Overhead irrigation is a method of water application that mimics natural rainfall by delivering water to crops from above the plant canopy. This technique uses a pressurized system to spray water into the air, allowing it to fall onto the foliage and soil below. The core mechanism involves a network of pipes, a pump, and specialized discharge devices that convert a continuous flow of water into a spray of small droplets. This approach is widely used across various agricultural settings, from small nurseries to large-scale commercial farms, offering a broad coverage area.
The Mechanics of Overhead Water Delivery
The process of overhead water delivery begins with a pump that draws water from a source and forces it through a main pipeline and a system of lateral pipes under pressure. The pressurized water then reaches specialized devices, such as sprinklers or nozzles, which are positioned on risers above the crop. These discharge devices are engineered to break the single stream of water into numerous droplets, which are then propelled into the air to achieve a wide distribution pattern.
The water pressure at the nozzle is a primary factor determining the resulting droplet size and the distance the water is thrown. High operating pressure produces smaller droplets, which cover a larger area but are more susceptible to environmental factors. Conversely, lower pressure results in larger droplets with less throw distance, requiring a denser arrangement of sprinklers for uniform coverage. Nozzle design and geometry also significantly influence the spray pattern and the uniformity of water distribution across the field.
Categorizing Common Overhead Systems
Overhead irrigation systems are broadly categorized based on their mobility and scale, which dictates their application in different farming environments.
Fixed Systems
Fixed systems, often referred to as solid-set systems, consist of permanently or semi-permanently installed pipes and risers with sprinklers that remain in one place for the entire growing season. These systems are common in orchards, nurseries, and smaller, high-value crop fields. They allow for precise, repeated application without the need for moving equipment, often watering the whole area simultaneously or in designated zones.
Automated Moving Systems
For large-scale row crops, the most recognizable systems are the automated moving systems, specifically the center pivot and lateral move irrigators. A center pivot system features a long lateral pipe supported by wheeled towers that rotates around a fixed central point, creating a circular irrigated area. The lateral move system, or linear move, moves in a straight line across a rectangular field, drawing water from a ditch or a hose. These systems are highly efficient for vast, flat fields and can cover hundreds of acres with minimal labor.
Traveling Gun Systems
A third major category includes the traveling gun or big gun systems, which use a single, high-volume sprinkler mounted on a wheeled cart. These guns are capable of projecting water over a very large radius, sometimes covering several acres from one position. They are typically towed across a field, making them useful for irregularly shaped fields or areas where a permanent system is not practical.
Water Efficiency and Environmental Trade-offs
The delivery of water through the air, while effective for broad coverage, introduces inherent trade-offs regarding water use efficiency. A significant portion of the water sprayed overhead is subject to evaporative loss and wind drift before it reaches the soil or the plant roots. In hot, dry, or windy conditions, a well-designed overhead system may lose 15% to 25% of the applied water, resulting in efficiencies that rarely exceed 75%.
The application of water directly onto the crop canopy can also have unintended consequences, particularly the creation of a moist environment that encourages the proliferation of certain plant diseases. Wet leaves provide an ideal habitat for many fungal and bacterial pathogens, potentially requiring farmers to increase the use of fungicides. Furthermore, the constant need to generate high pressure means that overhead systems have higher energy consumption compared to low-pressure methods like drip irrigation. This increased energy demand translates directly to higher operating costs.