Irrigation

Irrigation is the artificial application of water to soil to support crop growth where rainfall alone is not enough, is not on time, or is not reliable — which describes most of India’s cropped area for at least part of the year. It is not a backup for rain; for a rabi crop like wheat or mustard sown in a season with almost no rainfall at all, irrigation is the entire water supply.

The reason irrigation decides more of the season than any other single input is timing. A nutrient deficiency can often be corrected with a top-dressing days later. A missed irrigation at a genuinely critical stage — flowering, grain filling, tuber bulking — cannot be undone by irrigating twice as much the following week. The crop has already made its yield decision by then.

A little under half of India’s net sown area is irrigated; the rest depends on the monsoon arriving on time and in the right amount, which it does less reliably than farm planning would like. Every hectare added to assured irrigation raises average yield and, just as importantly, lowers the year-to-year swing in it — the difference between a bad monsoon costing a farmer half a crop and costing almost nothing.

Assured irrigation also changes what a farmer can afford to grow. A rainfed field is usually locked into low-water, low-value crops almost by definition — gram, bajra, rainfed soybean. The same land under assured irrigation opens up higher-value options like potato, tomato or sugarcane, which is the real economic case for investing in a well, a borewell, or a farm pond even before spending on drip or sprinkler equipment.

Surface irrigation moves water across the field by gravity alone — no pump running while the water spreads, which is exactly why it remains the cheapest method to set up. Flood irrigation floods the whole plot; border irrigation channels water down long, level strips bounded by low ridges; furrow irrigation runs water down channels between crop rows, wetting the root zone from the side rather than the whole surface.

The trade-off is efficiency: surface methods typically apply water at only 35–45% efficiency, the rest lost to deep percolation past the root zone and to runoff at the field’s low end. On a genuinely level field with heavy, water-retentive soil — the exact conditions paddy is grown under — that inefficiency matters less, which is why flood/border irrigation remains the standard method for puddled rice even on many otherwise well-equipped farms.

Drip irrigation delivers water in slow, precise drops directly at the base of each plant through a network of laterals and emitters, run off a filtered, often pressurised line. Because water goes only where the plant’s roots actually are, evaporation from bare soil between rows and deep percolation past the root zone both fall sharply — the 40–60% water saving quoted for drip against flood is not a marketing number, it is what direct root-zone delivery does mechanically.

Drip earns its cost back fastest on wide-spaced row crops with a real cash value — cotton, sugarcane, onion, tomato — where fertigation (see below) adds a second saving on top of the water one. It is a poor fit for closely sown or broadcast crops like wheat or gram, where laying enough laterals to cover every row costs more than the crop can return.

Sprinkler irrigation sprays water through the air under pressure, mimicking rainfall over the whole field rather than delivering it at the root alone. This makes it the practical choice for crops sown too closely or too broadcast for drip laterals to be worth laying — wheat, groundnut, most pulses — and its portability means one pump and one set of pipes can serve several plots in rotation rather than each field needing its own fixed installation.

The same overhead delivery is its weak point: wind drift wastes water and wets foliage in the process, which raises the risk of fungal disease on crops already prone to it. On heavy clay, sprinkler’s water-per-hour can outpace the soil’s infiltration rate, causing runoff exactly like flood irrigation would.

PMKSY groups drip and sprinkler together under the umbrella term "micro-irrigation" because both deliver water in small, frequent, precisely controlled amounts rather than one large event — the opposite philosophy from flood irrigation. Within that umbrella, micro-sprinklers and foggers are a distinct sub-type: low-pressure, low-throw devices built for orchards, nurseries and closely spaced high-value crops, wetting a small area gently rather than throwing water across a whole field like a rotary sprinkler does.

The practical reason to choose a micro-sprinkler over a full-size drip system is canopy and humidity control — a nursery raising seedlings, for instance, needs gentle, even wetting that a drip emitter’s point-source delivery does not provide as well.

Subsurface drip irrigation buries the lateral lines a few centimetres to a foot below the surface instead of laying them on top of it — the same drip principle, delivered where evaporation from the soil surface cannot touch it at all. It pushes efficiency higher still than surface drip, at a materially higher installation cost and the added complication of a buried line being harder to inspect for clogging or damage.

In India it remains a niche choice, mostly on high-value orchard and plantation crops where the extra cost is justified over a multi-year planting, rather than an annual field crop replanted every season.

A crop’s water requirement is the total depth of water — measured in millimetres, the same unit rainfall is measured in — it needs across its full growing season to reach its yield potential. It is not a single number for every crop: a short-duration vegetable like tomato needs 400–600 mm across roughly 100 days, while sugarcane, in the ground for a full year, needs 1,500–2,500 mm — nearly four times the total, spread over more than three times the duration.

The water requirement calculator above turns that seasonal figure into something a farmer can act on: a daily average and, combined with the soil’s water-holding capacity, how many days can safely pass between one irrigation and the next.

