Track soil moisture levels and generate irrigation schedules based on crop needs and weather forecasts.
Enter current soil moisture percentage, field capacity percentage, permanent wilting point percentage, daily crop evapotranspiration (ET) in mm, field area in hectares, and root zone depth in centimeters. Click "Calculate" to see available water (field capacity minus wilting point), days until irrigation is needed, total water needed to refill the root zone, estimated irrigation duration, and current moisture status assessment.
The soil moisture monitor and irrigation scheduler helps you determine when and how much to irrigate based on soil moisture levels and crop water needs. It calculates the plant-available water (the difference between field capacity and permanent wilting point), estimates how many days until moisture drops to the irrigation threshold (typically 50% available water depletion), and calculates water requirements. Irrigating based on soil moisture monitoring (rather than a fixed schedule) saves water, reduces nutrient leaching, prevents over- and under-watering, and improves crop yields and quality.
A: Field Capacity (FC) is the soil moisture content after gravitational water has drained away (typically 24-48 hours after a thorough irrigation or rain). At FC, water is readily available to plants and air-filled porosity is adequate for root respiration. FC values by texture: sand 8-12% by volume, loamy sand 12-18%, loam 20-30%, clay loam 28-35%, clay 30-40%. Permanent Wilting Point (PWP) is the moisture level at which plants can no longer extract water from the soil and wilt permanently (even in a humid atmosphere). PWP values: sand 3-5%, loam 10-15%, clay 15-25%. Plant-Available Water (PAW) = FC - PWP. PAW: sand 5-8%, loam 12-18%, clay 15-20% by volume. Note that clay has higher total water but similar available water to loam, because much of clay's water is held too tightly for plant uptake. The irrigation trigger is typically when 40-60% of PAW has been depleted (50% is standard for most crops). Sandy soils need more frequent, lighter irrigations; clay soils need less frequent, heavier irrigations.
A: Methods for measuring soil moisture: 1) Feel method (low-tech, free): take a soil sample from root zone, squeeze in hand — if it forms a ball that doesn't crumble and leaves moisture on fingers, moisture is adequate; if it crumbles easily, irrigation needed. Accuracy: ±10-15%, requires experience. 2) Tensiometer: measures soil water tension (suction), reads 0-100 centibars. Irrigate when reading reaches 20-30 cb for sandy soils, 40-60 cb for loams, 60-80 cb for clays. Cost: $50-150 each, requires maintenance (refilling water). 3) Capacitance / FDR sensors: measure volumetric water content via dielectric permittivity. Brands: Decagon (METER), Campbell Scientific, Sentek. Cost: $100-500 per sensor, very accurate (±1-2%), can be connected to data loggers for continuous monitoring. 4) Gypsum blocks: inexpensive ($10-20), measure electrical resistance related to moisture, less accurate, degrade over 1-2 years. 5) Neutron probe: very accurate but expensive ($5,000+) and requires licensing (radiation). For most farmers: install 2-3 capacitance sensors at different depths (15cm, 30cm, 60cm) in representative areas of the field, connect to a data logger or read manually 2-3 times per week. This investment ($300-1,000) typically pays for itself in one season through water savings and yield improvement.
A: Step 1: Determine current moisture deficit = (Field Capacity - Current Moisture) × Root Zone Depth × 10 (converts % volume × cm to mm of water). Example: FC=28%, current=18%, root depth=30cm → deficit = (28-18)% × 30cm × 10 = 10% × 30 × 10 = 30mm. Step 2: Convert mm to total volume: Water needed (m³) = Deficit (mm) × Area (ha) × 10. Example: 30mm × 2ha × 10 = 600 m³. Step 3: Account for irrigation efficiency: Actual water to apply = Water needed ÷ Efficiency. Drip efficiency 0.85-0.95, sprinkler 0.70-0.85, flood 0.50-0.70. Example: 600 ÷ 0.85 = 706 m³. Step 4: Calculate duration: Duration (hours) = Total water (m³) ÷ System flow rate (m³/h). Example: 706 ÷ 10 m³/h = 70.6 hours — this seems too long, which means you may need to split into multiple irrigation events or increase system flow. Alternatively, irrigate more frequently with smaller amounts. Step 5: Schedule: don't apply more water than the soil can hold in the root zone in one event (avoid deep percolation below roots). If calculated duration exceeds 8-12 hours, split into 2-3 events on consecutive days. After irrigation, re-check soil moisture to verify effectiveness and refine your calculations for next time.