Drip Irrigation for Cotton: Spacing, Scheduling, and What It Actually Costs Per Acre

Cotton has a reputation problem. Most people think of it as a dryland crop, something that gets by on whatever rain falls. That reputation is built on a half-truth. Cotton shrugs off drought better than corn or rice, no argument there. But it is also one of the thirstiest crops on the planet when you look at the whole season. A cotton plant pulls anywhere from 700 to 1,300 mm of water between planting and harvest, and the bulk of that arrives inside a six-week window when the plant is setting and filling bolls. Miss that window and you don’t just lose yield. You lose fiber quality too, and the buyer’s discount that comes with it.

That is exactly why drip irrigation for cotton keeps coming up, and why the conversation keeps circling back to subsurface drip. Around Lubbock in the Texas High Plains, where the Ogallala aquifer drops a foot or more every year, farmers have been burying drip lines under cotton for two decades. In Xinjiang, China, drip under plastic mulch now waters the largest cotton drip acreage on earth. The reason is boring and powerful at the same time: drip puts water where the roots are, not on the surface where wind and sun steal it.

Why cotton and drip actually fit

Cotton looks like a deep-rooted crop, and it is, sort of. A taproot will go down two meters hunting for water, which is where the drought tolerance comes from. But the feeder roots that actually pull in nutrients and drive boll growth sit in the top 30 to 40 cm of soil. Those roots are shallow and touchy. Let that top layer dry out during flowering and the plant sheds squares and young bolls. Let it waterlog and you get root rot and delayed maturity. Drip threads that needle, giving small, frequent doses right in the root zone without ever wetting the leaves.

There’s a second reason drip suits cotton specifically: salinity. Cotton is one of the more salt-tolerant row crops going, with a threshold of about 7.7 dS/m before yield starts sliding, and roughly 5.2% yield loss for every unit above that. That tolerance is why cotton holds on in places like Uzbekistan and the Indus basin where salt builds up in the soil. Drip helps here because it keeps the root zone continuously wet, which keeps salts diluted instead of letting them concentrate between irrigations the way flood does.

Surface drip vs subsurface: the decision that drives everything

For cotton you really have two choices, and they are not equal. Surface drip means laying thin-walled drip tape on the ground between rows. It is cheap, and in places like India and Pakistan it is the dominant approach because the tape is disposable and the subsidy math works. The problem is that surface tape sits in the way of cultivation, and cotton gets cultivated a lot. You also lose water to evaporation off the wetted strip.

Subsurface drip, or SDI, buries heavier tape 30 to 45 cm down and leaves it there for 15 to 25 years. You never move it. You cultivate, harvest, and spray right over it. Water goes straight to the root zone, so evaporation losses nearly vanish, which is why SDI cotton in the Texas High Plains commonly saves 20 to 30 percent more water than even a well-run center pivot. The tradeoff is upfront money, which I’ll get to. My take: if you plan to grow cotton on the same ground for years, SDI wins. If you rent land or rotate constantly, surface drip is the honest choice.

Spacing that actually works

Spacing is where cotton drip systems go wrong most often, because people borrow numbers from vegetables. Cotton in the US runs on 40-inch rows, or 76 to 102 cm. In India and Pakistan rows tighten to 67 to 90 cm. The rule that matters is this: a drip emitter wets a bulb of soil maybe 30 to 40 cm across in most soils, so you size lateral and emitter spacing to those wetting bulbs, not to the row width.

For surface drip, one tape per row is normal, with emitters every 30 cm. For SDI, one lateral per row is ideal, but plenty of Texas growers run one lateral per alternate row, 80 inches apart, to cut the pipe count nearly in half and still push water to both rows through capillary movement in the soil. Buried laterals go 30 to 45 cm deep, shallow enough that the water reaches the feeder roots but deep enough that a cultivator never finds the line. Flow rates run 0.5 to 1.0 liters per hour per emitter. If your soil is sandy and water drains fast, tighten the spacing and add emitters. If it is heavy clay, you can get away with wider spacing because water spreads sideways.

Scheduling around peak bloom and boll fill

The single most important thing to know about watering cotton is when the plant actually cares. Roughly 50 to 60 percent of the entire season’s water goes from first flower through boll opening, a stretch that starts around 60 days after planting and runs to 110 or so in full-season cotton. During peak bloom the crop drinks 0.35 to 0.45 inches a day. That is the window where a missed irrigation costs you bolls you never get back.

The flip side is that early season is forgiving. Cotton does fine with a mild deficit as a seedling and in early vegetative growth. In fact, many agronomists recommend a slight dry-down before first flower to push the plant toward reproductive growth instead of rank foliage. So the schedule looks like this: light, infrequent water early, then steady daily pulses once bloom starts, then taper off as bolls open and you head toward defoliation and harvest. Cutting water in the last weeks helps the crop dry down uniformly, which matters for harvest timing and fiber quality.

What it costs per acre, and when it pays back

Here is where the numbers get real. On the US side, a surface drip setup with disposable tape runs $150 to $400 per acre per season, but that is tape cost only. Headers, filtration, and a pressure regulator push the real installed number higher. SDI is a permanent capital investment: $1,000 to $2,500 an acre, with most Texas High Plains systems landing around $1,500. The system lasts 15 to 25 years, so you amortize that over a long horizon.

In India and Pakistan the picture is different. Surface drip for cotton runs about ₹40,000 to ₹60,000 per acre, roughly $500 to $750, before subsidy. After the 55 percent PMKSY smallholder subsidy, the net cost to the farmer drops to ₹18,000 to ₹27,000 an acre. That subsidy is the reason drip cotton acreage in Gujarat and Maharashtra keeps climbing.

Here is the per-acre math for a typical SDI cotton system in the US High Plains:

• Drip tape and laterals: $700 to $1,200
• Headers, filter station, and pressure regulation: $200 to $400
• Installation and trenching: $100 to $300
• Total: roughly $1,000 to $1,900 an acre

Payback lands in 2 to 4 years on most cotton ground, driven by the combination of 30 to 50 percent water savings and a 10 to 30 percent lint yield bump over furrow or dryland. In South Asia, where water is the constraint and the subsidy front-loads the savings, farmers often report getting their money back inside two to three seasons. The math is forgiving because cotton is a high-value crop and water is the scarce input, not land.

The honest tradeoff

Drip irrigation for cotton is not free water and it is not magic. It is a bet that steady, precise moisture at the root zone beats flooding the field and hoping. In the Texas High Plains and Xinjiang, where water is scarce enough to force the question, the bet has paid off. In places where cotton still runs on canal water at near-zero cost, the economics are thinner and the real argument for drip is yield and fiber quality, not the water bill. Know which situation you are in before you write the check, and get the spacing and the bloom-window scheduling right, because those two details decide whether the system pays for itself or just looks tidy.