranspiration (ETo) × crop coefficient (Kc)
For a weekly budget, adjust that estimate for rainfall and irrigation efficiency:
Net irrigation need = ETc − effective rainfall − usable stored soil water
Gross irrigation need = net irrigation need ÷ application efficiency
These calculations are estimates, not automatic instructions. Confirm them with soil-moisture observations, plant condition, infiltration behavior, and the operating limits of your system.
How to estimate
Begin by dividing the farm into irrigation zones. A zone should group areas with reasonably similar crop water demand, soil, slope, emitter or sprinkler output, and sun exposure. Separate shallow-rooted greens from established fruiting crops when possible. Separating sandy ground from heavier soil can also make the schedule more accurate.
- Record the weekly ETo. Use a reliable local weather source, farm weather station, or regional reference value. Enter the unit consistently, such as millimetres or inches per week.
- Choose a Kc for the crop stage. Early establishment, vegetative growth, flowering, fruit fill, and late-season senescence do not have identical water demands. If you lack a local crop coefficient, use a provisional value and label it as an assumption rather than treating it as a precise measurement.
- Calculate ETc. Multiply ETo by Kc. For example, an assumed ETo of 1.4 inches for a week and a provisional Kc of 0.75 produce an ETc estimate of 1.05 inches.
- Subtract effective rainfall. Do not automatically count every recorded storm as usable water. Short, intense rain may run off, while rainfall on already saturated soil may drain below the root zone. Record total rainfall, then estimate the portion that reached the crop root zone.
- Account for the irrigation system. If the system applies water unevenly or loses water to evaporation, wind, runoff, or leakage, the amount delivered must exceed the crop's net need. Use a measured application-efficiency assumption until you can test distribution more carefully.
- Convert depth to volume or run time. For field volume, multiply water depth by area. A useful conversion is: one inch of water over one acre equals approximately 27,154 gallons. For smaller areas, convert the area to acres before calculating. Then divide required gallons by the measured zone flow rate to estimate minutes.
A compact spreadsheet formula can therefore be written as:
Run time (minutes) = [gross gallons needed ÷ zone flow (gallons per minute)] × 60
Split long run times into cycles when the soil cannot absorb the full application without runoff. Allow enough pause between cycles for water to infiltrate, and verify the result with a soil-moisture check.
Inputs and assumptions
The quality of the schedule depends more on the inputs than on spreadsheet complexity. Record where each input came from and whether it was measured, estimated, or copied from a reference table.
| Input | What to record | Practical check |
|---|---|---|
| ETo | Weekly reference evapotranspiration and unit | Confirm the value matches your location and reporting period |
| Kc | Crop and growth stage | Replace provisional values with local or crop-specific guidance when available |
| Rainfall | Total rainfall and estimated effective amount | Check for runoff, ponding, and dry soil beneath the surface |
| Soil moisture | Reading, method, depth, and location | Measure at representative points, not only beside an emitter |
| System output | Flow rate, pressure, emitter or sprinkler spacing | Collect water from several outlets and compare volumes |
| Rooting depth | Approximate active root-zone depth | Use a probe or soil profile check; do not assume every crop uses the same depth |
Use the following crop evapotranspiration reference table as a planning framework, not a universal Kc authority. The values are deliberately expressed as working bands so you can replace them with locally appropriate figures.
| Crop stage | Relative water demand | Starting Kc approach |
|---|---|---|
| Newly seeded or transplanted | Low plant demand; frequent attention may still be needed near the surface | Use a low provisional value and monitor the seedbed closely |
| Vegetative growth | Increasing demand as canopy expands | Use a mid-range provisional value; increase only after canopy and soil checks |
| Flowering and fruit development | Often a high-sensitivity period | Use a higher provisional value and avoid large swings in soil moisture |
| Late season or senescence | Demand may decline, depending on crop and harvest goal | Reduce the estimate cautiously and confirm crop quality needs |
For a complete farm water budget, pair this schedule with the Farm Water Usage Calculator. Keep crop scheduling separate from infrastructure decisions: the crop may need a certain depth, while the pump, pipes, and emitters determine how efficiently and evenly that depth can be delivered.
Worked examples
Example 1: estimating weekly depth. Assume a vegetable block has a weekly ETo of 1.4 inches and a provisional Kc of 0.75. ETc is 1.05 inches. Suppose the block receives 0.40 inches of rainfall, but field observation suggests only 0.25 inches was effective because some water ran off. If no soil-water credit is taken, net irrigation need is 0.80 inches. With an assumed application efficiency of 80%, gross irrigation need is 1.00 inch. Record each assumption in the spreadsheet so it can be reviewed after the next soil-moisture check.
Example 2: converting depth to run time. A zone covers 0.25 acre and needs a gross application of 0.50 inch. The required volume is approximately 3,394 gallons: 0.50 × 0.25 × 27,154. If the zone delivers 20 gallons per minute, the estimated run time is about 170 minutes. That may be too long for one cycle on the farm's soil. The operator could divide it into several shorter cycles, then inspect for runoff and confirm moisture below the surface.
Example 3: checking the plan in the field. The spreadsheet calls for 60 minutes, but the soil probe finds a wet root zone at the target depth and standing water near the end of the bed. Do not apply the full planned time simply because the formula says so. Check for clogged or oversized outlets, uneven pressure, compacted soil, and a zone boundary that combines unlike fields. Correct the system or reduce the next application, then note why the planned and actual amounts differ.
For farm-wide records, link weekly irrigation totals to harvest and sales records using the Farm Harvest Planning Template. This can help you compare water use by crop without assuming that the crop with the lowest water use is automatically the most profitable.
When to recalculate
Recalculate the schedule at least once each week during active irrigation, and sooner when conditions change quickly. Update ETo after a major weather shift, Kc when a crop enters a new growth stage, and rainfall after every meaningful storm. Recheck the plan after transplanting, canopy expansion, harvest of a large portion of the crop, or changes in mulch and ground cover.
Inspect system performance whenever pressure changes, a pump or filter is serviced, emitters clog, sprinklers move, or a zone shows dry and wet patches. Measure flow again when you change pipe layout or add outlets. Revisit soil assumptions when cultivation, compost application, compaction, or heavy traffic changes infiltration.
At the end of each week, complete four actions: enter actual irrigation and rainfall, record at least one soil-moisture observation per zone, compare planned with applied water, and write one reason for any adjustment. Before the next irrigation, update the formula inputs and set a provisional run time. This weekly loop makes the irrigation scheduling template a working farm tool rather than a static calendar. For related planning, see the Farm Soil Testing Guide and the Small Farm Break-Even Analysis to connect field decisions with soil conditions and business results.
