RBSE SS Voc Micro-Irrigation Tec cheat sheet

Field capacity (FC) is the water content retained after free drainage, typically at soil matric potential of −10 to −33 kPa; permanent wilting point (PWP) is near −1500 kPa; available water capacity (AWC) = FC − PWP.

Management allowed depletion (MAD) is the fraction of AWC that may be used before irrigation; for most field crops MAD is 0.5, for sensitive horticultural crops 0.25–0.4.

Irrigation interval (days) ≈ (AWC × root zone depth × MAD) ÷ crop evapotranspiration (ETc); all depths in the same units.

ETc = Kc × ETo, where ETo is reference evapotranspiration and Kc is the crop coefficient that changes by growth stage (initial, development, mid-season, late season).

Infiltration rate must exceed application rate; if application rate exceeds the soil's basic infiltration rate, runoff and ponding occur.

Crop water use peaks at flowering/fruit set; water stress then causes the largest yield loss, while stress at ripening mainly affects quality.

Soil texture controls AWC: sandy soils hold about 60–100 mm/m, loams about 140–190 mm/m, and clays about 180–220 mm/m of available water.

Root zone depth increases through the season; design emitter depth and wetting pattern for the mature root system, not the seedling stage.

Drip/trickle applies water at low pressure (typically 0.5–2.0 bar at the emitter) directly to the root zone; micro-sprinklers and mini-sprinklers spray water over a wetted area around each plant.

A drip system head works sequence: water source → pump → check valve → fertilizer injection point → filters → pressure regulator → main line → sub-main → lateral with emitters.

Filters are placed downstream of the injection point so that fertigation residues are filtered before reaching laterals.

A check valve and vacuum breaker at the injection point prevent backflow of fertilizer into the water source and prevent suction of soil into the system at shutdown.

Laterals are usually 12–20 mm polyethylene; emitters are inline (built into the tubing at fixed spacing) or online (punched into the lateral at chosen spacing).

A flush valve at the end of each lateral or sub-main allows periodic removal of sediment; end caps or flush manifolds are mandatory on every lateral.

Pressure-compensating (PC) emitters maintain rated flow over a pressure range (often 0.5–4.0 bar) and allow longer laterals and level or undulating terrain.

Air valves at high points release trapped air that would otherwise cause uneven flow and water hammer; non-return valves protect the pump from backflow.

Emitter flow rate q (L/h) and spacing determine application rate: application rate (mm/h) = (q × number of emitters per m² ) ÷ 1, i.e. q ÷ (emitter spacing in m × lateral spacing in m).

Wetted percentage Pw = (wetted width × number of laterals per bed or row) ÷ total area × 100; design Pw is typically 30–60% for row crops and 60–90% for orchards.

Christiansen uniformity CU and distribution uniformity DU measure emission uniformity; DU = (average of lowest quarter of emitter flows) ÷ (mean emitter flow) × 100.

Emission uniformity EU = 100 × (1 − 1.27 × CV ÷ √n), where CV is manufacturer's coefficient of variation and n is emitters per plant; target EU ≥ 90% for good design.

Lateral length is limited by allowable pressure variation, commonly ±10% of nominal emitter pressure, or by manufacturer's maximum lateral length tables for PC and non-PC emitters.

Friction head loss in laterals and sub-mains is calculated with the Hazen-Williams or Darcy-Weisbach equations; multiple outlet (Christiansen) reduction factor F reduces the total loss.

Total design head = emitter operating pressure + filter loss + valve/fitting loss + friction loss in laterals, sub-mains and main + elevation difference + safety margin.

Fertigation and chemical treatment require flushing with clean water afterwards; chlorine is used at low concentration for organic clogging and acid for carbonate scaling.

Sprinkler application rate (mm/h) = (sprinkler discharge in L/h) ÷ (sprinkler spacing in m × lateral spacing in m); it must not exceed the soil's basic infiltration rate.

Sprinkler spacing along the lateral should not exceed 60% of the wetted diameter, and lateral spacing should not exceed 65% of wetted diameter for acceptable uniformity.

Operating pressure must be within the manufacturer's range; low pressure reduces wetted diameter and uniformity, high pressure increases drift, evaporation loss and droplet breakup.

Uniformity is described by Christiansen's coefficient of uniformity (CU), with CU ≥ 84% generally acceptable for field crops and higher values for horticulture.

Wind above about 3 m/s distorts the pattern; sprinkler spacing and orientation should be adjusted, and night irrigation reduces wind drift and evaporation losses.

Sprinkler systems are classified as solid set, semi-portable, portable, travelling gun, boom, or centre-pivot/linear-move; selection depends on field shape, crop and labour.

Impact and rotating sprinklers need a minimum pressure to turn; gear-drive and turbo sprinklers operate at lower pressure and are more energy-efficient.

Pump duty point must match system head plus flow; a pump curve intersecting the system curve too far left or right of design causes poor uniformity and possible cavitation.

Pump total head = static lift + friction losses in suction and delivery + velocity head + operating pressure at the outlet; flow and head define the duty point on the pump curve.

Centrifugal pumps are used for surface water; submersible pumps for bore wells; the suction lift for a centrifugal pump should not exceed about 7 m at sea level.

Cavitation occurs when net positive suction head available (NPSHa) falls below NPSH required by the pump; symptoms are noise, vibration and reduced flow.

Sand media filters remove organic and inorganic particles down to about 40–50 microns; screen filters typically 100–200 mesh (about 75–150 microns); disc filters 100–400 microns depending on rating.

Filtration selection depends on water source: canal/lake water needs media plus screen; clean bore water may need only screen or disc filters.

Venturi injectors and diaphragm/positive-displacement pumps are common fertigation devices; injection rate must be matched to irrigation flow and the fertilizer must be fully soluble.

