Irrigation systems: drip and sprinkler

In short

Drip and sprinkler irrigation are pressurised (micro and overhead) irrigation methods that deliver water through pipes directly to the crop instead of flooding the land, raising field application efficiency from about 40-60% in surface irrigation to 70-80% (sprinkler) and 85-95% (drip). They matter because India uses roughly 80-85% of its usable water in agriculture and groundwater is over-exploited in large parts of Punjab, Haryana, Rajasthan, Gujarat, Maharashtra and Tamil Nadu. The topic carries steady marks in Agricultural Engineering university exams and in GATE (AG) under Soil and Water Conservation Engineering, usually as design problems on system capacity, uniformity, application rate and pump power. It is examined and used in jobs with Jain Irrigation, Netafim India, Finolex Plastro, Premier Irrigation, EPC Industries, Mahindra EPC, state Micro Irrigation / Horticulture Missions, NABARD-funded projects, ICAR institutes (IARI, CIAE Bhopal, ICAR-IIWM) and in AE/AEE recruitment for state water resources and agriculture departments.

Explained

Classification and basic definitions

• Surface (gravity) methods: border, check basin, furrow — water flows over the soil; low cost, low efficiency, high labour.
• Pressurised methods: sprinkler (water thrown through air as a spray, simulating rainfall) and micro irrigation (water applied at low pressure and low discharge near the root zone).
• Micro irrigation family: surface drip, subsurface drip (SDI), drip tape / inline laterals, bubbler, micro-sprinkler and mini-sprinkler, micro-jet / spray, porous (emitting) pipe.
• Sprinkler family: periodically-moved lateral (portable, semi-permanent), solid-set / permanent, hose-reel travelling gun (raingun), centre pivot, linear move, perforated pipe.
• Key design terms: application rate (mm/h), wetted diameter (m), operating pressure (kg/cm² or m head), emitter discharge (L/h), wetted area fraction, irrigation interval, set time, system capacity (m³/h or L/s).
• Field application efficiency (Ea) = water stored in root zone / water delivered to field. Indicative values: surface 40-60%, sprinkler 70-80%, drip 85-95%. Water use efficiency = yield per unit of water (kg/ha-mm), always higher in micro irrigation because yields also rise.

Drip irrigation: components and working

1. Head control unit at the pump: non-return valve, pressure gauges, filters, fertigation unit, air-release valve, flow meter, pressure regulator.
2. Filtration (the single most important component): hydrocyclone / sand separator for sand in well water; media (gravel-sand) filter for algae and organic matter in canal or pond water; screen filter (typically 100-200 mesh, commonly 120 mesh) and disc filter as the final guard. Rule of thumb: filter openings must be 1/8 to 1/10 of the emitter passage diameter. Filters are back-flushed when the pressure drop across them rises by about 0.5 kg/cm².
3. Mainline and submains (rigid PVC or HDPE, usually buried), laterals (12 mm or 16 mm LDPE/LLDPE on the surface along crop rows), emitters/drippers.
4. Emitter types by flow path: long-path (microtube, labyrinth), orifice, vortex, and pressure-compensating (PC) emitters with a flexible diaphragm that holds discharge nearly constant over a pressure range — essential on undulating land. By mounting: online (punched into the lateral, 2/4/8 L/h, for orchards) and inline (built into the pipe at fixed spacing, for row crops and vegetables).
5. Working: water at 1.0-2.5 kg/cm² at the head reaches each emitter at about 0.7-1.5 kg/cm² and drips at 1-8 L/h, keeping the root-zone soil near field capacity continuously. Only a fraction of the land (30-70%) is wetted, so evaporation, deep percolation and weed growth fall.
6. Fertigation: water-soluble fertilizers injected by venturi injector (cheap, causes head loss), fertilizer tank (bypass, dilution not uniform) or piston/diaphragm injection pump (accurate, costliest). Advantages: 25-40% fertilizer saving, split doses matched to crop stage, no leaching below roots. Never inject phosphatic fertilizer with hard water (calcium phosphate precipitates); use urea, MOP, KNO₃, urea phosphate, 19:19:19.
7. Clogging — the main failure mode. Physical (sand, silt), biological (algae, slime, bacteria, roots entering SDI emitters) and chemical (CaCO₃, iron and manganese oxides). Remedies: proper filtration; chlorination (continuous 1-2 ppm free chlorine, or shock dose of about 10-30 ppm for 30-60 minutes); acid treatment (dilute HCl or phosphoric acid to bring line pH to about 4 for 30-60 minutes, then flush); flushing lateral ends weekly; vacuum breakers and root-intrusion-resistant emitters for SDI.
8. Water quality hazard (Bucks-Nakayama style criteria): low hazard if suspended solids below about 50 ppm, EC below 0.8 dS/m, pH 5-7, iron/manganese below 0.1 ppm, bicarbonate below 100 ppm; severe above roughly 100 ppm solids, pH above 8, Fe/Mn above 1.5 ppm.

