Irrigation and Rainfed Agriculture
There are two main ways farmers and ranchers use agricultural water to grow crops:

rainfed agriculture
irrigation
Rainfed agriculture is the natural application of water to the soil through direct rainfall. Relying on rainfall is unlikely to lead to food contamination, but water shortages can occur when rainfall decreases. On the other hand, artificial water increases the risk of contamination.

photo of sprinklers irrigating fields
Irrigation is the artificial application of water to the soil through various pipes, pumps and spray systems. Irrigation is often used in areas with irregular rainfall or dry times or expected drought. There are many types of irrigation systems in which water is evenly distributed throughout the field. Irrigation water can come from groundwater, springs or wells, surface water, rivers, lakes or reservoirs, or even other sources such as treated wastewater or desalinated water. Therefore, it is critical that farmers protect their agricultural water sources to minimize the potential for contamination. As with any groundwater removal, users of irrigation water need to be careful not to pump groundwater out of the aquifer faster than it can be replenished.

top of page

Types of Irrigation Systems
There are many different types of irrigation systems, depending on how the water is distributed throughout the farmland. Some common types of irrigation systems include:

surface irrigation
Water is distributed over land by gravity and no mechanical pumps are involved.

local irrigation
Water is distributed to each plant at low pressure through a network of pipes.

drip irrigation
A type of local irrigation that delivers water droplets to the plant roots at or near the roots. In this type of irrigation, evaporation and runoff are minimized.

sprinkler
Water is dispensed via overhead high pressure sprinklers or lances from a central location on site or sprinklers on mobile platforms.

Center Pivot Irrigation
Water is distributed by sprinkler systems that move in a circular pattern on wheeled towers. This system is common in flat areas of the United States.

Lateral mobile irrigation
The water is distributed through a series of pipes, each with a wheel and a set of sprinklers that can be rotated manually or using a dedicated mechanism. The sprinkler moves a certain distance on the field and then needs to be reconnected to the next distance. This system tends to be cheaper but requires more labor than other systems.

Secondary irrigation
By raising the water table, the water is distributed over land through a system of pumping stations, canals, gates and trenches. This type of irrigation is most effective in areas with high water tables.

manual irrigation
Water is distributed over the land through manual labor and watering cans. This system is very labor intensive.