Drip irrigation runtime = (Water needed per plant ÷ Emitter flow rate) × Number of emitters. For a tomato plant needing 2 liters/day with 2 emitters of 2 L/h each: runtime = 2 ÷ (2 × 2) = 0.5 hours (30 minutes). Adjust for soil type (sand needs more frequent, shorter sessions; clay needs less frequent, longer sessions) and crop growth stage.
Drip irrigation delivers water directly to the root zone through emitters, with 85-95% efficiency — compared to 75-85% for sprinklers and 50-70% for flood/furrow. Benefits: 30-60% water savings, reduced weed growth (water only where crops grow), less disease (foliage stays dry), nutrient application through fertigation, and automation potential. Drip is ideal for vegetables, orchards, vineyards, and high-value row crops. It is less suitable for closely spaced crops like wheat or rice (unless using drip tape).
Common emitter flow rates: 0.5 GPH (2 L/h) — for sandy soils, close spacing, small plants. 1 GPH (4 L/h) — standard for most vegetables and medium soils. 2 GPH (8 L/h) — for clay soils, wide spacing, large plants (trees, vines). 4 GPH (16 L/h) — for mature trees, high water demand. Pressure-compensating emitters maintain consistent flow regardless of pressure variations (important for long rows or hilly terrain). Non-compensating emitters are cheaper but flow varies with pressure.
Spacing depends on crop and soil: Sandy soil: 20-30 cm (water moves down, not sideways). Loam: 30-50 cm. Clay: 50-75 cm (water moves sideways more). Close-spaced crops (lettuce, strawberries): 15-30 cm. Row crops (tomato, pepper): 30-50 cm (one or two emitters per plant). Orchards/vineyards: 50-100 cm (multiple emitters per tree). The goal is overlapping wetting patterns — each plant's root zone should be fully wetted.
Most drip systems operate at 10-15 psi (0.7-1.0 bar). Too high pressure = emitter damage, uneven flow, misting. Too low = insufficient flow, uneven watering. Use a pressure regulator at the system inlet. Filtration is critical — emitters clog easily. Use: Screen filter (150 mesh) for clean water (municipal, well). Disc filter (120-150 mesh) for surface water (pond, canal). Sand/media filter for dirty water (canal, river with sediment). Flush lines monthly and inspect emitters quarterly.
1. Determine daily crop water requirement (ETc = ETo × crop coefficient). Use local weather station data or evapotranspiration charts.
2. Calculate water needed per plant: Daily water (L) = ETc (mm/day) × plant area (m²) × 0.85 (efficiency). Example: tomato at peak demand (6 mm/day), plant spacing 0.5m × 1m = 0.5 m²: 6 × 0.5 × 0.85 = 2.55 L/day/plant.
3. Calculate total emitter output per plant: Total L/h = Number of emitters × Flow rate per emitter. Example: 2 emitters × 2 L/h = 4 L/h.
4. Calculate runtime: Hours = Water needed (L) ÷ Total emitter output (L/h). Example: 2.55 ÷ 4 = 0.64 hours = 38 minutes.
5. Adjust for soil type: Sandy soil: split into 2-3 shorter sessions (e.g., 15 min × 3) to reduce leaching. Clay soil: one longer session is fine, but don't exceed infiltration rate. Loam: one or two sessions.
Tomato: 4-7 mm/day (peak fruit production). Corn: 5-8 mm/day (tasseling/silking). Lettuce: 3-5 mm/day. Strawberry: 3-5 mm/day. Grape: 3-6 mm/day (veraison to harvest). Apple: 4-6 mm/day (fruit expansion). Alfalfa: 5-8 mm/day (regrowth after cutting). These are peak demands — reduce by 30-50% during establishment and late maturity stages.
Symptoms: yellow leaves, root rot, wilting despite wet soil, nutrient leaching (especially N), algae growth on soil surface. Causes: running too long, too frequent, wrong emitter size. Fix: reduce runtime by 20-30%, increase interval between waterings, check soil moisture with a probe or shovel (wet at 15-30 cm = adequate). Over-watering is more common and more damaging than under-watering in drip systems.
Symptoms: wilting during hottest part of day (recovers at night = mild stress; doesn't recover = severe), small fruit, premature flowering, leaf curl. Causes: too short runtime, clogged emitters, insufficient pressure, wrong ET estimate. Fix: increase runtime by 20-30%, check and clean emitters, verify pressure, use local ET data. Mild water stress (wilting that recovers overnight) can actually improve fruit quality in some crops (grapes, tomatoes) but reduces yield.
Symptoms: some plants thrive, others struggle; streaks in the field; varying crop maturity. Causes: pressure variations (slope, long rows), clogged emitters, improper design (too many emitters on one line), elevation changes. Fix: install pressure regulators, use pressure-compensating emitters, flush lines, redesign with shorter rows or multiple zones, check elevation (each 1m elevation change = 1.4 psi pressure change).
Daily: check pressure gauge, look for leaks or broken lines, verify controller is running correctly. Weekly: inspect emitters for clogging, check soil moisture in 2-3 locations, flush end caps briefly. Monthly: flush main lines and submains, clean filters, check fertilizer injector if fertigating. Seasonally: pressure test system, replace damaged tubing, calibrate emitter flow, winterize (blow out lines with compressed air in freezing climates). A well-maintained drip system lasts 10-15 years; a neglected one may fail in 2-3 years.
Calculate your irrigation: Use our Irrigation Calculator for field-level water requirements. Check Temperature & Humidity to monitor evapotranspiration conditions.