Fertigation schedule: inject fertilizer in the middle third of the irrigation cycle, then flush with clean water for at least 10–15 minutes to prevent emitter clogging.

Automation uses controllers, solenoid valves, pressure switches and soil moisture or weather sensors; a rain sensor or float switch protects the pump and prevents overflow.

Routine maintenance schedule: flush laterals monthly or more often, clean filters when pressure differential across the filter exceeds about 0.5 bar, and check emitters each season.

Emitter clogging causes are physical (sand, silt), chemical (calcium carbonate, iron) and biological (algae, bacterial slime); each requires a different treatment.

Chlorination for organic clogging: inject chlorine to maintain 1–2 ppm free residual at the end of the lateral for 30–60 minutes, then flush.

Acid treatment for carbonate scaling: dilute hydrochloric or sulfuric acid to bring irrigation water pH to about 4.0–5.0, circulate, then flush thoroughly; acid is corrosive and requires PPE.

A quick field check for clogging is to compare emitter flows at the beginning, middle and end of a lateral; a variation above 10% indicates a problem.

Pressure gauge readings at the head and at the far end of the main reveal filter blockage, leaks, or a worn pump impeller.

Leaks and broken laterals are repaired with barbed connectors, goof plugs or compression fittings; the repair must not reduce the internal diameter enough to change flow.

Record-keeping of flush dates, chemical treatments, filter cleaning and pump servicing allows fault tracing and supports warranty claims.

Water quality for drip is assessed by pH, electrical conductivity (EC), total suspended solids, hardness, iron, manganese and bacterial load.

EC above about 1 dS/m may cause salinity stress in sensitive crops; leaching requirement (LR) = ECw ÷ (5 × ECe − ECw) for a target soil ECe.

Iron above 0.5 ppm and manganese above 0.1 ppm promote bacterial slime and chemical precipitation in drip lines and require aeration or oxidation treatment.

Hydrogen sulfide, high bicarbonate and high calcium cause scaling; water with high carbonate hardness needs acidification before fertigation.

Water source options include bore wells, canals, farm ponds, check dams, and treated wastewater; each has different filtration and permitting requirements.

Environmental safeguards: avoid over-irrigation that leaches nutrients into groundwater, maintain buffer strips near water bodies, and dispose of filter backwash and chemical rinses responsibly.

Soil salinity monitoring with EC of saturated paste extract or soil EC sensors guides leaching and crop choice; drip irrigation can maintain a leached zone near emitters.

Rainwater harvesting structures and storage tanks reduce dependence on groundwater and improve water availability during peak demand.

Project cost for a drip system includes head works, pump, filters, fertigation unit, main/sub-main/laterals, emitters, valves, fittings, installation and labour.

Simple payback period (years) = total investment ÷ annual net benefit, where annual net benefit = additional income from yield/quality gain + water and energy savings − maintenance cost.

Benefit-cost ratio (BCR) = present value of benefits ÷ present value of costs; a BCR above 1 indicates an economically viable investment.

Government support in India for micro-irrigation is delivered mainly through the Pradhan Mantri Krishi Sinchayee Yojana (PMKSY) - Per Drop More Crop component, with subsidy shared between centre and state.

Typical subsidy norms under PMKSY provide a percentage of the system cost to small and marginal farmers that is higher than for other farmers, subject to per-hectare ceilings.

A complete customer quotation should list area, crop, spacing, emitter type, flow rate, head, pipe sizes, filters, fertigation unit, installation, warranty and after-sales service.

After-sales service includes system commissioning, operator training, a maintenance calendar, spare parts availability and a complaint response time.

Entrepreneurship requires registration (GST, Udyam), a technical team, service vehicles, and demonstration plots that build farmer confidence.

Personal protective equipment for fertigation and chemical treatment: chemical-resistant gloves, goggles or face shield, apron, boots and respirator when handling acids or chlorine.

Always add acid to water, never water to acid, to avoid violent exothermic spattering.

Store fertilizers and chemicals in labelled, locked, ventilated areas away from water sources, feed and livestock, with a spill kit and material safety data sheets available.

Electrical safety: pump panels must be earthed, fitted with an MCB/ELCB, and only opened by authorised electricians; wet hands and flooded pump houses are high-risk.

Before servicing a pump or opening a filter, isolate power, close valves and release residual pressure; never open a filter housing under pressure.

Excavation for pipelines requires locating underground cables and utilities first; trenches deeper than 1.5 m need shoring to prevent collapse.

Heat stress prevention: schedule field work in cooler hours, provide drinking water and shade, and train workers to recognise heat exhaustion symptoms.

First aid for acid or chlorine splash: flush with copious clean water for at least 15 minutes and seek medical help; keep an eyewash station near the chemical store.

Field measurement of emitter flow: collect water from a known number of emitters for a measured time (e.g. 60 s) and convert to L/h; sample at head, middle and tail of the lateral.

Pressure measurement with a calibrated gauge at the first and last emitter of a lateral gives the actual pressure variation, which should be within ±10% of design.

Wetted front and wetted diameter are measured by excavating a soil profile or observing the surface wetting pattern after a known irrigation duration.

A field demonstration layout should show water source, head works, main, sub-main, laterals, emitters, flush valves and the area served, to scale.

Project work should include a site survey (area, slope, soil, water source, crop), a design calculation sheet, a bill of materials and a cost estimate.

Commissioning checks: flush all lines before installing emitters, pressure-test the network, verify flow at the farthest point, and record baseline readings.

Soil infiltration can be checked with a double-ring infiltrometer or a simple cylinder test to confirm the application rate is safe.

Training demonstrations should compare uniform versus non-uniform emission using catch cans or flow measurements, making the concept of DU visible to farmers.