Drip design procedure (as asked in exams)

1. Crop water requirement at peak: ETc = ET₀ × Kc, or pan method Ep × Kp × Kc.
2. Volume per plant per day = canopy (or plant spacing) area × ETc × wetted-area factor, divided by emission efficiency (0.85-0.95).
3. Choose emitter discharge and number per plant from soil texture (sandy soils need more, closer emitters; clayey soils fewer).
4. Operating time = volume per plant ÷ (number of emitters × emitter discharge).
5. Lateral and submain layout: laterals along contours wherever possible; limit emitter flow variation qvar = (qmax − qmin)/qmax to 10%, which permits about 20% pressure variation in a subunit (because q varies as hˣ with x ≈ 0.5 for turbulent-flow emitters).
6. Hydraulics: friction in a lateral with many outlets = friction for full flow over full length × Christiansen's F factor. Add or subtract elevation head.
7. Divide the field into subunits/zones so that pump discharge and head stay reasonable; fix pump and prime mover.
8. Check uniformity (EU or statistical uniformity) and accept if EU ≥ 90% for new systems on level land (≥ 85% on slopes).

Sprinkler irrigation: components, working and design

• Components: pump and prime mover, mainline and submains (PVC/HDPE/quick-coupling aluminium), laterals, risers, sprinkler heads, couplers, valves, pressure gauge.
• Head types: rotating impact (hammer) sprinkler (most common; the spring-loaded arm both breaks the jet and rotates the head), gear-driven, fixed/spray head, and raingun (large nozzle, 10-30 m³/h, wetted diameter 40-70 m, used for sugarcane, tea and fodder).
• Pressure classes (indicative): low 1.0-2.0 kg/cm² (micro/mini sprinklers), medium 2.0-4.0 kg/cm² (farm impact sprinklers), high above 4 kg/cm² (rainguns, long-range).
• Design rules:
  • Application rate must not exceed the basic (steady) infiltration rate of the soil, else runoff and surface sealing occur. Typical limits: sand 25-50 mm/h, loam 10-20 mm/h, clay 3-8 mm/h; reduce by about 25% on slopes above 8%.
  • Spacing as a fraction of the wetted diameter D: about 60-65% of D (no wind), 50-55% (wind up to 8 km/h), 40-45% (strong wind). Standard layouts: square (S×S), rectangular, triangular (gives the best overlap for the same number of heads).
  • Lay laterals across (perpendicular to) the prevailing wind and along contours; mainline up the slope.
  • Riser height above the crop canopy (0.3 m for low crops, up to 1.5-2 m for tall crops); riser must be vertical.
  • Losses: evaporation and wind drift 5-10% (higher in hot, dry, windy afternoons) — irrigate early morning or evening.
• Uniformity measures: Christiansen's uniformity coefficient (CU) from a catch-can grid test; distribution uniformity (DU) = mean of lowest quarter ÷ overall mean. Good sprinkler design: CU ≥ 85%, DU ≥ 75%.
• Special uses: frost protection (latent heat of freezing water protects buds), cooling crops, leaching salts, and applying soluble fertilizer/pesticide (chemigation). Not suitable for saline water on sensitive foliage (leaf burn), very windy sites, or crops damaged by wet leaves (blight-prone grapes, tomato).

