A farmer in Kenya who can do a thorough job of watering with hose in hand is rare indeed.
Assuming that the hose spews out about 11 litres a minute in a circle a bit bigger than a metre in diameter, I roughly calculate that the farmer would have to stand immobile for more than two minutes before moving on to the next metre-diameter circle of thirsty plants. Pretty boring and tiresome, if you’ve got a whole 1 acre farm to water.
Using a sprinkler is one solution.
Even better is “drip irrigation,” a method of applying water to plants slowly and over an extended period of time. Drip irrigation has many benefits, not the least of which is cutting down water use by about 60 per cent. That water saving comes from less evaporation and less waste; through the drip method, water isn’t wasted on paths or between widely spaced plants. So there’s also less weed growth. Farm plants grow better because they’re never thirsty, and dry leaves mean less disease.
A primitive drip irrigation system could be cobbled together by running water through an old farm hose that’s riddled with holes and has its end plugged. The problem is less water would drip from the holes at the end than from the ones at the beginning, and higher ground would get less water than the lower ground.
True drip Irrigation System
A drip irrigation system that you purchase has water emitters engineered to offer a consistent, specified output over wide changes in elevation and pressure. They’re also made to be resistant to clogging or root penetration. You can buy tubing with emitters installed, say, 15, 30 or 45 centimetres apart that is good for watering whole beds. Or you can buy solid plastic tubing and punch in emitters where you want – ideal for widely spaced plants.
Emitters, those that you plug in or those already installed, typically put out water at a leisurely rate of two to 15 litres an hour.
For a bed of closely spaced plants, such as carrots, tubing with emitters already installed wets the whole bed. Capillary attraction into small pores in the soil draw water sideways even as gravity is pulling water downward, so wetted areas within the soil overlap.
Water’s lateral spread depends on soil type, from about 30 cm in sandy soils to about a metre in clays. So in a bed, these dripper lines could be laid out a half metre to two metres apart, depending on whether the soil is, respectively, a sand or a clay. Soils are rarely pure sand or pure clay, so actual spacing lies somewhere in between.
And organic matter (humus) in soil helps sponge up water to increase the lateral spread of the wetting front.
For individual plants, such as widely spaced shrubs and fruit trees, figure on using tubing with one or more emitters next to each plant. Emitters that attach to the ends of thin flexible tubes are useful for watering plants in pots.
Right at the PE pipe below the tank is the best part of a drip irrigation system: the battery-operated timer. This timer automatically turns the water on and off, and at about the rate that farm plants are using water.
Of course, water use depends on the weather and the size and kind of plants, but a half hour of dripping per day is usually about right. That may seem like a lot of water, but remember, the water is just dripping. If a timer can turn the water on and off three times a day, set if for three 10-minute waterings; if six times a day, set it for six 5-minute waterings; etc.
The timer brings an important benefit of drip irrigation: It saves time. Rather than standing frozen in your farm with a hose, by using drip irrigation, you become free to do other things. Like watching your cows graze. 🙂