Irrigation Methods

Every irrigation method moves water from a source to a crop, but they differ hugely in efficiency, the fraction of applied water the crop actually uses. Flood irrigation covers the whole field in a sheet of water; it's cheap and simple but most water evaporates, runs off, or sinks past the root zone before the plant can use it, often near 40 percent efficient. Furrow irrigation sends water down trenches between crop rows, a bit more controlled than flooding but still loses a lot to seepage and evaporation. Spray or sprinkler systems pressurize water through nozzles, cutting losses to maybe 70-80 percent efficient, though wind and evaporation still steal some. Drip irrigation delivers water through tubes and emitters right at each plant's base, slowly, so almost nothing evaporates or runs off; efficiency can reach 90-95 percent.

Because efficiency measures useful water delivered per water pumped, a less efficient method forces a farmer to pump far more total water to satisfy the same crop need, which costs money, energy, and strains the water source. That source is often an aquifer, and pumping more than rainfall replaces causes the water table to drop year after year, sometimes forcing deeper and more expensive wells or drying up the aquifer entirely over decades.

This topic connects directly to the water footprint and sustainability ideas in this unit: the method a farmer chooses determines how much pressure irrigation puts on rivers, lakes, and groundwater. But efficiency alone doesn't decide the right choice. Drip systems are expensive to install and maintain, and some crops, especially flooded rice, actually depend on standing water, so flood irrigation remains appropriate there despite its low efficiency.