{
    "name": "Irrigation Scheduling Calculator",
    "url": "https://calculators.geekmidst.com/calculators/irrigation-scheduling-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/irrigation-scheduling-calculator.md",
    "category": "Agriculture",
    "description": "Estimate how often to irrigate and how much water to apply from ET₀, crop coefficient, soil water holding and root depth, using the FAO-56 method.",
    "summary": "The FAO-56 approach lets the root zone dry by the readily available water, then refills it. Interval = readily available water ÷ daily crop water use.",
    "also_called": [
        "Irrigation interval calculator",
        "Irrigation frequency calculator"
    ],
    "applies_to": "Worldwide",
    "last_updated": "2026-10-29",
    "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.",
    "inputs": [
        {
            "name": "et0",
            "label": "Reference evapotranspiration (ET₀)",
            "type": "number",
            "default": "5",
            "unit": "mm/day"
        },
        {
            "name": "kc",
            "label": "Crop coefficient (Kc)",
            "type": "number",
            "default": "1.15"
        },
        {
            "name": "fc",
            "label": "Field capacity",
            "type": "number",
            "default": "30",
            "unit": "% vol"
        },
        {
            "name": "wp",
            "label": "Wilting point",
            "type": "number",
            "default": "15",
            "unit": "% vol"
        },
        {
            "name": "root_depth",
            "label": "Effective root depth",
            "type": "number",
            "default": "0.8",
            "unit": "m"
        },
        {
            "name": "p",
            "label": "Allowable depletion (p)",
            "type": "number",
            "default": "0.5"
        },
        {
            "name": "efficiency",
            "label": "Application efficiency",
            "type": "number",
            "default": "85",
            "unit": "%"
        },
        {
            "name": "area",
            "label": "Area",
            "type": "number",
            "default": "2"
        },
        {
            "name": "area_unit",
            "label": "Area in",
            "type": "segmented",
            "default": "ha",
            "options": {
                "ha": "Hectares",
                "acre": "Acres"
            }
        }
    ],
    "outputs": [
        {
            "key": "interval_days",
            "label": "Days between irrigations",
            "format": "number"
        },
        {
            "key": "etc",
            "label": "Crop water use (ETc)",
            "format": "number"
        },
        {
            "key": "taw",
            "label": "Total available water (TAW)",
            "format": "number"
        },
        {
            "key": "raw",
            "label": "Readily available water (net depth)",
            "format": "number"
        },
        {
            "key": "gross_depth",
            "label": "Gross depth to apply",
            "format": "number"
        },
        {
            "key": "volume_m3_ha",
            "label": "Water per hectare",
            "format": "number"
        },
        {
            "key": "volume_m3",
            "label": "Water for the area",
            "format": "number"
        }
    ],
    "formula": {
        "text": "ETc = Kc × ET₀;  TAW = 1000 (θFC − θWP) Zr;  RAW = p × TAW;  Interval = RAW ÷ ETc;  Gross depth = RAW ÷ Efficiency",
        "variables": {
            "θFC, θWP": "water content at field capacity and wilting point (m³/m³)",
            "Zr": "root depth (m)",
            "p": "depletion fraction before stress",
            "ETc": "crop evapotranspiration"
        }
    },
    "worked_example": {
        "inputs": {
            "et0": "5",
            "kc": "1.15",
            "fc": "30",
            "wp": "15",
            "root_depth": "0.8",
            "p": "0.5",
            "efficiency": "85",
            "area": "2",
            "area_unit": "ha"
        },
        "steps": [
            "ETc = 1.15 × 5 = 5.75 mm/day.",
            "TAW = 1000 × (0.30 − 0.15) × 0.8 = 120 mm; RAW = 0.5 × 120 = 60 mm.",
            "Interval = 60 ÷ 5.75 = 10.43 days; gross depth = 60 ÷ 0.85 = 70.59 mm (705.88 m³/ha)."
        ],
        "result": "Irrigate about every 10 days, applying roughly 71 mm gross (706 m³ per hectare)."
    },
    "interpretation": "Round the interval down to a whole number of days, and recalculate as ET₀ and Kc change through the season. Rain that soaks in extends the interval.",
    "assumptions": [
        "The root zone starts at field capacity after each irrigation.",
        "No rain, capillary rise or deep percolation between irrigations."
    ],
    "limitations": [
        "Uses one soil layer and one ET₀ value; real schedules should be updated with weather data."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "Where do I get ET₀?",
            "answer": "Many national weather services and irrigation advisory services publish daily reference evapotranspiration. It can also be calculated with the FAO Penman–Monteith equation."
        },
        {
            "question": "What is the difference between net and gross depth?",
            "answer": "Net depth is what the root zone needs; gross depth is what you must pump, allowing for losses in application."
        }
    ],
    "sources": [
        {
            "title": "FAO Irrigation and Drainage Paper 56, Chapter 8: soil water availability",
            "url": "https://www.fao.org/3/x0490e/x0490e0e.htm"
        }
    ],
    "related": [
        {
            "name": "Soil Water Deficit Calculator",
            "url": "https://calculators.geekmidst.com/calculators/soil-water-deficit-calculator"
        },
        {
            "name": "Drip Irrigation Discharge Calculator",
            "url": "https://calculators.geekmidst.com/calculators/drip-irrigation-discharge-calculator"
        }
    ],
    "disclaimer": null,
    "publisher": "GM¹X CalcVerse"
}