Table of Contents
Maize is the staple crop on most Kenyan farms. An irrigation system for maize turns one rain-fed season into two reliable ones. The crop needs water most at tasselling, silking and grain filling. A dry spell at those stages can cancel the gain from a whole season of work. This guide sets out how much water a maize crop uses and how to lay out a system on rows about 75 cm apart. It also covers scheduling and the installation cost per acre.
In practice, a maize crop that receives steady moisture yields better than one that swings between drought and flood. The plant recovers slowly from stress during flowering. However, no amount of water later repairs the missing grains on a cob. Therefore, the aim of any irrigation system for maize is not to flood the field. It is to hold the root zone near field capacity through the four critical weeks around flowering.
Why a Maize Crop Needs Irrigation in Kenya
Kenya has two rainy seasons. The short rains fail often enough that a farmer cannot plan a second crop around them. Even in a good year, a maize crop spends 140 to 180 days in the field. It will meet at least one dry spell before harvest. The FAO crop coefficient table lists those two season lengths for East African maize. The same table gives a mid-season coefficient of 1.20. That means the crop drinks about a fifth more water than the reference grass at its peak.
That peak falls in the weeks around tasselling, when the plant is building the cob. Water stress then reduces the number of grains that set, and stress during grain filling reduces their weight. Both losses happen quietly, because the plant stays green while the yield potential drops. A system that keeps the field supplied through those weeks protects a yield you have already paid for.
How Much Water Maize Uses at Each Growth Stage
The table below uses the FAO crop coefficient table for maize. Those figures are coefficients, not litres. Then multiply the coefficient by the daily evaporation demand for your area to get the depth of water the crop needs. Finally, the last column works the sum at an evaporation rate of 5 mm per day. That is a fair figure for a clear day in the Rift Valley or western Kenya.
| Stage | Typical length | Crop coefficient | Water depth at 5 mm/day demand | What to do |
|---|---|---|---|---|
| Establishment | 25 to 30 days | 0.3 to 0.5 | 1.5 to 2.5 mm | Keep the top 20 cm moist so the seed germinates evenly |
| Vegetative growth | 40 to 50 days | 0.7 to 1.15 | 3.5 to 5.8 mm | Water deeper and less often to pull roots down |
| Tasselling and silking | 45 to 60 days | 1.20 | 6 mm | Never let the soil dry below half its available water |
| Grain fill to maturity | 30 to 40 days | 0.35 to 0.60 | 1.8 to 3 mm | Taper off as the crop dries down |
Stage lengths and crop coefficients for East African maize, from the FAO Irrigation and Drainage Paper 56 tables.
At peak demand, an irrigation system for maize needs about 24 cubic metres a day per acre. Therefore, that number is the planning anchor for the whole system. It sets the pump, the mainline and the size of the tank. For example, a borehole yielding 2 cubic metres an hour covers an acre in 12 hours. A modest source can therefore irrigate a small maize block. Measure the source before you buy the pump, not after.
Drip, Rain Gun or Furrow: Choosing an Irrigation System for Maize
Three methods fit maize. The right one depends on block size, water supply and how much labour you can spare. The table compares them on the points that decide the choice.
| Method | Water use | Best block size | Labour | Main risk |
|---|---|---|---|---|
| Drip, one line per row | Lowest, because only the root strip is wetted | Quarter acre to about 10 acres | Low once installed | Clogging if the filter is neglected |
| Rain gun | High, and wind losses add to it | 5 acres and above | Low per hectare, but the stand must be moved | Uneven coverage and runoff on sloping land |
| Furrow | Highest, with deep percolation losses | Flat land with a steady stream | High, because every channel needs opening | Erosion and waterlogging at the lower end |
A drip line is the most efficient way to water maize, while a rain gun suits large open blocks where moving pipe is not practical.
Drip wins on water use and on uniformity. A line along every row puts water at the base of the plant. The inter-row strip stays dry, so weeds have less to feed on. The trade-off is filtration, because emitters block if silt or organic matter reaches them. A screen filter of 120 mesh at the head of the block prevents most of that trouble.
A rain gun covers a large circle from one stand. On a big open block it is the cheaper way to cover ground. However, the jet is coarse and the pattern moves with the wind. A gun needs a firm base and careful spacing. The rain gun buying guide sets out the throw, flow and pump figures that a gun of this class needs.
Furrow irrigation still works on flat land beside a river, and it costs little to open. Yet the water arrives unevenly. The top of the field dries while the bottom waterlogs. In addition, each channel erodes a little more every season. On maize rows that run down a slope, furrow is the method most likely to wash soil away.
Planning an Irrigation System for Maize Around Row Spacing
Most Kenyan maize is planted on rows about 75 cm apart. Plants sit 25 to 30 cm apart in the row, which makes the layout simple. Run one 16 mm drip line beside each row. On heavy soil you can share one line between a pair of rows, because water moves sideways well. However, on sandy soil, keep one line per row.
Lay out an irrigation system for maize from the headland inward. Run the mainline along the headland and take a lateral into each block through a hydrant. Keep a lateral run under about 60 m on undulating ground. Friction and slope both steal pressure at the far end. Next, add a flush valve at the end of every lateral. Silt can then be pushed out instead of settling in the emitters. Cap the runs and test the whole block before the crop goes in.