Comparison, advantages and limitations

• Drip advantages: 40-70% water saving over surface irrigation, 20-50% yield increase, fertigation, weed control, saline water usable (salts pushed to the wetting-front edge), works on undulating and sandy land, low energy head, no land levelling or field channels.
• Drip limitations: high initial cost, clogging risk, rodent and labour damage to laterals, salt accumulation at the periphery, root restriction to the wetted bulb, skilled maintenance and reliable power needed.
• Sprinkler advantages: suits close-growing crops (wheat, groundnut, pulses, fodder, vegetables), shallow and undulating soils, light sandy soils, no field channels, can be moved, frost and heat protection.
• Sprinkler limitations: wind drift, higher operating pressure and energy cost, not for crops sensitive to wet foliage, poor with saline or silt-laden water, high evaporation loss in hot dry weather.
• Suitability by crop: drip for wide-spaced and high-value crops (banana, grape, pomegranate, mango, coconut, sugarcane, cotton, tomato, capsicum); sprinkler for close-spaced field crops; micro-sprinkler for groundnut, onion, nursery and tea.

Indian standards, schemes and practice

• BIS standards (quote the current edition; several older numbers have been revised or withdrawn — verify on the BIS catalogue): IS 8835 — guidelines for selection of sprinkler irrigation systems; IS 10799 — code of practice for design, installation and field evaluation of sprinkler irrigation systems; IS 12232 series — rotating sprinkler heads; IS 14151 (Parts 1 and 2) — HDPE/PVC pipes for sprinkler irrigation; IS 13487 / IS 13488 — emitting-pipe systems and emitters for drip irrigation; IS 12786 — PVC pipes for irrigation; IS 4985 — uPVC pipes for potable water supplies, widely used for mains. Standards also exist for media, screen and disc filters and for sand separators.
• ISI (BIS) marking is mandatory for subsidised micro-irrigation components under central and state schemes; only empanelled manufacturers' systems qualify.
• Schemes: micro irrigation is promoted through Per Drop More Crop (PDMC), originally a component of PMKSY (2015) and from 2022-23 implemented under the RKVY umbrella; central assistance is commonly 55% for small and marginal farmers and 45% for other farmers on notified cost norms, with many states (Gujarat, Andhra Pradesh, Maharashtra, Karnataka, Tamil Nadu, Rajasthan) adding top-up subsidy, in some cases to 80-90%. The Micro Irrigation Fund (MIF) with NABARD provides concessional loans to states. Rates, norms and corpus figures are revised periodically — confirm the current year's guidelines before quoting.
• Indicative capital cost (varies widely with spacing, crop and state schedule of rates): drip roughly ₹60,000-₹1,20,000 per hectare (closer spacing costs more), sprinkler roughly ₹20,000-₹45,000 per hectare, raingun systems less per hectare but with higher pumping cost. Cost norms are notified annually under PDMC.
• GST: the September 2025 rate rationalisation retained slabs of 5%, 18% and 40%; most agricultural machinery and micro-irrigation equipment, earlier at 12%, now attracts the lower slab — verify the current rate notification for the specific HS code before quoting a figure.
• Other relevant practice: groundwater abstraction needs CGWA / state groundwater authority clearance in notified over-exploited blocks; state Water Resources Regulatory Authorities (e.g. MWRRA in Maharashtra) and command-area rules in some states mandate micro irrigation for sugarcane.