Every crop has one or two growth stages where a moisture shortfall costs yield permanently, not just temporarily — commonly flowering and grain filling or fruit development, though the exact stage varies by crop. For wheat, the crown root initiation stage around 20–25 days after sowing is critical because it is when the plant is establishing the root system the rest of the season depends on; for mustard, flowering is the one irrigation that matters most on an otherwise largely rainfed crop.

The practical rule most extension advice converges on: if water is short and a farmer can only irrigate once, irrigate at the critical stage, not on the usual calendar. A skipped routine irrigation before or after the critical window costs far less yield than a skipped irrigation during it.

Water-use efficiency is the yield produced per unit of water applied — kilograms of grain per cubic metre of water, in the units agronomists actually use. It is the number that makes "how much water a crop needs" and "how much water a system wastes" comparable across very different crops and irrigation methods.

Two levers raise it: applying water more precisely (drip and sprinkler over flood), and reducing the water lost to anything other than the crop’s own use — evaporation, deep percolation, runoff — through mulching, land levelling and correctly timed irrigation. Both matter; a drip system installed on an unlevelled, badly mulched field captures only part of its potential efficiency gain.

Fertigation is the practice of dissolving water-soluble fertiliser into the irrigation water and applying both together, most commonly through a drip system’s existing network. Because the nutrient arrives exactly where the water does — at the root zone, in small frequent doses rather than one broadcast application — fertiliser-use efficiency typically rises by around 30% compared with a single soil-applied dose, since less nitrogen is lost to volatilisation or leaching past the root zone.

Fertigation needs water-soluble grades (not standard urea or DAP, which do not dissolve cleanly enough for emitters) and a venturi injector or fertigation pump to meter the dose into the line — a modest extra cost on top of the drip system itself, usually justified quickly on a crop already paying for fertigation-suitable inputs like NPK 19:19:19 or calcium nitrate.

The subsidy explained in full in the PDMC section above changes the arithmetic of switching from flood to drip or sprinkler more than most farmers realise before checking: a 55% capital subsidy on a ₹36,000-per-acre drip system brings the farmer’s actual outlay down to roughly ₹16,200 — often recoverable within two to three seasons on a cash crop through water, labour and fertiliser savings alone, before counting any yield gain.

The scheme also intersects with Government Schemes more broadly — a farmer applying for the PDMC micro-irrigation subsidy is often, in the same visit to the agriculture office, also eligible to ask about Kisan Credit Card financing for the farmer’s share of the cost.

A farm pond, check dam or percolation tank captures monsoon runoff that would otherwise leave the farm — turning an unpredictable, seasonal rainfall pattern into a stored, controllable source for at least one or two protective irrigations later in the season. For a genuinely rainfed farm with no canal or reliable borewell, this is very often the highest-return investment available, ahead of any drip or sprinkler purchase, because a system delivers water more efficiently only if there is water to deliver in the first place.

Most state governments subsidise farm-pond construction heavily under watershed development and PMKSY’s "Watershed Development" component — worth checking alongside the micro-irrigation subsidy rather than instead of it.

The common problems section above covers the specific symptoms and fixes; the pattern underneath most of them is irrigating on a fixed habit rather than on what the soil and crop are actually showing. Watering by the calendar regardless of recent rainfall, skipping the flowering-stage irrigation to save water at exactly the wrong moment, and running flood irrigation on an unlevelled field are the three mistakes that show up on the widest range of farms, across every crop.

A second, quieter mistake is buying an irrigation system before checking the water source can actually supply it — a drip system sized for one acre needs a pump and source that can sustain its design discharge for the several hours a full irrigation round takes, not just a burst of pressure at the start.

The system advisor above works through the same five questions an irrigation consultant would ask in person — crop, farm size, soil type, water source and budget — and returns a recommendation with its cost, subsidy and payback period. As a general rule: paddy stays on flood; wide-spaced cash crops on sandy or loam soil with a borewell or well justify drip; closely sown field crops on a tighter budget do well on sprinkler; and orchards or nurseries are the natural fit for micro-sprinklers.

Budget is not just the system cost — it includes whether the farmer can bridge the gap between paying the dealer in full and receiving the PMKSY subsidy as DBT afterward, which for many small farmers is the real constraint, not the net cost after subsidy.

A drip system that is not acid-flushed every season loses efficiency to clogging within two to three years, at which point it performs little better than a poorly maintained sprinkler — the water saving quoted for drip assumes basic maintenance is actually done, not just that the system is installed. Filters need cleaning on a schedule, not only when flow visibly drops; by the time flow drops, some emitters have likely already clogged silently.

Sprinkler nozzles wear and widen over years of use, which quietly raises the actual discharge above what the system was designed for — worth checking every few seasons against the pump and pipe sizing the equipment calculators above were built around.

Soil-moisture sensors, weather-linked automatic scheduling, and solar-powered pumps are moving from pilot projects to mainstream availability as component costs fall — a basic tensiometer already costs a few hundred rupees, and IoT-connected sensor kits that trigger irrigation automatically are increasingly sold alongside standard drip kits by the same dealers.

The direction all of this points in is the same one this hub is built around: irrigation driven by what the crop and soil actually need at that moment, not by a fixed calendar or by copying the neighbouring field — smart irrigation is really just that principle, automated.