If the field is new to irrigation, prepare the land first. The land preparation guide for drip irrigation covers ploughing depth, bed shaping and stone removal. The page on the drip irrigation system in Kenya sets out the wider choice of lines, filters and valves.
When to Run an Irrigation System for Maize
Typically, the crop tells you when it is short of water. Around midday the leaves roll and the plant looks grey, then it recovers by evening. That recovery is a warning, not a guarantee. Therefore, if soil at root depth crumbles instead of holding in a ball, the block is already short of water.
On sandy soil, water every two or three days. On clay, a four to six day interval is usually enough, because the soil holds more. Also, apply water early in the morning or in the evening. Midday irrigation loses a large share to evaporation, and wet leaves invite disease. Also, never split a peak demand day into a light sprinkle. As a result, shallow watering trains roots upward and leaves the crop exposed to the next dry spell.
A working irrigation system for maize replaces what the crop used since the last application. Keep a rain gauge beside the field and subtract rainfall from the week’s requirement. A single 20 mm storm can cover four days of peak demand. Irrigating straight after it wastes water and leaches nitrogen below the roots. A cheap soil probe or a hand-dug hole is enough to confirm what the gauge suggests.
Sizing the Pump and Mainline for an Irrigation System for Maize
Start from the daily figure of about 24 cubic metres per acre at peak. Then decide how many hours the system will run each week. For example, a one-acre block needs 168 cubic metres a week. Spread over three 8-hour sessions, that is about 7 cubic metres an hour, before head is added.
Head is the part farmers underestimate. First, the pump must lift water from the source and push it through the filter. It must still leave enough pressure at the far lateral. Every elbow, valve and metre of pipe takes a share. Therefore, size the mainline for the flow, not for the pump outlet. A 50 mm mainline suits one or two acres, while a larger block needs 63 mm or more.
Where the source is a borehole, confirm its yield and water quality before the pump is chosen. A groundwater hydrogeological survey in Kenya gives the sustainable yield and the iron or hardness level. Therefore, those figures decide whether a filter alone is enough. Hard or iron-rich water needs more than a screen filter, or the emitters will scale within a season.
What an Irrigation System for Maize Costs
The price of an irrigation system for maize follows the number of drip rows per bed. The one-acre table published on this site lists KSh 105,000 for a single row per bed. Two rows are priced at KSh 145,000 and three rows at KSh 180,000. Maize on 75 cm rows normally falls in the two-row band. Budget about KSh 145,000 per acre for the drip installation, before the tank, pump and survey.
Tank, pump and filtration can add a large share to that figure, and the water source decides how much. A gravity system fed from a raised tank avoids the pump cost but needs a stand and a reliable refill. A borehole system needs a pump, a pressure line and a power source. For the full breakdown, see what a drip system costs in Kenya. That page separates the kit from the pump and the survey.
A rain gun block can cost less per acre on a large field. One gun and a pump cover several acres. However, the running cost is higher, since the gun throws water over the whole field, not just the root strip. On a small maize plot, drip usually wins on both water and yield. On 20 acres of open land, the gun is often the practical choice.
Mistakes That Waste Water on Maize
Most failures with an irrigation system for maize come from the same handful of habits.
- Buying the pump before measuring the source. A pump that outdraws a borehole runs dry and burns out. Measure yield first, then size the pump.
- Watering a little every day. Light applications wet only the surface, and the roots stay shallow. Apply enough to reach 30 cm and then wait.
- Skipping the filter clean-out. A blocked screen drops pressure across the block, and the last rows starve. Clean the screen weekly and flush the laterals monthly.
- Irrigating at midday. Evaporation takes a share of the water and wet leaves raise the risk of fungal disease.
- Ignoring the rain gauge. Irrigating after a 20 mm storm wastes water and pushes nitrogen past the root zone.
- Planting into dry soil. Pre-wet the bed before sowing, or the seed sits in dry ground while the system is being commissioned.
Frequently Asked Questions About Irrigation System for Maize
How much water does maize need per day? At peak demand the crop uses about 6 mm a day, which is roughly 24 cubic metres per acre. Early in the season the figure is closer to 2 mm. It falls again as the crop dries down.
Is drip or a rain gun better for maize? Drip uses less water and gives a more even result on blocks up to about 10 acres. A rain gun is easier to run on a large open field, but it uses more water and loses coverage in wind.
How often should I irrigate maize? Every two or three days on sandy soil, and every four to six days on clay. Replace what the crop used since the last application. Check the soil at root depth rather than following a fixed calendar.
Which growth stage matters most? Tasselling and silking. Water stress in those weeks reduces the number of grains that set. The loss cannot be recovered later.
What does an irrigation system for maize cost per acre? The published one-acre drip installation figures range between KSh 105,000 and KSh 180,000, depending on the number of rows per bed. Maize usually sits in the KSh 145,000 two-row band. The tank, pump and survey are quoted separately.
To plan a block, send four figures: field size, row spacing, source yield and the distance to the field. Eunidrip Irrigation Systems designs and installs the system, from the survey through to the first irrigation. Call 0728 163329 or email info@eunidripirrigationsystems.com to book a site visit.