Key points

• Micro irrigation - water applied at low pressure and low discharge near the root zone; drip, micro-sprinkler and bubbler belong to it.
• Application efficiency - drip 85-95%, sprinkler 70-80%, surface 40-60%; drip saves water by cutting evaporation, runoff and deep percolation.
• Emitter discharge equation - q = k hˣ; x ≈ 0 for pressure-compensating, ≈ 0.5 for turbulent-flow, ≈ 1.0 for laminar long-path emitters.
• Allowable variation - 10% emitter discharge variation, equivalent to about 20% pressure variation in a drip subunit.
• Emission uniformity (EU) - 100 × (mean of lowest quarter of emitter discharges / mean discharge); ≥ 90% acceptable for new level-land systems.
• Manufacturer's coefficient of variation (CV) - scatter in discharge of new identical emitters; below 0.05 is good, above 0.15 unacceptable.
• Filtration rule - filter opening 1/8 to 1/10 of emitter passage; back-flush when head loss rises about 0.5 kg/cm².
• Clogging control - chlorination (1-2 ppm continuous or 10-30 ppm shock) for biological, acid flush to pH ≈ 4 for chemical, flushing for physical.
• Fertigation - venturi, fertilizer tank or injection pump; saves 25-40% fertilizer; avoid phosphates with hard water.
• Application rate ≤ basic infiltration rate - the governing sprinkler criterion; otherwise runoff and sealing.
• Sprinkler spacing - 50-65% of wetted diameter, reduced with wind; laterals across the wind, mainline up the slope.
• Wind and evaporation loss - 5-10% in sprinklers; irrigate in the early morning or evening.
• Christiansen's F factor - multiplies full-flow friction loss in a pipe with many equally spaced outlets; ≈ 0.36-0.38 for many outlets with Hazen-Williams.
• Christiansen's CU - catch-can based uniformity index; good sprinkler systems give 85% or more.
• System capacity - Q = 10 A d / (F · H · Ea) with A in ha, d in mm, F days of interval, H hours per day.
• Pump power - P = ρgQH/(1000 η); total head = suction lift + friction + emitter/nozzle operating head + elevation.
• Subsidy - PDMC under RKVY, commonly 55% for small and marginal and 45% for other farmers on notified norms, with state top-ups; BIS-marked equipment only.
• Salinity - drip keeps salts at the periphery of the wetted bulb and tolerates poorer water; sprinklers with saline water scorch leaves.

Formulas and examples

Example 1 — Drip design for a mango orchard. Spacing 5 m × 5 m, canopy diameter 3 m, pan evaporation 8 mm/day, Kp = 0.7, Kc = 0.8, emission efficiency 0.90, four 4 L/h online emitters per tree.

• Canopy area A_p = (π/4) × 3² = 7.07 m².
• ETc = 8 × 0.7 × 0.8 = 4.48 mm/day.
• V = 7.07 × 4.48 / 0.90 = 31.67/0.90 = 35.2 L/tree/day.
• Emitter capacity per tree = 4 × 4 = 16 L/h → t = 35.2/16 = 2.2 hours per day.
• Trees per hectare = 10,000/25 = 400 → daily volume = 400 × 35.2 = 14,080 L = 14.1 m³/ha/day; at 2.2 h operation the zone flow is 400 × 16 = 6,400 L/h = 6.4 m³/h per hectare.

Example 2 — Emitter exponent and uniformity. A dripper gives 4.0 L/h at 10 m head and 5.6 L/h at 20 m head.

• x = ln(5.6/4.0)/ln(20/10) = ln 1.4/ln 2 = 0.3365/0.6931 = 0.486 (turbulent-flow emitter).
• k = 4.0/10^0.486 = 4.0/3.06 = 1.31; check at 15 m: q = 1.31 × 15^0.486 = 1.31 × 3.72 = 4.87 L/h.
• So a 20% head drop (10 m → 8 m) gives q = 1.31 × 8^0.486 = 1.31 × 2.75 = 3.60 L/h, i.e. qvar = (4.0 − 3.60)/4.0 = 10.0% — right at the 10% limit. This is exactly why 20% pressure variation is the accepted design limit (and why x much above 0.5 needs a tighter pressure band).
• With CV = 0.04, n_e = 2 emitters per plant and q_min/q̄ = 0.95: EU = 100 (1 − 1.27 × 0.04/√2)(0.95) = 100 × 0.9641 × 0.95 = 91.6% — acceptable.

Example 3 — Sprinkler application rate and set time. Sprinkler discharge 1,200 L/h, spacing 12 m × 12 m, net depth required 50 mm, Ea = 75%, loam soil with basic infiltration 10 mm/h.

