Here trickle irrigation is being used above ground.
Trickle irrigation usually consists of a main feeder hose that runs perpendicular to the rows, with trickle tape running under the plastic parallel to the rows, connected to the feeder hose. The trickle tape consists of low flow watering devices, called emitters, which place water directly in the root zone. The water is slowly released from the emitters. The rate of irrigation depends on the water pressure and spacing between emitters.
Use of trickle irrigation also allows for fertigation, or application of fertilizer through the irrigation system. Trickle irrigation has many benefits including using less irrigation water because the water is placed where the plants need it. It also helps control many disease problems, because unlike overhead irrigation which gets the plants foliage wet and splashes from plant to plant, the water is only released near the soil surface.