• I = 1,200/(12 × 12) = 1,200/144 = 8.33 mm/h < 10 mm/h → acceptable.
• d_gross = 50/0.75 = 66.7 mm → set time = 66.7/8.33 = 8.0 hours per position.
• Operating 16 h/day gives 2 sets per day. For 4 ha on a 10-day interval, 20 sets are available, so area per set = 4/20 = 0.2 ha = 2,000 m² → sprinklers per set = 2,000/144 = 14.
• System discharge = 14 × 1.2 = 16.8 m³/h. Cross-check with the capacity formula: Q = 10 × 4 × 50/(10 × 16 × 0.75) = 2,000/120 = 16.7 m³/h — consistent.

Example 4 — Pump and motor for the above sprinkler system. Q = 16.8 m³/h = 0.00467 m³/s. Nozzle pressure 2.5 kg/cm² = 25 m, suction lift 6 m, pipe and fitting friction 7 m, riser 2 m → total head H = 40 m.

• Water power = 1000 × 9.81 × 0.00467 × 40 = 1,832 W = 1.83 kW.
• Pump efficiency 65% → shaft power = 1.83/0.65 = 2.82 kW = 3.78 hp.
• Motor efficiency 90% → input = 2.82/0.90 = 3.13 kW. Select the next standard size: 5 hp motor.
• Energy for one set of 8 h = 3.13 × 8 = 25.0 kWh; at ₹6/kWh that is ₹150 per set, about ₹3,000 per 4-ha irrigation of 20 sets (agricultural tariffs differ by state and are often subsidised or flat-rate).

Example 5 — Lateral friction loss with the F factor. 16 mm LDPE lateral (inner diameter 14 mm), 60 m long, 30 inline emitters at 2 m spacing, each 4 L/h, C = 140.

• Lateral inflow Q = 30 × 4 = 120 L/h = 3.33 × 10⁻⁵ m³/s.
• Full-flow loss: hf = 10.67 × 60 × (3.33×10⁻⁵)^1.852 / (140^1.852 × 0.014^4.87) = 10.67 × 60 × 5.11×10⁻⁹ / (9,434 × 9.36×10⁻¹⁰) = 3.27×10⁻⁶/8.83×10⁻⁶ = 0.37 m.
• F for m = 30, n = 1.852: F = 1/2.852 + 1/60 + √0.852/(6 × 900) = 0.351 + 0.017 + 0.0002 = 0.368.
• hf_lateral = 0.37 × 0.368 = 0.14 m — far below the allowable 20% of 10 m (2 m), so the 16 mm lateral and even a longer run are safe; the allowance can be spent on the submain or on slope.

Where it is used

• Micro-irrigation manufacturing and design: Jain Irrigation, Netafim India, Finolex Plastro, Premier Irrigation Adritec, EPC Industries (Mahindra EPC), Captain Polyplast — roles in system design, hydraulic layout (often using CAD and vendor design software), dealer training and after-sales service.
• Government and project roles: AE/AEE in state Agriculture, Horticulture and Water Resources departments; State Micro Irrigation Missions under PDMC; command-area development; NABARD/MIF-funded cluster projects; third-party inspection of subsidised installations.
• Commercial horticulture and plantations: grape and pomegranate in Nashik and Solapur, banana in Jalgaon and Theni, sugarcane drip in Maharashtra and Karnataka, cotton in Gujarat, coconut and arecanut in Kerala and Karnataka, polyhouse and nursery micro-sprinklers, tea in Assam and the Nilgiris with rainguns.
• Protected cultivation and precision agriculture: automated fertigation with soil-moisture sensors, solenoid valves and controllers; solar-pumped drip under PM-KUSUM; IoT-based scheduling startups.
• Landscape, municipal and industrial: golf courses, highway and park landscaping, dust suppression and lawn sprinklers; sprinklers for frost protection in apple orchards in Himachal and Kashmir.
• Research and teaching: ICAR-IIWM Bhubaneswar, ICAR-CIAE Bhopal, ICAR-IARI and state agricultural universities evaluate uniformity, subsurface drip and treated-wastewater drip.

Interview questions

• Q: Why is drip irrigation more efficient than furrow irrigation? A: It applies small quantities directly at the root zone, wetting only 30-70% of the soil, so evaporation, surface runoff, deep percolation and conveyance losses are almost eliminated — efficiency rises from about 50% to 90%.
• Q: What is the emitter exponent and what does it tell you? A: In q = k hˣ, x measures sensitivity of discharge to pressure: x ≈ 1 for laminar long-path emitters, ≈ 0.5 for turbulent-flow, and near 0 for pressure-compensating emitters, which are therefore chosen for sloping or long-lateral fields.
• Q: Why is 20% pressure variation allowed in a drip subunit? A: Because with x ≈ 0.5 a 20% head variation produces only about 10% discharge variation, which is the accepted limit for uniformity.
• Q: What governs the choice of sprinkler application rate? A: It must not exceed the soil's basic infiltration rate, adjusted downward for slope and crop cover, so that no runoff or surface sealing occurs.
• Q: Why are sprinkler laterals laid perpendicular to the prevailing wind? A: So that wind distortion of the spray pattern is shared across the overlap between adjacent sprinklers rather than along a line, keeping uniformity acceptable.
• Q: Three ways emitters clog, and the remedy for each? A: Physical (sand, silt) — filtration and flushing; biological (algae, bacterial slime) — chlorination; chemical (carbonate, iron, manganese precipitates) — acid treatment to about pH 4 followed by flushing.
• Q: How do you size a filter for a drip system? A: Match it to the water source and flow, then make the filter opening 1/8 to 1/10 of the emitter passage — typically a 120-mesh screen or disc filter after a sand filter for open-water sources, and a hydrocyclone for sandy borewell water.
• Q: Why is the Christiansen F factor used? A: A lateral discharges water at many outlets, so the flow — and hence friction loss — reduces along its length; F (about 0.36-0.38 for many outlets) scales the full-flow loss to the true value.
• Q: Can saline water be used with drip? With sprinkler? A: Drip tolerates moderately saline water because continuous wetting keeps salts moving to the edge of the wetted bulb; sprinkler is poor because droplets evaporate on the leaves and cause scorching.
• Q: Why does fertigation save fertilizer? A: Soluble nutrients are placed in the small, actively-rooted wetted volume in small split doses matched to crop uptake, so volatilisation, fixation and leaching losses fall — typically a 25-40% saving.
• Q: What subsidy support exists in India for micro irrigation? A: Per Drop More Crop (originally under PMKSY, implemented under the RKVY umbrella since 2022-23) gives assistance on notified cost norms — commonly 55% for small and marginal farmers and 45% for others, with state top-ups and NABARD's Micro Irrigation Fund; only BIS-marked equipment from empanelled suppliers qualifies, and the rates are revised periodically.
• Q: When would you recommend a raingun over drip? A: For close-growing or tall bulk crops such as sugarcane, fodder and tea on large plots where low capital cost and quick coverage matter more than efficiency, and where wind is moderate and water is not saline.

Common mistakes

• Treating 1 mm of water as 1 litre per plant instead of 1 litre per square metre, which wrecks the volume-per-plant calculation.
• Forgetting to divide by the efficiency (using net instead of gross depth) when computing system capacity, set time or pump discharge.
• Using the full-flow friction loss for a lateral without applying the Christiansen F factor, overestimating the loss roughly threefold.
• Designing a sprinkler application rate above the soil's infiltration rate, or ignoring the slope reduction, and then blaming runoff on the sprinkler.
• Spacing sprinklers at the wetted diameter instead of 50-65% of it, leaving dry patches between overlaps.
• Omitting or undersizing filtration and flushing arrangements, then attributing poor uniformity to the emitters; and injecting phosphatic fertilizer into hard water.
• Mixing units — L/h with L/s, kg/cm² with metres of head (1 kg/cm² ≈ 10 m), m³/h with m³/s — in capacity and pump-power problems.

Related topics

• Soil and water conservation engineering · Drainage engineering · Watershed management · Soil physics: moisture retention and infiltration · Crop water requirement and irrigation scheduling · Pumps and farm power for irrigation.